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Persistence of Vision(tm) Ray-Tracer
(POV-Ray(tm))
User's Documentation 3.0.10
Copyright 1996 POV-Team(tm)
1 Introduction
1.1 Notation
2 Program Description
2.1 What is Ray-Tracing?
2.2 What is POV-Ray?
2.3 Which Version of POV-Ray should you use?
2.3.1 IBM-PC and Compatibles
2.3.1.1 MS-Dos
2.3.1.2 Windows
2.3.1.3 Linux
2.3.2 Apple Macintosh
2.3.3 Commodore Amiga
2.3.4 SunOS
2.3.5 Generic Unix
2.3.6 All Versions
2.3.7 Compiling POV-Ray
2.3.7.1 Directroy Structure
2.3.7.2 Configuring POV-Ray Source
2.3.7.3 Conclusion
2.4 Where to Find POV-Ray Files
2.4.1 Graphics Developer Forum on CompuServe
2.4.2 Internet
2.4.3 PC Graphics Area on America On-Line
2.4.4 The Graphics Alternative BBS in El Cerrito, CA
2.4.5 PCGNet
2.4.6 POV-Ray Related Books and CD-ROMs
3 Quick Start
3.1 Installing POV-Ray
3.2 Basic Usage
3.2.1 Running Files in Other Directories
3.2.2 INI Files
3.2.3 Alternatives to POVRAY.INI
3.2.4 Batch Files
3.2.5 Display Types
4 Beginning Tutorial
4.1 Your First Image
4.1.1 Understanding POV-Ray's Coordinate System
4.1.2 Adding Standard Include Files
4.1.3 Adding a Camera
4.1.4 Describing an Object
4.1.5 Adding Texture to an Object
4.1.6 Defining a Light Source
4.2 Using the Camera
4.2.1 Camera Types
4.2.2 Using Focal Blur
4.2.3 Using Camera Ray Perturbation
4.3 Simple Shapes
4.3.1 Box Object
4.3.2 Cone Object
4.3.3 Cylinder Object
4.3.4 Plane Object
4.3.5 Standard Include Objects
4.4 Advanced Shapes
4.4.1 Bicubic Patch Object
4.4.2 Blob Object
4.4.3 Height Field Object
4.4.4 Julia Fractal Object
4.4.5 Lathe Object
4.4.6 Mesh Object
4.4.7 Polygon Object
4.4.8 Prism Object
4.4.9 Superquadric Ellipsoid Object
4.4.10 Surface of Revolution Object
4.4.11 Text Object
4.4.12 Torus Object
4.5 CSG Objects
4.5.1 What is CSG?
4.5.2 CSG Union
4.5.3 CSG Intersection
4.5.4 CSG Difference
4.5.5 CSG Merge
4.5.6 CSG Pitfalls
4.5.6.1 Coincidence Surfaces
4.6 The Light Source
4.6.1 The Ambient Light Source
4.6.2 The Point Light Source
4.6.3 The Spotlight Source
4.6.4 The Cylindrical Light Source
4.6.5 The Area Light Source
4.6.6 Assigning an Object to a Light Source
4.6.7 Light Source Specials
4.6.7.1 Using Shadowless Lights
4.6.7.2 Using Light Fading
4.6.7.3 Light Sources and Atmosphere
4.7 Simple Texture Options
4.7.1 Surface Finishes
4.7.2 Adding Bumpiness
4.7.3 Creating Color Patterns
4.7.4 Pre-defined Textures
4.8 Advanced Texture Options
4.8.1 Pigment and Normal Patterns
4.8.2 Pigments
4.8.2.1 Using Color List Pigments
4.8.2.2 Using Pigment and Patterns
4.8.2.3 Using Pattern Modifiers
4.8.2.4 Using Transparent Pigments and Layered Textures
4.8.2.5 Using Pigment Maps
4.8.3 Normals
4.8.3.1 Using Basic Normal Modifiers
4.8.3.2 Blending Normals
4.8.4 Finishes
4.8.4.1 Using Ambient
4.8.4.2 Using Surface Highlights
4.8.4.3 Using Reflection and Metallic
4.8.4.4 Using Refraction
4.8.4.5 Light Attenuation and Caustics
4.8.4.6 Using Iridescence
4.8.5 Halos
4.8.5.1 What are Halos?
4.8.5.2 The Emitting Halo
4.8.5.2.1 Starting with a Basic Halo
4.8.5.2.2 Increasing the Brightness
4.8.5.2.3 Adding Some Turbulence
4.8.5.2.4 Resizing the Halo
4.8.5.2.5 Using Frequency to Improve Realism
4.8.5.2.6 Changing the Halo Color
4.8.5.3 The Glowing Halo
4.8.5.4 The Attenuating Halo
4.8.5.4.1 Making a Cloud
4.8.5.4.2 Scaling the Halo Container
4.8.5.4.3 Adding Additional Halos
4.8.5.5 The Dust Halo
4.8.5.5.1 Starting With an Object Lit by a Spotlight
4.8.5.5.2 Adding Some Dust
4.8.5.5.3 Decreasing the Dust Density
4.8.5.5.4 Making the Shadows Look Good
4.8.5.5.5 Adding Turbulence
4.8.5.5.6 Using a Coloured Dust
4.8.5.6 Halo Pitfalls
4.8.5.6.1 Where Halos are Allowed
4.8.5.6.2 Overlapping Container Objects
4.8.5.6.3 Multiple Attenuating Halos
4.8.5.6.4 Halos and Hollow Objects
4.8.5.6.5 Scaling a Halo Container
4.8.5.6.6 Choosing a Sampling Rate
4.8.5.6.7 Using Turbulence
4.9 Using Atmospheric Effects
4.9.1 The Background
4.9.2 The Sky Sphere
4.9.2.1 Creating a Sky with a Color Gradient
4.9.2.2 Adding the Sun
4.9.2.3 Adding Some Clouds
4.9.3 The Fog
4.9.3.1 A Constant Fog
4.9.3.2 Setting a Minimum Translucency
4.9.3.3 Creating a Filtering Fog
4.9.3.4 Adding Some Turbulence to the Fog
4.9.3.5 Using Ground Fog
4.9.3.6 Using Multiple Layers of Fog
4.9.3.7 Fog and Hollow Objects
4.9.4 The Atmosphere
4.9.4.1 Starting With an Empty Room
4.9.4.2 Adding Dust to the Room
4.9.4.3 Choosing a Good Sampling Rate
4.9.4.4 Using a Coloured Atmosphere
4.9.4.5 Atmosphere Tips
4.9.4.5.1 Choosing the Distance and Scattering Parameters
4.9.4.5.2 Atmosphere and Light Sources
4.9.4.5.3 Atmosphere Scattering Types
4.9.4.5.4 Increasing the Image Resolution
4.9.4.5.5 Using Hollow Objects and Atmosphere
4.9.5 The Rainbow
4.9.5.1 Starting With a Simple Rainbow
4.9.5.2 Increasing the Rainbow's Translucency
4.9.5.3 Using a Rainbow Arc
5 POV-Ray Reference
6 POV-Ray Options
6.1 Setting POV-Ray Options
6.1.1 Command Line Switches
6.1.2 Using INI Files
6.1.3 Using the POVINI Environment Variable
6.2 Options Reference
6.2.1 Animation Options
6.2.1.1 External Animation Loop
6.2.1.2 Internal Animation Loop
6.2.1.3 Subsets of Animation Frames
6.2.1.4 Cyclic Animation
6.2.1.5 Field Rendering
6.2.2 Output Options
6.2.2.1 General Output Options
6.2.2.1.1 Height and Width of Output
6.2.2.1.2 Partial Output Options
6.2.2.1.3 Interrupting Options
6.2.2.1.4 Resuming Options
6.2.2.2 Display Output Options
6.2.2.2.1 Display Hardware Settings
6.2.2.2.2 Display Related Settings
6.2.2.2.3 Mosaic Preview
6.2.2.3 File Output Options
6.2.2.3.1 Output File Type
6.2.2.3.2 Output File Name
6.2.2.3.3 Output File Buffer
6.2.2.4 CPU Utilization Histogram
6.2.2.4.1 File Type
6.2.2.4.2 File Name
6.2.2.4.3 Grid Size
6.2.2.5 Input File Name
6.2.2.6 Library Paths
6.2.2.7 Language Version
6.2.2.8 Removing User Bounding
6.2.3 Shell-out to Operating System
6.2.3.1 String Substitution in Shell Commands
6.2.3.2 Shell Command Sequencing
6.2.3.3 Shell Command Return Actions
6.2.4 Text Output
6.2.4.1 Text Streams
6.2.4.2 Console Text Output
6.2.4.3 Directing Text Streams to Files
6.2.4.4 Help Screen Switches
6.2.5 Tracing Options
6.2.5.1 Quality Settings
6.2.5.2 Radiosity Setting
6.2.5.3 Automatic Bounding Control
6.2.5.4 Anti-Aliasing Options
7 Scene Description Language
7.1 Language Basics
7.1.1 Identifiers and Keywords
7.1.2 Comments
7.1.3 Float Expressions
7.1.3.1 Float Identifiers
7.1.3.2 Float Operators
7.1.4 Vector Expressions
7.1.4.1 Vector Literals
7.1.4.2 Vector Identifiers
7.1.4.3 Vector Operators
7.1.4.4 Operator Promotion
7.1.5 Specifying Colors
7.1.5.1 Color Vectors
7.1.5.2 Color Keywords
7.1.5.3 Color Identifiers
7.1.5.4 Color Operators
7.1.5.5 Common Color Pitfalls
7.1.6 Strings
7.1.6.1 String Literals
7.1.6.2 String Identifiers
7.1.7 Built-in Identifiers
7.1.7.1 Constant Built-in Identifiers
7.1.7.2 Built-in Identifier 'clock'
7.1.7.3 Built-in Identifier 'version'
7.1.8 Functions
7.1.8.1 Float Functions
7.1.8.2 Vector Functions
7.1.8.3 String Functions
7.2 Language Directives
7.2.1 Include Files
7.2.2 Declare
7.2.2.1 Declaring identifiers
7.2.3 Default Directive
7.2.4 Version Directive
7.2.5 Conditional Directives
7.2.5.1 IF ELSE Directives
7.2.5.2 IFDEF Directives
7.2.5.3 IFNDEF Directives
7.2.5.4 SWITCH CASE and RANGE Directives
7.2.5.5 WHILE Directive
7.2.6 User Message Directives
7.2.6.1 Text Message Streams
7.2.6.2 Text Formatting
7.3 POV-Ray Coordinate System
7.3.1 Transformations
7.3.1.1 Translate
7.3.1.2 Scale
7.3.1.3 Rotate
7.3.1.4 Matrix Keyword
7.3.2 Transformation Order
7.3.3 Transform Identifiers
7.3.4 Transforming Textures and Objects
7.4 Camera
7.4.1 Type of Projection
7.4.2 Focal Blur
7.4.3 Camera Ray Perturbation
7.4.4 Placing the Camera
7.4.4.1 Location and Look_At
7.4.4.2 The Sky Vector
7.4.4.3 The Direction Vector
7.4.4.4 Angle
7.4.4.5 Up and Right Vectors
7.4.4.5.1 Aspect Ratio
7.4.4.5.2 Handedness
7.4.4.6 Transforming the Camera
7.4.5 Camera Identifiers
7.5 Objects
7.5.1 Empty and Solid Objects
7.5.1.1 Halo Pitfall
7.5.1.2 Refraction Pitfall
7.5.2 Finite Solid Primitives
7.5.2.1 Blob
7.5.2.2 Box
7.5.2.3 Cone
7.5.2.4 Cylinder
7.5.2.5 Height Field
7.5.2.6 Julia Fractal
7.5.2.7 Lathe
7.5.2.8 Prism
7.5.2.9 Sphere
7.5.2.10 Superquadric Ellipsoid
7.5.2.11 Surface of Revolution
7.5.2.12 Text
7.5.2.13 Torus
7.5.3 Finite Patch Primitives
7.5.3.1 Bicubic Patch
7.5.3.2 Disc
7.5.3.3 Mesh
7.5.3.4 Polygon
7.5.3.5 Triangle and Smooth Triangle
7.5.4 Infinite Solid Primitives
7.5.4.1 Plane
7.5.4.2 Poly, Cubic and Quartic
7.5.4.3 Quadric
7.5.5 Constructive Solid Geometry
7.5.5.1 About CSG
7.5.5.2 Inside and Outside
7.5.5.3 Inverse
7.5.5.4 Union
7.5.5.5 Intersection
7.5.5.6 Difference
7.5.5.7 Merge
7.5.6 Light Sources
7.5.6.1 Point Lights
7.5.6.2 Spotlights
7.5.6.3 Cylindrical Lights
7.5.6.4 Area Lights
7.5.6.5 Shadowless Lights
7.5.6.6 Looks_like
7.5.6.7 Light Fading
7.5.6.8 Atmosphere Interaction
7.5.6.9 Atmospheric Attenuation
7.5.7 Object Modifiers
7.5.7.1 Clipped_By
7.5.7.2 Bounded_By
7.5.7.3 Hollow
7.5.7.4 No_Shadow
7.5.7.5 Sturm
7.6 Textures
7.6.1 Pigment
7.6.1.1 Solid Color Pigments
7.6.1.2 Color List Pigments
7.6.1.3 Color Maps
7.6.1.4 Pigment Maps
7.6.1.5 Image Maps
7.6.1.5.1 Specifying an Image Map
7.6.1.5.2 The map_type Option
7.6.1.5.3 The Filter and Transmit Bitmap Modifiers
7.6.1.5.4 Using the Alpha Channel
7.6.1.6 Quick Color
7.6.2 Normal
7.6.2.1 Slope Maps
7.6.2.2 Normal Maps
7.6.2.3 Bump Maps
7.6.2.3.1 Specifying a Bump Map
7.6.2.3.2 Bump_Size
7.6.2.3.3 Use_Index and Use_Color
7.6.3 Finish
7.6.3.1 Ambient
7.6.3.2 Diffuse Reflection Items
7.6.3.2.1 Diffuse
7.6.3.2.2 Brilliance
7.6.3.2.3 Crand Graininess
7.6.3.3 Highlights
7.6.3.3.1 Phong Highlights
7.6.3.3.2 Specular Highlight
7.6.3.3.3 Metallic Highlight Modifier
7.6.3.4 Specular Reflection
7.6.3.5 Refraction
7.6.3.5.1 Light Attenuation
7.6.3.5.2 Faked Caustics
7.6.3.6 Iridescence
7.6.4 Halo
7.6.4.1 Halo Mapping
7.6.4.2 Multiple Halos
7.6.4.3 Halo Type
7.6.4.3.1 Attenuating
7.6.4.3.2 Dust
7.6.4.3.3 Emitting
7.6.4.3.4 Glowing
7.6.4.4 Density Mapping
7.6.4.4.1 Box Mapping
7.6.4.4.2 Cylindrical Mapping
7.6.4.4.3 Planar Mapping
7.6.4.4.4 Spherical Mapping
7.6.4.5 Density Function
7.6.4.5.1 Constant
7.6.4.5.2 Linear
7.6.4.5.3 Cubic
7.6.4.5.4 Poly
7.6.4.6 Halo Color Map
7.6.4.7 Halo Sampling
7.6.4.7.1 Number of Samples
7.6.4.7.2 Super-Sampling
7.6.4.7.3 Jitter
7.6.4.8 Halo Modifiers
7.6.4.8.1 Turbulence Modifier
7.6.4.8.2 Octaves Modifier
7.6.4.8.3 Omega Modifier
7.6.4.8.4 Lambda Modifier
7.6.4.8.5 Frequency Modifier
7.6.4.8.6 Phase Modifier
7.6.4.8.7 Transformation Modifiers
7.6.5 Special Textures
7.6.5.1 Texture Maps
7.6.5.2 Tiles
7.6.5.3 Material Maps
7.6.5.3.1 Specifying a Material Map
7.6.6 Layered Textures
7.6.7 Patterns
7.6.7.1 Agate
7.6.7.2 Average
7.6.7.3 Bozo
7.6.7.4 Brick
7.6.7.5 Bumps
7.6.7.6 Checker
7.6.7.7 Crackle
7.6.7.8 Dents
7.6.7.9 Gradient
7.6.7.10 Granite
7.6.7.11 Hexagon
7.6.7.12 Leopard
7.6.7.13 Mandel
7.6.7.14 Marble
7.6.7.15 Onion
7.6.7.16 Quilted
7.6.7.17 Radial
7.6.7.18 Ripples
7.6.7.19 Spiral1
7.6.7.20 Spiral2
7.6.7.21 Spotted
7.6.7.22 Waves
7.6.7.23 Wood
7.6.7.24 Wrinkles
7.6.8 Pattern Modifiers
7.6.8.1 Transforming Patterns
7.6.8.2 Frequency and Phase
7.6.8.3 Waveform
7.6.8.4 Turbulence
7.6.8.5 Octaves
7.6.8.6 Lambda
7.6.8.7 Omega
7.6.8.8 Warps
7.6.8.8.1 Black Hole Warp
7.6.8.8.2 Repeat Warp
7.6.8.8.3 Turbulence Warp
7.6.8.9 Bitmap Modifiers
7.6.8.9.1 The once Option
7.6.8.9.2 The "map_type" Option
7.6.8.9.3 The interpolate Option
7.7 Atmospheric Effects
7.7.1 Atmosphere
7.7.2 Background
7.7.3 Fog
7.7.4 Sky Sphere
7.7.5 Rainbow
7.8 Global Settings
7.8.1 ADC_Bailout
7.8.2 Ambient Light
7.8.3 Assumed_Gamma
7.8.3.1 Monitor Gamma
7.8.3.2 Image File Gamma
7.8.3.3 Scene File Gamma
7.8.4 HF_Gray_16
7.8.5 Irid_Wavelength
7.8.6 Max_Trace_Level
7.8.7 Max_Intersections
7.8.8 Number_Of_Waves
7.8.9 Radiosity
7.8.9.1 How Radiosity Works
7.8.9.2 Adjusting Radiosity
7.8.9.2.1 brightness
7.8.9.2.2 count
7.8.9.2.3 distance_maximum
7.8.9.2.4 error_bound
7.8.9.2.5 gray_threshold
7.8.9.2.6 low_error_factor
7.8.9.2.7 minimum_reuse
7.8.9.2.8 nearest_count
7.8.9.2.9 radiosity_quality
7.8.9.2.10 recursion_limit
7.8.9.3 Tips on Radiosity
*** APPENDICES ***
A Copyright
A.1 General License Agreement
A.2 Usage Provisions
A.3 General Rules for All Distributions
A.4 Definition of "Full Package"
A.5 Conditions for On-Line Services and BBS's Including Inter
A.6 Online or Remote Execution of POV-Ray
A.7 Conditions for Distribution of Custom Versions
A.8 Conditions for Commercial Bundling
A.9 Other Provisions
A.10 Revocation of License
A.11 Disclaimer
A.12 Technical Support
B Authors
C Contacting the Authors
D Postcards for POV-Ray Team Members
E POV-Ray Output Messages
E.1 Options in Use
E.2 Warning Messages
E.2.1 Warnings during the Parsing Stage
E.2.2 Other Warnings
E.3 Error Messages
E.3.1 Scene File Errors
E.3.2 Other Errors
E.4 Statistics
F Tips and Hints
F.1 Scene Design Tips
F.2 Scene Debugging Tips
F.3 Animation Tips
F.4 Texture Tips
F.5 Height Field Tips
F.6 Converting "Handedness"
G Frequently Asked Questions
G.1 General Questions
G.2 POV-Ray Option Questions
G.3 Atmosphere Questions
H Suggested Reading
I Help on Help
1 Introduction
***********************************************************
Note that this document is still in work and there may (and will) be some
larger changes. Do not waste your time, money and paper to print this
document!
***********************************************************
This document details the use of the Persistence of Vision(tm) Ray Tracer
(POV-Ray(tm)). It is broken down into four parts: the installation guide, the
tutorial guide, the reference guide and the appendix. The first part (see
chapter "Program Description" chapter and "Quick Start" ) tells you where to
get and how to install POV-Ray. It also gives a short introduction to
ray-tracing. The tutorial explains step by step how to use the different
features of POV-Ray (see chapter "Beginning Tutorial" ). The reference gives
a complete description of all features available in POV-Ray by explaining all
command line options (INI file keywords) and the scene description language
(see chapter "POV-Ray Reference" , chapter "POV-Ray Options" and chapter
"Scene Description Language" ). The appendix includes some tips and hints,
suggested reading, contact addresses and legal information.
1.1 Notation
Throughout this document the following notation is used to mark keywords of
the scene description language, command line options, INI file keywords and
file names.
name scene description keyword
name command line option
name INI file keyword
name file name
name Internet address, Usenet group
2 Program Description
The Persistence of Vision(tm) Ray-Tracer creates three-dimensional,
photo-realistic images using a rendering technique called ray-tracing. It
reads in a text file containing information describing the objects and
lighting in a scene and generates an image of that scene from the view point
of a camera also described in the text file. Ray-tracing is not a fast
process by any means, but it produces very high quality images with realistic
reflections, shading, perspective and other effects.
2.1 What is Ray-Tracing?
Ray-tracing is a rendering technique that calculates an image of a scene by
shooting rays into the scene. The scene is build from shapes, light sources,
a camera, materials, special features, etc.
For every pixel in the final image a viewing ray is shot into the scene and
tested for intersection with any of the objects in the scene. Viewing rays
originate from the viewer, represented by the camera, and pass through the
viewing window (representing the final image).
Every time an object is hit, the color of the surface at that point is
calculated. For this purpose the amount of light coming from any light source
in the scene is determined to tell wether the surface point lies in shadow or
not. If the surface is reflective or translucent new rays are set up and
traced in order to determine the contribution of the reflected and refracted
light to the final surface color.
Special features like interdiffuse reflection (radiosity), atmospheric
effects and area lights make it necessary to shoot a lot of additional rays
into the scene for every pixel.
2.2 What is POV-Ray?
The Persistence of Vision(tm) Ray-Tracer was developed from DKBTrace 2.12
(written by David K. Buck and Aaron A. Collins) by a bunch of people, called
the POV-Team(tm), in their spare time. The headquarters of the POV-Team is in
the GRAPHDEV forum on CompuServe (see "Graphics Developer Forum on
CompuServe" for more details).
The POV-Ray(tm) package includes detailed instructions on using the
ray-tracer and creating scenes. Many stunning scenes are included with
POV-Ray so you can start creating images immediately when you get the
package. These scenes can be modified so you don't have to start from
scratch.
In addition to the pre-defined scenes is a large library of predefined shapes
and materials that you can use in your own scenes by just including the
appropriate files and typing the name of the shape or material.
Here are some highlights of POV-Ray's features:
* Easy to use scene description language.
* Large library of stunning example scene files.
* Standard include files that pre-define many shapes, colors and textures.
* Very high quality output image files (up to 48-bit color).
* 15 and 24 bit color display on IBM-PC's using appropriate hardware.
* Create landscapes using smoothed height fields.
* Spotlights, cylindrical lights and area lights for sophisticated
lighting.
* Phong and specular highlighting for more realistic-looking surfaces.
* Interdiffuse reflection (radiosity) for more realistic lighting.
* Atmospheric effects like atmosphere, fog and rainbow.
* Halos to model effects like clouds, dust, fire and steam.
* Several image file output formats including Targa, PNG and PPM.
* Basic shape primitives such as ... spheres, boxes, quadrics, cylinders,
cones, triangles and planes.
* Advanced shape primitives such as ... torii (donuts), hyperboloids,
paraboloids, bezier patches, height fields (mountains), blobs, quartics,
smooth triangles, text, fractals, superquadrics, surfaces of revolution,
prisms, polygons, lathes and fractals.
* Shapes can easily be combined to create new complex shapes using
Constructive Solid Geometry (CSG). POV-Ray supports unions, merges,
intersections and differences.
* Objects are assigned materials called textures (a texture describes the
coloring and surface properties of a shape).
* Built-in color and normal patterns: Agate, Bozo, Bumps, Checker, Crackle,
Dents, Granite, Gradient, Hexagon, Leopard, Mandel, Marble, Onion,
Quilted, Ripples, Spotted, Sprial, Radial, Waves, Wood, Wrinkles and
image file mapping.
* Users can create their own textures or use pre-defined textures such as
... Brass, Chrome, Copper, Gold, Silver, Stone, Wood.
* Combine textures using layering of semi-transparent textures or tiles of
textures or material map files.
* Display preview of image while computing (not available on all
platforms).
* Halt rendering when part way through.
* Continue rendering a halted partial scene later.
2.3 Which Version of POV-Ray should you use?
POV-Ray can be used under MS-Dos, Windows 3.x, 95 and NT; Apple Macintosh 68k
and Power PC; Commodore Amiga; Linux, UNIX and other platforms.
The latest versions of the necessary files are available over CompuServe,
Internet, America Online and several BBS's. See section "Where to Find
POV-Ray Files" for more info.
2.3.1 IBM-PC and Compatibles
Currently there are three different versions for the IBM-PC running under
different operating systems (MS-Dos, Windows, Linux) as described below.
2.3.1.1 MS-Dos
The MS-Dos version runs under Ms-Dos or as a dos application under
Windows'95, Windows NT, Windows 3.1 or 3.11. It also runs under OS/2 and
Warp.
Required hardware and software:
- A 386 or better CPU and at least 4 meg of RAM.
- About 6 meg disk space to install and 2-10 meg or more beyond that for
working space.
- A text editor capable of editing plain ASCII text files. The EDIT program
that comes with MS-Dos will work for moderate size files.
- Graphic file viewer capable of viewing GIF and perhaps TGA and PNG
formats.
Required POV-Ray files:
- POVMSDOS.EXE - a self-extracting archive containing the program, sample
scenes, standard include files and documentation in a hypertext help
format with help viewer. This file may be split into smaller files for
easier downloading. Check the directory of your download or ftp site to
see if other files are needed.
Recommended:
- Pentium or 486dx or math co-processor for 386 or 486sx.
- 8 meg or more RAM.
- SVGA display preferably with VESA interface and high color or true color
ability.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous.
- POVMSD_S.ZIP - The C source code for POV-Ray for MS-Dos Contains generic
parts and MS-Dos specific parts. It does not include sample scenes,
standard include files and documentation so you should also get the
executable archive as well
- A C compiler that can create 32-bit protected mode applications. We
support Watcom 10.5a, Borland 4.52 with Dos Power Pack and limited
graphics under DJGPP 1.12maint4. DJGPP 2.0 not supported.
2.3.1.2 Windows
The Windows version runs under Windows'95, Windows NT and under Windows 3.1
or 3.11 if Win32s extensions are added. Also runs under OS/2 Warp.
Required hardware and software:
- A 386 or better CPU and at least 8 meg of RAM.
- About 12 meg disk space to install and 2-10 meg or more beyond that for
working space.
Required POV-Ray files:
- User archive POVWIN3.EXE - a self-extracting archive containing the
program, sample scenes, standard include files and documentation. This
file may be split into smaller files for easier downloading. Check the
directory of your download or ftp site to see if other files are needed.
Recommended:
- Pentium or 486dx or math co-processor for 386 or 486sx.
- 16 meg or more RAM.
- SVGA display preferably with high color or true color ability and drivers
installed.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous.
- POVWIN_S.ZIP - The C source code for POV-Ray for Windows. Contains
generic parts and Windows specific parts. It does not include sample
scenes, standard include files and documentation so you should also get
the executable archive as well.
- POV-Ray can only be compiled using C compilers that create 32-bit Windows
applications. We support Watcom 10.5a, Borland 4.52/5.0 compilers. The
source code is not needed to use POV-Ray. It is provided for the curious
and adventurous.
2.3.1.3 Linux
Required hardware and software:
- A 386 or better CPU and at least 4 meg of RAM.
- About 6 meg disk space to install and 2-10 meg or more beyond that for
working space.
- A text editor capable of editing plain ASCII text files.
- Any recent (1994 onwards) Linux kernel and support for ELF format
binaries. POV-Ray for Linux is not in a.out-format.
- ELF libraries libc.so.5, libm.so.5 and one or both of libX11.so.6 or
libvga.so.1.
Required POV-Ray files:
- POVLINUX.TGZ or POVLINUX.TAR.GZ - archive containing an official binary
for each SVGALib and X-Windows modes. Also contains sample scenes,
standard include files and documentation.
Recommended:
- Pentium or 486dx or math co-processor for 386 or 486sx.
- 8 meg or more RAM.
- SVGA display preferably high color or true color ability.
- If you want display, you'll need either SVGALib or X-Windows.
- Graphic file viewer capable of viewing PPM, TGA or PNG formats.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous.
- POVUNI_S.TAR.GZ or POVUNI_S.TGZ - The C source code for POV-Ray for
Linux. Contains generic parts and Linux specific parts. It does not
include sample scenes, standard include files and documentation so you
should also get the executable archive as well.
- The GNU C compiler and (optionally) the X include files and libraries and
KNOWLEDGE OF HOW TO USE IT. Although we provide source code for generic
Unix systems, we do not provide technical support on how to compile the
program.
2.3.2 Apple Macintosh
The Macintosh versions run under Apple's MacOS operating system version 7.0
or better, on any 68020/030/040-based Macintosh (with or without a floating
point coprocessor) or any of the Power Macintosh computers.
Required hardware and software:
- A 68020 or better CPU without a floating point unit (LC or Performa or
Centris series) and at least 8 meg RAM or
- A 68020 or better CPU *with* a floating point unit (Mac II or Quadra
series) and at least 8 meg RAM or
- Any Power Macintosh computer and at least 8 meg RAM.
- System 7 or newer and color QuickDraw (System 6 is no longer supported).
- About 6 meg free disk space to install and an additional 2-10 meg free
space for working space.
- Graphic file viewer utility capable of viewing Mac PICT, GIF and perhaps
TGA and PNG formats (the shareware GIFConverter or GraphicConverter
applications are good.)
Required POV-Ray files:
- POVMACNF.SIT or POVMACNF.SIT.HQX - a Stuffit archive containing the
non-FPU 68K Macintosh application, sample scenes, standard include files
and documentation (slower version for Macs without an FPU) or
- POVMAC68.SIT or POVMAC68.SIT.HQX - a Stuffit archive containing the FPU
68K Macintosh application, sample scenes, standard include files and
documentation (faster version for Macs WITH an FPU) or
- POVPMAC.SIT or POVPMAC.SIT.HQX - a Stuffit archive containing the native
Power Macintosh application, sample scenes, standard include files and
documentation.
Recommended:
- 68030/33 or faster with FPU, or any Power Macintosh
- 8 meg or more RAM for 68K Macintosh; 16 meg or more for Power Macintosh
systems.
- Color monitor preferred, 256 colors OK, but thousands or millions of
colors is even better.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous. POV-Ray can be compiled using Apple's MPW 3.3,
Metrowerks CodeWarrior 8 or Symantec 8.
- POVMACS.SIT or POVMACS.SIT.HQX - The full C source code for POV-Ray for
Macintosh. Contains generic parts and Macintosh specific parts. It does
not include sample scenes, standard include files and documentation so
you should also get the executable archive as well.
2.3.3 Commodore Amiga
The Amiga version comes in several flavors: 68000/68020 without FPU (not
recommended, very slow), 68020/68881(68882), 68030/68882 and 68040. There are
also two sub-versions, one with a CLI-only interface, and one with a GUI
(requires MUI 3.1). All versions run under OS2.1 and up. Support exists for
pensharing and window display under OS3.x with 256 color palettes and CybeGFX
display library support.
Required:
- at least 4 meg of RAM.
- at least 2 meg of hard disk space for the necessities, 5-20 more
recommended for workspace.
- an ASCII text editor, GUI configurable to launch the editor of your
choice.
- Graphic file viewer - POV-Ray outputs to PNG, Targa (TGA) and PPM
formats, converters from the PPMBIN distribution are included to convert
these to IFF ILBM files.
Required POV-Ray files:
- POVAMI.LHA - a LHA archive containing executible, sample scenes, standard
include files and documentation.
Recommended:
- 8 meg or more of RAM.
- 68030 and 68882 or higher processor.
- 24bit display card (CyberGFX library supported)
As soon as a stable compiler is released for Amiga PowerPC systems, plans are
to add this to the flavor list.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous.
- POVLHA_S.ZIP - The C source code for POV-Ray for Amiga. Contains generic
parts and Amiga specific parts. It does not include sample scenes,
standard include files and documentation so you should also get the
executable archive as well.
2.3.4 SunOS
Required hardware and software:
- A Sun SPARC processor and at least 4 meg of RAM.
- About 6 meg disk space to install and 2-10 meg or more beyond that for
working space.
- A text editor capable of editing plain ASCII text files.
- SunOS 4.1.3 or other operating system capable of running such a binary
(Solaris or possibly Linux for Sparc).
Required POV-Ray files:
- POVSUNOS.TGZ or POVSUNOS.TAR.GZ - archive containing an official binary
for each text-only and X-Windows modes. Also contains sample scenes,
standard include files and documentation.
Recommended:
- 8 meg or more RAM.
- If you want display, you'll need X-Windows or an X-Term.
- preferably 24-bit TrueColor display ability, although the X display code
is known to work with ANY combination of visual and color depth.
- Graphic file viewer capable of viewing PPM, TGA or PNG formats.
Optional: The source code is not needed to use POV-Ray. It is provided for
the curious and adventurous.
- POVUNI_S.TGZ or POVUNI_S.TAR.GZ - The C source code for POV-Ray for UNIX.
Contains generic UNIX parts and Linux specific parts. It does not include
sample scenes, standard include files and documentation so you should
also get the executable archive as well.
- A C compiler and (optionally) the X include files and libraries and
knowledge of how to use it.
Although we provide source code for generic Unix systems, we do not provide
technical support on how to compile the program.
2.3.5 Generic Unix
Required:
- POVUNI_S.TGZ or POVUNI_S.TAR.GZ - The C source code for POV-Ray for Unix.
Either archive contains full generic source, Unix and X-Windows specific
source.
- POVUNI_D.TGZ or POVUNI_D.TAR.GZ or any archive containing the sample
scenes, standard include files and documentation. This could be the Linux
or SunOS executable archives described above.
- A C compiler for your computer and KNOWLEDGE OF HOW TO USE IT. Although
we provide source code for generic Unix systems, we do not provide
technical support on how to compile the program.
- A text editor capable of editing plain ASCII text files.
Recommended:
- Math co-processor.
- 8 meg or more RAM.
- Graphic file viewer capable of viewing PPM, TGA or PNG formats.
Optional:
- X Windows if you want to be able to display as you render.
- You will need the X-Windows include files as well. If you're not familiar
with compiling programs for X-Windows you may need some help from someone
who is knowledgeable at your installation because the X include files and
libraries are not always in a standard place.
2.3.6 All Versions
Each executable archive includes full documentation for POV-Ray itself as
well as specific instructions for using POV-Ray with your type of platform.
All versions of the program share the same ray-tracing features like shapes,
lighting and textures. In other words, an IBM-PC can create the same pictures
as a Cray supercomputer as long as it has enough memory.
The user will want to get the executable that best matches their computer
hardware. See the section "Where to Find POV-Ray Files" for where to find
these files. You can contact those sources to find out what the best version
is for you and your computer.
2.3.7 Compiling POV-Ray
The following sections will help you to compile the portable C source code
into a working executable version of POV-Ray. They are only for those people
who want to compile a custom version of POV-Ray or to port it to an
unsupported platform or compiler.
The first question you should ask yourself before proceeding is Do I really
need to compile POV-Ray at all? Official POV-Ray Team executable versions are
available for MS-Dos, Windows 3.1x/95/NT, Mac 68k, Mac Power PC, Amiga, Linux
for Intel x86, and SunOS. Other unofficial compiles may soon be available for
other platforms. If you do not intend to add any custom or experimental
features to the program and if an executable already exists for your platform
then you need not compile this program yourself.
If you do want to proceed you should be aware that you are very nearly on
your own. The following sections and other related compiling documentation
assume you know what you are doing. It assumes you have an adequate C
compiler installed and working. It assumes you know how to compile and link
large, multi-part programs using a make utility or an IDE project file if
your compiler supports them. Because makefiles and project files often
specify drive, directory or path information, we cannot promise our makefiles
or projects will work on your system. We assume you know how to make changes
to makefiles and projects to specify where your system libraries and other
necessary files are located.
In general you should not expect any technical support from the POV-Ray Team
on how to compile the program. Everything is provided here as is. All we can
say with any certainty is that we were able to compile it on our systems. If
it doesn't work for you we probably cannot tell you why.
There is no technical documentation for the source code itself except for the
comments in the source files. We try our best to write clear, well- commented
code but some sections are barely commented at all and some comments may be
out dated. We do not provide any technical support to help you to add
features. We do not explain how a particular feature works. In some
instances, the person who wrote a part of the program is no longer active in
the Team and we don't know exactly how it works.
When making any custom version of POV-Ray or any unofficial compile, please
make sure you read and follow all provisions of our license in "Copyright" .
In general you can modify and use POV-Ray on your own however you want but if
you distribute your unofficial version you must follow our rules. You may not
under any circumstances use portions of POV-Ray source code in other
programs.
2.3.7.1 Directroy Structure
POV-Ray source code is distributed in archives with files arranged in a
particular hierarchy of directories or folders. When extracting the archives
you should do so in a way that keeps the directory structure intact. In
general we suggest you create a directory called povray3 and extract the
files from there. The extraction will create a directory called source with
many files and sub-directories.
In general, there are separate archives for each hardware platform and
operating system but each of these archives may support more than one
compiler. For example here is the directory structure for the MS-Dos archive.
SOURCE
SOURCE\LIBPNG
SOURCE\ZLIB
SOURCE\MSDOS
SOURCE\MSDOS\PMODE
SOURCE\MSDOS\BORLAND
SOURCE\MSDOS\DJGPP
SOURCE\MSDOS\WATCOM
The source directory contains source files for the generic parts of POV-Ray
that are the same on all platforms. The source\libpng contains files for
compiling a library of routines used in reading and writing PNG (Portable
Network Graphics) image files. The source\zlib contains files for compiling a
library of routines used by LIBPNG to compress and uncompress data streams.
All of these files are used by all platforms and compilers. They are in every
version of the source archives.
The source\msdos directory contains all source files for the MS-Dos version
common to all supported MS-Dos compilers. The pmode sub-directory contains
source files for pmode.lib which is required by all MS-Dos versions. The
borland , djgpp , and watcom sub-directories contain source, makefiles and
project files for C compilers by Borland, DJGPP and Watcom.
The source\msdos directory is only in the MS-Dos archive. Similarly the
Windows archive contains a source\windows directory. The Unix archive
contains source/unix etc.
The source\msdos directory contains a file cmpl_msd.doc which contains
compiling information specific to the MS-Dos version. Other platform specific
directories contain similar cmpl_xxx.doc files and the compiler specific
sub-directories also contain compiler specific cmpl_xxx.doc files. Be sure to
read all pertinent cmpl_xxx.doc files for your platform and compiler.
2.3.7.2 Configuring POV-Ray Source
Every platform has a header file config.h that is generally in the platform
specific directory but may be in the compiler specific directory. Some
platforms have multiple versions of this file and you may need to copy or
rename it as config.h . This file is included in every module of POV-Ray. It
contains any prototypes, macros or other definitions that may be needed in
the generic parts of POV-Ray but must be customized for a particular platform
or compiler.
For example different operating systems use different characters as a
separator between directories and file names. MS-Dos uses back slash, Unix a
front slash or Mac a colon. The config.h file for MS-Dos and Windows contains
the following:
#define FILENAME_SEPARATOR '\\'
which tells the generic part of POV-Ray to use a back slash.
Every customization that the generic part of the code needs has a default
setting in the file source\frame.h which is also included in every module
after config.h . The frame.h header contains many groups of defines such as
this:
#ifndef FILENAME_SEPARATOR
#define FILENAME_SEPARATOR '/'
#endif
which basically says if we didn't define this previously in config.h then
here's a default value . See frame.h to see what other values you might wish
to configure.
If any definitions are used to specify platform specific functions you should
also include a prototype for that function. The file source\msdos\config.h ,
for example, not only contains the macro:
#define POV_DISPLAY_INIT(w,h) MSDOS_Display_Init ((w), (h));
to define the name of the graphics display initialization function, it
contains the prototype:
void MSDOS_Display_Init (int w, int h);
If you plan to port POV-Ray to an unsupported platform you should probably
start with the simplest, non-display generic Unix version. Then add new
custom pieces via the config.h file.
2.3.7.3 Conclusion
We understand that the above sections are only the most trivial first steps
but half the fun of working on POV-Ray source is digging in and figuring it
out on your own. That's how the POV-Ray Team members got started. We've tried
to make the code as clear as we can.
Be sure to read the cmpl_xxx.doc files in your platform specific and compiler
specific directories for some more minor help if you are working on a
supported platform or compiler.
2.4 Where to Find POV-Ray Files
The latest versions of the POV-Ray software are available from the following
sources.
2.4.1 Graphics Developer Forum on CompuServe
POV-Ray's headquarters are on CompuServe, GRAPHDEV forum, ray-tracing
sections. We meet there to share info and graphics and discuss ray tracing,
fractals and other kinds of computer art. Everyone is welcome to join in on
the action on CIS GRAPHDEV. Hope to see you there! You can get information on
joining CompuServe by calling (800)848-8990 or visit the CompuServe home page
http://www.compuserve.com . Direct CompuServe access is also available in
Japan, Europe and many other countries.
2.4.2 Internet
The internet home of POV-Ray is reachable on the World Wide Web via the
address http://www.povray.org and via ftp as ftp.povray.org . Please stop by
often for the latest files, utilities, news and images from the official
POV-Ray internet site.
The comp.graphics.rendering.raytracing newsgroup has many competent POV-Ray
users that are very willing to share their knowledge. They generally ask that
you first browse a few files to see if someone has already answered the same
question, and of course, that you follow proper "netiquette". If you have any
doubts about the qualifications of the folks that frequent the group, a few
minutes spend at the Ray Tracing Competition pages at www.povray.org will
quickly convince you!
2.4.3 PC Graphics Area on America On-Line
There's an area now on America On-Line dedicated to POV-Ray support and
information. You can find it in the PC Graphics section of AOL. Jump keyword
POV (the keyword PCGRAPHICS brings you to the top of the graphics related
section). This area includes the Apple Macintosh executables also. It is best
if messages are left in the Company Support section. Currently, Bill Pulver
(BPulver) is our representative there.
2.4.4 The Graphics Alternative BBS in El Cerrito, CA
For those on the West coast, you may want to find the POV-Ray files on The
Graphics Alternative BBS . It's a great graphics BBS run by Adam Shiffman.
TGA is high quality, active and progressive BBS system which offers both
quality messaging and files to its 1300+ users.
510-524-2780 (PM14400FXSA v.32bis 14.4k, Public)
510-524-2165 (USR DS v.32bis/HST 14.4k, Subscribers)
2.4.5 PCGNet
The Professional CAD and Graphics Network (PCGnet) serves both the CAD and
Graphics communities by making information useful to them widely available.
Formerly known as ADEnet, PCGnet is a new network created from the ground up,
incorporating new nodes and focusing evenly on both CAD and graphics related
topics, including, but not limited to the following topics: design, drafting,
engineering, 2d and 3d modeling, multimedia, systems, raster imaging,
raytracing, 3d rendering and animation.
PCGnet is designed to serve the needs of all callers by stimulating interest
and generating support forums for active users who have an interest in the
CAD and graphics related topics previously mentioned; interest and support is
generated through PCGnet's message conferences, file sharing across the
network, and industry news and press releases. PCGnet's message conference
are moderated forums designed to accommodate friendly, yet professional and
informative discussion of CAD and graphics related subjects.
TGA BBS serves as the central hub for a large network of graphics-oriented
BBS systems around the world. Following is a concise listing of active PCGNet
nodes at the time of this writing. The POV-Team can not vouch for the
currency of this information, nor verify that any of these boards may carry
POV-Ray.
USA and Canada
411-Exchange Alpharetta GA 404-345-0008
Autodesk Global Village San Rafael CA 415-507-5921
CAD/Engineering Services Hendersonville TN 615-822-2539
Canis Major Nashville TN 615-385-4268
CEAO BBS Columbus OH 614-481-3194
CHAOS BBS Columbia MO 314-874-2930
Joes CODE BBS West Bloomfield MI 810-855-0894
John's Graphics Brooklyn Park MN 612-425-4436
PC-AUG Phoenix AZ 602-952-0638
SAUG BBS Bellevue WA 206-644-7115
Space Command BBS Kennewick WA 509-735-4894
The CAD/fx BBS Mesa AZ 602-835-0274
The Drawing Board BBS Anchorage AK 907-349-5412
The Graphics Alternative El Cerrito CA 510-524-2780
The Happy Canyon Denver CO 303-759-3598
The New Graphics BBS Piscataway NJ 908-271-8878
The University Shrewsbury Twp NJ 908-544-8193
The Virtual Dimension Oceanside CA 619-722-0746
Time-Out BBS Sadsburyville PA 610-857-2648
Australia
MULTI-CAD Magazine BBS Toowong QLD 61-7-878-2940
My Computer Company Erskineville NSW 61-2-557-1489
Sydney PCUG Compaq BBS Caringbah NSW 61-2-540-1842
The Baud Room Melbourne VIC 61-3-481-8720
Austria
Austrian AutoCAD User Group Graz 43-316-574-426
Belgium
Lucas Visions BBS Boom 32-3-8447-229
Denmark
Horreby SuperBBS Nykoebing Falster 45-53-84-7074
Finland
DH-Online Jari Hiltunen 358-0-40562248
Triplex BBS Helsinki 358-0-5062277
France
CAD Connection Montesson 33-1-39529854
Zyllius BBS! Saint Paul 33-93320505
Germany
Ray BBS Munich Munich 49-89-984723
Tower of Magic Gelsenkirchen 49-209-780670
Netherlands
BBS Bennekom: Fractal Board Bennekom 31-318-415331
CAD-BBS Nieuwegein 31-30-6090287
31-30-6056353
Foundation One Baarn 31-35-5422143
New Zealand
The Graphics Connection Wellington 64-4-566-8450
The Graphics Connection II New Plymouth 64-6-757-8092
The Graphics Connection III Auckland 64-9-309-2237
Slovenia
MicroArt Koper 386-66-34986
Sweden
Autodesk On-line Gothenburg 46-31-401718
United Kingdom
CADenza BBS Leicester, UK 44-116-259-6725
Raytech BBS Tain, Scotland 44-1862-83-2020
The Missing Link Surrey, England 44-181-641-8593
Country or long distance dial numbers may require additional numbers to be
used. Consult your local phone company.
2.4.6 POV-Ray Related Books and CD-ROMs
The following items were produced by POV-Team members. Although they are only
current to POV-Ray 2.2 they will still be helpful. Steps are being taken to
update the POV-Ray CDROM to version 3.0, with a new version expected around
October 1996.
The books listed below have been recently listed as out-of-print but may
still be found in some bookstores or libraries (Visit
http://www.dnai.com:80/waite/ for more details).
Ray Tracing Creations, 2d Ed.
Chris Young and Drew Wells
ISBN 1-878739-69-7
Waite Group Press 1994
700 pages with color insert and POV-Ray 2.2 on 3.5" MS-Dos disk.
Ray Tracing Worlds with POV-Ray
Alexander Enzmann, Lutz Kretzschmar, Chris Young,
ISBN 1-878739-64-6
Waite Group Press 1994
Includes Moray 1.5x modeler and POV-Ray 2.2 on 3.5" MS-Dos disks.
Ray Tracing for the Macintosh CD
Eduard Schwan
ISBN 1-878739-72-7
Waite Group Press, 1994
Comes with a CD-ROM full of scenes, images, and QuickTime movies,
and an interactive keyword reference. Also a floppy with POV-Ray for
those who don't have a CD ROM drive.
'The Official POV-Ray CDROM' The Official POV-Ray CDROM: The Official POV-Ray
CDROM is a compilation of images, scene source, program source, utilities and
tips on POV-Ray and 3D graphics from the Internet and Compuserve. This CD is
aimed not only at those who want to create their own images or do general 3D
programming work, but also at those who want simply to experience some
high-quality renderings done by some of the best POV-Ray artists, and to
learn from their source code. The CDROM contains over 500 ray-traced images.
It's a good resource for those learning POV-Ray as well as those who are
already proficient, and contains a Microsoft Windows-based interactive
tutorial. The disk comes with a fold-out poster and reference sheet. The CD
is compatible with DOS/Windows and Macintosh formats.
The CDROM is available for free retrieval and browsing on the World Wide Web
at http://www.povray.org/pov-cdrom . For more details you may also visit
http://www.povray.org/povcd .
3 Quick Start
The next section describes how to quickly install POV-Ray and render sample
scenes on your computer. It is assumed that you are using an IBM-PC
compatible computer with MS-Dos. For other platforms you must refer to the
specific documentation included in POV-Ray's archive.
3.1 Installing POV-Ray
[*** STILL BEING WRITTEN ***]
Specific installation instructions are included with the executable program
for your computer. In general, there are two ways to install POV-Ray.
[ Note that the generic word "directory" is used throughout. Your operating
system may use another word (subdirectory, folder, etc.) ]
1) The messy way: Create a directory called POVRAY and copy all POV-Ray files
into it. Edit and run all files and programs from this directory. This method
works, but is not recommended.
Or the preferred way:
2) Create a directory called POVRAY and several subdirectories called
INCLUDE, DEMO, SCENES, UTIL. The self-extracting archives used in some
versions of the program will create subdirectories for you. If you create
your own, the file tree for this should look something like this:
\-
|
+POVRAY -
|
+INCLUDE
|
+DEMO
|
+SCENES
|
+UTIL
Copy the executable file and docs into the directory POVRAY. Copy the
standard include files into the subdirectory INCLUDE. Copy the sample scene
files into the subdirectory SCENES. And copy any POV-Ray related utility
programs and their related files into the subdirectory UTIL. Your own scene
files will go into the SCENES subdirectory. Also, you'll need to add the
directories \POVRAY and \POVRAY\UTIL to your "search path" so the executable
programs can be run from any directory.
Note that some operating systems don't have an equivalent to the multi-path
search command.
The second method is a bit more difficult to set-up, but is preferred. There
are many files associated with POV-Ray and they are far easier to deal with
when separated into several directories.
3.2 Basic Usage
Notice: If you did not install the program using the install.exe system, the
examples and instructions given here may not work! The installation process
configures povray.ini and several important batch files. Without these files
configured, the examples herein may not work.
POV-Ray's basic purpose is to read a scene description written in the POV
language and to write an image file. The scene files are plain ASCII text
files that you create using a text editor. Dozens of sample files are
included with this package to illustrate the various features.
You invoke POV-Ray by typing a command at the MS-Dos prompt. The command is
POVRAY and it must be followed by one or more command line switches. Each
switch begins with a plus or minus sign. Blanks separate the switches. The
switches may be upper or lower case.
Note: The examples in this documentation assume you installed POV-Ray in the
c:\povray3 directory. The installer will let you install POV-Ray anywhere and
will properly configure it for the drive and directory you specified. You
just substitute that drive and directory anywhere we tell you to use
c:\povray3 . Change to that directory now. Then type the following command
line and press [ENTER]
POVRAY +ISHAPES +D1
The +I command (for input ) tells the program what file to read as input. If
you don't give an extension on the file name, .pov is assumed. Thus +I shapes
tells it to read in shapes.pov to be rendered.
The +D switch (for display ) tells the program to turn the graphic preview
display on. A -D would turn it off. The number "1" tells it what type of
display to use. Type "1" is the old fashioned standard generic VGA at 320 by
200 resolution and just 256 colors. This is pretty much guaranteed to work on
any VGA video system.
There are other options in effect besides those you typed on the command
line. They are stored in a file called povray.ini which was created by the
install system. POV-Ray automatically looks for this file in the same
directory where povray.exe resides. See "INI Files" and "Using INI Files" for
more information on povray.ini and other INI files.
When you enter the command shown above, you will see brightly colored
geometric shapes begin to appear as POV-Ray calculates the color of each
pixel row by row. You will probably be disappointed with the graphic display
results. That is because this is only a preview display. The actual image is
in full 24-bit color but we cannot display that high quality using simple VGA
with a fixed set of 256 colors. If your hardware supports the VESA interface
standard or you have a VESA TSR driver loaded, try running with +DG rather
than +D1 . This will give you access to all of the various modes your video
hardware can use. If you have 15-bit or 16- bit high color capability try
+DGH or if you have 24-bit true color capability try +DGT to see the image in
all its glory. See section "Display Types" below for more information on
graphics preview.
When the program finishes, you will hear beeps. After admiring the image,
press [ENTER]. You will see a text screen of statistics. If the text is too
much to fit on the screen you may press [CURSOR UP] or [CURSOR DOWN] keys to
read more text. Notice that there are tabs at the bottom of the screen. Press
[CURSOR LEFT] or [CURSOR RIGHT] keys to view other interesting text
information. Press [ENTER] again to exit POV-Ray.
If you do not have high color or true color ability you will have to view the
image file to see the real colors. The image file shapes.tga is written to
your current directory. By default POV-Ray creates files in TGA format. This
is a standard format for storing 24-bit true-color images. You will need an
image viewing program to view the file. Such programs are usually available
from the same place where you obtained POV-Ray but a viewer is not included
in this package.
If you cannot view TGA files you may add the switch +FN and POV-Ray will
output PNG (Portable Network Graphic) format. If PNG format viewer is not
available then type the following
T2G SHAPES
and press [ENTER]. This will run a batch file that invokes the tga2gif
program. The program will read your shapes.tga file, create an optimal 256
color palette and write a GIF format file shapes.gif . Most image viewing
programs support GIF.
3.2.1 Running Files in Other Directories
Normally POV-Ray only looks in the current directory for the files it needs.
It does not search your MS-Dos path for data files; it only searches for
programs. In the sample scene you just ran, file shapes.pov was in the
current directory so this was no problem. That scene also needed other files
but your povray.ini file tells POV-Ray other places to search for necessary
files.
If you allowed the install system to update your autoexec.bat file, then you
can change to any drive or directory and can run POV-Ray from that directory.
You will also be able to use the batch files and utilities that came with
this package in any directory. For future reference let's call the "use-
c:\povray3 -in-your-path-plan" as plan one .
There are some circumstances where you may not want to put c:\povray3 in your
path. There is a limit of 128 characters in your path statement and you may
not have room for it. Try rendering the shapes example from a different
directory. If it doesn't work, then you forgot to re-boot your system so the
new path takes effect. If after re-booting it still doesn't work, it probably
means your path is too full. You will have to adopt a different plan.
Chances are, you already have several directories in your path. Most systems
have c:\dos , c:\windows or some directory such as c:\utility already in the
path. We have provided several small batch files that you can copy to that
directory. For future reference we'll call the
"put-batch-files-in-a-directory-already-on-the-path-plan" as plan two .
At any dos prompt, type the word path and press [ENTER]. It will show you
what directories are already on your path. Then copy the following files from
your c:\povray3 directory to any of the directories already on your path. The
files are:
RUNPOV.BAT RERUNPOV.BAT RUNPHELP.BAT T2G.BAT
Once you have copied these files, try the following example. In this case, do
not invoke the program with the command povray . Instead use runpov as
follows:
cd \POVRAY3\POV3DEMO\SHOWOFF
RUNPOV +ISUNSET3 +D1
This changes to the \povray3\pov3demo\showoff directory where the file
sunset3.pov is found. It runs the file runpov.bat . That batch file is set up
to run POV-Ray even if it is not on the dos path. It also passes the switches
along to POV-Ray. These batch files have other uses, even if you are using
plan one as described above or plan three as described below. For more on
these batch files, see "Batch Files" .
All of the early examples in this document assumed you were running POV-Ray
from the directory where it was installed such as c:\BS povray3 . This
approach of always using the installation directory is in fact plan three .
If you are using this method, you need to tell POV-Ray where else to look for
files. In the case of sunset3.pov you could do this:
POVRAY +IC:\POVRAY3\POV3DEMO\SHOWOFF\SUNSET3 +D1
However some scenes need more than one file. For example the directory drums2
that can be found under \povray3\povscn\BS level3 contains three files:
drums.pov , drums.inc and rednewt.gif all of which are required for that one
scene. In this case you should use the +L switch (for library ) to add new
library paths to those that POV-Ray will search. You would render the scene
with this command.
POVRAY +L\POVRAY3\POVSCN\LEVEL3\DRUMS2 +IDRUMS +D1
3.2.2 INI Files
There were more options used in these renderings than just the switches +I ,
+D , and +L that you specify. When you run the program, POV- Ray
automatically looks for the file povray.ini in whatever directory that
povray.exe is in. The povray.ini file contains many options that control how
POV-Ray works. We have set this file up so that it is especially easy to run
your first scene with minimal problems. The file should be placed in the same
directory as povray.exe and it will automatically read when POV-Ray is run.
If you ever move povray.exe to a different directory, be sure to move
povray.ini too.
Complete details on all of the available switches and options that can be
given on the command line or in povray.ini are given in "POV-Ray Options" .
You may also create INI files of your own with switches or options similar to
povray.ini . If you put a file name on the command line without a plus or
minus sign before it, POV-Ray reads it as an INI file. Try this...
POVRAY RES120 +ISHAPES +D1
This causes POV-Ray to look for a file called res120.ini which we have
provided. It sets your resolution to 120 by 90 pixels for a quick preview.
The following INI files have been provided for you.
RES120.INI Sets resolution to 120 by 90.
RES320.INI Sets resolution to 320 by 200.
RES640.INI Sets resolution to 640 by 480.
RES800.INI Sets resolution to 800 by 600.
RES1K.INI Sets resolution to 1024 by 768.
LOW.INI Sets low quality at 120 by 90.
SLOW.INI Turns on radiosity and anti-aliasing; very slow but
beautiful.
TGAFLI.INI TGAFLC.INI Create an FLI/FLC animation from TGA images.
PNGFLI.INI PNGFLC.INI Create an FLI/FLC animation from DTA images.
ZIPFLI.INI ZIPFLC.INI Create an FLI/FLC animation from zipped images. See
"ANIMATION TIPS" below.
You can create your own custom INI's which can contain any command in the
reference guide.
3.2.3 Alternatives to POVRAY.INI
The povray.ini file is supposed to hold your favorite global default options
that you want to use all the time. You should feel free to edit it with new
options that suit your needs. However it must be located in the same
directory as povray.exe or it won't be found. The dos path isn't searched nor
will +L commands help because povray.ini is processed before any command line
switches.
If your povray.exe resides on a CD-ROM then you can't edit the povray.ini on
the CD. There is an alternative. You may use an environment variable to
specify an alternative global default.
In your autoexec.bat file add a line similar to this:
set POVINI=D:\DIRECT\FILE.INI
which sets the POVINI environment variable to whatever drive, directory and
INI file you choose. If you specify any POVINI environment variable then
povray.ini is not read . This is true even if the file you named doesn't
exist. Note that you are specifying an entire path and file name. This is not
a pointer to a directory containing povray.ini . It is a pointer to the
actual file itself.
Note that the POVRAYOPT environment variable in previous versions of POV-Ray
is no longer supported.
3.2.4 Batch Files
We've already described how the file runpov.bat can be used as an alternative
to running POV-Ray directly. runpov.bat also has one other use. It uses the
+GI switch to create a file called rerun.ini . This makes it very easy to run
the same file over again with the same parameters. When creating your own
scene files you will probably make dozens of test renders. This is a very
valuable feature. Here is how it works... Suppose you render a scene as
follows:
RUNPOV +IMYSCENE +D1 RES120
This renders myscene.pov at 120 by 90 resolution. Note there is no such
scene. This is hypothetical. After viewing it, you noticed a mistake which
you fixed with your text editor. To rerun the scene type:
RERUNPOV
and that's all. It will rerun the same scene you just ran. Suppose you want
more detail on the next run. You can add more switches or INI files. For
example:
RERUNPOV RES320
will rerun at higher resolution. Subsequent uses of rerunpov will be at 320
by 200 until you tell it differently. As another example, the +A switch turns
on anti-aliasing. Typing " rerunpov +A " reruns with anti- aliasing on. All
subsequent reruns will have it on until you do a " rerunpov -A " to turn it
off. Note if you do another runpov it starts over from your povray.ini
defaults and it overwrites the old rerun.ini .
Two other batch files are included. runphelp.bat is only used as an
alternative way to run povhelp from another directory. If you used
installation plan two then use runphelp.bat rather than povhelp.exe . This
batch file serves no other purpose.
Finally t2g.bat invokes the tga2gif.exe program for converting TGA files to
GIF files. You could run \FILE {tga2gif} directly but its default parameters
do not generally produce the best results. If you use T2G instead, it adds
some command line switches which work better. For a full list of switches
available for tga2gif , type tga2gif with no parameters and it will display
the available switches and options.
3.2.5 Display Types
You have already seen how to turn on graphics preview using +D1 . Here are
details on other variations of the +D switch. Use -D to turn the display off.
If you use -D then you will probably want to add the +V switch to turn on
verbose status messages so you can monitor the progress of the rendering
while in progress.
The number "1" after the +D tells it what kind of video hardware to use. If
you use +D alone or +D0 then POV-Ray will attempt to auto detect your
hardware type. Use +D? to see a message about what type of hardware POV-Ray
found.
You may also explicitly tell POV-Ray what hardware to use. The following
chart lists all of the supported types.
+D0 Auto detect (S)VGA type (Default)
+D1 Standard VGA 320x200
+D2 Standard VGA 360 x 480
+D3 Tseng Labs 3000 SVGA 640x480
+D4 Tseng Labs 4000 SVGA
+D5 AT&T VDC600 SVGA 640x400
+D6 Oak Technologies SVGA 640x480
+D7 Video 7 SVGA 640x480
+D8 Video 7 Vega (Cirrus) VGA 360x480
+D9 Paradise SVGA 640x480
+DA Ahead Systems Ver. A SVGA 640x480
+DB Ahead Systems Ver. B SVGA 640x480
+DC Chips & Technologies SVGA 640x480
+DD ATI SGVA 640x480
+DE Everex SVGA 640x480
+DF Trident SVGA 640x480
+DG VESA Standard SVGA Adapter
+DH ATI XL display card
+DI Diamond Computer Systems SpeedSTAR 24X
The most common type is a VESA standard card which uses +DG . VESA is a
standard software interface that works on a wide variety of cards. Those
cards which do not have VESA support directly built-in, generally have a
video driver that you can load to provide VESA support. The program UniVBE is
a high quality universal VESA driver that may work for you. It can be found
at http://www.povray.org or possibly other POV-Ray sites.
The options listed above had been tested worked under earlier versions of
POV-Ray but there have been many changes in the program and we cannot
guarantee these all still work. If you can use VESA then do so. It has been
well tested and will give you the most flexibility.
After the +D and the type, you may specify a 3rd character that specifies the
palette type.
+D?3 Use 332 palette with dithering (default and best for VGA systems).
This is a fixed palette of 256 colors with each color consisting
3-bits of red data, 3-bits green and 2-bits blue.
+D?0 Use HSV palette option for VGA display. This is a fixed palette of 256
colors where colors are matched according to hue, saturation and
intensity rather than the amount of red, green and blue.
+D?G Use fixed gray scale palette option for VGA display.
+D?H Use HiColor option. Displays more than 32,000 colors with dithering.
Supported on VESA, SpeedSTAR 24X, ATI XL HiColor and Tseng 4000 based
cards with high color 15 or 16 bit options.
+D?T For Truecolor 24 bit cards. Use 24 bit color. Supported on the Diamond
SpeedSTAR 24X and cards with 24bit VESA support only.
Here are some examples:
+D0H Auto detect the VGA display type and display the image to the
screen as it's being worked on. Use the 15-bit HiColor chip and
dithering to display more than 32,000 colors on screen.
+D4 Display to a TSENG 4000 chipset VGA using the 332 palette option.
+D4H Display to a TSENG 4000 chipset VGA using the HiColor option.
+DG0 Display to a VESA VGA adapter and use the HSV palette option.
+DG3 Display to a VESA VGA adapter and use the 332 palette option.
+DGH Display to a VESA VGA adapter and use the HiColor option for
over 32,000 colors.
+DGT Display to a VESA VGA adapter and use the TrueColor option for
over 16 million colors.
Note that your VESA BIOS must support these options in order for you to use
them. Some cards may support HiColor and/or TrueColor at the hardware level
but not through their VESA BIOS.
4 Beginning Tutorial
The beginning tutorial explains step by step how to use POV-Ray's scene
description language to create your own scenes. The use of almost every
feature of POV-Ray's language is explained in detail. You will learn basic
things like placing cameras and light sources. You will also learn how to
create a large variety of objects and how to assign different textures to
them. The more sophisticated features like radiosity, halos, and atmospheric
effects will also be explaind in detail.
The following sections explain the features in roughly the same order as they
are described in the reference chapter.
4.1 Your First Image
Let's create the scene file for a simple picture. Since ray-tracers thrive on
spheres, that's what we'll render first.
4.1.1 Understanding POV-Ray's Coordinate System
First, we have to tell POV-Ray where our camera is and where it's looking. To
do this, we use 3D coordinates. The usual coordinate system for POV-Ray has
the positive Y axis pointing up, the positive X axis pointing to the right,
and the positive Z axis pointing into the screen as follows:
^+Y
| /+Z
| /
| /
-X |/ +X
<--|-->
/|
/ |
/ |
-Z/ |
v-Y
The left-handed coordinate system (the z-axis is pointing away from you).
This kind of coordinate system is called a left-handed coordinate system. If
you use your left hand's fingers you can easily see why it is called
left-handed. Just point your thumb in the direction of the positive x-axis,
your index finger in the direction of the positive y-axis and your middle
finger in the positive z-axis direction. You can only do this with your left
hand. If you had used your right hand you would not have been able to point
the middle finger in the correct direction.
The left hand can also be used to determine rotation directions. To do this
you must perform the famous Computer Graphics Aerobics exercise. Hold up your
left hand. Point your thumb in the positive direction of the axis of
rotation. Your fingers will curl in the positive direction of rotation.
Similarly if you point your thumb in the negative direction of the axis your
fingers will curl in the negative direction of rotation.
^
+Y| +Z/ _
| /_| |_ _
| _| | | |/ \
| | | | | | |
| /| | | | | V
-X |/ | | | | | +X
<--+-|-|-|-|-|->
/| | ____
/ | | ___|
/ | /
/ | | /
-Z/ -Y|
/ |
"Computer Graphics Aerobics" to determine the rotation direction.
In the above illustration, the left hand is curling around the x-axis. The
thumb points in the positive x direction and the fingers curl over in the
positive rotation direction.
If you want to use a right-handed system, as some CAD systems such as AutoCAD
do, the right vector in the camera specification needs to be changed. See the
detailed description in "Handedness" . In a right-handed system you use your
right hand for the Aerobics .
Note that there is some controversy over whether POV-Ray's method of doing a
right-handed system is really proper. If you want to avoid problems we
suggest you stick with the left-handed system which is not in dispute.
4.1.2 Adding Standard Include Files
Using your personal favorite text editor, create a file called demo.pov . Now
type in the following (the input is case sensitive, so be sure to get capital
and lowercase letters correct).
#include "colors.inc" // The include files contain
#include "shapes.inc" // pre-defined scene elements
#include "finish.inc"
#include "glass.inc"
#include "metals.inc"
#include "stones.inc"
#include "woods.inc"
The first include statement reads in definitions for various useful colors.
The second include statement reads in some useful shapes. The next read
pre-defined finishes, glass, metal, stone, and wood textures. When you get a
chance, have a look through them to see but a few of the many possible shapes
and textures available.
You should only include files you really need in your scene. Some of the
include files coming with POV-Ray are quite large and you should better save
the parsing time (and memory) if you don't need them. In the following
examples we will only use the colors.inc , finish.inc and stones.inc include
files so you'll better remove the appropriate lines from your scene file.
You may have as many include files as needed in a scene file. Include files
may themselves contain include files, but you are limited to declaring
includes nested only ten levels "deep".
Filenames specified in the include statements will be searched for in the
current directory first and, if not found, will then be searched for in
directories specified by any +L or Library_Path options active. This would
facilitate keeping all your "include" ( .inc ) files such as shapes.inc ,
colors.inc , and textures.inc in an "include" subdirectory, and giving an +L
option on the command line to where your library of include files are.
4.1.3 Adding a Camera
The camera declaration describes where and how the camera sees the scene. It
gives x, y, z coordinates to indicate the position of the camera and what
part of the scene it is pointing at. You describe x, y, z coordinates using a
three-part vector . A vector is specified by putting three numeric values
between a pair of angle brackets and separating the values with commas.
Add the following camera statement to the scene.
camera {
location <0, 2, -3>
look_at <0, 1, 2>
}
Briefly, location <0,2,-3> places the camera up two units and back three
units from the center of the ray-tracing universe which is at <0,0,0>.
Remember that by default +z is into the screen and -z is back out of the
screen.
Also look_at <0,1,2> rotates the camera to point at x, y, z coordinates
<0,1,2>. A point 5 units in front of and 1 unit lower than the camera. The
look_at point should be the center of attention of your image.
4.1.4 Describing an Object
Now that the camera is set up to record the scene, let's place a yellow
sphere into the scene. Add the following to your scene file:
sphere {
<0, 1, 2>, 2
texture {
pigment { color Yellow }
}
}
The first vector specifies the center of the sphere. In this example the x
coordinate is zero so it is centered left and right. It is also at y=1 or 1
unit up from the origin. The z coordinate is 2 which is 5 units in front of
the camera, which is at z=-3. After the center vector is a comma followed by
the radius which in this case is 2 units. Since the radius is half the width
of a sphere, the sphere is 4 units wide.
4.1.5 Adding Texture to an Object
After we have defined the location and size of the sphere, we need to
describe the appearance of the surface. The texture {... } block specifies
these parameters. Texture blocks describe the color, bumpiness and finish
properties of an object. In this example we will specify the color only. This
is the minimum we must do. All other texture options except color will use
default values.
The color you define is the way you want it to look if fully illuminated. If
you were painting a picture of a sphere you would use dark shades of a color
to indicate the shadowed side and bright shades on the illuminated side.
However ray-tracing takes care of that for you. You pick the basic color
inherent in the object and POV-Ray brightens or darkens it depending on the
lighting in the scene. Because we are defining the basic color the object
actually has rather than how it looks the parameter is called pigment .
Many types of color patterns are available for use in a pigment {... }
statement. The keyword color specifies that the whole object is to be one
solid color rather than some pattern of colors. You can use one of the color
identifiers previously defined in the standard include file colors.inc .
If no standard color is available for your needs, you may define your own
color by using the color keyword followed by red , green and blue keywords
specifying the amount of red, green and blue to be mixed. For example a nice
shade of pink can be specified by:
color red 1.0 green 0.8 blue 0.8
The values after each keyword should be in the range 0.0 to 1.0. Any of the
three components not specified will default to 0. A shortcut notation may
also be used. The following produces the same shade of pink:
color rgb <1.0, 0.8, 0.8>
4.1.6 Defining a Light Source
One more detail is needed for our scene. We need a light source. Until you
create one, there is no light in this virtual world. Thus add the line
light_source { <2, 4, -3> color White}
to your scene file to get your first complete POV-Ray scene file as shown
below.
#include "colors.inc"
background { color Cyan }
camera {
location <0, 2, -3>
look_at <0, 1, 2>
}
sphere {
<0, 1, 2>, 2
texture {
pigment { color Yellow }
}
}
light_source { <2, 4, -3> color White}
The vector in the light_source statement specifies the location of the light
as 2 units to our right, 4 units above the origin and 3 units back from the
origin. The light source is invisible, it only casts light, so no texture is
needed.
That's it! Close the file and render a small picture of it using the command
povray +w160 +h120 +p +x +d0 -v -idemo.pov
If your computer does not use the command line, see your platform specific
docs for the correct command to render a scene.
You may also set any other command line options you like. The scene is
written to the image file demo.tga (or some suffix other than .tga if your
computer uses a different default file format).
The scene you just traced isn't quite state of the art but we'll have to
start with the basics before we soon get to much more fascinating features
and scenes.
4.2 Using the Camera
4.2.1 Camera Types
4.2.2 Using Focal Blur
4.2.3 Using Camera Ray Perturbation
4.3 Simple Shapes
So far we've just used the sphere shape. There are many other types of shapes
that can be rendered by POV-Ray. The following sections will describe how to
use some of the more simple objects as a replacement for the sphere used
above.
4.3.1 Box Object
The box is one of the most common objects used. Try this example in place of
the sphere:
box {
<-1, 0, -1>, // Near lower left corner
< 1, 0.5, 3> // Far upper right corner
texture {
T_Stone25 // Pre-defined from stones.inc
scale 4 // Scale by the same amount in all
// directions
}
rotate y*20 // Equivalent to "rotate <0,20,0>"
}
In this example you can see that a box is defined by specifying the 3D
coordinates of its opposite corners. The first vector must be the minimum x,
y, z coordinates and the 2nd vector must be the maximum x, y, z values. Box
objects can only be defined parallel to the axes of the world coordinate
system. You can later rotate them to any angle. Note that you can perform
simple math on values and vectors. In the rotate parameter we multiplied the
vector identifier y by 20. This is the same as <0,1,0>*20 or <0,20,0>.
4.3.2 Cone Object
Here's another example showing how to use a cone:
cone {
<0, 1, 0>, 0.3 // Center and radius of one end
<1, 2, 3>, 1.0 // Center and radius of other end
texture { T_Stone25 scale 4 }
}
The cone shape is defined by the center and radius of each end. In this
example one end is at location <0,1,0> and has radius of 0.3 while the other
end is centered at <1,2,3> with radius=1. If you want the cone to come to a
sharp point then use radius=0. The solid end caps are parallel to each other
and perpendicular to the cone axis. If you want an open cone with no end caps
then add the keyword open after the 2nd radius like this:
cone {
<0, 1, 0>, 0.3 // Center and radius of one end
<1, 2, 3>, 1.0 // Center and radius of other end
open // Removes end caps
texture { T_Stone25 scale 4 }
}
4.3.3 Cylinder Object
You may also define a cylinder like this:
cylinder {
<0, 1, 0>, // Center of one end
<1, 2, 3>, // Center of other end
0.5 // Radius
open // Remove end caps
texture { T_Stone25 scale 4 }
}
4.3.4 Plane Object
Let's try out a computer graphics standard - The Checkered Floor . Add the
following object to the first version of the demo.pov file, the one including
the sphere.
plane { <0, 1, 0>, -1
pigment {
checker color Red, color Blue
}
}
The object defined here is an infinite plane. The vector <0,1,0> is the
surface normal of the plane (i.e. if you were standing on the surface, the
normal points straight up). The number afterward is the distance that the
plane is displaced along the normal from the origin - in this case, the floor
is placed at y=-1 so that the sphere at y=1, radius=2, is resting on it.
Notice that there is no texture {... } statement. There really is an implied
texture there. You might find that continually typing statements that are
nested like texture {pigment {... }} can get to be a tiresome so POV-Ray lets
you leave out the texture {... } under many circumstances. In general you
only need the texture block surrounding a texture identifier (like the
T_Stone25 example above), or when creating layered textures (which are
covered later).
This pigment uses the checker color pattern and specifies that the two colors
red and blue should be used.
Because the vectors <1,0,0>, <0,1,0> and <0,0,1> are used frequently, POV-Ray
has three built-in vector identifiers x , y , and z respectively that can be
used as a shorthand. Thus the plane could be defined as:
plane { y, -1
pigment { ... }
}
Note that you do not use angle brackets around vector identifiers.
Looking at the floor, you'll notice that the ball casts a shadow on the
floor. Shadows are calculated very accurately by the ray-tracer, which
creates precise, sharp shadows. In the real world, penumbral or "soft"
shadows are often seen. Later you'll learn how to use extended light sources
to soften the shadows.
4.3.5 Standard Include Objects
The standard include file shapes.inc contains some pre-defined shapes that
are about the size of a sphere with a radius of one unit. You can invoke them
like this:
#include "shapes.inc"
object {
UnitBox
texture { T_Stone25 scale 4 }
scale 0.75
rotate <-20,25,0>
translate y
}
4.4 Advanced Shapes
After you have gained some experience with the simpler shapes available in
POV-Ray it is time to go on to the more advanced, thrilling shapes.
You should be aware that the shapes described below are not trivial to
understand. Don't worry if you do not know how to use them or how they work.
Just try the examples and play with the features described in the reference
chapter. There is nothing better than learning by doing.
4.4.1 Bicubic Patch Object
Bicubic or Bezier patches are useful surface representations because they
allow an easy definition of surfaces using only a few control points. For ray
tracing (or rendering) the patches are approximated using triangles. The
control points serve to determine the shape of the patch. Instead of defining
the vertices of triangles, you simply give the coordinates of the control
points. A single patch has 16 control points, four at each corner, and the
rest positioned to divide the patch into smaller sections. Bezier patches are
almost always created using a third party modeler so for this tutorial, we
will use moray (any other modeler that supports Bezier patches and POV can
also be used). We will use moray only to create the patch itself, not the
other elements of the scene.
Bezier patches are actually very useful and, with a little practice, some
pretty amazing things can be created with them. For our first tutorial, let's
make a sort of a teepee/tent shape using a single sheet patch.
First, start moray and, from the main edit screen, click on "CREATE". Name
your object Teepee . The "CREATE BEZIER PATCH" dialogue box will appear. Make
sure that "SHEET" is depressed. Click on "OK, CREATE". At the bottom of the
main edit screen, click on "EXTENDED EDIT".
Hold the cursor over the "TOP" view and right click to make the pop-up menu
appear. Click on "MAXIMIZE". [ALT]-drag to zoom in a little. Click on "MARK
ALL", and under the transformation mode box, "UFRM SCL". Drag the mouse to
scale the patch until it is approximately four units wide. Click on
"TRANSLATE", and move the patch so that its center is over the origin. Right
click - "MINIMIZE", "UNMARK ALL".
[SHIFT]-drag a box around the lower right control point to mark it.
[ALT]-zoom into the "FRONT" view so that you can see the patch better. In the
"FRONT" view, "TRANSLATE" that point 10 units along the negative z-axis (note
that in MORAY z is up). "UNMARK ALL". Repeat this procedure for each of the
other three corner points. Make sure you remember to "UNMARK ALL" once each
point has been translated. You should have a shape that looks as though it is
standing on four pointed legs. "UNMARK ALL".
Working once again in the "TOP" view, [SHIFT]-drag a box around the four
center control points to mark them. Right-click over the "TOP" view,
"MAXIMIZE". Click on "UFRM SCL" and drag the mouse to scale the four points
close together. [ALT]-drag to zoom closer and get them as close together as
you can. [ALT]-drag to zoom out, right click, "MINIMIZE".
In the "FRONT" view, "TRANSLATE" the marked points 10 units along the
positive z-axis. "UNMARK ALL". The resulting shape is quite interesting, was
simple to model, and could not be produced using CSG primitives. Now let's
use it in a scene.
Click on "DONE" to return to the main edit screen. Notice that U_STEPS and
V_STEPS are both set to 3 and flatness is set to 0.01. Leave them alone for
now. Click on "FILES", and then "SAVE SEL" (save selection). Name your new
file teepee1.mdl . Press [F3] and open teepee1.mdl . There is no need to save
the original file. When teepee1 is open, create a quick "dummy" texture (
moray will not allow you to export data without a texture), say, white with
default finish, name it TeePeeTex , and apply it to the object. Save the file
and press [CTRL-F9]. moray will create two files: teepee1.inc and teepee1.pov
.
Exit moray and copy teepee1.inc and teepee1.pov into your working directory
where you are doing these tutorials. Create a new file called bezdemo.pov and
edit it as follows:
#include "colors.inc"
camera {
location <0, .1, -60>
look_at 0
angle 36
}
background { color Gray25 } //to make the patch easier to see
light_source { <300, 300, -700> White }
plane { y, -12
texture {
pigment {
checker
color Green
color Yellow
}
}
}
Using a text editor, create and declare a simple texture for your teepee
object:
#declare TeePeeTex = texture {
pigment {
color rgb <1, 1, 1,>
}
finish {
ambient .2
diffuse .6
}
}
Now, paste in the bezier patch data from teepee1.pov (the additional object
keywords added by moray were removed):
bicubic_patch {
type 1 flatness 0.0100 u_steps 3 v_steps 3,
<-5.174134, 5.528420, -13.211995>,
<-1.769023, 5.528420, 0.000000>,
<1.636088, 5.528420, 0.000000>,
<5.041199, 5.528420, -13.003932>,
<-5.174134, 1.862827, 0.000000>,
<0.038471, 0.031270, 18.101474>,
<0.036657, 0.031270, 18.101474>,
<5.041199, 1.862827, 0.000000>,
<-5.174134, -1.802766, 0.000000>,
<0.038471, 0.028792, 18.101474>,
<0.036657, 0.028792, 18.101474>,
<5.041199, -1.802766, 0.000000>,
<-5.174134, -5.468359, -13.070366>,
<-1.769023, -5.468359, 0.000000>,
<1.636088, -5.468359, 0.000000>,
<4.974128, -5.468359, -12.801446>
texture {
TeePeeTex
}
rotate -90*x // to orient the object to LHC
rotate 25*y // to see the four "legs" better
}
Add the above rotations so that the patch is oriented to POV's left-handed
coordinate system (remember the patch was made in moray in a right handed
coordinate system) and so we can see all four legs. Rendering this at 200x150
-a we see pretty much what we expect, a white teepee over a green and yellow
checkered plane. Let's take a little closer look. Render it again, this time
at 320x200.
Now we see that something is amiss. There appears to be sharp angling, almost
like faceting, especially near the top. This is indeed a kind of faceting and
is due to the U_STEPS and V_STEPS parameters. Let's change these from 3 to 4
and see what happens.
That's much better, but it took a little longer to render. This is an
unavoidable tradeoff. If you want even finer detail, use a U_STEPS and
V_STEPS value of 5 and set flatness to 0. But expect to use lots of memory
and an even longer tracing time.
Well, we can't just leave this scene without adding a few items just for
interest. Declare the patch object and scatter a few of them around the
scene:
#declare TeePee = bicubic_patch {
type 1 flatness 0.0100 u_steps 3 v_steps 3,
<-5.174134, 5.528420, -13.211995>,
<-1.769023, 5.528420, 0.000000>,
<1.636088, 5.528420, 0.000000>,
<5.041199, 5.528420, -13.003932>,
<-5.174134, 1.862827, 0.000000>,
<0.038471, 0.031270, 18.101474>,
<0.036657, 0.031270, 18.101474>,
<5.041199, 1.862827, 0.000000>,
<-5.174134, -1.802766, 0.000000>,
<0.038471, 0.028792, 18.101474>,
<0.036657, 0.028792, 18.101474>,
<5.041199, -1.802766, 0.000000>,
<-5.174134, -5.468359, -13.070366>,
<-1.769023, -5.468359, 0.000000>,
<1.636088, -5.468359, 0.000000>,
<4.974128, -5.468359, -12.801446>
texture {
TeePeeTex
}
rotate -90*x // to orient the object to LHC
rotate 25*y // to see the four "legs" better
}
object { TeePee }
object { TeePee translate <8, 0, 8> }
object { TeePee translate <-9, 0, 9> }
object { TeePee translate <18, 0, 24> }
object { TeePee translate <-18, 0, 24> }
That looks good. Let's do something about that boring gray background. Delete
the background declaration and replace it with:
plane { y, 500
texture {
pigment { SkyBlue }
finish { ambient 1 diffuse 0}
}
texture {
pigment {
bozo
turbulence .5
color_map {
[0 White]
[1 White filter 1]
}
}
finish { ambient 1 diffuse 0 }
scale <1000, 250, 250>
rotate <5, 45, 0>
}
}
This adds a pleasing cirrus-cloud filled sky. Now, let's change the checkered
plane to rippled sand dunes:
plane {y,-12
texture {
pigment {
color <.85, .5, .15>
}
finish {
ambient .25
diffuse .6
crand .5
}
normal {
ripples .35
turbulence .25
frequency 5
}
scale 10
translate 50*x
}
}
Render this at 320x240 -a. Not bad! Let's just add one more element. Let's
place a golden egg under each of the teepees. And since this is a bezier
patch tutorial, let's make the eggs out of bezier patches.
Return to moray and create another bezier patch. Name it Egg1 and select
"CYLINDRICAL 2 - PATCH" from the "CREATE BEZIER PATCH" dialogue box. Click on
"EXTENDED EDIT". "MARK ALL", and rotate the patch so that the cylinder lays
on its side. "UNMARK ALL". In the "FRONT" view, [SHIFT]-drag a box around the
four points on the right end to mark them. In the "SIDE" view, right click,
"MAXIMIZE". [ALT]-drag to zoom in a little closer. "UFRM SCL" the points
together as close as possible. Zoom in closer to get them nice and tight.
Zoom out, right click, "MINIMIZE".
Click on "TRANSLATE" and drag the points to the left so that they are aligned
on the z-axis with the next group of four points. This should create a blunt
end to the patch. Repeat this procedure for the other end. "UNMARK ALL".
In the "FRONT" view, the control grid should be a rectangle now and the patch
should be an ellipsoid. [SHIFT]-drag a box around the upper right corner of
the control grid to mark those points. Then [SHIFT]-drag a box around the
lower
right corner to mark those points as well. In the "SIDE" view, "UFRM SCL" the
points apart a little to make that end of the egg a little wider than the
other. "UNMARK ALL".
The egg may need a little proportional adjustment. You should be able to
"MARK ALL" and "LOCAL SCL" in the three views until you get it to look like
an egg. When you are satisfied that it does, "UNMARK ALL" and click on done.
Learning from our teepee object, we now go ahead and change U_STEPS and
V_STEPS to 4.
Create a dummy texture, white with default finish, name it EggTex , and apply
it to the egg. From the FILES menu, "SAVE SEL" to filename egg1.mdl . Load
this file and export ([CTRL F9]). Exit moray and copy the files egg1.inc and
egg1.pov into your working directory.
Back in bezdemo.pov , create a nice, shiny gold texture:
#declare EggTex = texture {
pigment { BrightGold }
finish {
ambient .1
diffuse .4
specular 1
roughness 0.001
reflection .5
metallic
}
}
And while we're at it, let's dandy up our TeePeeTex :
#declare TeePeeTex = texture {
pigment { Silver }
finish {
ambient .1
diffuse .4
specular 1
roughness 0.001
reflection .5
metallic
}
}
Now paste in your egg patch data and declare your egg:
#declare Egg = union { // Egg1
bicubic_patch {
type 1 flatness 0.0100 u_steps 4 v_steps 4,
<2.023314, 0.000000, 4.355987>,
<2.023314, -0.000726, 4.355987>,
<2.023312, -0.000726, 4.356867>,
<2.023312, 0.000000, 4.356867>,
<2.032037, 0.000000, 2.734598>,
<2.032037, -1.758562, 2.734598>,
<2.027431, -1.758562, 6.141971>,
<2.027431, 0.000000, 6.141971>,
<-1.045672, 0.000000, 3.281572>,
<-1.045672, -1.758562, 3.281572>,
<-1.050279, -1.758562, 5.414183>,
<-1.050279, 0.000000, 5.414183>,
<-1.044333, 0.000000, 4.341816>,
<-1.044333, -0.002947, 4.341816>,
<-1.044341, -0.002947, 4.345389>,
<-1.044341, 0.000000, 4.345389>
}
bicubic_patch {
type 1 flatness 0.0100 u_steps 4 v_steps 4,
<2.023312, 0.000000, 4.356867>,
<2.023312, 0.000726, 4.356867>,
<2.023314, 0.000726, 4.355987>,
<2.023314, 0.000000, 4.355987>,
<2.027431, 0.000000, 6.141971>,
<2.027431, 1.758562, 6.141971>,
<2.032037, 1.758562, 2.734598>,
<2.032037, 0.000000, 2.734598>,
<-1.050279, 0.000000, 5.414183>,
<-1.050279, 1.758562, 5.414183>,
<-1.045672, 1.758562, 3.281572>,
<-1.045672, 0.000000, 3.281572>,
<-1.044341, 0.000000, 4.345389>,
<-1.044341, 0.002947, 4.345389>,
<-1.044333, 0.002947, 4.341816>,
<-1.044333, 0.000000, 4.341816>
}
texture { EggTex }
translate <0.5, 0, -5> // centers the egg around the origin
translate -9.8*y // places the egg on the ground
}
Now place a copy of the egg under each teepee. This should require only the x
and z coordinates of each teepee:
object { Egg }
object { Egg translate <8, 0, 8> }
object { Egg translate <-9, 0, 9> }
object { Egg translate <18, 0, 24> }
object { Egg translate <-18, 0, 24> }
Scene build with different Bezier patches.
Render this at 320x240 -A . Everything looks good so run it again at 640x480
+A . Now we see that there is still some faceting near the top of the teepees
and on the eggs as well. The only solution is to raise U_STEPS and V_STEPS
from 4 to 5 and set flatness to 0 for all our bezier objects. Make the
changes and render it again at 640x480 +A .
4.4.2 Blob Object
4.4.3 Height Field Object
A height field is an object that has a surface that is determined by the
color value or palette index number of an image designed for that purpose.
With height fields, realistic mountains and other types of terrain can easily
be made. First, you need an image from which to create the height field. It
just so happens that POV-Ray is ideal for creating such an image.
Make a new file called image.pov and edit it to contain the following:
#include "colors.inc"
global_settings {
assumed_gamma 2.2
hf_gray_16
}
The hf_gray_16 keyword causes the output to be in a special 16 bit grayscale
that is perfect for generating height fields. The normal 8 bit output will
lead to less smooth surfaces.
Now create a camera positioned so that it points directly down the z-axis at
the origin.
camera {
location <0, 0, -10>
look_at 0
}
Then create a plane positioned like a wall at z=0. This plane will completely
fill the screen. It will be colored with white and gray wrinkles.
plane { z, 10
pigment {
wrinkles
color_map {
[0 0.3*White]
[1 White]
}
}
}
Finally, create a light source.
light_source { <0, 20, -100> color White }
Render this scene at 640x480 +A0.1 +FT . You will get an image that will
produce an excellent height_field.
Now we will use this image to create a height field. Create a new file called
hfdemo.pov and edit it as follows:
#include "colors.inc"
Add a camera that is two units above the origin and ten units back ...
camera{
location <0, 2, -10>
look_at 0
angle 15
}
... and a light source.
light_source{ <1000,1000,-1000> White }
Now add the height field. In the following syntax, a Targa image file is
specified, the height field is smoothed , it is given a simple white pigment,
it is translated to center it around the origin, and it is scaled so that it
resembles mountains and fills the screen.
height_field {
tga "image.tga"
smooth
pigment { White }
translate <-.5, -.5, -.5>
scale <17, 1.75, 17>
}
Save the file and render it at 320x240 -A . Later, when you are satisfied
that the height field is the way you want it render it at a higher resolution
with antialiasing.
A height field created completely with POV-Ray.
4.4.4 Julia Fractal Object
4.4.5 Lathe Object
4.4.6 Mesh Object
Mesh objects are very useful because they allow you to create objects
containing hundreds or thousands of triangles. Compared to a simple union of
triangles the mesh object stores the triangles more efficiently. Copies of
mesh objects need only a little additional memory because the triangles are
stored only once.
Almost every object can be approximated using triangles but you may need a
lot of triangles to create more complex shapes. Thus we will only create a
very simple mesh example. This example will show a very useful feature of the
triangles meshs though: a different texture can be assigned to each triangle
in the mesh.
Now let us start. We'll create a simple box with differently colored sides.
Create an empty file called meshdemo.pov and add the following lines.
camera {
location <20, 20, -50>
look_at <0, 5, 0>
}
light_source { <50, 50, -50> color rgb<1, 1, 1> }
#declare Red = texture {
pigment { color rgb<0.8, 0.2, 0.2> }
finish { ambient 0.2 diffuse 0.5 }
}
#declare Green = texture {
pigment { color rgb<0.2, 0.8, 0.2> }
finish { ambient 0.2 diffuse 0.5 }
}
#declare Blue = texture {
pigment { color rgb<0.2, 0.2, 0.8> }
finish { ambient 0.2 diffuse 0.5 }
}
We must declare all textures we want to use inside the mesh before the mesh
is created. Textures cannot be specified inside the mesh due to the worser
memory performance that would result.
Now add the mesh object. Three sides of the box will use individual textures
while the other will use the "global" mesh texture.
mesh {
/* top side */
triangle { <-10, 10, -10>, <10, 10, -10>, <10, 10, 10>
texture { Red }
}
triangle { <-10, 10, -10>, <-10, 10, 10>, <10, 10, 10>
texture { Red }
}
/* bottom side */
triangle { <-10, -10, -10>, <10, -10, -10>, <10, -10, 10> }
triangle { <-10, -10, -10>, <-10, -10, 10>, <10, -10, 10> }
/* left side */
triangle { <-10, -10, -10>, <-10, -10, 10>, <-10, 10, 10> }
triangle { <-10, -10, -10>, <-10, 10, -10>, <-10, 10, 10> }
/* right side */
triangle { <10, -10, -10>, <10, -10, 10>, <10, 10, 10>
texture { Green }
}
triangle { <10, -10, -10>, <10, 10, -10>, <10, 10, 10>
texture { Green }
}
/* front side */
triangle { <-10, -10, -10>, <10, -10, -10>, <-10, 10, -10>
texture { Blue }
}
triangle { <-10, 10, -10>, <10, 10, -10>, <10, -10, -10>
texture { Blue }
}
/* back side */
triangle { <-10, -10, 10>, <10, -10, 10>, <-10, 10, 10> }
triangle { <-10, 10, 10>, <10, 10, 10>, <10, -10, 10> }
texture {
pigment { color rgb<0.9, 0.9, 0.9> }
finish { ambient 0.2 diffuse 0.7 }
}
}
Trace the scene at 320x240. You'll see that the top, right, and front side of
the box have different textures. Thought this is not a very impressive
example it shows what you can do with mesh objects. More complex examples,
also using smooth triangles, can be found under the scene directory as
chesmsh.pov and robotmsh.pov .
4.4.7 Polygon Object
The polygon object can be used to create any planar, n-sided shapes like
squares, rectangles, pentagons, hexagons, octagons, etc.
A polygon is defined by a number of points that describe its shape. Since
polygons have to be closed the first point has to be repeated at the end of
the point sequence.
In the following example we will create the word POV using just one polygon
statement.
We start with thinking about the points we need to describe the desired
shape. We want the letters to lie in the x-y-plane with the letter O being at
the center. The letters extend from y=0 to y=1. Thus we get the following
points for each letter (the z coordinate is automatically set to zero).
Letter P (outer polygon):
<-0.8, 0.0>, <-0.8, 1.0>,
<-0.3, 1.0>, <-0.3, 0.5>,
<-0.7, 0.5>, <-0.7, 0.0>
Letter P (inner polygon):
<-0.7, 0.6>, <-0.7, 0.9>,
<-0.4, 0.9>, <-0.4, 0.6>
Letter O (outer polygon):
<-0.25, 0.0>, <-0.25, 1.0>,
< 0.25, 1.0>, < 0.25, 0.0>
Letter O (inner polygon):
<-0.15, 0.1>, <-0.15, 0.9>,
< 0.15, 0.9>, < 0.15, 0.1>
Letter V:
<0.45, 0.0>, <0.30, 1.0>,
<0.40, 1.0>, <0.55, 0.1>,
<0.70, 1.0>, <0.80, 1.0>,
<0.65, 0.0>
Both letters P and O have a hole while the letter V consists of only one
polygon. We'll start with the letter V because it is easier to define than
the other two letters.
Create a new file called polygdem.pov and add the following text.
camera {
orthographic
location <0, 0, -10>
right 1.3 * 4/3 * x
up 1.3 * y
look_at <0, 0.5, 0>
}
light_source { <25, 25, -100> color rgb 1 }
polygon {
8,
<0.45, 0.0>, <0.30, 1.0>, // Letter "V"
<0.40, 1.0>, <0.55, 0.1>,
<0.70, 1.0>, <0.80, 1.0>,
<0.65, 0.0>,
<0.45, 0.0>
pigment { color rgb <1, 0, 0> }
}
As noted above the polygon has to be closed by appending the first point to
the point sequence. A closed polygon is always defined by a sequence of
points that ends when a point is the same as the first point.
After we have created the letter V we'll continue with the letter P . Since
it has a hole we have to find a way of cutting this hole into the basic
shape. This is quite easy. We just define the outer shape of the letter P ,
which is a closed polygon, and add the sequence of points that describes the
hole, which is also a closed polygon. That's all we have to do. There'll be a
hole where both polygons overlap.
In general you'll get holes whenever an even number of sub-polygons inside a
single polygon statement overlap. A sub-polygon is defined by a closed
sequence of points.
The letter P consists of two sub-polyons, one for the outer shape and one for
the hole. Since the hole polygon overlaps the outer shape polygon we'll get a
hole.
After you've understood how multiple sub-polygons in a single polygon
statement work, it's quite easy to add the missing O letter.
Finally, we get the complete word POV .
polygon {
30,
<-0.8, 0.0>, <-0.8, 1.0>, // Letter "P"
<-0.3, 1.0>, <-0.3, 0.5>, // outer shape
<-0.7, 0.5>, <-0.7, 0.0>,
<-0.8, 0.0>,
<-0.7, 0.6>, <-0.7, 0.9>, // whole
<-0.4, 0.9>, <-0.4, 0.6>,
<-0.7, 0.6>
<-0.25, 0.0>, <-0.25, 1.0>, // Letter "O"
< 0.25, 1.0>, < 0.25, 0.0>, // outer shape
<-0.25, 0.0>,
<-0.15, 0.1>, <-0.15, 0.9>, // whole
< 0.15, 0.9>, < 0.15, 0.1>,
<-0.15, 0.1>,
<0.45, 0.0>, <0.30, 1.0>, // Letter "V"
<0.40, 1.0>, <0.55, 0.1>,
<0.70, 1.0>, <0.80, 1.0>,
<0.65, 0.0>,
<0.45, 0.0>
pigment { color rgb <1, 0, 0> }
}
4.4.8 Prism Object
4.4.9 Superquadric Ellipsoid Object
Sometimes we want to make an object that does not have perfectly sharp edges
like a box does. Then, the super quadric ellipsoid is a useful object. It is
described by the simple syntax:
superellipsoid { <r, n> }
Where r and n are float values greater than zero and less than or equal to
one. Let's make a superellipsoid and experiement with the values of r and n
to see what kind of shapes we can make.
Create a file called supellps.pov and edit it as follows:
#include "colors.inc"
camera {
location <10, 5, -20>
look_at 0
angle 15
}
background { color rgb <.5, .5, .5> }
light_source { <10, 50, -100> White }
The addition of a gray background makes it a little easier to see our object.
Now type:
superellipsoid { <.25, .25>
pigment { Red }
}
Save the file and trace it at 200x150 -A to see the shape. It will look like
a box, but the edges will be rounded off. Now let's experiment with different
values of r and n. For the next trace, try <1, 0.2>. The shape now looks like
a cylinder, but the top edges are rounded. Now try <0.1, 1>. This shape is an
odd one! We don't know exactly what to call it, but it is interesting.
Finally, lets try <1, 1>. Well, this is more familiar... a sphere!
There are a couple of facts about superellipsoids you should know. First, you
should not use a value of 0 for either r nor n. This will cause POV-Ray to
incorrectly make a black box instead of your desired shape. Second, very
small values of r and n may yield strange results so they should be avoided.
Finally, the Sturmian root solver will not work with superellipsoids.
Superellipsoids are finite objects so they respond to auto-bounding and can
be used in CSG.
Now let's use the superellipsoid to make something that would be useful in a
scene. We will make a tiled floor and place a couple of superellipsoid
objects hovering over it. We can start with the file we have already made.
Rename it tiles.pov . Edit it so that it reads as follows:
#include "colors.inc"
#include "textures.inc"
camera {
location <10, 5, -20>
look_at 0
angle 15
}
background { color rgb <.5, .5, .5> }
light_source{ <10, 50, -100> White }
Note that we have added #include "textures.inc" so we can use pre-defined
textures. Now we want to define the superellipsoid which will be our tile.
#declare Tile = superellipsoid { <0.5, 0.1>
scale <1, .05, 1>
}
Superellipsoids are roughly 2*2*2 units unless you scale them otherwise. If
we wish to lay a bunch of our tiles side by side, they will have to be offset
from each other so they don't overlap. We should select an offset value that
is slightly more than 2 so that we have some space between the tiles to fill
with grout. So now add this:
#declare Offset = 2.1
We now want to lay down a row of tiles. Each tile will be offset from the
original by an ever-increasing amount in both the +z and -z directions. We
refer to our offset and multiply by the tile's rank to determine the position
of each tile in the row. We also union these tiles into a single object
called Row like this:
#declare Row = union {
object { Tile }
object { Tile translate z*Offset }
object { Tile translate z*Offset*2 }
object { Tile translate z*Offset*3 }
object { Tile translate z*Offset*4 }
object { Tile translate z*Offset*5 }
object { Tile translate z*Offset*6 }
object { Tile translate z*Offset*7 }
object { Tile translate z*Offset*8 }
object { Tile translate z*Offset*9 }
object { Tile translate z*Offset*10 }
object { Tile translate -z*Offset }
object { Tile translate -z*Offset*2 }
object { Tile translate -z*Offset*3 }
object { Tile translate -z*Offset*4 }
object { Tile translate -z*Offset*5 }
object { Tile translate -z*Offset*6 }
}
This gives us a single row of 17 tiles, more than enough to fill the screen.
Now we must make copies of the Row and translate them, again by the offset
value, in both the +x and -x directions in ever increasing amounts in the
same manner.
object { Row }
object { Row translate x*Offset }
object { Row translate x*Offset*2 }
object { Row translate x*Offset*3 }
object { Row translate x*Offset*4 }
object { Row translate x*Offset*5 }
object { Row translate x*Offset*6 }
object { Row translate x*Offset*7 }
object { Row translate -x*Offset }
object { Row translate -x*Offset*2 }
object { Row translate -x*Offset*3 }
object { Row translate -x*Offset*4 }
object { Row translate -x*Offset*5 }
object { Row translate -x*Offset*6 }
object { Row translate -x*Offset*7 }
Finally, our tiles are complete. But we need a texture for them. To do this
we union all of the Rows together and apply a White Marble pigment and a
somewhat shiny refelctive surface to it:
union{
object { Row }
object { Row translate x*Offset }
object { Row translate x*Offset*2 }
object { Row translate x*Offset*3 }
object { Row translate x*Offset*4 }
object { Row translate x*Offset*5 }
object { Row translate x*Offset*6 }
object { Row translate x*Offset*7 }
object { Row translate -x*Offset }
object { Row translate -x*Offset*2 }
object { Row translate -x*Offset*3 }
object { Row translate -x*Offset*4 }
object { Row translate -x*Offset*5 }
object { Row translate -x*Offset*6 }
object { Row translate -x*Offset*7 }
pigment { White_Marble }
finish { phong 1 phong_size 50 reflection .35 }
}
We now need to add the grout . This can simply be a white plane. We have
stepped up the ambient here a little so it looks whiter.
plane { y, 0 //this is the grout
pigment { color White }
finish { ambient .4 diffuse .7 }
}
To complete our scene, let's add five different superellipsoids, each a
different color, so that they hover over our tiles and are reflected in them.
superellipsoid {
<0.1, 1>
pigment { Red }
translate <5, 3, 0>
scale .45
}
superellipsoid {
<1, 0.25>
pigment { Blue }
translate <-5, 3, 0>
scale .45
}
superellipsoid {
<0.2, 0.6>
pigment { Green }
translate <0, 3, 5>
scale .45
}
superellipsoid {
<0.25, 0.25>
pigment { Yellow }
translate <0, 3, -5>
scale .45
}
superellipsoid {
<1, 1>
pigment { Pink }
translate y*3
scale .45
}
Some superellipsoids hovering above a tiled floor.
Trace the scene at 320x200 -A to see the result. If you are happy with that,
do a final trace at 640x480 +A0.2 .
4.4.10 Surface of Revolution Object
Bottles, vases, and glasses make nice objects in ray-traced scenes. We want
to create a golden, cup using the surface of revolution object (SOR object).
We first start by thinking about the shape of the final object. It is quite
difficult to come up with a set of points that describe a given curve without
the help of a modelling program supporting POV's surface of revolution
object. If such a program is available you should take advantage of it.
The point configuration of our cup object.
We will use the point configuration shown in the figure above. There are
eight points describing the curve that will be rotated about the y-axis to
get our cup. The curve was calculated using the method described in the
reference section (see "Surface of Revolution" ).
Now it is time to come up with a scene that uses the above SOR object. Edit a
file called sordemo.pov and enter the following text.
#include "colors.inc"
#include "golds.inc"
global_settings { assumed_gamma 2.2 }
camera {
location <10, 15, -20>
look_at <0, 5, 0>
angle 45
}
background { color rgb<0.2, 0.4, 0.8> }
light_source { <100, 100, -100> color rgb 1 }
plane { y, 0
pigment { checker color Red, color Green scale 10 }
}
sor {
8,
<0.0, -0.5>,
<3.0, 0.0>,
<1.0, 0.2>,
<0.5, 0.4>,
<0.5, 4.0>,
<1.0, 5.0>,
<3.0, 10.0>,
<4.0, 11.0>
texture { T_Gold_1B }
}
The scene contains our cup object resting on a checkered plane. Tracing this
scene at a resolution of 320x200 results in the image below.
A surface of revolution object.
The surface of revolution is described by starting with the number of points
followed by the points with ascending heights. Each point determines the
radius the curve for a given height. E. g. the first point tells POV-Ray that
at height -0.5 the radius is 0. You should take care that each point has a
larger height than its predecessor. If this is not the case the program will
abort with an error message.
4.4.11 Text Object
Creating text objects using POV-Ray always used to mean that the letters had
to be built either from CSG, a painstaking process, or by using a black and
white image of the letters as a height field, a method that was only somewhat
satisfactory. Now, for POV-Ray 3.0, a new primitive has been introduced that
can use any TrueType font to create text objects. These objects can be used
in CSG, transformed, and textured just like any other POV primitive.
For this tutorial, we will make two uses of the text object. First, let's
just make some block letters sitting on a checkered plane. Any TTF font
should do, but for this tutorial, we will use the ones bundled with POV-Ray
3.0.
Create a file called textdemo.pov and edit it as follows:
#include "colors.inc"
camera {
location <0, 1, -10>
look_at 0
angle 36
}
light_source { <500,500,-1000> White }
plane { y,0
pigment { checker Green White }
}
Now let's add the text object. We will use the font timrom.ttf and we will
create the string POV-RAY 3.0 . For now, we will just make the letters red.
The syntax is very simple. The first string in quotes is the font name, the
second one is the string to be rendered. The two floats are the thickness and
offset values. The thickness float determines how thick the block letters
will be. Values of .5 to 2 are usually best for this. The offset value will
add to the kerning distance of the letters. We will leave this a 0 for now.
text { ttf "timrom.ttf" "POV-RAY 3.0" 1, 0
pigment { Red }
}
Rendering this at 200x150 -A , we notice that the letters are off to the
right of the screen. This is because they are placed so that the lower left
front corner of the first letter is at the origin. To center the string we
need to translate it -x some distance. But how far? In the docs we see that
the letters are all 0.5 to 0.75 units high. If we assume that each one takes
about 0.5 units of space on the x-axis, this means that the string is about 6
units long (12 characters and spaces). Let's translate the string 3 units
along the negative x-axis.
text { ttf "timrom.ttf" "POV-RAY 3.0" 1, 0
pigment { Red }
translate -3*x
}
That's better. Now let's play around with some of the parameters of the text
object. First, let's raise the thickness float to something outlandish... say
25!
text { ttf "timrom.ttf" "POV-RAY 3.0" 25, 0
pigment { Red }
translate -2.25*x
}
Actually, that's kind of cool. Now let's return the thickness value to 1 and
try a different offset value. Change the offset float from 0 to 0.1 and
render it again.
Wait a minute?! The letters go wandering off up at an angle! That is not what
the docs describe! It almost looks as if the offset value applies in both the
x- and y-axis instead of just the x axis like we intended. Could it be that a
vector is called for here instead of a float? Let's try it. Replace 0.1 with
0.1*x and render it again.
That works! The letters are still in a straight line along the x axis, just a
little further apart. Let's verify this and try to offset just in the y axis.
Replace 0.1*x with 0.1*y . Again, this works as expected with the letters
going up to the right at an angle with no additional distance added along the
x axis. Now let's try the z axis. Replace 0.1*y with 0.1*z . Rendering this
yields a disappointment. No offset occurs! The offset value can only be
applied in the x and y directions.
Let's finish our scene by giving a fancier texture to the block letters,
using that cool large thickness value, and adding a slight y offset. For fun,
we will throw in a sky sphere, dandy up our plane a bit, and use a little
more interesting camera viewpoint (render the following scene at 640x480
+A0.2 ):
#include "colors.inc"
camera {
location <-5,.15,-2>
look_at <.3,.2,1>
angle 36
}
light_source { <500,500,-1000> White }
plane { y,0
texture {
pigment { SeaGreen }
finish { reflection .35 specular 1 }
normal { ripples .35 turbulence .5 scale .25 }
}
}
text { ttf "timrom.ttf" "POV-RAY 3.0" 25, 0.1*y
pigment { BrightGold }
finish { reflection .25 specular 1 }
translate -3*x
}
#include "skies.inc"
sky_sphere { S_Cloud5 }
Now. let's try using text in a CSG object. We will attempt to create an inlay
in a stone block using a text object. Create a new file called textcsg.pov
and edit it as follows:
#include "colors.inc"
#include "stones.inc"
background { color rgb 1 }
camera {
location <-3, 5, -15>
look_at 0
angle 25
}
light_source { <500,500,-1000> White }
Now let's create the block. We want it to be about eight units across because
our text string ( POV-RAY 3.0 ) is about six units long. We also want it
about four units high and about one unit deep. But we need to avoid a
potential coincident surface with the text object so we will make the first z
coordinate 0.1 instead of 0. Finally, we will give this block a nice stone
texture.
box { <-3.5, -1, 0.1>, <3.5, 1, 1>
texture { T_Stone10 }
}
Next, we want to make the text object. We can use the same object we used in
the first turorial except we will use slightly different thickness and offset
values.
text { ttf "timrom.ttf" "POV-RAY 3.0" 0.15, 0
pigment { BrightGold }
finish { reflection .25 specular 1 }
translate -3*x
}
Remember that the text object is placed by default so that its front surface
lies directly on the x-y-plane. If the front of the box begins at z=0.1 and
thickness is set at 0.15, the depth of the "inlay" will be 0.05 units. Go
ahead and place a difference block around the two objects.
difference {
box { <-3.5, -1, 0.1>, <3.5, 1, 1>
texture { T_Stone10 }
}
text { ttf "timrom.ttf" "POV-RAY 3.0" 0.15, 0
pigment { BrightGold }
finish { reflection .25 specular 1 }
translate -3*x
}
}
Text carved from stone.
Render this at 200x150 -A . We can see the inlay clearly and that it is
indeed a bright gold color. Render this at 640x480 +A0.2 to see the results
more clearly, but be forewarned... this trace will take a little time.
4.4.12 Torus Object
A torus can be thought of as a donut or an innertube. It is a shape that is
vastly useful in many kinds of CSG so POV-Ray has adopted this 4th order
quartic polynomial as a primitive shape. The syntax for a torus is so simple
that it makes it a very easy shape to work with once you learn what the two
float values mean. Instead of a lecture on the subject, let's create one and
do some experiments with it.
Create a file called tordemo.pov . Edit it as follows:
#include "colors.inc"
camera {
location <0, .1, -25>
look_at 0
angle 36
}
background { color Gray50 } // to make the torus easy to see
light_source{ <300, 300, -1000> White }
torus { 4, 1 // major and minor radius
rotate -90*x // so we can see it from the top
pigment { Green }
}
Go ahead and trace this. Well, it's a donut allright. Let's try changing the
major and minor radius values and see what happens. Change them as follows:
torus { 5, .25 // major and minor radius
That looks more like a hula-hoop! Let's try this:
torus { 3.5, 2.5 // major and minor radius
Whoa! A donut with a serious weight problem!
With such a simple syntax, there isn't much else you can do to a torus
besides change its texture... or is there? Let's see...
Torus' are very useful objects in CSG. Let's try a little experiment. Make a
difference of a torus and a box:
difference {
torus { 4, 1
rotate x*-90 // so we can see it from the top
}
box { <-5, -5, -1>, <5, 0, 1> }
pigment { Green }
}
Interesting... a half-torus. So? So, now add another one flipped the other
way. Only, let's declare the original half-torus and the necessary
transformations so we can use them again:
#declare Half_Torus = difference {
torus { 4, 1
rotate -90*x // so we can see it from the top
}
box { <-5, -5, -1>, <5, 0, 1> }
pigment { Green }
}
#declare Flip_It_Over = 180*x
#declare Torus_Translate = 8 // twice the major radius
Now create a union of two Half_Torus objects:
union {
object { Half_Torus }
object { Half_Torus
rotate Flip_It_Over
translate Torus_Translate*x
}
}
This makes an S -shaped object, but we can't see the whole thing from our
present camera. Let's add a few more links, three in each direction, move the
object along the +z direction and rotate it about the +y axis so we can see
more of it. We also notice that there appears to be a small gap where the
Half_Torus' meet. This is due to the fact that we are viewing this scene from
directly on the x-z plane. We will change the camera y coordinate from 0 to
0.1 to eliminate this.
union {
object { Half_Torus }
object { Half_Torus
rotate Flip_It_Over
translate x*Torus_Translate
}
object { Half_Torus
translate x*Torus_Translate*2
}
object { Half_Torus
rotate Flip_It_Over
translate x*Torus_Translate*3
}
object { Half_Torus
rotate Flip_It_Over
translate -x*Torus_Translate
}
object { Half_Torus
translate -x*Torus_Translate*2
}
object { Half_Torus
rotate Flip_It_Over
translate -x*Torus_Translate*3
}
object { Half_Torus
translate -x*Torus_Translate*4
}
rotate y*45
translate z*20
}
Rendering this we see a cool, undulating, snake-like something-or-other.
Neato. But we want to model something useful, something that we might see in
real
life. How about a chain?
Thinking about it for a moment, we realize that a single link of a chain can
be easily modeled using two half toruses and two cylinders. Go ahead and
create a new file. You can use the same camera, background, light source, and
declared objects and transformations as you used in tordemo.pov :
#include "colors.inc"
camera {
location <0, .1, -25>
look_at 0
angle 36
}
background { color Gray50 }
light_source{ <300, 300, -1000> White }
#declare Half_Torus = difference {
torus { 4,1
sturm
rotate x*-90 // so we can see it from the top
}
box { <-5, -5, -1>, <5, 0, 1> }
pigment { Green }
}
#declare Flip_It_Over = x*180
#declare Torus_Translate = 8
Now, make a complete torus of two half toruses:
union {
object { Half_Torus }
object { Half_Torus rotate Flip_It_Over }
}
This may seem like a wasteful way to make a complete torus, but we are really
going to move each half apart to make room for the cylinders. First, add the
declared cylinder before the union:
#declare Chain_Segment = cylinder { <0, 4, 0>, <0, -4, 0>, 1
pigment { Green }
}
Then add two Chain_Segments to the union and translate them so that they line
up with the minor radius of the torus on each side:
union {
object { Half_Torus }
object { Half_Torus rotate Flip_It_Over }
object { Chain_Segment translate x*Torus_Translate/2 }
object { Chain_Segment translate -x*Torus_Translate/2 }
}
Now translate the two half toruses +y and -y so that the clipped ends meet
the ends of the cylinders. This distance is equal to half of the previously
declared Torus_Translate :
union {
object { Half_Torus
translate y*Torus_Translate/2
}
object { Half_Torus
rotate Flip_It_Over
translate -y*Torus_Translate/2
}
object { Chain_Segment
translate x*Torus_Translate/2
}
object { Chain_Segment
translate -x*Torus_Translate/2
}
}
Render this and voila! A single link of a chain. But we aren't done yet!
Whoever heard of a green chain? We would rather use a nice metallic color
instead. First, remove any pigment blocks in the declared toruses and
cylinders. Then add the following before the union:
#declare Chain_Gold = texture {
pigment { BrightGold }
finish {
ambient .1
diffuse .4
reflection .25
specular 1
metallic
}
}
Then add the texture to the union and declare the union as a single link:
#declare Link = union {
object { Half_Torus
translate y*Torus_Translate/2
}
object { Half_Torus
rotate Flip_It_Over
translate -y*Torus_Translate/2
}
object { Chain_Segment
translate x*Torus_Translate/2
}
object { Chain_Segment
translate -x*Torus_Translate/2
}
texture { Chain_Gold }
}
Now make a union of two links. The second one will have to be translated +y
so that its inner wall just meets the inner wall of the other link, just like
the links of a chain. This distance turns out to be double the previously
declared Torus_Translate minus 2 (twice the minor radius). This can be
described by the expression:
Torus_Translate*2-2*y
Declare this expression as follows:
#declare Link_Translate = Torus_Translate*2-2*y
In the object block, we will use this declared value so that we can multiply
it to create other links. Now, rotate the second link 90*y so that it is
perpendicular to the first, just like links of a chain. Finally, scale the
union by 1/4 so that we can see the whole thing:
union {
object { Link }
object { Link translate y*Link_Translate rotate y*90 }
scale .25
}
Render this and you will see a very realistic pair of links. If we want to
make an entire chain, we must declare the above union and then create another
union of this declared object. Be sure to remove the scaling from the
declared object:
#declare Link_Pair =
union {
object { Link }
object { Link translate y*Link_Translate rotate y*90 }
}
Now declare your chain:
#declare Chain = union {
object { Link_Pair}
object { Link_Pair translate y*Link_Translate*2 }
object { Link_Pair translate y*Link_Translate*4 }
object { Link_Pair translate y*Link_Translate*6 }
object { Link_Pair translate -y*Link_Translate*2 }
object { Link_Pair translate -y*Link_Translate*4 }
object { Link_Pair translate -y*Link_Translate*6 }
}
And, finally create your chain with a couple of transformations to make it
easier to see. These include scaling it down by a factor of 1/10, and
rotating it so that you can clearly see each link:
object { Chain scale .1 rotate <0, 45, -45> }
The torus object can be used to create chains.
Render this and you should see a very realistic gold chain stretched
diagonally across the screen.
4.5 CSG Objects
Constructive solid geomerty, CSG, is a powerful tool to combine primitve
objects to create more complex objects as shown in the following sections.
4.5.1 What is CSG?
CSG stands for Constructive Solid Geometry . POV-Ray allows you to construct
complex solids by combining primitive shapes in four different ways. These
are union, where two or more shapes are added together, intersection where
two or more shapes are combined to make a new shape that consists of the area
common to both shapes, difference where subsequent shapes are subtracted from
the first shape, and merge which is like a union where the surfaces inside
the union are removed (useful in transparent CSG objects). We will deal with
each of these in detail in the next few sections.
CSG objects can be extremely complex. They can be deeply nested. In other
words there can be unions of differences or intersections of merges or
differences of intersections or even unions of intersections of differences
of merges... ad infinitum. CSG objects are (almost always) finite objects and
so respond to auto-bounding and can be transformed like any other POV
primitive shape.
4.5.2 CSG Union
Let's try making a simple union. Create a file called csgdemo.pov and edit it
as follows:
#include "colors.inc"
camera {
location <0, 1, -10>
look_at 0
angle 36
}
light_source { <500, 500, -1000> White }
plane { y, -1.5
pigment { checker Green White }
}
Now let's add two spheres each translated 0.5 units along the x-axis in each
direction. Color one blue and the other red.
sphere { <0, 0, 0>, 1
pigment { Blue }
translate -0.5*x
}
sphere { <0, 0, 0>, 1
pigment { Red }
translate 0.5*x
}
Try tracing this file now at 200x150 -A . Now place a union block around the
two spheres. This will create a single CSG union out of the two objects.
union{
sphere { <0, 0, 0>, 1
pigment { Blue }
translate -0.5*x
}
sphere { <0, 0, 0>, 1
pigment { Red }
translate 0.5*x
}
}
Trace the file again. The union will appear no different from what each
sphere looked like on its own, but now we can give the entire union a single
texture and transform it as a whole. Let's do that now.
union{
sphere { <0, 0, 0>, 1
translate -0.5*x*
}
sphere { <0, 0, 0>, 1
translate 0.5*x
}
pigment { Red }
scale <1, .25, 1>
rotate <30, 0, 45>
}
Trace the file again. As you can see, the object has changed dramatically.
Experiment with different values of scale and rotate and try some different
textures.
There are some advantages of assigning only one texture to a CSG object
instead of assigning the texture to each individual component. First, it is
much easier to use one texture if your CSG object has a lot of components
because changing the objects appereance involves changing only one single
texture. Second, the file parses faster because the texture has to be parsed
only once. This may be a great factor when doing large scenes or animatons.
Third, using only one texture saves memory because the texture is only stored
once and referenced by all components of the CSG object. Assigning the
texture to all n components means that it is stored n times.
4.5.3 CSG Intersection
Now let's use these same spheres to illustrate the next kind of CSG object,
the intersection . Change the word union to intersection and delete the scale
and rotate statements:
intersection {
sphere { <0, 0, 0>, 1
translate -0.5*x
}
sphere { <0, 0, 0>, 1
translate 0.5*x
}
pigment { Red }
}
Trace the file and you will see a lens-shaped object instead of the two
spheres. This is because an intersection consists of the area shared by both
shapes, in this case the lens-shaped area where the two spheres overlap. We
like this lens-shaped object so we will use it to demostrate differences.
4.5.4 CSG Difference
Rotate the lens-shaped intersection about the y-axis so that the broad side
is facing the camera.
intersection{
sphere { <0, 0, 0>, 1
translate -0.5*x
}
sphere { <0, 0, 0>, 1
translate 0.5*x
}
pigment { Red }
rotate 90*y
}
Now let's create a cylinder and stick it right in the middle of the lens.
cylinder { <0, 0, -1> <0, 0, 1>, .35
pigment { Blue }
}
Render the scene now to see the position of the cylinder. We will place a
difference block around both the lens-shaped intersection and the cylinder
like this:
difference {
intersection {
sphere { <0, 0, 0>, 1
translate -0.5*x
}
sphere { <0, 0, 0>, 1
translate 0.5*x
}
pigment { Red }
rotate 90*y
}
cylinder { <0, 0, -1> <0, 0, 1>, .35
pigment { Blue }
}
}
Now render the file. You should see the lens-shaped intersection with a neat
hole in the middle of it where the cylinder was. The cylinder has been
subtracted from the intersection. Note that the pigment of the cylinder
causes the surface of the hole to be colored blue. If you eliminate this
pigment the surface of the hole will be red.
OK, let's get a little wilder now. Let's declare our perforated lens object
to give it a name. Let's also eliminate all textures in the declared object
because we will want them to be in the final union instead.
#declare Lens_With_Hole = difference {
intersection {
sphere { <0, 0, 0>, 1
translate -0.5*x
}
sphere { <0, 0, 0>, 1
translate 0.5*x
}
rotate 90*y
}
cylinder { <0, 0, -1> <0, 0, 1>, .35 }
}
Now, let's use union to build a complex shape composed of copies of this
object.
union {
object { Lens_With_Hole translate <-.65, .65, 0> }
object { Lens_With_Hole translate <.65, .65, 0> }
object { Lens_With_Hole translate <-.65, -.65, 0> }
object { Lens_With_Hole translate <.65, -.65, 0> }
pigment { Red }
}
Render it. An interesting object to be sure. But let's try something more.
Let's make it a partially-transparent object by adding some filter to the
pigment block.
union {
object { Lens_With_Hole translate <-.65, .65, 0> }
object { Lens_With_Hole translate <.65, .65, 0> }
object { Lens_With_Hole translate <-.65, -.65, 0> }
object { Lens_With_Hole translate <.65, -.65, 0> }
pigment { Red filter .5 }
}
Now render the file again. This looks pretty good... only... you can see
parts of each of the lens objects inside the union! This is no good.
4.5.5 CSG Merge
This brings us to the fourth kind of CSG object, the merge . Merges are the
same as unions, but the geometry of the objects in the CSG that is inside the
merge is not traced. This should eliminate the problem with our object. Let's
try it.
merge {
object { Lens_With_Hole translate <-.65, .65, 0> }
object { Lens_With_Hole translate <.65, .65, 0> }
object { Lens_With_Hole translate <-.65, -.65, 0> }
object { Lens_With_Hole translate <.65, -.65, 0> }
pigment { Red filter .5 }
}
4.5.6 CSG Pitfalls
There is a severe pitfall in the POV-Ray's CSG code that you have to be aware
of.
4.5.6.1 Coincidence Surfaces
POV-Ray uses inside/outside tests to determine the points at which a ray
intersects a CSG object. A problem arises when the surfaces of two different
shapes coincide because there is no way (due to numerical problems) to tell
wether a point on the coincident surface belongs to one shape or the other.
Look at the following example where a cylinder is used to cut a hole in a
larger box.
difference {
box { -1, 1 pigment { Red } }
cylinder { -z, z, 0.5 pigment { Green } }
}
If you trace this object you'll see red speckles where the hole is supposed
to be. This is caused by the coincident surfaces of the cylinder and the box.
One time the cylinder's surface is hit first by a viewing ray, resulting in
the correct rendering of the hole, and another time the box is hit first,
leading to a wrong result where the hole vanishes and red speckles appear.
This problem can be avoided by increasing the size of the cylinder to get rid
of the coincidence surface. This is done by:
difference {
box { -1, 1 pigment { Red } }
cylinder { -1.001*z, 1.001*z, 0.5 pigment { Green } }
}
In general you have to make the subtracted object a little bit larger in a
CSG difference. Just look for coincident surfaces and increase the subtracted
object appropreatly to get rid of those surfaces.
The same problem occurs in CSG intersections and is also avoided by scaling
some of the involved objects.
4.6 The Light Source
In any ray-traced scene, the light needed to illuminate your objects and
their surfaces must come from a light source. There are many kinds of light
sources available in POV-Ray and careful use of the correct kind can yield
very impressive results. Let's take a moment to explore some of the different
kinds of light sources and their various parameters.
4.6.1 The Ambient Light Source
The ambient light source is used to simulate the effect of interdiffuse
reflection. If there wasn't interdiffuse reflection all areas not directly
lit by a light source would be completely dark. POV-Ray uses the ambient
keyword to determine how much light coming from the ambient light source is
reflected by a surface.
By default the ambient light source, which emits its light everywhere and in
all directions, is pure white (rgb<1,1,1>). Changing its color can be used to
create interesting effects. First of all the overall light level of the scene
can be adjusted easily. Instead of changing all ambient values only the
ambient light source is modified. By assigning different colors you can
create nice effects like a moody reddish ambient lighting. For more details
about the ambient light source see "Ambient Light" .
Below is an example of a red ambient light source.
global_settings { ambient_light rgb<1, 0, 0> }
4.6.2 The Point Light Source
Pointlights are exactly what the name indicates. A pointlight has no size, is
invisible, and illuminates everything in the scene equally no matter how far
away from the light source it may be. This is the simplest and most basic
light source. There are only two important parameters, location and color.
Let's design a simple scene and place a pointlight source in it.
Create a new file and name it litedemo.pov . Edit it as follows:
#include "colors.inc"
#include "textures.inc"
camera {
location <-4, 3, -9>
look_at <0, 0, 0>
angle 48
}
Add the following simple objects:
plane { y, -1
texture {
pigment {
checker
color rgb<0.5, 0, 0>
color rgb<0, 0.5, 0.5>
}
finish {
diffuse 0.4
ambient 0.2
phong 1
phong_size 100
reflection 0.25
}
}
}
torus { 1.5, 0.5
texture { Brown_Agate }
rotate <90, 160, 0>
translate <-1, 1, 3>
}
box { <-1, -1, -1>, <1, 1, 1>
texture { DMFLightOak }
translate <2, 0, 2.3>
}
cone { <0,1,0>, 0, <0,0,0>, 1
texture { PinkAlabaster }
scale <1, 3, 1>
translate <-2, -1, -1>
}
sphere { <0,0,0>,1
texture { Sapphire_Agate }
translate <1.5, 0, -2>
}
Now add a pointlight:
light_source {
<2, 10, -3>
color White
}
Render this at 200x150 -A . You will see that the objects are clearly visible
with sharp shadows. The sides of curved objects nearest the light source are
brightest in color with the areas that are facing away from the light source
darkest. Note also that the checkered plane is illuminated evenly all the way
to the horizon. This allows us to see the plane, but it is not very
realistic.
4.6.3 The Spotlight Source
Spotlights are a very useful type of light source. They can be used to add
highlights and illuminate features much as a photographer uses spots to do
the same thing. There are a few more parameters with spotlights than with
pointlights. These are radius , falloff , tightness , and point_at . The
radius parameter is the angle of the fully illuminated cone. The falloff
parameter is the angle of the umbra cone where the light falls off to
darkness. The tightness is a parameter that determines the rate of the light
falloff. point_at is just what it says, where the spotlight is pointing to.
Let's change the light in our scene as follows:
light_source {
<0, 10, -3>
color White
spotlight
radius 15
falloff 20
tightness 10
point_at <0, 0, 0>
}
Render this at 200x150 -A and you will see that only the objects are
illuminated. The rest of the plane and the outer portions of the objects are
now unlit. There is a broad falloff area, but the shadows are still razor
sharp. Let's try fiddling with some of these parameters to see what they do.
Try changing the falloff value to 16 (it must always be larger than radius )
and render again. Now the falloff is very narrow, and the objects are either
brightly lit, or in total darkness. Now, change falloff back to 20 and change
the tightness value to 100 (higher is tighter) and render again. The
spotlight appears to have gotten much smaller, but what has really happened
is that the falloff has become so steep that the radius actually appears
smaller.
We decide that a tightness value of 10 (the default) and a falloff value of
18 are best for this spotlight and we now want to put a few spots around the
scene for effect. Lets place a slightly narrower blue and a red one in
addition to the white one we already have:
light_source {
<10, 10, -1>
color Red
spotlight
radius 12
falloff 14
tightness 10
point_at <2, 0, 0>
}
light_source {
<-12, 10, -1>
color Blue
spotlight
radius 12
falloff 14
tightness 10
point_at <-2, 0, 0>
}
Rendering this we see that the scene now has a wonderfully mysterious air to
it. The three spotlights all converge on the objects making them blue on one
side and red on the other with enough white in the middle to provide a
balance.
4.6.4 The Cylindrical Light Source
Spotlights are cone shaped, meaning that their effect will change with
distance. The farther away from the spotlight an object is, the larger the
apparant radius will be. But we may want the radius and falloff to be a
particular size no matter how far away the spotlight is. For this reason,
cylindrical light sources are needed. A cylindrical light source is just like
a spotlight, except that the radius and falloff regions are the same no
matter how far from the light source your object is. The shape is therefore a
cylinder rather than a cone. You can specify a cylindrical lightsource by
replacing the spotlight keyword with cylinder . Try this now with our scene.
Replace all three spotlights with cylinder lights and render again. We see
that the scene is much dimmer. This is because the cylindrical constraints do
not let the light spread out like in a spotlight. Larger radius and falloff
values are needed to do the job. Try a radius of 20 and a falloff of 30 for
all three lights. That's the ticket!
4.6.5 The Area Light Source
So far all of our light sources have one thing in common. They produce sharp
shadows. This is because the actual light source is a point that is
infinitely small. Objects are either in direct sight of the light, in which
case they are fully illuminated, or they are not, in which case they are
fully shaded. In real life, this kind of stark light and shadow situation
exists only in outer space where the direct light of the sun pierces the
total blackness of space. But here on Earth, light bends around objects,
bounces off objects, and usually the source has some dimension, meaning that
it can be partially hidden from sight (shadows are not sharp anymore). They
have what is known as an umbra, or an area of fuzziness where there is
neither total light or shade. In order to simulate these soft shadows, a
ray-tracer must give its light sources dimension. POV-Ray accomplishes this
with a feature known as an area light.
Area lights have dimension in two axis'. These are specified by the first two
vectors in the area light syntax. You must also specify how many lights are
to be in the array. More will give you cleaner soft shadows but will take
longer to render. Usually a 3*3 or a 5*5 array will suffice. You also have
the option of specifying an adaptive value. The adaptive command tells the
ray-tracer that it can adapt to the situation and send only the needed rays
to determine the value of the pixel. If adaptive is not used, a separate ray
will be sent for every light in the area light. This can really slow things
down. The higher the adaptive value the cleaner the umbra will be but the
longer the trace will take. Usually an adaptive value of 1 is sufficient.
Finally, you probably should use the jitter command. This tells the raytracer
to slightly move the position of each light in the area light so that the
shadows appear truely soft instead of giving you an umbra consisting of
closely banded shadows.
OK, let's try one. Comment out the cylinder lights and add the following:
light_source {
<2, 10, -3>
color White
area_light <5, 0, 0>, <0, 0, 5>, 5, 5
adaptive 1
jitter
}
This is a white area light centered at <2,10,-3>. It is 5 units (along the
x-axis) by 5 units (along the z-axis) in size, and has 25 (5*5) lights in it.
We have specified adaptive 1 and jitter. Render this at 200x150 -A .
Right away we notice two things. The trace takes quite a bit longer than it
did with a point or a spotlight, and the shadows are no longer sharp! They
all have nice soft umbras around them. Wait, it gets better.
Spotlights and cylinder lights can be area lights too! Remember those sharp
shadows from the spotlights in our scene? It would not make much sense to use
a 5*5 array for a spotlight, but a smaller array might do a good job of
giving us just the right amount of umbra for a spotlight. Let's try it.
Comment out the area light and change the cylinder lights so that they read
as follows:
light_source {
<2, 10, -3>
color White
spotlight
radius 15
falloff 18
tightness 10
area_light <1, 0, 0>, <0, 0, 1>, 2, 2
adaptive 1
jitter
point_at <0, 0, 0>
}
light_source {
<10, 10, -1>
color Red
spotlight
radius 12
falloff 14
tightness 10
area_light <1, 0, 0>, <0, 0, 1>, 2, 2
adaptive 1
jitter
point_at <2, 0, 0>
}
light_source {
<-12, 10, -1>
color Blue
spotlight
radius 12
falloff 14
tightness 10
area_light <1, 0, 0>, <0, 0, 1>, 2, 2
adaptive 1
jitter
point_at <-2, 0, 0>
}
You now have three area-spotlights, one unit square consisting of an array of
four (2*2) lights, three different colors, all shining on your scene. Render
this at 200x150 -A . This appears to work perfectly. All our shadows have
small, tight umbras, just the sort you would expect to find on an object
under a real spotlight.
4.6.6 Assigning an Object to a Light Source
Light sources are invisible. They are just a location where the light appears
to be coming from. They have no true size or shape. If you want your light
source to be a visible shape, you can use the looks_like keyword. You can
specify that your light source can look like any object you choose. When you
use looks_like , no_shadow is applied to the object automatically. This is
done so that the object will not block any illumination from the light
source. If you want some blocking to occur (as in a lampshade), it is better
to simply use a union to do the same thing. Let's add such an object to our
scene. Here is a light bulb I have made just for this purpose:
#declare Lightbulb = union {
merge {
sphere { <0,0,0>,1 }
cylinder { <0,0,1>, <0,0,0>, 1
scale <0.35, 0.35, 1.0>
translate 0.5*z
}
texture {
pigment {color rgb <1, 1, 1>}
finish {ambient .8 diffuse .6}
}
}
cylinder { <0,0,1>, <0,0,0>, 1
scale <0.4, 0.4, 0.5>
texture { Brass_Texture }
translate 1.5*z
}
rotate -90*x
scale .5
}
Now add the light source:
light_source {
<0, 2, 0>
color White
looks_like { Lightbulb }
}
Rendering this we see that a fairly believable light bulb now illuminates the
scene. However, if we do not specify a high ambient value, the light bulb is
not lit by the light source. On the plus side, all of the shadows fall away
from the light bulb, just as they would in a real situation. The shadows are
sharp, so let's make our bulb an area light:
light_source {
<0, 2, 0>
color White
area_light <1, 0, 0>, <0, 1, 0>, 2, 2
adaptive 1
jitter
looks_like { Lightbulb }
}
Note that we have placed this area light in the x-y-plane instead of the
x-z-plane. Note also that the actual appearance of the light bulb is not
affected in any way by the light source. The bulb must be illuminated by some
other light source or by, as in this case, a high ambient value. More
interesting results might therefore be obtained in this case by using halos
(see section "Halos" ).
4.6.7 Light Source Specials
4.6.7.1 Using Shadowless Lights
Light sources can be assigned the shadowless keyword and no shadows will be
cast due to its presence in a scene. What good is that you may ask.
Sometimes, scenes are difficult to illuminate properly using the lights you
have chosen to illuminate your objects. It is impractical and unrealisitic to
apply a higher ambient value to the texture of every object in the scene. So
instead, you would place a couple of fill lights around the scene. Fill
lights are simply dimmer lights with the shadowless keyword that act to boost
the illumination of other areas of the scene that may not be lit well. Let's
try using one in our scene.
Remember the three colored area spotlights? Go back now and uncomment them
and comment out any other lights you have made. Now add the following:
%%% %%% light_source {
%%% <0, 20, 0>
%%% color Gray75
%%% shadowless
%%% }
%%%
This is a fairly dim ( Gray75 ) light 20 units over the center of the scene.
It will give a dim illumination to all objects including the plane in the
background. Render it and see.
4.6.7.2 Using Light Fading
If it is realism we want, it is not realistic for the plane to be evenly
illuminated off into the distance. In real life, light gets scattered as it
travels so it diminishes its ability to illuminate objects the farther it
gets from its source. To simulate this, POV-Ray allows you to use two
keywords: fade_distance , which specifies the distance at which full
illumination is achieved; and fade_power , an exponential value which
determines the actual rate of attenuation. Let's apply these keywords to our
fill light.
First, make the fill light a little brighter by changing Gray75 to Gray50 .
Now change that fill light as follows:
light_source {
<0, 20, 0>
color Gray50
fade_distance 5
fade_power 1
shadowless
}
This means that the full value of the fill light will be achieved at a
distance of 5 units away from the light source. The fade_power of 1 means
that the falloff will be linear (the light falls of at a constant rate).
Render this to see the result.
That definitely worked! Now let's try a fade_power of 2 and a fade_distance
of 10. Again, this works well. The falloff is much sharper with a fade_power
of 2 so we had ot raise the fade_distance to 10.
4.6.7.3 Light Sources and Atmosphere
By definition more than default, light sources are affected by atmosphere,
i.e. their light is scattered by the atmosphere. This can be turned off by
adding atmosphere off to the light source block. The light emitted by a light
source can also be attenuated by the atmosphere (and also fog), that is it
will be diminished as it travells through it, by adding
atmospheric_attenuation on . The falloff is exponential and dependes on the
distance parameter of the atmosphere (or fog). You should note that this
featuer only affects light coming directly from the light source. Reflected
and refracted light is ignored.
Let's experiment with these keywords. First we must add an atmosphere to our
scene:
#include "atmos.inc"
atmosphere { Atmosphere2 }
Then, so the trace will not take as long and the effect will be easier to
see, comment out the three lines that turn each of the three spotlights into
area lights:
//area_light <1, 0, 0>, <0, 0, 1>, 2, 2
//adaptive 1
//jitter
Tracing the scene at 200x150 -A we see that indeed the spotlights are
visible. We can see where the blue and red spots cross each other and where
the white overhead light shines down through the center of the scene. We also
notice that the spotlights appear to diminish in their intensity as the light
descends from the light source to the objects. The red light is all but gone
in the lower left part of the scene and the blue light all but gone in the
lower right. This is due to the atmospheric attenuation and lends a further
realism to the scene. The atmosphere-lightsource interaction gives our scene
a smoky, mysterious appearance, but the trace took a long time. Make those
spotlights area lights and it will take even longer. This is an inevitable
trade-off - tracing speed for image quality.
4.7 Simple Texture Options
The pictures rendered so far where somewhat boring regarding the appearance
of the objects. Let's add some fancy features to the texture.
4.7.1 Surface Finishes
One of the main features of a ray-tracer is its ability to do interesting
things with surface finishes such as highlights and reflection. Let's add a
nice little phong highlight (shiny spot) to the sphere. To do this you need a
finish parameter. Change the definition of the sphere to this:
sphere { <0, 1, 2>, 2
texture {
pigment { color Yellow } // Yellow is pre-defined in COLORS.INC
finish { phong 1 }
}
}
Now render this the same way you did before. The phong keyword adds a
highlight the same color of the light shining on the object. It adds a lot of
credibility to the picture and makes the object look smooth and shiny. Lower
values of phong will make the highlight less bright (values should be between
0 and 1).
4.7.2 Adding Bumpiness
The highlight you've added illustrates how much of our perception depends on
the reflective properties of an object. Ray-tracing can exploit this by
playing tricks on our perception to make us see complex details that aren't
really there.
Suppose you wanted a very bumpy surface on the object. It would be very
difficult to mathematically model lots of bumps. We can however simulate the
way bumps look by altering the way light reflects off of the surface.
Reflection calculations depend on a vector called a surface normal vector.
This is a vector which points away from the surface and is perpendicular to
it. By artificially modifying (or perturbing) this normal vector you can
simulate bumps. Change the scene to read as follows and render it:
sphere { <0, 1, 2>, 2
texture {
pigment { color Yellow }
normal { bumps 0.4 scale 0.2 }
finish { phong 1}
}
}
This tells POV-Ray to use a bump pattern to modify the surface normal. The
value 0.4 controls the apparent depth of the bumps. Usually the bumps are
about 1 unit wide which doesn't work very well with a sphere of radius 2. The
scale makes the bumps 1/5th as wide but does not affect their depth.
4.7.3 Creating Color Patterns
You can do more than assign a solid color to an object. You can create
complex patterns in the pigment block. Consider this example:
sphere { <0, 1, 2>, 2
texture {
pigment {
wood
color_map {
[0.0 color DarkTan]
[0.9 color DarkBrown]
[1.0 color VeryDarkBrown]
}
turbulence 0.05
scale <0.2, 0.3, 1>
}
finish { phong 1 }
}
}
The keyword wood specifies a pigment pattern of concentric rings like rings
in wood. The color_map specifies that the color of the wood should blend from
DarkTan to DarkBrown over the first 90% of the vein and from DarkBrown to
VeryDarkBrown over the remaining 10%. The turbulence slightly stirs up the
pattern so the veins aren't perfect circles and the scale factor adjusts the
size of the pattern.
Most patterns are set up by default to give you one feature across a sphere
of radius 1.0. A feature is very roughly defined as a color transition. For
example, a wood texture would have one band on a sphere of radius 1.0. In
this example we scale the pattern using the scale keyword followed by a
vector. In this case we scaled 0.2 in the x direction, 0.3 in the y direction
and the z direction is scaled by 1, which leaves it unchanged. Scale values
larger than one will stretch an element. Scale values smaller than one will
squish an element. And a scale value of one will leave an element unchanged.
4.7.4 Pre-defined Textures
POV-Ray has some very sophisticated textures pre-defined in the standard
include files glass.inc , metals.inc , stones.inc and woods.inc . Some are
entire textures with pigment , normal and/or finish parameters already
defined. Some are just pigments or just finishes. Change the definition of
our sphere to the following and then re-render it:
sphere { <0, 1, 2>, 2
texture {
pigment {
DMFWood4 // pre-defined in textures.inc
scale 4 // scale by the same amount in all
// directions
}
finish { Shiny } // pre-defined in finish.inc
}
}
The pigment identifier DMFWood4 has already been scaled down quite small when
it was defined. For this example we want to scale the pattern larger. Because
we want to scale it uniformly we can put a single value after the scale
keyword rather than a vector of x, y, z scale factors.
Look through the file textures.inc to see what pigments and finishes are
defined and try them out. Just insert the name of the new pigment where
DMFWood4 is now or try a different finish in place of Shiny and re-render
your file.
Here is an example of using a complete texture identifier rather than just
the pieces.
sphere { <0, 1, 2>, 2
texture { PinkAlabaster }
}
4.8 Advanced Texture Options
The extremely powerful texturing ability is one thing that really sets
POV-Ray apart from other raytracers. So far we have not really tried anything
too complex but by now you should be comfortable enough with the program's
syntax to try some of the more advanced texture options.
Obviously, we cannot try them all. It would take a tutorial a lot more pages
to use every texturing option available in POV-Ray. For this limited
tutorial, we will content ourselves to just trying a few of them to give you
an idea of how textures are created. With a little practice, you will soon be
creating beautiful textures of your own.
4.8.1 Pigment and Normal Patterns
Previous versions of POV-Ray made a distinction between pigment and normal
patterns, i. e. patterns that could be used inside a normal {... } or pigment
{... } statement. With POV-Ray 3.0 this restriction was removed so that all
patterns listed in section "Patterns" can be used as a pigment or normal
pattern.
4.8.2 Pigments
Every surface must have a color. In POV-Ray, this color is called a pigment .
It does not have to be a single color. It can be a color pattern, a color
list, or even an image map. Pigments can also be layered one on top of the
next so long as the uppermost layers are at least partially transparent so
the ones beneath can show through. Let's play around with some of these kinds
of pigments.
Create a file called texdemo.pov and edit it as follows:
#include "colors.inc"
camera {
location <1, 1, -7>
look_at 0
angle 36
}
light_source { <1000, 1000, -1000> White }
plane { y, -1.5
pigment { checker Green, White }
}
sphere { <0,0,0>, 1
pigment { Red }
}
Giving this file a quick test render at 200x150 -A we see that it is a simple
red sphere against a green and white checkered plane. We will be using the
sphere for our textures.
4.8.2.1 Using Color List Pigments
Before we begin you should note that we have already made one kind of
pigment, the color list pigment. In the previous example we have used a
checkered pattern on our plane. There are two other kinds of color list
pigments, brick and hexagon . Let's quickly try each of these. First, change
the plane's pigment as follows:
pigment { hexagon Green, White, Yellow }
Rendering this we see a three-color hexagonal pattern. Note that this pattern
requires three colors. Now change the pigment to...
pigment { brick Gray75, Red rotate -90*x scale .25 }
Looking at the resulting image see that the plane now has a brick pattern.
Note that we had to rotate the pattern to make it appear correctly on the
flat plane. This pattern normally is meant to be used on vertical surfaces.
We also had to scale the pattern down a bit so we could see it more easily.
Feel free to play around with these color list pigments, change the colors,
etc. until you get a floor that you like.
4.8.2.2 Using Pigment and Patterns
Let's begin texturing our sphere by using a pattern and a color map
consisting of three colors. Replace the pigment block with the following.
pigment {
gradient x
color_map {
[0.00 color Red]
[0.33 color Blue]
[0.66 color Yellow]
[1.00 color Red]
}
}
Rendering this we see that it gives us an interesting pattern of vertical
stripes. Try changing the gradient direction to y. The stripes are horizontal
now. Try changing the gradient direction to z. The stripes are now more like
concentric rings. This is because the gradient direction is directly away
from the camera. Change the direction back to x and add the following change
to the pigment block.
pigment {
gradient x
color_map {
[0.00 color Red]
[0.33 color Blue]
[0.66 color Yellow]
[1.00 color Red]
}
rotate -45*z // <- add this line
}
The vertical bars are now slanted at a 45 degree angle. All patterns can be
rotated, scaled, and translated in this manner. Let's now try some different
types of patterns. One at a time, substitute the following keywords for
gradient x and render to see the result: bozo , marble , agate , granite ,
leopard , spotted , and wood (if you like you can test all patterns listed in
section "Patterns" ).
Rendering these we see that each results in a slightly different pattern. But
to get really good results each type of pattern requires the use of some
pattern modifiers.
4.8.2.3 Using Pattern Modifiers
Let's take a look at some pattern modifiers. First, change the pattern type
to bozo. Then add the following change.
pigment {
bozo
frequency 3 // <- add this line
color_map {
[0.00 color Red]
[0.33 color Blue]
[0.66 color Yellow]
[1.00 color Red]
}
rotate -45*z
}
The frequency modifier determines the number of times the color map repeats
itself per unit of size. This change makes the bozo pattern we saw earlier
have many more bands in it. Now change the pattern type to marble . When we
rendered this earlier, we saw a banded pattern similar to gradient y that
really did not look much like marble at all. This is because marble really is
a kind of gradient and it needs another pattern modifier to look like marble.
This modifier is called turbulence . Change the line frequency 3 to
turbulence 1 and render again. That's better! Now let's put frequency 3 back
in right after the turbulence and take another look. Even more interesting!
But wait, it gets better! Turbulence itself has some modifiers of its own.
You can adjust the turbulence several ways. First, the float that follows the
turbulence keyword can be any value with higher values giving you more
turbulence. Second, you can use the keywords omega , lambda , and octaves to
change the turbulence parameters. Let's try this now:
pigment {
marble
turbulence 0.5
lambda 1.5
omega 0.8
octaves 5
frequency 3
color_map {
[0.00 color Red]
[0.33 color Blue]
[0.66 color Yellow]
[1.00 color Red]
}
rotate 45*z
}
Rendering this we see that the turbulence has changed and the pattern looks
different. Go ahead and play around with the numerical values of turbulence ,
lambda , omega , and octaves to see what they do.
4.8.2.4 Using Transparent Pigments and Layered Textures
Pigments are described by numerical values that give the rgb value of the
color to be used (like color rgb<1, 0, 0> giving you a red color). But this
syntax will give you more than just the rgb values. You can specify filtering
transparency by changing it as follows: color rgbf<1, 0, 0, 1> . The f stands
for filter , POV-Ray's word for filtered transparency. A value of one means
that the color is completely transparent, but still filters the light
according to what the pigment is. In this case, the color will be a
transparent red, like red cellophane.
There is another kind of transparency in POV-Ray. It is called transmittance
or non-filtering transparency (the keyword is transmit ). It is different
from filter in that it does not filter the light according to the pigment
color. It instead allows all the light to pass through unchanged. It can be
specified like this: rgbt<1, 0, 0, 1> .
Let's use some transparent pigments to create another kind of texture, the
layered texture. Returning to our previous example, declare the following
texture.
#declare LandArea = texture {
pigment {
agate
turbulence 1
lambda 1.5
omega .8
octaves 8
color_map {
[0.00 color rgb <.5, .25, .15>]
[0.33 color rgb <.1, .5, .4>]
[0.86 color rgb <.6, .3, .1>]
[1.00 color rgb <.5, .25, .15>]
}
}
}
}
This texture will be the land area. Now let's make the oceans by declaring
the following.
#declare OceanArea = texture {
pigment {
bozo
turbulence .5
lambda 2
color_map {
[0.00, 0.33 color rgb <0, 0, 1>
color rgb <0, 0, 1>]
[0.33, 0.66 color rgbf <1, 1, 1, 1>
color rgbf <1, 1, 1, 1>]
[0.66, 1.00 color rgb <0, 0, 1>
color rgb <0, 0, 1>]
}
}
}
}
Note how the ocean is the opaque blue area, and the land is the clear area
which will allow the underlying texture to show through.
Now, let's declare one more texture to simulate an atmosphere with swirling
clouds.
#declare CloudArea = texture {
pigment {
agate
turbulence 1
lambda 2
frequency 2
color_map {
[0.0 color rgbf <1, 1, 1, 1>]
[0.5 color rgbf <1, 1, 1, .35>]
[1.0 color rgbf <1, 1, 1, 1>]
}
}
}
Now apply all of these to our sphere.
sphere { <0,0,0>, 1
texture { LandArea }
texture { OceanArea }
texture { CloudArea }
}
Render this and you'll have a pretty good rendition of a little planetoid.
But it could be better. We don't particularly like the appearance of the
clouds. There is a way they could be done that would be much more realistic.
4.8.2.5 Using Pigment Maps
Pigments may be blended together in the same way as the colors in a color_map
using the same pattern keywords that you can use for pigments. Rather than
trying to impress you with the possible implications of this powerful
feature, let's just give it a try.
Add the following declarations, making sure they appear before the other
declarations in the file.
#declare Clouds1 = pigment {
bozo
turbulence 1
color_map {
[0.0 color White filter 1]
[0.5 color White]
[1.0 color White filter 1]
}
}
#declare Clouds2 = pigment {
agate
turbulence 1
color_map {
[0.0 color White filter 1]
[0.5 color White]
[1.0 color White filter 1]
}
}
#declare Clouds3 = pigment {
marble
turbulence 1
color_map {
[0.0 color White filter 1]
[0.5 color White]
[1.0 color White filter 1]
}
}
#declare Clouds4 = pigment {
granite
turbulence 1
color_map {
[0.0 color White filter 1]
[0.5 color White]
[1.0 color White filter 1]
}
}
Now use these declared pigments in our cloud layer on our planetoid. Replace
the declared cloud layer with.
#declare CloudArea = texture {
pigment {
gradient y
pigment_map {
[0.00 Clouds1]
[0.25 Clouds2]
[0.50 Clouds3]
[0.75 Clouds4]
[1.00 Clouds1]
}
}
}
Render this and you'll see a remarkable pattern that looks very much like
weather patterns on the planet earth. They are separated into bands,
simulating the different weather types found at different latitudes.
4.8.3 Normals
Objects in POV-Ray have very smooth surfaces. This is not very realistic so
there are several ways to disturb the smoothness of an object by perturbing
the surface normal. The surface normal is the vector that is perpendicular to
the angle of the surface. By changing this normal the surface can be made to
appear bumpy, wrinkled, or any of the many patterns available. Let's try a
couple of them.
4.8.3.1 Using Basic Normal Modifiers
Comment out the planetoid sphere for now and, at the bottom of the file,
create a new sphere with a simple, single color texture.
sphere { <0,0,0>, 1
pigment { Gray75 }
normal { bumps 1 scale .2 }
}
Here we have added a normal block in addition to the pigment block (note that
these do not have to be included in a texture block unless they need to be
transformed together or need to be part of a layered texture). Render this to
see what it looks like. Now, one at a time, substitute for the keyword bumps
the following keyowrds: dents , wrinkles , ripples , and waves (you can also
use any of the patterns listed in "Patterns" ). Render each to see what they
look like. Play around with the float value that follows the keyword. Try
experimenting with the scale value too.
For added interest, change the plane texture to a single color with a normal
as follows.
plane { y, -1.5
pigment { color rgb <.65, .45, .35> }
normal { dents .75 scale .25 }
}
4.8.3.2 Blending Normals
Normals can be layered similar to pigments but the results can be unexpected.
Let's try that now by editing the sphere as follows.
sphere { <0,0,0>, 1
pigment { Gray75 }
normal { radial frequency 10 }
normal { gradient y scale .2 }
}
As you can see, the resulting pattern is neither a radial nor a gradient. It
is instead the result of first calculating a radial pattern and then
calculating a gradient pattern. The results are simply additive. This can be
difficult to control so POV-Ray gives the user other ways to blend normals.
One way is to use normal maps. A normal map works the same way as the pigment
map we used earlier. Let's change our sphere texture as follows.
sphere { <0,0,0>, 1
pigment { Gray75 }
normal {
gradient y
frequency 3
turbulence .5
normal_map {
[0.00 granite]
[0.25 spotted turbulence .35]
[0.50 marble turbulence .5]
[0.75 bozo turbulence .25]
[1.00 granite]
}
}
}
Rendering this we see that the sphere now has a very irregular bumpy surface.
The gradient pattern type separates the normals into bands but they are
turbulated, giving the surface a chaotic appearance. But this give us an
idea.
Suppose we use the same pattern for a normal map that we used to create the
oceans on our planetoid and applied it to the land areas. Does it follow that
if we use the same pattern and modifiers on a sphere the same size that the
shape of the pattern would be the same? Wouldn't that make the land areas
bumpy while leaving the oceans smooth? Let's try it. First, let's render the
two spheres side-by-side so we can see if the pattern is indeed the same.
Un-comment the planetoid sphere and make the following changes.
sphere { <0,0,0>, 1
texture { LandArea }
texture { OceanArea }
//texture { CloudArea } // <-comment this out
translate -x // <- add this transformation
}
Now change the gray sphere as follows.
sphere { <0,0,0>, 1
pigment { Gray75 }
normal {
bozo
turbulence .5
lambda 2
normal_map {
[0.4 dents .15 scale .01]
[0.6 agate turbulence 1]
[1.0 dents .15 scale .01]
}
}
translate x // <- add this transformation
}
Now render this to see if the pattern is the same. We see that indeed it is.
So let's comment out the gray sphere and add the normal block it contains to
the land area texture of our planetoid. Remove the transformations so that
the planetoid is centered in the scene again.
#declare LandArea = texture {
pigment {
agate
turbulence 1
lambda 1.5
omega .8
octaves 8
color_map {
[0.00 color rgb <.5, .25, .15>]
[0.33 color rgb <.1, .5, .4>]
[0.86 color rgb <.6, .3, .1>]
[1.00 color rgb <.5, .25, .15>]
}
}
normal {
bozo
turbulence .5
lambda 2
normal_map {
[0.4 dents .15 scale .01]
[0.6 agate turbulence 1]
[1.0 dents .15 scale .01]
}
}
}
Looking at the resulting image we see that indeed our idea works! The land
areas are bumpy while the oceans are smooth. Add the cloud layer back in and
our planetoid is complete.
There is much more that we did not cover here due to space constraints. On
your own, you should take the time to explore slope_map , average , and
bump_map .
4.8.4 Finishes
The final part of a POV-Ray texture is the finish . It controls the
properties of the surface of an object. It can make it shiny and reflective,
or dull and flat. It can also specify what happens to light that passes
through transparent pigments, what happens to light that is scattered by
less-than-perfectly-smooth surfaces, and what happens to light that is
reflected by surfaces with thin-film interference properties. There are
twelve different properties available in POV-Ray to specify the finish of a
given object. These are ambient , diffuse , brilliance , phong , specular ,
metallic , reflection , refraction , caustics , attenuation , crand , and
iridescence . Let's design a couple of textures that make use of these
parameters.
4.8.4.1 Using Ambient
Since objects in POV-Ray are illuminated by light sources, the portions of
those objects that are in shadow would be completely black were it not for
the first two finish properties, ambient and diffuse . Ambient is used to
simulate the light that is scattered around the scene that does not come
directly from a light source. Diffuse determines how much of the light that
is seen comes directly from a light source. These two keywords work together
to control the simulation of ambient light. Let's use our gray sphere to
demonstrate this. Let's also change our plane back to its original green and
white checkered pattern.
plane {y,-1.5
pigment {checker Green, White}
}
sphere { <0,0,0>, 1
pigment {Gray75}
finish {
ambient .2
diffuse .6
}
In the above example, the default values for ambient and diffuse are used.
Render this to see what the effect is and then make the following change to
the finish.
ambient 0
diffuse 0
The sphere is black because we have specified that none of the light coming
from any light source will be reflected by the sphere. Let's change diffuse
back to the default of 0.6.
Now we see the gray surface color where the light from the light source falls
directly on the sphere but the shaded side is still absolutely black. Now
let's change diffuse to 0.3 and ambient to 0.3.
The sphere now looks almost flat. This is because we have specified a fairly
high degree of ambient light and only a low amount of the light coming from
the light source is diffusely reflected towards the camera. The default
values of ambient and diffuse are pretty good averages and a good starting
point. In most cases, an ambient value of 0.1 ... 0.2 is sufficient and a
diffuse value of 0.5 ... 0.7 will usually do the job. There are a couple of
exceptions. If you have a completely transparent surface with high refractive
and/or reflective values, low values of both ambient and diffuse may be best.
Here is an example.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient 0
diffuse 0
reflection .25
refraction 1
ior 1.33
specular 1
roughness .001
}
}
}
This is glass, obviously. Glass is a material that takes nearly all of its
appearance from its surroundings. Very little of the surface is seen because
it transmits or reflects practically all of the light that shines on it. See
glass.inc for some other examples.
If you ever need an object to be completely illuminated independently of the
lighting situation in a given scene, you can do this artificially by
specifying an ambient value of 1 and a diffuse value of 0. This will
eliminate all shading and simply give the object its fullest and brightest
color value at all points. This is good for simulating objects that emit
light like lightbulbs, and for skies in scenes where the sky may not be
adequately lit by any other means.
Let's try this with our sphere now.
sphere { <0,0,0>, 1
pigment { White }
finish {
ambient 1
diffuse 0
}
}
}
Rendering this we get a blinding white sphere with no visible highlights or
shaded parts. It would make a pretty good streetlight.
4.8.4.2 Using Surface Highlights
In the glass example above, we noticed that there were bright little hotspots
on the surface. This gave the sphere a hard, shiny appearance. POV-Ray gives
you two ways to specify surface specular highlights. The first is called
Phong highlighting . Usually, Phong highlights are described using two
keywords: phong and phong_size . The float that follows phong determines the
brightness of the highlight while the float following phong_size determines
its size. Let's try this.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
phong .75
phong_size 25
}
}
Rendering this we see a fairly broad, soft highlight that gives the sphere a
kind of plastic appearance. Now let's change phong_size to 150. This makes a
much smaller highlight which gives the sphere the appearance of being much
harder and shinier.
There is another kind of highlight that is calculated by a different means
called specular highlighting . It is specified using the keyword specular and
operates in conjunction with another keyword called roughness . These two
keywords work together in much the same way as phong and phong_size to create
highlights that alter the apparent shininess of the surface. Let's try using
specular in our sphere.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
specular .75
roughness .1
}
}
}
Looking at th result we see a broad, soft highlight similar to what we had
when we used phong_size of 25. Change roughness to .001 and render again. Now
we see a small, tight highlight similar to what we had when we used
phong_size of 150. Generally speaking, specular is slightly more accurate and
therefore slightly more realistic than phong but you should try both methods
when designing a texture. There are even times when both phong and specular
may be used on a finish.
4.8.4.3 Using Reflection and Metallic
There is another surface parameter that goes hand in hand with highlights,
reflection . Surfaces that are very shiny usually have a degree of reflection
to them. Let's take a look at an example.
sphere { <0,0,0>, 1
pigment { Gray50 }
finish {
ambient .2
diffuse .6
specular .75
roughness .001
reflection .5
}
}
}
We see that our sphere now reflects the green and white checkered plane and
the black background but the gray color of the sphere seems out of place.
This is another time when a lower diffuse value is needed. Generally, the
higher reflection is the lower diffuse should be. Try lowering the diffuse
value to 0.3 and the ambient value to 0.1 and render again. That is much
better. Let's make our sphere as shiny as a polished gold ball bearing.
sphere { <0,0,0>, 1
pigment { BrightGold }
finish {
ambient .1
diffuse .1
specular 1
roughness .001
reflection .75
}
}
}
That is very close but there is something wrong with the highlight. To make
the surface appear more like metal the keyword metallic is used. Add it now
to see the difference.
sphere { <0,0,0>, 1
pigment { BrightGold }
finish {
ambient .1
diffuse .1
specular 1
roughness .001
reflection .75
metallic
}
}
}
We see that the highlight has taken on the color of the surface rather than
the light source. This gives the surface a more metallic appearance.
4.8.4.4 Using Refraction
Objects that are transparent allow light to pass through them. With some
substances, the light is bent as it traves from one substance into the other
because of the differing optical densities of the objects. This is called
refraction . Water and glass both bend light in this manner so to create
water or glass, POV-Ray gives you a way to specify refraction. This is done
with the keywords refraction and ior . The amount of light that passes
through an object is determined by the value of the filtering and/or
transmittance channel in the pigment. You should use the refraction value
only to switch refraction on or off using vaules of 1 or 0 respectively (or
the boolean values on and off ). See section "Refraction" for a detailed
explanation of the reasons.
The degree of refraction, i. e. the amount of bending that occurs, is given
by the keyword ior , short for index of refraction . If you know the index of
refraction of the substance you are trying to create, you may just use that.
For instance, water is 1.33, glass is around 1.45 and diamond is 1.75. Let's
return to the example of a glass sphere we used earlier.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient 0
diffuse 0
reflection .25
refraction 1
ior 1.45
specular 1
roughness .001
}
}
}
Render this again and notice how the plane that is visible through the sphere
is distorted and turned upside-down. This is because the light passing
through the sphere is being bent or refracted to the degree specified. Try
reducing ior to 1.25. Try increasing it to 1.75. Notice how the distortion
changes.
4.8.4.5 Light Attenuation and Caustics
Transparent objects can be made to cause the intensity of light passing
through them to be reduced. In reality, this is due to impurities in
scattering the light. Two float values determine the effect: fade_distance is
the distance the light has to travel to reach one-half its original intensity
and fade_power is the degree of falloff. Let's try an example of this.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient .1
diffuse .1
reflection .15
refraction 1
ior 1.45
specular 1
roughness .001
fade_distance 5
fade_power 1
}
}
This gives the sphere a slightly clouded look as if not all of the light was
able to pass through it. For interesting variations of this texture, try
lowering ior to 1.15 and raising reflection to 0.5.
One thing we do notice is that the shadow of the sphere is still the same old
flat gray shadow we have had all along. If there is all this light refraction
going on shouldn't there be something going on with the shadow as well? That
something would be due to an effect known as caustics . POV-Ray cannot do
caustics but it can fake them to some degree. This is an easy one. Simply add
caustics 1 to the finish block and re-render to see the effect. What we see
is a highlight in the shadow that simulates the effect of light passing
through the sphere and being focused because of the curved surface. Remember
that this is not real caustics, so changing other finish parameters like ior
will not affect the caustic highlight. The faked caustic is limited to the
area shadowed by the corresponding object.
4.8.4.6 Using Iridescence
Iridescence is what you see on the surface of an oil slick when the sun
shines on it. The rainbow effect is created by something called thin-film
interference (read section "Iridescence" for details). For now let's just try
using it. Iridescence is specified by the irid keyword and three values:
amount , thickness and turbulence . The amount is the contribution to the
overall surface color. Usually 0.1 to 0.5 is sufficient here. The thickness
affects the busyness of the effect. Keep this between 0.25 and 1 for best
results. The turbulence is a little different from pigment or normal
turbulence. You cannot set octaves , lambda or omega but you can specify an
amount which will affect the thickness in a slightly different way from the
thickness value. Values between 0.25 and 1 work best here too. Finally,
iridescence will respond to the surface normal since it depends on the angle
of incidence of the light rays striking the surface. With all of this in
mind, let's add some iridescence our glass sphere.
sphere { <0,0,0>, 1
pigment { White filter 1 }
finish {
ambient .1
diffuse .1
reflection .2
refraction 1
ior 1.5
specular 1
roughness .001
fade_distance 5
fade_power 1
caustics 1
irid {
0.35
thickness .5
turbulence .5
}
}
}
Try varying the values for amount , thickness and turbulence to see what
changes they make. Try adding a normal block to see what happens.
4.8.5 Halos
Halos are a powerful feature that can be used to create a lot of different
effects like clouds, fogs, fire, lasers, etc. The name actually comes from
the ability to render halos with it, like the ones seen around the moon or
the sun.
Due to the complexity of the halo feature and the large amount of parameters
provided it is very difficult to get satisfying results. The following
sections will help you to create a halo step by step, starting with the basic
things and going to the more subtle stuff.
It is also helpful to read the halo reference sections to get a better
understanding of the halo feature. You should especially read the sections
"Empty and Solid Objects" and "Halo Mapping" because they are essential for
understanding halos.
4.8.5.1 What are Halos?
Halos are a texture feature allowing you to fill the interior of an object
with particles. The distribution of these particles can be modified using
several density mappings and density functions. The particles can emit light
to give fire- or laser-like effects or they can absorb light to create clouds
or fog.
A halo is attached to an object, the so called container object, just like a
pigment, normal or finish. This object is completely filled by the halo but
you won't see anything if you do not make sure that the object is hollow and
the surface is translucent. How this is accomplished will be shown in the
next section.
When working with halos you always have to keep in mind that the container
object has to be hollow and translucent.
4.8.5.2 The Emitting Halo
We start with one of the simpler types, the emitting halo. It uses particles
that only emit light. There are no particles that absorb the light coming
from other particles.
4.8.5.2.1 Starting with a Basic Halo
A clever approach in designing a nice halo effect is to start with a simple,
unit-sized shape that sits on the coordinate system's origin.
In the first example ( halo01.pov ) we try to create a fiery explosion, which
the sphere is best suited for. We start with a simple scene consisting of a
camera, a light source (we don't care about shadows so we add the shadowless
keyword), a checkered plane and a unit-sized sphere containing the halo.
camera {
location <0, 0, -2.5>
look_at <0, 0, 0>
}
light_source { <10, 10, -10> color rgb 1 shadowless }
plane { z, 2
pigment { checker color rgb 0, color rgb 1 }
finish { ambient 1 diffuse 0 }
scale 0.5
hollow
}
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
emitting
spherical_mapping
linear
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 1, 0, 0> ]
}
samples 10
}
hollow
}
You'll note that the sphere is set to be hollow and has a translucent surface
(the transmittance channel in the pigment color is 1), just like it is
required for halos. You'll also note that the plane has a hollow keyword even
though it has no halo. Why is this necessary?
The reason is quite simple. As described in section "Empty and Solid Objects"
there can be no halo inside any other non-hollow object. Since the camera is
inside the plane object, i.e. it is one the side of the plane that is
considered be inside, the halo will never be visible unless the plane is made
hollow (or the negative keyword is added to bring the camera on the outside
side of the plane).
What do all those halo keywords and values mean? At the beginning of the halo
the emitting keyword is used to specify what type of halo we want to use. The
emitting halo emits light. That's what's best suited for our fiery explosion.
The spherical_mapping and linear keyword need a more detailed explanation of
how a halo work (this is also done in chapter "Halo" in more detail).
As noted above the halo is made up of lots of small particles. The
distribution of these particles is described by a density function. In
general, a density function tells us how much particles we'll find at a given
location.
Instead of using an explicitly, mathematical density function, halos rely on
a given set of density mappings and density functions to model a variety of
particle distributions.
The first step in this model is the density mapping function that is used to
map three-dimensional points onto a one-dimensional range of values. In our
example we use a spherical mapping, i.e. we take the distance of a point from
the center of the coordinate system. This is the reason why it is clever to
start with a container object sitting on the coordinate system's center.
Since all density mappings are made relative to this center you won't see
anything if you start with an object sitting somewhere else. Moving the whole
object (including textures and halos) to another location is the correct way
of placing a container object.
Now we have a single value in the range from 0 to 1. This value will be
transformed using a density function to get density values instead of
distance values. Just using this single value won't work because we want to
have particle distributions were the density decreases as we move from the
middle the container object to the outside.
This is done by the density function. There are several alternatives
available as described in the halo reference (see section "Density Function"
). We use the simple linear function that just maps values between 0 and 1
onto a 1 to 0 range. Thus we get a density value of 1 at the center of our
sphere and a value of 0 at its surface.
Now that we have a density function what do we do to see something? This is
where the colour_map keyword comes into play. It is used to describe a color
map that actually tells the program what colors have to be used for what
density. The relation is quite simple: colors at the beginning of the color
map (with small values) will be used for low density values and colors at the
end of the map (high values) will be used for high densities. In our example
the halo will be yellow at the center of the sphere where the density is
greatest and it will blend to red at the surface of the sphere where the
density approaches zero.
The transmittance channel of the colors in the color map is used to model the
translucency of the density field. A value of 0 represents no translucency,
i. e. that areas with the corresponding density will be (almost) opaque,
while a value of 1 means (almost) total translucency.
In our example we use
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 1, 0, 0> ]
}
which results in a halo with a very translucent, reddish outer area and a
nearly opaque, yellowish inner areas as you can see after tracing the example
image.
The basic halo used in modelling a fiery explosion.
There is one parameter that still needs to be explained: the samples keyword.
This keyword tells POV-Ray how many samples along any ray travelling through
the halo have to be taken to calculate the halo. Using a low value will
result in a high tracing speed while a high value will lead to a low speed.
The sample value has to be increased if the halo looks somewhat strange , i.
e. if some artifacts of the low sampling rate appear. For more details see
section "Halo Sampling" .
4.8.5.2.2 Increasing the Brightness
The colors of the halo in the above image are somewhat dim. There is too much
of the background visible through the halo. That does not look much like
fire, does it? An easy way to fix this is to decrease the transparency of the
particles in the areas of high density. Just use the following color map
instead of the old one (the negative transmittance is correct).
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 1, 0, -1> ]
}
Looking at the result of halo02.pov we will see that the halo is indeed much
brighter.
4.8.5.2.3 Adding Some Turbulence
What we now have does not look like a fiery explosion. It's more a glowing
ball than anything else. Somehow we have to make it look more chaotic , we
have to add some turbulence to it.
This is done by using the turbulence keyword together with the amount of
turbulence we want to add. Just like in the following example.
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
emitting
spherical_mapping
linear
turbulence 1.5
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 1, 0, -1> ]
}
samples 10
}
hollow
}
Adding turbulence to the halo moves all points inside the halo container in a
pseudo-random manner. This results in a particle distribution that looks like
there was some kind of flow in the halo (depending on the amount of
turbulence you'll get a laminar or turbulent flow). The hight turbulence
value is used because an explosion is highly turbulent.
Looking at the example image ( halo03.pov ) you'll see that this looks more
like a fiery explosion than the glowing ball we got until now.
Adding some turbulence makes the fiery explosion more realistic.
You'll notice that the time it took to render the image increased after we
added the turbulence. This is due to the fact that for every sample taken
from the halo the slow turbulence function has to be evaluated.
4.8.5.2.4 Resizing the Halo
There is one strange thing about our fiery explosion though. It still looks
like a sphere. Why does this happen and what can we do to avoid it?
As noted above adding turbulence moves the particles inside the halo
container around. The problem is that some of the particles are actually
moved out of the container object. This leads to high densities at the
surface of the container object revealing the shape of the object (all
particles outside the container are lost and will not visible resulting in a
large, highly visible density change at the surface).
An easy way of avoiding this is to make sure that the particles stay inside
the container object even if we add some turbulence. This is done by scaling
the halo to reduce its size. We do not scale the container object, just the
halo.
This is done by adding the scale keyword inside the halo statement.
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
emitting
spherical_mapping
linear
turbulence 1.5
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 1, 0, -1> ]
}
samples 10
scale 0.5
}
hollow
scale 1.5
}
The scale 0.5 command tells POV-Ray to scale all points inside the halo by
this amount. This effectively scales the radius we get after the density
mapping to a range of 0 to 0.5 instead of 0 to 1 (without turbulence). If we
now add the turbulence the points are allowed to move half a unit in every
direction without leaving the container object. That is excactly what we
want.
To compensate for the smaller halo we would get we scale the sphere (and the
halo inside) by 1.5.
Looking at the new example image ( halo04.pov ) you will no longer see any
signs of the container sphere. We finally have a nice fiery explosion.
Resizing the halo makes it look much better.
The amount by which to scale the halo depends on the amount of turbulence you
use. The higher the turbulence value the smaller the halo has to be scaled.
That is something to experiment with.
Another way to avoid that points move out of the sphere is to use a larger
sphere, i. e. a sphere with a radius larger than one. It is important to
resize the sphere before the halo is added because otherwise the halo will
also be scaled.
You should note that this only works for spherical and box mapping (and a
non-constant density function). All other mapping types are (partially)
infinite, i.e. the resulting particle distribution covers an infinite space
(see also "Halo Mapping" ).
4.8.5.2.5 Using Frequency to Improve Realism
Another very good way of improving the realism of our explosion is to use a
frequency value other than one. The way frequency works is explained in
section "Frequency Modifier" in the reference part.
The rather mathematical explanation used there doesn't help much in
understanding how this feature is used. It is quite simple though. The
frequency value just tells the program how many times the color map will be
repeated in the density range from 0 to 1. If a frequency of one (the
default) is specified the color map will be visible once in the density
field, e. g. the color at 0 will be used for density 0, color at 0.5 will be
used for density 0.5 and the color at 1 will be used for density 1. Simple,
isn't it?
If you choose a frequency of two, the color at 0 will be used for density 0,
the color at 0.5 will be used for density 0.25 and the color at 1 will be
used for density 0.5. What about the densities above 0.5? Since there are no
entries in the color map for values above 1 we just start at 0 again. Thus
the color at 0.1 will be used for density 0.55 ((2*0.55) mod 1 = 1.1 mod 1 =
0.1), the color at 0.5 will be used for density 0.75 and the color at 1 will
be used for density 1.
If you are good at mathematics you'll note that the above example is not
quite right because (1 * 2) mod 1 = 0 and not 1. Just think that we used a
value slightly smaller than one and everything will be fine.
You may have noticed that in order to avoid sudden changes in the halo color
for frequencies larger than one you'll have to used a periodic color map,
i.e. a color map whose entries at 0 and 1 are the same.
We'll change our example by using a periodic color map and changing the
frequency value to two.
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
emitting
spherical_mapping
linear
turbulence 1.5
color_map {
[ 0.0 color rgbt <1, 0, 0, 1> ]
[ 0.5 color rgbt <1, 1, 0, -1> ]
[ 1.0 color rgbt <1, 0, 0, 1> ]
}
frequency 2
samples 20
scale 0.5
}
hollow
scale 1.5
}
Using a periodic color map and a frequency of two gives a much nicer
explosion.
Looking at the result of ( halo05.pov ) we can be quite satisfied with the
explosion we just have created, can't we?
There's one thing left you should be aware of when increasing the frequency
value. It is often necessary to increase the sample rate in (nearly) the same
way as you change the frequency. If you don't do this you'll probably get
some severe aliasing artefacts (like color jumps or strange bands of colors).
If this happens just change the samples value according to the frequency
value (twice sampling rate for a doubled frequency).
4.8.5.2.6 Changing the Halo Color
We have a nice fiery explosion but we want to try to add some science fiction
touch to it by using different colors. How about a nice green, less turbulent
explosion that gets red at its borders?
Nothing easier than that!
sphere { 0, 1.5
pigment { color rgbt <1, 1, 1, 1> }
halo {
emitting
spherical_mapping
linear
turbulence 0.5
color_map {
[ 0 color rgbt <0, 1, 0, 1> ]
[ 1 color rgbt <1, 0, 0, -1> ]
}
samples 10
scale 0.75
}
hollow
scale 1.5
}
Using red and green colors gives an unexpected result.
This should do the trick. Looking at the result of halo06.pov you may be
disappointed. Where is the red center of the explosion? The borders are green
as expected but there is a lot of yellow in the center and only a little bit
red. What is happening?
We use an emitting halo in our example. According to the corresponding
section in the halo reference chapter (see "Emitting" ) this type of halo
uses very small particles that do not attenuate light passing through the
halo. Especially particles near the viewer do not attenuate the light coming
from particles far away from the viewer.
During the calculation of the halo's color near the center of the container
sphere, the ray steps through nearly all possible densities of the particle
distribution. Thus we get red and green colors as we march on, depending on
the current position in the halo. The sum of these colors is used which will
gives as a yellow color (the sum of red and green is yellow). This is what is
happening here.
How can we still get what we want? The answer is to use a glowing halo
instead of the emitting halo. The glowing halo is very similar to the
emitting one except that it attenuates the light passing through. Thus the
light of particles lying behind other particles will be attenuated by the
particles in front.
4.8.5.3 The Glowing Halo
We have mentioned the glowing halo in the section about the emitting halo as
one way to avoid the color mixing that is happening with emitting halos.
The gowing halo is very similar to the emitting halo except that it also
absorbs light. You can view it as a combination of the emitting and the
attenuating halo described in section "The Attenuating Halo" .
By just replacing the emitting keyword in the example in section "Changing
the Halo Color" with the glowing keyword we get the desired effect as shown
in the example image ( halo11.pov ).
Using a glowing halo gives the expected result.
Even though the red color of the high density areas is not very visible
because the green colored, lower density areas lying in front absorb most of
the red light, you don't get yellow color where you would have expected a red
one.
Due to its similarity with the emitting halo we leave it up to you to make
some experiments with this halo type. You just have to keep all those things
you learned in the previous sections in mind to get some satisfying results.
4.8.5.4 The Attenuating Halo
Another simple halo type is the attenuating halo that only absorbs light. It
doesn't radiate on its own.
A great difference between the attenuating halo and the other halo types is
that the color of the attenuating halo is calculated from the halo's color
map using the total particle density along a given ray. The other types
calculated a (weighted) average of the colors calculated from the density at
each sample.
4.8.5.4.1 Making a Cloud
Attenuating halos are ideal to create clouds and smoke. In the following
examples we will try to make a neat little cloud. We start again by using a
unit-sized sphere that is filled with a basic attenuating halo ( halo21.pov
).
camera {
location <0, 0, -2.5>
look_at <0, 0, 0>
}
light_source { <10, 10, -10> color rgb 1 shadowless }
plane { z, 2
pigment { checker color rgb 0, color rgb 1 }
finish { ambient 1 diffuse 0 }
scale 0.5
hollow
}
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
attenuating
spherical_mapping
linear
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 0, 0, 0> ]
}
samples 10
}
hollow
}
Even though clouds normally are not red but white or gray, we use the red
color to make it more visible against the black/white checkerboard
background.
The color of an attenuating halo is calculated from the total accumulated
density after a ray has marched through the complete particle field. This has
to be kept in mind when creating the color map. We want the areas of the
cloud with a low density to have a high translucency so we use a color of
rgbt<1,0,0,1> and we want the high density areas to be opaque so we choose a
color of rgbt<1,0,0,0>.
4.8.5.4.2 Scaling the Halo Container
The cloud we have created so far doesn't look very realistic. It's just a
red, partially translucent ball. In order to get a better result we use some
of the methods we have already learned in the sections about emitting halos
above. We add some turbulence to get a more realistic shape, we scale the
halo to avoid the container object's surface to become visible and we
decrease the translucency of the areas with a high particle density.
Another idea is to scale the container object to get an ellipsoid shape that
can be used to model a cloud pretty good. This is done by the scale <1.5,
0.75, 1> command at the end of the sphere. It scales both, the sphere and the
halo inside.
sphere { 0, 1
pigment { color rgbt <1, 1, 1, 1> }
halo {
attenuating
spherical_mapping
linear
turbulence 1
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 0, 0, -1> ]
}
samples 10
scale 0.75
}
hollow
scale <1.5, 0.75, 1>
}
Looking at the results of halo22.pov you'll see that this looks more like a
real cloud (besides the color).
4.8.5.4.3 Adding Additional Halos
Another trick to get some more realism is to use multiple halos. If you look
at cumulus clouds e. g. you'll notice that they often extend at the top while
they are quite flat at the bottom.
We want to model this appearance by adding two additional halos to our
current container object (see section "Multiple Halos" for more details).
This is done in the following way:
sphere { 0, 1.5
pigment { color rgbt <1, 1, 1, 1> }
halo {
attenuating
spherical_mapping
linear
turbulence 1
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 0, 0, -1> ]
}
samples 10
scale <0.75, 0.5, 1>
translate <-0.4, 0, 0>
}
halo {
attenuating
spherical_mapping
linear
turbulence 1
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 0, 0, -1> ]
}
samples 10
scale <0.75, 0.5, 1>
translate <0.4, 0, 0>
}
halo {
attenuating
spherical_mapping
linear
turbulence 1
color_map {
[ 0 color rgbt <1, 0, 0, 1> ]
[ 1 color rgbt <1, 0, 0, -1> ]
}
samples 10
scale 0.5
translate <0, 0.2, 0>
}
hollow
}
The three halos used differ only in their location, i. e. in the translation
vector we have used. The first two halos are used to form the base of the
cloud while the last sits on top of the others. The sphere has a different
radius than the previous ones because more space is needed for all three
halos.
The result of halo23.pov somehwat looks like a cloud, even though it may need
some work.
4.8.5.5 The Dust Halo
The dust halo is a very complex halo type. It allows you to see the
interaction of light coming from light sources with the particles in the
halo. Those particles do absorb light like the attenuating halo. In addition
they scatter light coming from light sources passing through them. This makes
beams of light and shadows cast by objects onto the halo become visible.
4.8.5.5.1 Starting With an Object Lit by a Spotlight
We start with a box shaped object that is lit by a spotlight. We don't use
any halo at this moment because we want to see if the object is completely
lit by the light source ( halo31.pov ).
camera {
location <0, 0, -2.5>
look_at <0, 0, 0>
}
background { color rgb <0.2, 0.4, 0.8> }
light_source {
<2.5, 2.5, -2.5>
colour rgb <1, 1, 1>
spotlight
point_at <0, 0, 0>
radius 12
falloff 15
tightness 1
}
difference {
box { -1, 1 }
box { <-1.1, -0.8, -0.8>, <1.1, 0.8, 0.8> }
box { <-0.8, -1.1, -0.8>, <0.8, 1.1, 0.8> }
box { <-0.8, -0.8, -1.1>, <0.8, 0.8, 1.1> }
pigment { color rgb <1, 0.2, 0.2> }
scale 0.5
rotate 45*y
rotate 45*x
}
The object we want to use.
As you see the whole object is lit by the light source. Now we can start to
add some dust.
4.8.5.5.2 Adding Some Dust
We use a box to contain the dust halo. Since we use a constant density
function it doesn't matter what kind of density mapping is used. The density
has the value specified by the max_value keyword everywhere inside the halo
(the default value is one). The isotropic scattering is selected with
dust_type .
box { -1, 1
pigment { colour rgbt <1, 1, 1, 1> }
halo {
dust
dust_type 1
box_mapping
constant
colour_map {
[ 0 color rgbt <1, 1, 1, 1> ]
[ 1 color rgbt <1, 1, 1, 0> ]
}
samples 10
}
hollow
scale 5
}
This dust is too thick.
The result of halo32.pov is too bright. The dust is too thick and we can only
see some parts of the object and no background.
4.8.5.5.3 Decreasing the Dust Density
The density inside the halo has the constant value one. This means that only
the color map entry at position one is used to determine the density and
color of the dust.
We use a transmittance value of 0.7 to get a much thinner dust.
box { -1, 1
pigment { colour rgbt <1, 1, 1, 1> }
halo {
dust
dust_type 1
box_mapping
constant
colour_map {
[ 0 color rgbt <1, 1, 1, 1.0> ]
[ 1 color rgbt <1, 1, 1, 0.7> ]
}
samples 10
}
hollow
scale 5
}
A thinner dust looks much better.
Beside the ugly aliasing artefacts the image looks much better. We can see
the whole object and even the background is slightly visible ( halo33.pov ).
4.8.5.5.4 Making the Shadows Look Good
In order to reduce the aliasing artefacts we use three different techniques:
jittering, super-sampling and an increased overall sampling rate.
The jittering is used to add some randomness to the sampling points making
the image look more noisy. This helps because the regular aliasing artefacts
are more annoying than noise. A low jitter value is a good choice.
The super-sampling tries to detect fine features by taking additional samples
in areas of high intensity changes. The threshold at which super-sampling is
used and the maximum recursion level can be specified using the aa_threshold
and aa_level keywords.
The approach that always works is to increase the overall sampling rate.
Since this is also the slowest method you should always try to use the other
methods first. If they don't suffice you'll have to increase the sampling
rate.
We use the following halo to reduce the aliasing artefacts ( halo34.pov ).
box { -1, 1
pigment { colour rgbt <1, 1, 1, 1> }
halo {
dust
dust_type 1
box_mapping
constant
colour_map {
[ 0 color rgbt <1, 1, 1, 1.0> ]
[ 1 color rgbt <1, 1, 1, 0.7> ]
}
samples 50
aa_level 3
aa_threshold 0.2
jitter 0.1
}
hollow
scale 5
}
Different anti-aliasing methods help to get a satisfying result.
The image looks much better now. There are hardly any aliasing artefacts
left.
The same parameters we have used are discussed in the section about the
atmosphere feature (see "The Atmosphere" for further explanations).
4.8.5.5.5 Adding Turbulence
The major difference between the halo's dust and the atmosphere described in
"The Atmosphere" is the ability to choose a non-uniform particle distribution
for the dust. This includes the fact that the halo is limited to a container
object as well as the different density mappings and functions.
Another interesting way of getting an irregular disribution is to add some
turbulence to the dust. This is done with the turbulence keyword followed by
the amount of turbulence to use, like the following example shows (
halo35.pov ).
box { -1, 1
pigment { colour rgbt <1, 1, 1, 1> }
halo {
dust
dust_type 1
box_mapping
linear
turbulence 1
colour_map {
[ 0 color rgbt <1, 1, 1, 1.0> ]
[ 1 color rgbt <1, 1, 1, 0.5> ]
}
samples 50
aa_level 3
aa_threshold 0.2
jitter 0.1
}
hollow
scale 5
}
Adding turbulence to the dust makes it much more interesting.
The image we now get looks much more interesting due to the shifts in the
particle density.
You should note that we use a linear density function instead of the previous
constant one. This is necessary because with a constant density function the
density has the same value everywhere. Adding turbulence would have no effect
because wherever the points are moved the density will have this same value.
Only a non-constant density distribution makes sense when turbulence is
added.
The fact that the turbulence value is actually a vector can be used to create
effects like waterfalls by using a large turbulence value in on direction
only (e.g. turbulence <0.2, 1, 0.2> ).
4.8.5.5.6 Using a Coloured Dust
If you want to create a colored dust you can easily do this by using a
non-white color in the halo's color map. In this case you'll also have to set
the filter channels in the color map to non-zero values to specify the amount
of light that will be filtered by the dust's color.
Use the following color map to get a partially filtering, red dust for
example:
colour_map {
[ 0 color rgbft <1, 0, 0, 0.5, 1.0> ]
[ 1 color rgbft <1, 0, 0, 0.5, 0.7> ]
}
4.8.5.6 Halo Pitfalls
Due to the complexity of the halo feature and the few experiences people have
made so far there are a lot of things still to discover.
Some of the most common problems and pitfalls are described below in order to
help you to avoid the most common problems.
4.8.5.6.1 Where Halos are Allowed
As mentioned above a halo completly fills the interior of an object. Keeping
this in mind it is reasonable that the following example does not make sense.
sphere { 0, 1
pigment {
checker
texture {
pigment { color Clear }
halo { ... }
}
texture {
pigment { color Red }
}
}
hollow
}
What's wrong with this example? It's simply that a halo is used to describe
the interior of an object and that you cannot describe this interior by
describing how the surface of the object looks like. But that's what was done
in the example above. Can you imagine what the interior of the sphere will
look like? Will it be filled completey with the halo? Will there be areas
filled by the halo and some filled by air? How will those areas look like?
You won't be able to tell the interior's properties from looking at the
surface. It's just not possible. This should always be kept in mind.
If the above example was meant to create a sphere filled with a halo and
covered with a checker board pattern that partially hid the halo you would
have used the following syntax:
sphere { 0, 1
pigment {
checker
texture {
pigment { color Clear }
}
texture {
pigment { color Red }
}
}
halo { ... }
hollow
}
A halo is always applied to an object in the following way:
OBJECT {
texture {
pigment { ... }
normal { ... }
finish { ... }
halo { ... }
}
hollow
}
There's no halo allowed inside any pigment statement, color map, pigment map,
texture map, material map, or whatever. You are not hindered to do this but
you will not get what you want.
You can use a halo with a layered textures as long as you make sure that the
halos are only attached to the lowest layer (this layer has to be partially
transparent to see the halo of course).
4.8.5.6.2 Overlapping Container Objects
POV-Ray is not able to handle overlapping container objects correctly. If you
create two overlapping spheres that contain a halo you won't get correct
results where the spheres overlap. The halo effect is calculated
independently for each sphere and the results are added.
If you want to add different halos you have to put all halos inside a single
container object to make sure the halo is calculated correctly (see also
"Multiple Halos" ).
You should also note non-overlapping, stacked halo containers are handled
correctly. If you put a container object in front of another container object
the halos are rendered correctly.
4.8.5.6.3 Multiple Attenuating Halos
It is currently not possible to use mutliple attenuating halos with different
color maps. The color map of the last halo will be used for all halos in the
container object.
4.8.5.6.4 Halos and Hollow Objects
In order to correctly render halo effects you have to make sure that all
objects the camera is inside are hollow. This is done by adding the hollow
keyword.
4.8.5.6.5 Scaling a Halo Container
If you scale a halo container object you should keep in mind that it makes a
great difference where you place the scale keyword.
Scaling the object before the halo statement will only scale the container
object not the halo. This is useful if you want to avoid that the surface of
the container object becomes visible due to the use of turbulence. As you've
learned in the sections above particles may move out of the container object
- where they are invisible - if turbulence is added. This only works for
spherical and box mapping because the density fields described by the other
mapping types don't have finite dimensions.
If the scale keyword is used after the halo statement both, the halo and the
container object, are scaled. This is useful to scale the halo to your needs.
The halo keeps its appearance regardless of the transformations applied to
the container object (after the halo), i.e. the halo's translucency, color
and turbulence characteristics will not change.
4.8.5.6.6 Choosing a Sampling Rate
Normally you'll start with a low sampling rate and you'll only increase it if
any aliasing artefacts turn up (and don't vanish by using super-sampling and
jittering).
The halo's appearance is independent from the sampling rate as long as there
are enough samples to get a good estimate of what the halo really looks like.
This means that one or two samples are hardly ever enough to determine the
halo's appearance. As you increase the number of samples the halo will
quickly approach its real appearance.
To put it in a nutshell, the halo will not change its appearance with the
sample rate as long as you have a sufficient number of samples and no
aliasing artefacts occur.
4.8.5.6.7 Using Turbulence
As noted in one of the above sections turbulence will have no effect if the
constant density function is used (keyword constant). It doesn't matter how
much or where you move a point if the density is constant and thus does not
depend on the points location. You'll get the same density value for all
location.
Whenever you add turbulence to a halo do not use the constant density
function.
4.9 Using Atmospheric Effects
POV-Ray offers a variety of atmospheric effects, i. e. features that affect
the background of the scene or the air by which everything is surrounded.
It is easy to assign a simple color or a complex color pattern to a virtual
sky sphere. You can create anything from a cloud free, blue summer sky to a
stormy, heavy clouded sky. Even starfields can easily be created.
You can use different kinds of fog to create foggy scenes. Multiple fog
layers of different colors can add an eerie touch to your scene.
A much more realistic effect can be created by using an atmosphere, a
constant fog that interacts with the light coming from light sources. Beams
of light become visible and objects will cast shadows into the fog.
4.9.1 The Background
The background feature is used to assign a color to all rays that don't hit
any object. This is done in the following way.
camera {
location <0, 0, -10>
look_at <0, 0, 0>
}
background { color rgb <0.2, 0.2, 0.3> }
sphere { 0, 1
pigment { color rgb <0.8, 0.5, 0.2> }
}
The background color will be visible if a sky sphere is used and if some
translucency remains after all sky sphere pigment layers are processed.
4.9.2 The Sky Sphere
The sky sphere can be used to easily create a cloud covered sky, a nightly
star sky or whatever sky you have in mind.
In the following examples we'll start with a very simple sky sphere that will
get more and more complex as we add new features to it.
4.9.2.1 Creating a Sky with a Color Gradient
Beside the single color sky sphere that is covered with the background
feature the simplest sky sphere is a color gradient.
You may have noticed that the color of the sky varies with the angle to the
earth's surface normal. If you look straight up the sky normally has a much
deeper blue than it has at the horizon.
We want to model this effect using the sky sphere as shown in the scene below
( skysph1.pov ).
#include "colors.inc"
camera {
location <0, 1, -4>
look_at <0, 2, 0>
angle 82
}
light_source { <10, 10, -10> White }
sphere { 2*y, 1
pigment { color rgb <1, 1, 1> }
finish { ambient 0.2 diffuse 0 reflection 0.6 }
}
sky_sphere {
pigment {
gradient y
color_map {
[0 color Red]
[1 color Blue]
}
scale 2
translate -1
}
}
The interesting part is the sky sphere statement. It contains a pigment that
describe the look of the sky sphere. We want to create a color gradient along
the viewing angle measured against the earth's surface normal. Since the ray
direction vector is used to calculate the pigment colors we have to use the
y-gradient.
The scale and translate transformation are used to map the points derived
from the direction vector to the right range. Without those transformations
the pattern would be repeated twice on the sky sphere. The scale statement is
used to avoid the repetition and the translate -1 statement moves the color
at index zero to the bottom of the sky sphere (that's the point of the sky
sphere you'll see if you look straight down).
After this transformation the color entry at position 0 will be at the bottom
of the sky sphere, i. e. below us, and the color at position 1 will be at the
top, i. e. above us.
The colors for all other positions are interpolated between those two colors
as you can see in the resulting image.
A simple gradient sky sphere.
If you want to start one of the colors at a specific angle you'll first have
to convert the angle to a color map index. This is done by using the formula
color_map_index = (1 - cos(angle)) / 2
where the angle is measured against the negated earth's surface normal. This
is the surface normal pointing towards the center of the earth. An angle of 0
degrees describes the point below us while an angle of 180 degrees represents
the zenith.
In POV-Ray you first have to convert the degree value to radian values as it
is shown in the following example.
sky_sphere {
pigment {
gradient y
color_map {
[(1-cos(radians( 30)))/2 color Red]
[(1-cos(radians(120)))/2 color Blue]
}
scale 2
translate -1
}
}
This scene uses a color gradient that starts with a red color at 30 degrees
and blends into the blue color at 120 degrees. Below 30 degrees everything is
red while above 120 degrees all is blue.
4.9.2.2 Adding the Sun
In the following example we will create a sky with a red sun surrounded by a
red color halo that blends into the dark blue night sky. We'll do this using
only the sky sphere feature.
The sky sphere we use is shown below. A ground plane is also added for
greater realism ( skysph2.pov ).
sky_sphere {
pigment {
gradient y
color_map {
[0.000 0.002 color rgb <1.0, 0.2, 0.0>
color rgb <1.0, 0.2, 0.0>]
[0.002 0.200 color rgb <0.8, 0.1, 0.0>
color rgb <0.2, 0.2, 0.3>]
}
scale 2
translate -1
}
rotate -135*x
}
plane { y, 0
pigment { color Green }
finish { ambient .3 diffuse .7 }
}
The gradient pattern and the transformation inside the pigment are the same
as in the example in the previous section.
The color map consists of three colors. A bright, slightly yellowish red that
is used for the sun, a darker red for the halo and a dark blue for the night
sky. The sun's color covers only a very small portion of the sky sphere
because we don't want the sun to become too big. The color is used at the
color map values 0.000 and 0.002 to get a sharp contrast at value 0.002 (we
don't want the sun to blend into the sky). The darker red color used for the
halo blends into the dark blue sky color from value 0.002 to 0.200. All
values above 0.200 will reveal the dark blue sky.
The rotate -135*x statement is used to rotate the sun and the complete sky
sphere to its final position. Without this rotation the sun would be at 0
degrees, i.e. right below us.
A red sun descends into the night.
Looking at the resulting image you'll see what impressive effects you can
achieve with the sky sphere.
4.9.2.3 Adding Some Clouds
To further improve our image we want to add some clouds by adding a second
pigment. This new pigment uses the bozo pattern to create some nice clouds.
Since it lays on top of the other pigment it needs some translucent colors in
the color map (look at entries 0.5 to 1.0).
sky_sphere {
pigment {
gradient y
color_map {
[0.000 0.002 color rgb <1.0, 0.2, 0.0>
color rgb <1.0, 0.2, 0.0>]
[0.002 0.200 color rgb <0.8, 0.1, 0.0>
color rgb <0.2, 0.2, 0.3>]
}
scale 2
translate -1
}
pigment {
bozo
turbulence 0.65
octaves 6
omega 0.7
lambda 2
color_map {
[0.0 0.1 color rgb <0.85, 0.85, 0.85>
color rgb <0.75, 0.75, 0.75>]
[0.1 0.5 color rgb <0.75, 0.75, 0.75>
color rgbt <1, 1, 1, 1>]
[0.5 1.0 color rgbt <1, 1, 1, 1>
color rgbt <1, 1, 1, 1>]
}
scale <0.2, 0.5, 0.2>
}
rotate -135*x
}
A cloudy sky with a setting sun.
The sky sphere has one drawback as you might notice when looking at the final
image ( skysph3.pov ). The sun doesn't emit any light and the clouds will not
cast any shadows. If you want to have clouds that cast shadows you'll have to
use a real, large sphere with an appropriate texture and a light source
somewhere outside the sphere.
4.9.3 The Fog
You can use the fog feature to add fog of two different types to your scene:
constant fog and ground fog. The constant fog has a constant density
everywhere while the ground fog's density decreases as you move upwards.
The usage of both fog types will be described in the next sections in detail.
4.9.3.1 A Constant Fog
The simplest fog type is the constant fog that has a constant density in all
locations. It is specified by a distance keyword which actually describes the
fog's density and a fog color .
The distance value determines the distance at which 36.8% of the background
are still visible (for a more detailed explanation of how the fog is
calculated read the reference section "Fog" ).
The fog color can be used to create anything from a pure white to a red,
bloodish fog. You can also use a black fog to simulate the effect of a
limited range of vision.
The following example will show you how to add fog to a simple scene (
fog1.pov ).
#include "colors.inc"
camera {
location <0, 20, -100>
}
background { colour SkyBlue }
plane { y, -10
pigment {
checker colour Yellow colour Green
scale 20
}
}
sphere { <0, 25, 0>, 40
pigment { Red }
finish { phong 1.0 phong_size 20 }
}
sphere { <-100, 150, 200>, 20
pigment { Green }
finish { phong 1.0 phong_size 20 }
}
sphere { <100, 25, 100>, 30
pigment { Blue }
finish { phong 1.0 phong_size 20 }
}
light_source { <100, 120, 40> colour White}
fog {
distance 150
colour rgb<0.3, 0.5, 0.2>
}
A foggy scene.
According to their distance the spheres in this scene more or less vanish in
the greenish fog we used, as does the checkerboard plane.
4.9.3.2 Setting a Minimum Translucency
If you want to make sure that the background does not completely vanish in
the fog you can set the transmittance channel of the fog's color to the
amount of background you always want to be visible.
Using as transmittance value of 0.2 as in
fog {
distance 150
colour rgbt<0.3, 0.5, 0.2, 0.2>
}
the fog's translucency never drops below 20% as you can see in the resulting
image ( fog2.pov ).
Adding a translucency threshold you make sure that the background does not
vanish.
4.9.3.3 Creating a Filtering Fog
The greenish fog we have used so far doesn't filter the light passing through
it. All it does is to diminish the light's intensity. We can change this by
using a non-zero filter channel in the fog's color ( fog3.pov ).
fog {
distance 150
colour rgbf<0.3, 0.5, 0.2, 1.0>
}
The filter value determines the amount of light that is filtered by the fog.
In our example 100% of the light passing through the fog will be filtered by
the fog. If we had used a value of 0.7 only 70% of the light would have been
filtered. The remaining 30% would have passed unfiltered.
A filtering fog.
You'll notice that the intensity of the objects in the fog is not only
diminished due to the fog's color but that the colors are actually influenced
by the fog. The red and especially the blue sphere got a green hue.
4.9.3.4 Adding Some Turbulence to the Fog
In order to make our somewhat boring fog a little bit more interesting we can
add some turbulence, making it look like it had a non-constant density (
fog4.pov ).
fog {
distance 150
colour rgbf<0.3, 0.5, 0.2, 1.0>
turbulence 0.2
turb_depth 0.3
}
Adding some turbulence makes the fog more interesting.
The tubulence keyword is used to specify the amount of turbulence used while
the turb_depth value is used to move the point at which the turbulence value
is calculated along the viewing ray. Values near zero move the point to the
viewer while values near one move it to the intersection point (the default
value is 0.5). This parameter can be used to avoid noise that may appear in
the fog due to the turbulence (this normally happens at very far away
intersecion points, especially if no intersection occurs, i. e. the
background is hit). If this happens just lower the turb_depth value until the
noise vanishes.
You should keep in mind that the actual density of the fog does not change.
Only the distance-based attenuation value of the fog is modified by the
turbulence value at a point along the viewing ray.
4.9.3.5 Using Ground Fog
The much more interesting and flexible fog type is the ground fog, which is
selected with the fog_type statement. It's appearance is described with the
fog_offset and fog_alt keywords. The fog_offset specifies the height, i. e. y
value, below which the fog has a constant density of one. The fog_alt keyword
determines how fast the density of the fog will approach zero as one moves
along the y axis. At a height of fog_offset+fog_alt the fog will have a
density of 25%.
The following example ( fog5.pov ) uses a ground fog which has a constant
density below y=25 (the center of the red sphere) and quickly falls off for
increasing altitudes.
fog {
distance 150
colour rgbf<0.3, 0.5, 0.2, 1.0>
fog_type 2
fog_offset 25
fog_alt 1
}
4.9.3.6 Using Multiple Layers of Fog
It is possible to use several layers of fog by using more than one fog
statement in your scene file. This is quite useful if you want to get nice
effects using turbulent ground fogs. You could add up several, differently
colored fogs to create an eerie scene for example.
Just try the following example ( fog6.pov ).
fog {
distance 150
colour rgb<0.3, 0.5, 0.2>
fog_type 2
fog_offset 25
fog_alt 1
turbulence 0.1
turb_depth 0.2
}
fog {
distance 150
colour rgb<0.5, 0.1, 0.1>
fog_type 2
fog_offset 15
fog_alt 4
turbulence 0.2
turb_depth 0.2
}
fog {
distance 150
colour rgb<0.1, 0.1, 0.6>
fog_type 2
fog_offset 10
fog_alt 2
}
Quite nice results can be achieved using multiple layers of fog.
You can combinate constant density fogs, ground fogs, filtering fogs,
non-filtering fogs, fogs with a translucency threshold, etc.
4.9.3.7 Fog and Hollow Objects
Whenever you use the fog feature and the camera is inside a non-hollow object
you won't get any fog effects. For a detailed explanation why this happens
see "Empty and Solid Objects" .
In order to avoid this problem you have to make all those objects hollow by
either making sure the camera is outside these objects (using the inverse
keyword) or by adding the hollow to them (which is much easier).
4.9.4 The Atmosphere
The atmosphere feature can be used to model the interaction of light with
particles in the air. Beams of light will become visible and objects will
cast shadows into the fog or dust that's filling the air.
The atmosphere model used in POV-Ray assumes a constant particle density
everywhere except solid objects. If you want to create cloud like fogs or
smoke you'll have to use the halo texturing feature described in section
"Halos" .
4.9.4.1 Starting With an Empty Room
We want to create a simple scene to explain how the atmosphere feature works
and how you'll get good results.
Imagine a simple room with a window. Light falls through the window and is
scattered by the dust particles in the air. You'll see beams of light coming
from the window and shining on the floor.
We want to model this scene step by step. The following examples start with
the room, the window and a spotlight somewhere outside the room. Currently
there's no atmosphere to be able to verify if the lighting is correct (
atmos1.pov ).
camera {
location <-10, 8, -19>
look_at <0, 5, 0>
angle 82
}
background { color rgb <0.2, 0.4, 0.8> }
light_source { <0, 19, 0> color rgb 0.5 atmosphere off }
light_source {
<40, 25, 0> color rgb <1, 1, 1>
spotlight
point_at <0, 5, 0>
radius 20
falloff 20
atmospheric_attenuation on
}
union {
difference {
box { <-21, -1, -21>, <21, 21, 21> }
box { <-20, 0, -20>, <20, 20, 20> }
box { <19.9, 5, -3>, <21.1, 15, 3> }
}
box { <20, 5, -0.25>, <21, 15, 0.25> }
box { <20, 9.775, -3>, <21, 10.25, 3> }
pigment { color red 1 green 1 blue 1 }
finish { ambient 0.2 diffuse 0.5 }
}
The empty room we want to start with.
The point light source is used to illuminate the room from inside without any
interaction with the atmosphere. This is done by adding atmosphere off . We
don't have to care about this light when we add the atmosphere later.
The spotlight is used with the atmospheric_attenuation keyword. This means
that light coming from the spotlight will be diminished by the atmosphere.
The union object is used to model the room and the window. Since we use the
difference between two boxes to model the room (the first two boxes in the
difference statement) there is no need for setting the union hollow. If we
are inside this room we actually will be outside the object (see also "Using
Hollow Objects and Atmosphere" ).
4.9.4.2 Adding Dust to the Room
The next step is to add an atmosphere to the room. This is done by the
following few lines ( atmos2.pov ).
atmosphere {
type 1
samples 10
distance 40
scattering 0.2
}
The type keyword selects the type of atmospheric scattering we want to use.
In this case we use the isotropic scattering that equally scatters light in
all directions (see "Atmosphere" for more details about the different
scattering types).
The samples keyword determines the number of samples used in accumulating the
atmospheric effect. For every ray samples are taken along the ray to
determine wether a sample is lit by a light source or not. If the sample is
lit the amount of light scattered into the direction of the viewer is
determined and added to the total intensity.
You can always start with an arbitrary number of samples. If the results do
not fit your ideas you can increase the sampling rate to get better results.
The problem of choosing a good sampling rate is the trade-off between a
satisfying image and a fast rendering. A high sampling rate will almost
always work but the rendering will also take a very long time. That's
something to experiment with.
The distance keyword specifies the density of the atmosphere. It works in the
same way as the distance parameter of the fog feature.
Last but not least will the scattering value determine the amount of light
that is scattered by the particles (the remaining light is absorbed). As
you'll later see this parameter is very useful in adjusting the overall
brightness of the atmosphere.
After adding some dust beams of light become visible.
Looking at the image created from the above scene you'll notice some very
ugly anti-aliasing artefacts known as mach-bands. They are the result of a
low sampling rate.
4.9.4.3 Choosing a Good Sampling Rate
As you've seen a too low sampling rate can cause some ugly results. There are
some ways of reducing or even avoiding those problems.
The brute force approach is to increase the sampling rate until the artefacts
vanish and you get a satisfying image. Though this will always work it is a
bad idea because it is very time consuming. A better approach is to use
jittering and anti-aliasing first. If both features don't help you'll have to
increase the sampling rate.
Jittering moves each sample point by a small, random amount along the
sampling direction. This helps to reduce regular features resulting from
aliasing. There is (hardly) nothing more annyoing to the human visual system
than the regular features resulting from a low sampling rate. It's much
better to add some extra noise to the image by jittering the sample
positions. The human eye is much more forgiving to that.
Use the jitter keyword followed by the amount of jittering you want to use.
Good jittering values are up to 0.5, higher values result in too much noise.
You should be aware that jittering can not fix the artefacts introduced by a
too low sampling rate. It can only make them less visible.
An additional and better way of reducing aliasing artefacts is to use
(adaptive) super-sampling. This method casts additional samples where it is
likely that they are needed. If the intensity between two adjactent samples
differs too much additional samples are taken inbetween. This step is done
recursively until a specified recursion level is reached or the sample get
close to each other.
The aa_level and aa_threshold keywords are used to control the
super-sampling. The aa_level keyword determines the maximum recursion level
while the aa_threshold keyword specifies the maximum allowed difference
between two sample before the super-sampling is done.
After all this theory we get back to our sample scene and add the appropriate
keywords to use both jittering and supersamling ( atmos3.pov ).
atmosphere {
type 1
samples 50
distance 40
scattering 0.2
aa_level 4
aa_threshold 0.1
jitter 0.2
}
A very low threshold value was choosen to super-sample even between adjactent
points with a very similar intensity. The maximum recursion level of 4 will
lead to a maximum of fifteen super-samples.
If you are looking at the results that you get after adding jittering and
super-sampling you won't be satisfied. The only way of reducing the still
visible artefacts is to increase the sampling rate by choosing a higher
number of samples.
A high sampling rate leads to a satisfying image.
Doing this you'll get a good result showing (almost) no artefacts. Btw. the
amount of dust floating around in this room may be a little bit exaggerated
but it's just an example. And examples tend to be exaggerated.
4.9.4.4 Using a Coloured Atmosphere
You can assign a color to the atmosphere that gives you more control over the
atmosphere's appearance. First of all the color is used to filter all light
passing through it, wether it comes from light sources, relfected and
refracted rays, or the background. The amount by which the passing light is
filtered by the atmosphere's color is determined by the color's filter value.
A value of 0 means that the light is not influenced by the atmosphere's color
while a value of 1 means that all light will be filtered by the color.
If you want to create a reddish atmosphere for example, you can add the
following line to the atmosphere statement used in the above example.
color rgbf <1, 0, 0, 0.25>
Just using rgb <1,0,0> does not work because the color's filter value will be
zero and thus no light will be filtered by the color, i. e. no light will be
multiplied with the color's RGB components.
The filter value of 0.25 means that 25% of the light passing through the
atmosphere will be filtered by the red color and 75% will pass unfiltered.
The transmittance channel of the atmosphere's color is used to specify a
minimum translucency. By default the transmittance channel is zero and thus
there is no such minimum translucency. Using a positive value lets you
determine the amount of background light that will always pass through the
atmosphere, regardless of its thickness set by the distance keyword.
If you use e.g. a color of rgbt <0,0,0,0.3> with our room example you can
make the blue background become visible. Until now it was hidden by the
atmosphere.
4.9.4.5 Atmosphere Tips
It is very difficult to get satisfying results when using the atmosphere
feature. Some of the more common problems will be discussed in the next
sections to help you to solve them (see also the FAQ section about the
atmosphere in "Atmosphere Questions" ).
4.9.4.5.1 Choosing the Distance and Scattering Parameters
The first difficult step is to choose a good distance and scattering value.
You need to be able to control the visibility of the objects in the scene and
the atmospheric effects.
The best approach is to choose the distance value first. This value
determines the visibility of the objects in the scene regardless of
atmospheric light scattering. It works in the same way as the distance value
of the fog feature.
Since fog is very similar to the unlit atmosphere you can use a fog instead
of an atmosphere to quickly choose a working distance value. If you do this
with room scene we used earlier you would use the following fog statement
instead of the atmosphere ( atmos4.pov ).
fog {
distance 40
color rgb <0, 0, 0>
}
A black fog can be used to get a working distance value for the atmosphere.
The black color is used to simulate the attenuation you'll get in those parts
of the atmosphere scene lying in shadow.
If you want to use a colored atmosphere you'll have to use the same color for
the fog as you want to use for the atmosphere, including the filter and
transmittance channel values (see "Using a Coloured Atmosphere" and
"Atmosphere" for an explanation of the atmosphere's color).
If you (roughly) want to simulate the appearance of those parts lit by a
light source you can use the color of the atmosphere inside the fog statement
instead.
After you are satisfied with the distance value you'll have to choose a
scattering value. This value lets you fit the atmosphere's intensity to your
needs. Starting with a value of one you have to increase the value if the
atmosphere effects are hardly visible. If you don't see anything in the lit
parts of the atmosphere you'll have to decrease the value.
You should be aware that you may have to use very small or very large values
to get the desired results.
4.9.4.5.2 Atmosphere and Light Sources
The best results are generated with spotlights and cylindrical light sources.
They create nice beams of light and are fast to render because the
atmospheric sampling takes only place inside the light cone of the spotlight
or light cylinder of the cylindrical light.
If you want to add a light source that does not interact with the atmosphere
you can use the atmosphere keyword inside the light source statement (see
"Atmosphere Interaction" ). Just add atmosphere off .
By default the light coming from any light source will not be diminished by
the atmosphere. Thus the highlights in your scene will normally be too
bright. This can be changed with atmospheric_attenuation on .
4.9.4.5.3 Atmosphere Scattering Types
The different scattering types listed in "Atmosphere" can be used to model
different types of particles. This is something for you to experiment with.
The Rayleigh scattering is used for small particles like dust and smoke while
the Mie scattering is used for fog.
If you ever saw the lighthouse scene in the movie Casper you'll know what
effect the scattering type has. In this scene the beam of light coming from
the lighthouse becomes visible while it points nearly towards the viewer. As
it starts to point away from the viewer it vanishes. This behaviour is
typical for miniscule water droplets as modeled by the Mie scattering.
4.9.4.5.4 Increasing the Image Resolution
You have to be aware that you may have to increase the atmosphere sampling
rate if you increase the resolution of the image. Otherwise some aliasing
artefacts that were no visible at the lower resolution may become visible.
4.9.4.5.5 Using Hollow Objects and Atmosphere
Whenever you use the atmosphere feature you have to make sure that all
objects that ought to be filled with atmosphere are set to hollow using the
hollow keyword.
Even though this is not obvious this holds for infinite and patch objects
like quadrics, quartics, triangles, polygons, etc. Whenever you add one of
those objects you should add the hollow keyword as long as you are not
absolutely sure you don't need it. You also have to make sure that all
objects the camera is inside are set to be hollow.
Whenever you get unexpected results you should check for solid objects and
set them to be hollow.
4.9.5 The Rainbow
The rainbow feature can be used to create rainbows and maybe other more
strange effects. The rainbow is a fog like effect that is restricted to a
cone-like volume.
4.9.5.1 Starting With a Simple Rainbow
The rainbow is specified with a lot of parameters: the angle under which it
is visible, the width of the color band, the direction of the incoming light,
the fog-like distance based particle density and last not least the color map
to be used.
The size and shape of the rainbow are determined by the angle and width
keywords. The direction keyword is used to set the direction of the incoming
light, thus setting the rainbow's position. The rainbow is visible when the
angle between the direction vector and the incident light direction is larger
than angle-width/2 and smaller than angle+width/2.
The incoming light is the virtual light source that is responsible for the
rainbow. There needn't be a real light source to create the rainbow effect.
The rainbow is a fog-like effect, i.e. the rainbow's color is mixed with the
background color based on the distance to the intersection point. If you
choose small distance values the rainbow will be visible on objects, not just
in the background. You can avoid this by using a very large distance value.
The color map is the crucial part of the rainbow since it contains all the
colors that normally can be seen in a rainbow. The color of the innermost
color band is taken from the color map entry 0 while the outermost band is
take from entry 1. You should note that due to the limited color range any
monitor can display it is impossible to create a real rainbow. There are just
some colors that you cannot display.
The filter channel of the rainbow's color map is used in the same way as with
fogs. It determines how much of the light passing through the rainbow is
filtered by the color.
The following example shows a simple scene with a ground plane, three spheres
and a somewhat exaggerated rainbow ( rainbow1.pov ).
#include "colors.inc"
camera {
location <0, 20, -100>
look_at <0, 25, 0>
angle 82
}
background { color SkyBlue }
plane { y, -10 pigment { colour Green } }
light_source {<100, 120, 40> colour White}
// declare rainbow's colours
#declare r_violet1 = colour rgbf<1.0, 0.5, 1.0, 1.0>
#declare r_violet2 = colour rgbf<1.0, 0.5, 1.0, 0.8>
#declare r_indigo = colour rgbf<0.5, 0.5, 1.0, 0.8>
#declare r_blue = colour rgbf<0.2, 0.2, 1.0, 0.8>
#declare r_cyan = colour rgbf<0.2, 1.0, 1.0, 0.8>
#declare r_green = colour rgbf<0.2, 1.0, 0.2, 0.8>
#declare r_yellow = colour rgbf<1.0, 1.0, 0.2, 0.8>
#declare r_orange = colour rgbf<1.0, 0.5, 0.2, 0.8>
#declare r_red1 = colour rgbf<1.0, 0.2, 0.2, 0.8>
#declare r_red2 = colour rgbf<1.0, 0.2, 0.2, 1.0>
// create the rainbow
rainbow {
angle 42.5
width 5
distance 1.0e7
direction <-0.2, -0.2, 1>
jitter 0.01
colour_map {
[0.000 colour r_violet1]
[0.100 colour r_violet2]
[0.214 colour r_indigo]
[0.328 colour r_blue]
[0.442 colour r_cyan]
[0.556 colour r_green]
[0.670 colour r_yellow]
[0.784 colour r_orange]
[0.900 colour r_red1]
}
}
Some irregularity is added to the color bands using the jitter keyword.
A colorful rainbow.
The rainbow in our sample is much too bright. You'll never see a rainbow like
this in reality. You can decrease the rainbow's colors by decreasing the RGB
values in the color map.
4.9.5.2 Increasing the Rainbow's Translucency
The result we have so far looks much too bright. Just reducing the rainbow's
color helps but it's much better to increase the translucency of the rainbow
because it is more realistic if the background is visible through the
rainbow.
We can use the transmittance channel of the colors in the color map to
specify a minimum translucency, just like we did with the fog. To get
realistic results we have to use very large transmittance values as you can
see in the following example ( rainbow2.pov ).
rainbow {
angle 42.5
width 5
distance 1.0e7
direction <-0.2, -0.2, 1>
jitter 0.01
colour_map {
[0.000 colour r_violet1 transmit 0.98]
[0.100 colour r_violet2 transmit 0.96]
[0.214 colour r_indigo transmit 0.94]
[0.328 colour r_blue transmit 0.92]
[0.442 colour r_cyan transmit 0.90]
[0.556 colour r_green transmit 0.92]
[0.670 colour r_yellow transmit 0.94]
[0.784 colour r_orange transmit 0.96]
[0.900 colour r_red1 transmit 0.98]
}
}
The transmittance values increase at the outer bands of the rainbow to make
it softly blend into the background.
A much more realistc rainbow.
4.9.5.3 Using a Rainbow Arc
Currently our rainbow has a circular shape, even though most of it is hidden
below the ground plane. You can easily create a rainbow arc by using the
arc_angle keyword with an angle below 360 degrees.
If you use arc_angle 120 for example you'll get a rainbow arc that abruptly
vanishes at the arc's ends. This does not look good. To avoid this the
falloff_angle keyword can be used to specify a region where the arc smoothly
blends into the background.
As explained in the rainbow's reference section (see "Rainbow" ) the arc
extends from -arc_angle/2 to arc_angle/2 while the blending takes place from
-arc_angle/2 to -falloff_angle/2 and falloff_angle/2 to arc_angle/2. This is
the reason why the falloff_angle has to be smaller or equal to the arc_angle
.
In the following examples we use an 120 degrees arc with a 45 degree falloff
region on both sides of the arc ( rainbow3.pov ).
rainbow {
angle 42.5
width 5
arc_angle 120
falloff_angle 30
distance 1.0e7
direction <-0.2, -0.2, 1>
jitter 0.01
colour_map {
[0.000 colour r_violet1 transmit 0.98]
[0.100 colour r_violet2 transmit 0.96]
[0.214 colour r_indigo transmit 0.94]
[0.328 colour r_blue transmit 0.92]
[0.442 colour r_cyan transmit 0.90]
[0.556 colour r_green transmit 0.92]
[0.670 colour r_yellow transmit 0.94]
[0.784 colour r_orange transmit 0.96]
[0.900 colour r_red1 transmit 0.98]
}
}
The arc angles are measured against the rainbows up direction which can be
specified using the up keyword. By default the up direction is the y-axis.
A rainbow arc.
5 POV-Ray Reference
The reference section describes all command line options and INI file
switches, the scene description language and all other features that are part
of POV-Ray. It is supposed to be used as a reference for looking up things.
It does not contain detailed explanations on how scenes are written or how
POV-Ray is used. It just explains all features, their syntax, applications,
limits, drawbacks, etc.
6 POV-Ray Options
POV-Ray was originally created as a command-line program for operating
systems without graphical interfaces, dialog boxes and pull-down menus. Most
versions of POV-Ray still use command-line switches to tell it what to do.
This documentation assumes you are using the command-line version. If you are
using Macintosh, MS-Windows or other GUI versions, there will be dialog boxes
or menus which do the same thing. There is system-specific documentation for
each system describing the specific commands.
6.1 Setting POV-Ray Options
There are two distinct ways of setting POV-Ray options: command line switches
and INI file keywords. Both are explained in detail in the following
sections.
6.1.1 Command Line Switches
Command line switches consist of a + (plus) or - (minus) sign, followed by
one or more alphabetic characters and possibly a numeric value. Here is a
typical command line with switches.
POVRAY +Isimple.pov +V +W80 +H60
povray is the name of the program and it is followed by several switches.
Each switch begins with a plus or minus sign. The +I switch with the filename
tells POV-Ray what scene file it should use as input and +V tells the program
to output its status to the text screen as it's working. The +W and +H
switches set the width and height of the image in pixels. This image will be
80 pixels wide by 60 pixels high.
In switches which toggle a feature, the plus turns it on and minus turns it
off. For example +P turns on the pause for keypress when finished option
while -P turns it off. Other switches are used to specify values and do not
toggle a feature. Either plus or minus may be used in that instance. For
example +W 320 sets the width to 320 pixels. You could also use -W 320 and
get the same results.
Switches may be specified in upper or lower case. They are read left to right
but in general may be specified in any order. If you specify a switch more
than once, the previous value is generally overwritten with the last
specification. The only exception is the +L switch for setting library paths.
Up to ten unique paths may be specified.
Almost all + / - switches have an equivalent option which can be used in an
INI file which is described in the next section. A detailed description of
each switch is given in the option reference section.
6.1.2 Using INI Files
Because it is difficult to set more than a few options on a command line, you
have the ability to put multiple options in one or more text files. These
initialization files or INI files have .ini as their default extension.
Previous versions of POV-Ray called them default files or DEF files . You may
still use existing DEF files with this version of POV-Ray.
The majority of options you use will be stored in INI files. The command line
switches are recommended for options which you will turn off or on frequently
as you perform test renderings of a scene you are developing. The file
povray.ini is automatically read if present. You may specify additional INI
files on the command-line by simply typing the file name on the command line.
For example:
POVRAY MYOPTS.INI
If no extension is given, then .ini is assumed. POV-Ray knows this is not a
switch because it is not preceded by a plus or minus. In fact a common error
among new users is that they forget to put the +I switch before the input
file name. Without the switch, POV-Ray thinks that the scene file simple.pov
is an INI file. Don't forget! If no plus or minus precedes a command line
switch, it is assumed to be an INI file name.
You may have multiple INI files on the command line along with switches. For
example:
POVRAY MYOPTS +V OTHER
This reads options from myopts.ini , then sets the +V switch, then reads
options from other.ini .
An INI file is a plain ASCII text file with options of the form...
Option_keyword=VALUE ; Text after semicolon is a comment
For example the INI equivalent of the switch +I simple.pov is...
Input_File_Name=simple.pov
Options are read top to bottom in the file but in general may be specified in
any order. If you specify an option more than once, the previous values are
generally overwritten with the last specification. The only exception is the
Library_Path = path options. Up to ten unique paths may be specified.
Almost all INI-style options have equivalent + / - switches. The option
reference section gives a detailed description of all POV-Ray options. It
includes both the INI-style settings and the + / - switches.
The INI keywords are not case sensitive. Only one INI option is permitted per
line of text. You may also include switches in your INI file if they are
easier for you. You may have multiple switches per line but you should not
mix switches and INI options on the same line. You may nest INI files by
simply putting the file name on a line by itself with no equals sign after
it. Nesting may occur up to ten levels deep.
For example:
; This is a sample INI file. This entire line is a comment.
; Blank lines are permitted.
Input_File_Name=simple.pov ;This sets the input file name
+W80 +H60 ; Traditional +/- switches are permitted too
MOREOPT ; Read MOREOPT.INI and continue with next line
+V ; Another switch
; That's all folks!
INI files may have labeled sections so that more than one set of options may
be stored in a single file. Each section begins with a label in [] brackets.
For example:
; RES.INI
; This sample INI file is used to set resolution.
+W120 +H100 ; This section has no label.
; Select it with "RES"
[Low]
+W80 +H60 ; This section has a label.
; Select it with "RES[Low]"
[Med]
+W320 +H200 ; This section has a label.
; Select it with "RES[Med]"
[High]
+W640 +H480 ; Labels are not case sensitive.
; "RES[high]" works
[Really High]
+W800 +H600 ; Labels may contain blanks
When you specify the INI file you should follow it with the section label in
brackets. For example...
POVRAY RES[Med] +Imyfile.pov
POV-Ray reads res.ini and skips all options until it finds the label Med . It
processes options after that label until it finds another label and then it
skips. If no label is specified on the command line then only the unlabeled
area at the top of the file is read. If a label is specified, the unlabeled
area is ignored.
6.1.3 Using the POVINI Environment Variable
The environment variable POVINI is used to specify the location and name of a
default INI file that is read every time POV-Ray is executed. If POVINI is
not specified a default INI file may be read depending on the platform used.
If the specified file does not exist a warning message is printed.
To set the environment variable under MS-Dos you might put the following line
in your autoexec.bat file...
set POVINI=c:\povray3\default.ini
On most operating systems the sequence of reading options is as follows:
1. Read options from default INI file specified by the POVINI environment
variable or platform specific INI file.
2. Read switches from command line (this includes reading any specified
INI/DEF files).
The POVRAYOPT environment variable supported by previous POV-Ray versions is
no longer available.
6.2 Options Reference
As explained in the previous section, options may be specified by switches or
INI-style options. Almost all INI-style options have equivalent + / -
switches and most switches have equivalent INI-style option. The following
sections give a detailed description of each POV-Ray option. It includes both
the INI-style settings and the + / - switches.
The notation and terminology used is described in the tables below.
Keyword=bool turn Keyword on if bool equals true, yes, on or 1 and turn it
off if it is any other value.
Keyword=true do this option if true, yes, on or 1 is specified.
Keyword=false do this option if false, no, off or 0 is specified.
Keyword=file any valid file name. Note: some options prohibit the use of
any of the above true or false values as a file name. They
are noted in later sections.
n any integer such as in +W320
n.n any float such as in Clock=3.45
0.n any float < 1.0 even if it has no leading 0
s any string of text
xor y any single character
path any directory name, drive optional, no final path separator ("\" or
"/", depending on the operating system)
Unless otherwise specifically noted, you may assume that either a plus or
minus sign before a switch will produce the same results.
6.2.1 Animation Options
POV-Ray 3.0 greatly improved its animation capability with the addition of an
internal animation loop, automatic output file name numbering and the ability
to shell out to the operating system to external utilities which can assemble
individual frames into an animation. The internal animation loop is simple
yet flexible. You may still use external programs or batch files to create
animations without the internal loop as you may have done in POV-Ray 2.
6.2.1.1 External Animation Loop
Clock=n.n Sets "clock" float identifier to n.n
+Kn.n Same as Clock=n.n
The Clock =n.n option or the +K n.n switch may be used to pass a single float
value to the program for basic animation. The value is stored in the float
identifier clock . If an object had a rotate <0,clock,0> attached then you
could rotate the object by different amounts over different frames by setting
+K 10.0, +K 20.0... etc. on successive renderings. It is up to the user to
repeatedly invoke POV-Ray with a different Clock value and a different
Output_File_Name for each frame.
6.2.1.2 Internal Animation Loop
Initial_Frame=n Sets initial frame number to n
Final_Frame=n Sets final frame number
Initial_Clock=n.n Sets initial clock value
Final_Clock=n.n Sets final clock value
+KFIn Same as Initial_Frame=n
+KFFn Same as Final_Frame=n
+KIn.n Same as Initial_Clock=n.n
+KFn.n Same as Final_Clock=n.n
The internal animation loop new to POV-Ray 3.0 relieves the user of the task
of generating complicated sets of batch files to invoke POV-Ray multiple
times with different settings. While the multitude of options may look
intimidating, the clever set of default values means that you will probably
only need to specify the Final_Frame =n or the +KFF n option to specify the
number of frames. All other values may remain at their defaults.
Any Final_Frame setting other than -1 will trigger POV-Ray's internal
animation loop. For example Final_Frame =10 or +KFF 10 causes POV-Ray to
render your scene 10 times. If you specified Output_File_Name = file.tga then
each frame would be output as file01.tga , file02.tga , file03.tga etc. The
number of zero-padded digits in the file name depends upon the final frame
number. For example +KFF 100 would generate file001.tga through file100.tga .
The frame number may encroach upon the file name. On MS-Dos with an eight
character limit, myscene.pov would render to mysce001.tga through
mysce100.tga .
The default Initial_Frame =1 will probably never have to be changed. You
would only change it if you were assembling a long animation sequence in
pieces. One scene might run from frame 1 to 50 and the next from 51 to 100.
The Initial_Frame =n or +KFI n option is for this purpose.
Note that if you wish to render a subset of frames such as 30 through 40 out
of a 1 to 100 animation, you should not change Frame_Initial or Frame_Final .
Instead you should use the subset commands described in section "Subsets of
Animation Frames" .
Unlike some animation packages, the action in POV-Ray animated scenes does
not depend upon the integer frame numbers. Rather you should design your
scenes based upon the float identifier clock. By default, the clock value is
0.0 for the initial frame and 1.0 for the final frame. All other frames are
interpolated between these values. For example if your object is supposed to
rotate one full turn over the course of the animation, you could specify
rotate 360*clock*y . Then as clock runs from 0.0 to 1.0, the object rotates
about the y-axis from 0 to 360 degrees.
The major advantage of this system is that you can render a 10 frame
animation or a 100 frame or 500 frame or 329 frame animation yet you still
get one full 360 degree rotation. Test renders of a few frames work exactly
like final renders of many frames.
In effect you define the motion over a continuous float valued parameter (the
clock) and you take discrete samples at some fixed intervals (the frames). If
you take a movie or video tape of a real scene it works the same way. An
object's actual motion depends only on time. It does not depend on the frame
rate of your camera.
Many users have already created scenes for POV-Ray 2 that expect clock values
over a range other than the default 0.0 to 1.0. For this reason we provide
the Initial_Clock =n.n or +KI n.n and Final_Clock =n.n or +KF n.n options.
For example to run the clock from 25.0 to 75.0 you would specify
Initial_Clock =25.0 and Final_Clock =75.0. Then the clock would be set to
25.0 for the initial frame and 75.0 for the final frame. Inbetween frames
would have clock values interpolated from 25.0 through 75.0 proportionally.
Users who are accustomed to using frame numbers rather than clock values
could specify Initial_Clock =1.0 and Final_Clock =10.0 and Frame_Final =10
for a 10 frame animation.
For new scenes, we recommend you do not change the Initial_Clock or
Final_Clock from their default 0.0 to 1.0 values. If you want the clock to
vary over a different range than the default 0.0 to 1.0, we recommend you
handle this inside your scene file as follows...
#declare Start = 25.0
#declare End = 75.0
#declare My_Clock = Start+(End-Start)*clock
Then use My_Clock in the scene description. This keeps the critical values
25.0 and 75.0 in your .pov file.
Note that more details concerning the inner workings of the animation loop
are in the section on shell-out operating system commands in section
"Shell-out to Operating System" .
6.2.1.3 Subsets of Animation Frames
Subset_Start_Frame=n Set subset starting frame to n
Subset_Start_Frame=0.n Set subset starting frame to n percent
Subset_End_Frame=n Set subset ending frame to n
Subset_End_Frame=0.n Set subset ending frame to n percent
+SFn or +SF0.n Same as Subset_Start_Frame
+EFn or +EF0.n Same as Subset_End_Frame
When creating a long animation, it may be handy to render only a portion of
the animation to see what it looks like. Suppose you have 100 frames but only
want to render frames 30 through 40. If you set Initial_Frame =30 and
Final_Frame =40 then the clock would vary from 0.0 to 1.0 from frames 30
through 40 rather than 0.30 through 0.40 as it should. Therefore you should
leave Initial_Frame =1 and Final_Frame =100 and use Subset_Start_Frame =30
and Subset_End_Frame =40 to selectively render part of the scene. POV-Ray
will then properly compute the clock values.
Usually you will specify the subset using the actual integer frame numbers
however an alternate form of the subset commands takes a float value in the
range 0.0 <=n.nnn <=1.0 which is interpreted as a fraction of the whole
animation. For example, Subset_Start_Frame =0.333 and Subset_End_Frame =0.667
would render the middle 1/3rd of a sequence regardless of the number of
frames.
6.2.1.4 Cyclic Animation
Cyclic_Animation=bool Turn cyclic animation on/off
+KC Turn cyclic animation on
-KC Turn cyclic animation off
Many computer animation sequences are designed to be run in a continuous
loop. Suppose you have an object that rotates exactly 360 degrees over the
course of your animation and you did rotate 360*clock*y to do so. Both the
first and last frames would be identical. Upon playback there would be a
brief one frame jerkiness. To eliminate this problem you need to adjust the
clock so that the last frame does not match the first. For example a ten
frame cyclic animation should not use clock 0.0 to 1.0. It should run from
0.0 to 0.9 in 0.1 increments. However if you change to 20 frames it should
run from 0.0 to 0.95 in 0.05 increments. This complicates things because you
would have to change the final clock value every time you changed Final_Frame
. Setting Cyclic_Animation =on or using +KC will cause POV-Ray to
automatically adjust the final clock value for cyclic animation regardless of
how many total frames. The default value for this setting is off.
6.2.1.5 Field Rendering
Field_Render=bool Turn field rendering on/off
Odd_Field=bool Set odd field flag
+UF Turn field rendering on
-UF Turn field rendering off
+UO Set odd field flag on
-UO Set odd field flag off
Field rendering is sometimes used for animations when the animation is being
output for television. TVs only display alternate scan lines on each vertical
refresh. When each frame is being displayed the fields are interlaced to give
the impression of a higher resolution image. The even scan lines make up the
even field, and are drawn first (i. e. scan lines 0, 2, 4, etc.), followed by
the odd field, made up of the odd numbered scan lines are drawn afterwards.
If objects in an animation are moving quickly, their position can change
noticably from one field to the next. As a result, it may be desirable in
these cases to have POV-Ray render alternate fields at the actual field rate
(which is twice the frame rate), rather than rendering full frames at the
normal frame rate. This would save a great deal of time compared to rendering
the entire animation at twice the frame rate, and then only using half of
each frame.
By default, field rendering is not used. Setting Field_Render =on or using
+UF will cause alternate frames in an animation to be only the even or odd
fields of an animation. By default, the first frame is the even field,
followed by the odd field. You can have POV-Ray render the odd field first by
specifying Odd_Field =on, or by using the +UO switch.
6.2.2 Output Options
6.2.2.1 General Output Options
6.2.2.1.1 Height and Width of Output
Height=n Set screen height to n
Width=n Sets screen width to n pixels
+Hn Same as Height=n (when n > 8)
+Wn Same as Width=n
These switches set the height and width of the image in pixels. This
specifies the image size for file output. The preview display, if on, will
generally attempt to pick a video mode to accommodate this size but the
display settings do not in any way affect the resulting file output.
6.2.2.1.2 Partial Output Options
Start_Column=n Set first column to n
Start_Column=0.n Set first column to n percent of width
+SCn or +SC0.n Same as Start_Column
Start_Row=n Set first row to n pixels
Start_Row=0.n Set first row to n percent of height
+SRn or +Sn Same as Start_Row=n
+SR0.n or +S0.n Same as Start_Row=0.n
End_Column=n Set last column to n pixels
End_Column=0.n Set last column to n percent of width
+ECn or +EC0.n Same as End_Column
End_Row=n Set last row to n pixels
End_Row=0.n Set last row to n percent of height
+ERn or +En Same as End_Row=n
+ER0.n or +E0.n Same as End_Row=0.n
When doing test rendering it is often convenient to define a small,
rectangular sub-section of the whole screen so you can quickly check out one
area of the image. The Start_Row , End_Row , Start_Column and End_Column
options allow you to define the subset area to be rendered. The default
values are the full size of the image from (1,1) which is the upper left to
(w,h) on the lower right where w and h are the Width =n and Height =n values
you have set.
Note if the number specified is greater than 1 then it is interpreted as an
absolute row or column number in pixels. If it is a decimal value between 0.0
and 1.0 then it is interpreted as a percent of the total width or height of
the image. For example: Start_Row =0.75 and Start_Column =0.75 starts on a
row 75% down from the top at a column 75% from the left. Thus it renders only
the lower-right 25% of the image regardless of the specified width and
height.
The +SR , +ER , +SC and +EC switches work in the same way as the
corresponding INI-style settings for both absolute settings or percentages.
Early versions of POV-Ray allowed only start and end rows to be specified
with +S n and +E n so they are still supported in addition to +SR and +ER .
6.2.2.1.3 Interrupting Options
Test_Abort=bool Turn test for user abort on/off
+X Turn test abort on
-X Turn test abort off
Test_Abort_Count=n Set to test for abort every n pixels
+Xn Set to test for abort every n pixels on
-Xn Set to test for abort off (in future test every n
pixels)
On some operating systems once you start a rendering you must let it finish.
The Test_Abort =on option or +X switch causes POV-Ray to test the keyboard
for keypress. If you have pressed a key, it will generate a controlled user
abort. Files will be flushed and closed but only data through the last full
row of pixels is saved. POV-Ray exits with an error code 2 (normally POV-Ray
returns 0 for a successful run or 1 for a fatal error).
When this option is on, the keyboard is polled on every line while parsing
the scene file and on every pixel while rendering. Because polling the
keyboard can slow down a rendering, the Test_Abort_Count =n option or +X n
switch causes the test to be performed only every n pixels rendered or scene
lines parsed.
6.2.2.1.4 Resuming Options
Continue_Trace=bool Sets continued trace on/off
+C Sets continued trace on
-C Sets continued trace off
Create_Ini=file Generate an INI file to file
Create_Ini=true Generate file.ini where file is scene name.
Create_Ini=false Turn off generation of previously set file.ini
+GIsss Same as Create_Ini=sss
If you abort a render while it's in progress or if you used the End_Row
option to end the render prematurely, you can use Continue_Trace =on or +C
option to continue the render later at the point where you left off. This
option reads in the previously generated output file, displays the partial
image rendered so far, then proceeds with the ray-tracing. This option cannot
be used if file output is disabled with Output_to_file =off or -F .
The Continue_Trace option may not work if the Start_Row option has been set
to anything but the top of the file, depending on the output format being
used.
POV-Ray tries to figure out where to resume an interrupted trace by reading
any previously generated data in the specified output file. All file formats
contain the image size, so this will override any image size settings
specified. Some file formats (namely TGA and PNG) also store information
about where the file started (i. e. +SC n and +SR n options), alpha output
+UA , and bit-depth +FN n, which will override these settings. It is up to
the user to make sure that all other options are set the same as the original
render.
The Create_Ini option or +GI switch provides an easy way to create an INI
file with all of the rendering options, so you can re-run files with the same
options, or ensure you have all the same options when resuming. This option
creates an INI file with every option set at the value used for that
rendering. This includes default values which you have not specified. For
example if you run POV-Ray with...
POVRAY +Isimple.pov MYOPTS +GIrerun.ini MOREOPTS
POV-Ray will create a file called rerun.ini with all of the options used to
generate this scene. The file is not written until all options have been
processed. This means that in the above example, the file will include
options from both myopts.ini and moreopts.ini despite the fact that the +GI
switch is specified between them. You may now re-run the scene with...
POVRAY RERUN
or resume an interrupted trace with
POVRAY RERUN +C
If you add other switches with the rerun.ini reference, they will be included
in future re-runs because the file is re-written every time you use it.
The Create_Ini option is also useful for documenting how a scene was
rendered. If you render waycool.pov with Create_Ini =on then it will create a
file waycool.ini that you could distribute along with your scene file so
other users can exactly re-create your image.
6.2.2.2 Display Output Options
6.2.2.2.1 Display Hardware Settings
Display=bool Turns graphic display on/off
+D Turns graphic display on
-D Turns graphic display off
Video_Mode=x Set video mode to 'x'; does not affect on/off
+Dx Set display on; Set mode to 'x'
-Dx Set display off; but for future use mode 'x'
Palette=y Set display palette to 'y'; does not affect on/off
+Dxy Set display on; Set mode 'x'; Set palette 'y'
-Dxy Set display off; use mode 'x', palette 'y' in future
Display_Gamma=n.n Sets the display gamma to n.n
%%% LATEX-ONLY \begin {LIST} {Display_Gamma =n.n} \item[ Display =bool] Turns
graphic display on/off \item[ +D ] Turns graphic display on \item[ -D ] Turns
graphic display off \item[] \item[ Video_Mode =x] Set video mode to x ; does
not affect on/off \item[ +D x] Set display on; Set mode to x \item[ -D x] Set
display off; but for future use mode x \item[] \item[ Palette =y] Set display
palette to y ; d oes not affect on/off \item[ +D xy] Set display on; Set mode
x ; Set palette y \item[ -D xy] Set display off; use mode x , palette y in
future \item[ Display_Gamma =n.n] Sets the display gamma to n.n \end {LIST}
%%% END
The Display =on or +D switch will turn on the graphics display of the image
while it is being rendered. Even on some non-graphics systems, POV-Ray may
display an 80 by 24 character ASCII-Art version of your image. Where
available, the display may be full, 24-bit true color. Setting Display =off
or using the -D switch will turn off the graphics display which is the
default.
The Video_Mode =x option sets the display mode or hardware type chosen where
x is a single digit or letter that is machine dependent (see section "Display
Types" for a description of the modes supported by the MS-Dos version).
Generally Video_Mode =0 means the default or an auto-detected setting should
be used. When using switches, this character immediately follows the switch.
For example the +D0 switch will turn on the graphics display in the default
mode.
The Palette =y option selects the palette to be used. Typically the single
character parameter y is a digit which selects one of several fixed palettes
or a letter such G for gray scale, H for 15-bit or 16-bit high color or T for
24-bit true color. When using switches, this character is the 2nd character
after the switch. For example the +D0T switch will turn on the graphics
display in the default mode with a true color palette.
The Display_Gamma =n.n setting is new with POV-Ray 3.0, and is not available
as a command-line switch. The Display_Gamma setting overcomes the problem of
images (whether ray-traced or not) having different brightness when being
displayed on different monitors, different video cards, and under different
operating systems. Note that the Display_Gamma is a setting based on your
computer's display hardware, and should be set correctly once and not
changed. The Display_Gamma INI setting works in conjunction with the new
assumed_gamma global setting to ensure that POV scenes and the images they
create look the same on all systems. See section "Assumed_Gamma" which
describes the assumed_gamma global setting and describes gamma more
thoroughly.
While the Display_Gamma can be different for each system, there are a few
general rules that can be used for setting Display_Gamma if you don't know it
exactly. If the Display_Gamma keyword does not appear in the INI file,
POV-Ray assumes that the display gamma is 2.2. This is because most PC
monitors have a gamma value in the range 1.6 to 2.6 (newer models seem to
have a lower gamma value). MacOS has the ability to do gamma correction
inside the system software (based on a user setting in the gamma control
panel). If the gamma control panel is turned off, or is not available, the
default Macintosh system gamma is 1.8. Some high-end PC graphics cards can do
hardware gamma correction and should use the current Display_Gamma setting,
usually 1.0. A gamma test image is also available to help users to set their
Display_Gamma accurately.
For scene files that do not have an assumed_gamma global setting the
Display_Gamma will not have any affect on the preview output of POV-Ray or
for most output file formats. However, the Display_Gamma value is used when
creating PNG format output files, and also when rendering the POV-Ray example
files (because they have an assumed_gamma ), so it should still be correctly
set for your system to ensure proper results.
6.2.2.2.2 Display Related Settings
Pause_When_Done=bool Sets pause when done on/off
+P Sets pause when done on
-P Sets pause when done off
Verbose=bool Set verbose messages on/off
+V Set verbose messages on
-V Set verbose messages off
Draw_Vistas=bool Turn draw vistas on/off
+UD Turn draw vistas on
-UD Turn draw vistas off
On some systems, when the image is complete, the graphics display is cleared
and POV-Ray switches back into text mode to print the final statistics and to
exit. Normally when the graphics display is on, you want to look at the image
awhile before continuing. Using Pause_When_Done =on or +P causes POV-Ray to
pause in graphics mode until you to press a key to continue. The default is
not to pause ( -P ).
When the graphics display is not used, it is often desirable to monitor
progress of the rendering. Using Verbose =on or +V turns on verbose reporting
of your rendering progress. This reports the number of the line currently
being rendered, the elapsed time for the current frame and other information.
On some systems, this textual information can conflict with the graphics
display. You may need to turn this off when the display is on. The default
setting is off ( -V ).
The option Draw_Vistas =on or +UD was originally a debugging help for
POV-Ray's vista buffer feature but it was such fun we decided to keep it.
Vista buffering is a spatial sub-division method that projects the 2-D
extents of bounding boxes onto the viewing window. POV-Ray tests the 2-D x, y
pixel location against these rectangular areas to determine quickly which
objects, if any, the viewing ray will hit. This option shows you the 2-D
rectangles used. The default setting is off ( -UD ) because the drawing of
the rectangles can take considerable time on complex scenes and it serves no
critical purpose. See section "Automatic Bounding Control" for more details.
6.2.2.2.3 Mosaic Preview
Preview_Start_Size=n Set mosaic preview start size to n
+SPn Same as Preview_Start_Size=n
Preview_End_Size=n Set mosaic preview end size to n
+EPn Same as Preview_End_Size=n
Typically, while you are developing a scene, you will do many low resolution
test renders to see if objects are placed properly. Often this low resolution
version doesn't give you sufficient detail and you have to render the scene
again at a higher resolution. A feature called mosaic preview solves this
problem by automatically rendering your image in several passes.
The early passes paint a rough overview of the entire image using large
blocks of pixels that look like mosaic tiles. The image is then refined using
higher resolutions on subsequent passes. This display method very quickly
displays the entire image at a low resolution, letting you look for any major
problems with the scene. As it refines the image, you can concentrate on more
details, like shadows and textures. You don't have to wait for a full
resolution render to find problems, since you can interrupt the rendering
early and fix the scene, or if things look good, you can let it continue and
render the scene at high quality and resolution.
To use this feature you should first select a width and height value that is
the highest resolution you will need. Mosaic preview is enabled by specifying
how big the mosaic blocks will be on the first pass using Preview_Start_Size
=n or +SP n. The value n should be a number greater than zero that is a power
of two (1, 2, 4, 8, 16, 32, etc.) If it is not a power of two, the nearest
power of two less than n is substituted. This sets the size of the squares,
measured in pixels. A value of 16 will draw every 16th pixel as a 16*16 pixel
square on the first pass. Subsequent passes will use half the previous value
(such as 8*8, 4*4 and so on.)
The process continues until it reaches 1*1 pixels or until it reaches the
size you set with Preview_End_Size =n or +EP n. Again the value n should be a
number greater than zero that is a power of two and less than or equal to
Preview_Start_Size . If it is not a power of two, the nearest power of two
less than n is substituted. The default ending value is 1. If you set
Preview_End_Size to a value greater than 1 the mosaic passes will end before
reaching 1*1, but POV-Ray will always finish with a 1*1. For example, if you
want a single 8*8 mosaic pass before rendering the final image, set
Preview_Start_Size =8 and Preview_End_Size =8.
No file output is performed until the final 1*1 pass is reached. Although the
preliminary passes render only as many pixels as needed, the 1*1 pass
re-renders every pixel so that anti-aliasing and file output streams work
properly. This makes the scene take up to 25% longer than the regular 1*1
pass to render, so it is suggested that mosaic preview not be used for final
rendering. Also, the lack of file output until the final pass means that
renderings which are interrupted before the 1*1 pass can not be resumed
without starting over from the beginning.
Future versions of POV-Ray will include some system of temporary files or
buffers which will eliminate these inefficiencies and limitations. Mosaic
preview is still a very useful feature for test renderings.
6.2.2.3 File Output Options
Output_to_File=bool Sets file output on/off
+F Sets file output on (use default type)
-F Sets file output off
By default, POV-Ray writes an image file to disk. When you are developing a
scene and doing test renders, the graphic preview may be sufficient. To save
time and disk activity you may turn file output off with Output_to_File =off
or -F .
6.2.2.3.1 Output File Type
Output_File_Type=x Sets file output format to 'x'
+Fxn Sets file output on; sets format 'x', depth 'n'
-Fxn Sets file output off; but in future use format 'x',
depth 'n'
Output_Alpha=bool Sets alpha output on/off
+UA Sets alpha output on
-UA Sets alpha output off
Bits_Per_Color=n Sets file output bits/color to 'n'
The default type of image file depends on which platform you are using.
MS-Dos and most others default to 24-bit uncompressed Targa. See your
platform-specific documentation to see what your default file type is. You
may select one of several different file types using Output_File_Type =x or
+F x where x is one of the following...
+FC Compressed Targa-24 format (RLE, run length encoded)
+FN New PNG (portable network graphics) format
+FP Unix PPM format
+FS System-specific such as Mac Pict or Windows BMP
+FT Uncompressed Targa-24 format
Note that the obsolete +FD dump format and +FR raw format have been dropped
from POV-Ray 3.0 because they were rarely used and no longer necessary. PPM,
PNG, and system specific formats have been added. PPM format images are
uncompressed, and have a simple text header, which makes it a widely portable
image format. PNG is a new image format designed not only to replace GIF, but
to improve on its shortcomings. PNG offers the highest compression available
without loss for high quality applications, such as ray-tracing. The system
specific format depends on the platform used and is covered in the
appropriate system specififc documentation.
Most of these formats output 24 bits per pixel with 8 bits for each of red,
green and blue data. PNG allows you to optionally specify the output bit
depth from 5 to 16 bits for each of the red, green, and blue colors, giving
from 15 to 48 bits of color information per pixel. The default output depth
for all formats is 8 bits/color (16 million possible colors), but this may be
changed for PNG format files by setting Bits_Per_Color =n or by specifying
+FN n, where n is the desired bit depth.
Specifying a smaller color depth like 5 bits/color (32768 colors) may be
enough for people with 8- or 16-bit (256 or 65536 color) displays, and will
improve compression of the PNG file. Higher bit depths like 10 or 12 may be
useful for video or publishing applications, and 16 bits/color is good for
grayscale height field output (See section "Height Field" for details on
height fields).
Targa format also allows 8 bits of alpha transparency data to be output,
while PNG format allows 5 to 16 bits of alpha transparency data, depending on
the color bit depth as specified above. You may turn this option on with
Output_Alpha =on or +UA . The default is off or -UA . See section "Using the
Alpha Channel" for further details on transparency.
In addition to support for variable bit-depths, alpha channel, and grayscale
formats, PNG files also store the Display_Gamma value so the image displays
properly on all systems (see section "Display Hardware Settings" ). The
hf_gray_16 global setting, as described in section "HF_Gray_16" will also
affect the type of data written to the output file.
6.2.2.3.2 Output File Name
Output_File_Name=file Sets output file to file
+Ofile Same as Output_File_Name=file
The default output filename is created from the scene name and need not be
specified. The scene name is the input name with all drive, path, and
extension information stripped. For example if the input file name is
c:\povray3\mystuff\myfile.pov the scene name is myfile . The proper extension
is appended to the scene name based on the file type. For example myfile.tga
or myfile.png might be used.
You may override the default output name using Output_File_Name = file or +O
file . For example:
Input_File_Name=myinput.pov
Output_File_Name=myoutput.tga
%%% BEGIN-LATEX \begin {QUOTE} Input_File_Name = myinput.pov \\
Output_File_Name = myoutput.tga \end {QUOTE} %%% END
If an output file name of "-" is specified (a single minus sign), then the
image will be written to standard output, usually the screen. The output can
then be piped into another program or to a GUI if desired.
6.2.2.3.3 Output File Buffer
Buffer_Output=bool Turn output buffering on/off
+B Turn output buffering on
-B Turn output buffering off
Buffer_Size=n Set output buffer size to 'n' kilobytes. If n is zero,
no buffering. If n < system default, the system default
is used.
+Bn Turn buffer on, set size n
-Bn Turn buffer off, but for future set size n
%%% LATEX-ONLY \begin {LIST} {Buffer_Output =bool} \item[ Buffer_Output
=bool] Turn output buffering on/off \item[ +B ] Turn output buffering on
\item[ -B ] Turn output buffering off \item[] \item[ Buffer_Size =n] Set
output buffer size to n kilobytes. If n is zero, no buffering occurs. If n is
smaller than the default, the system default is used. \item[ +B n] Turn
buffer on, set size n \item[ -B n] Turn buffer off, but for future set size n
\end {LIST} %%% END
The Buffer_Output and Buffer_Size options and the +B switch allows you to
assign large buffers to the output file. This reduces the amount of time
spent writing to the disk. If this parameter is not specified, then as each
row of pixels is finished, the line is written to the file and the file is
flushed. On most systems, this operation ensures that the file is written to
the disk so that in the event of a system crash or other catastrophic event,
at least a part of the picture has been stored properly and retrievable on
disk. The default is not to use any buffer.
6.2.2.4 CPU Utilization Histogram
The CPU utilization histogram is a way of finding out where POV-Ray is
spending its rendering time, as well as an interesting way of generating
heightfields. The histogram splits up the screen into a rectangular grid of
blocks. As POV-Ray renders the image, it calculates the amount of time it
spends rendering each pixel and then adds this time to the total rendering
time for each grid block. When the rendering is complete, the histogram is a
file which represents how much time was spent computing the pixels in each
grid block.
Not all versions of POV-Ray allow the creation of histograms. The histogram
output is dependent on the file type and the system that POV-Ray is being run
on.
6.2.2.4.1 File Type
Histogram_Type=x Set histogram type to x (turn off if type is 'X')
+HTx Same as Histogram_Type=x
The histogram output file type is nearly the same as that used for the image
output file types in "Output File Type" . The available histogram file types
are as follows.
+HTC Comma separated values (CSV) often used in spreadsheets
+HTN New PNG (portable network graphics) format grayscale
+HTP Unix PPM format
+HTS System-specific such as Mac Pict or Windows BMP
+HTT Uncompressed Targa-24 format (TGA)
+HTX No histogram file output is generated
Note that +HTC does not generate a compressed Targa-24 format output file but
rather a text file with a comma-separated list of the time spent in each grid
block, in left-to-right and top-to bottom order. The units of time output to
the CSV file are system dependent. See the system specific documentation for
further details on the time units in CSV files.
The Targa and PPM format files are in the POV heightfield format (see "Height
Field" ), so the histogram information is stored in both the red and green
parts of the image, which makes it unsuitable for viewing. When used as a
height field, lower values indicate less time spent calculating the pixels in
that block, while higher indicate more time spent in that block.
PNG format images are stored as grayscale images and are useful for both
viewing the histogram data as well as for use as a heightfield. In PNG files,
the darker (lower) areas indicate less time spent in that grid block, while
the brighter (higher) areas indicate more time spent in that grid block.
6.2.2.4.2 File Name
Histogram_Name=file Set histogram name to file
+HNfile Same as Histogram_Name=file
The histogram file name is the name of the file in which to write the
histogram data. If the file name is not specified it will default to
histgram.ext , where ext is based on the file type specified previously. Note
that if the histogram name is specified the file name extension should match
the file type.
6.2.2.4.3 Grid Size
Histogram_Grid_Size=xx.yy Set histogram grid to xx by yy
+HSxx.yy Same as Histogram_Grid_Size=xx.yy
The histogram grid size gives the number of times the image is split up in
both the horizontal and vertical directions. For example
povray +Isample +W640 +H480 +HTN +HS160.120 +HNhistogrm.png
%%% LATEX-ONLY \subsection {Scene Parsing Options} \label {Scene Parsing
Options} %%% END
POV-Ray reads in your scene file and processes it to create an internal model
of your scene. The process is called parsing . As your file is parsed other
files may be read along the way. This section covers options concerning what
to parse, where to find it and what version specific assumptions it should
make while parsing it.
6.2.2.5 Input File Name
Input_File_Name=file Sets input file name to file
+Ifile Same as Input_File_Name=file
You will probably always set this option but if you do not the default input
filename is object.pov . If you do not have an extension then .pov is
assumed. On case-sensitive operating systems both .pov and .POV are tried. A
full path specification may be used (on MS-Dos systems
+Ic:\povray3\mystuff\BS myfile.pov is allowed for example). In addition to
specifying the input file name this also establishes the scene name .
The scene name is the input name with drive, path and extension stripped. In
the above example the scene name is myfile . This name is used to create a
default output file name and it is referenced other places.
If you use "-" as the input file name the input will be read from standard
input. Thus you can pipe a scene created by a program to POV-Ray and render
it without having a scene file.
Under MS-Dos you can try this feature by typing.
type ANYSCENE.POV | povray +I-
6.2.2.6 Library Paths
Library_Path=path Add path to list of library paths
+Lpath Same as Library_Path=path
POV-Ray looks for files in the current directory. If it does not find a file
it needs it looks in various other library directories which you specify.
POV-Ray does not search your operating system path. It only searches the
current directory and directories which you specify with this option. For
example the standard include files are usually kept in one special directory.
You tell POV-Ray to look there with...
Library_Path=c:\povray3\include
You must not specify any final path seperators ("\BS" or "/") at the end.
Multiple uses of this option switch do not override previous settings. Up to
ten unique paths may be specified. If you specify the exact same path twice
it is only counts once. The current directory will be searched first followed
by the indicated library directories in the order in which you specified
them.
6.2.2.7 Language Version
Version=n.n Set initial language compatibility to version n.n
+MVn.n Same as Version=n.n
While many language changes have been made for POV-Ray 3.0, all of version
2.0 syntax and most of version 1.0 syntax still works. Whenever possible we
try to maintain backwards compatibility. One feature introduced in 2.0 that
was incompatible with any 1.0 scene files is the parsing of float
expressions. Setting Version =1.0 or using +MV 1.0 turns off expression
parsing as well as many warning messages so that nearly all 1.0 files will
still work. The changes between 2.0 and 3.0 are not as extensive. Setting
Version =2.0 is only necessary to eliminate some warning messages. Naturally
the default setting for this option is Version =3.0.
The #version language directive can also be used to change modes several
times within scene files. The above options affect only the initial setting.
See "Version Directive" for more details about the language version
directive.
6.2.2.8 Removing User Bounding
Remove_Bounds=bool Turn unnecessary bounds removal on/off
+UR Turn unnecessary bounds removal on
-UR Turn unnecessary bounds removal off
Split_Unions=bool Turn split bounded unions on/off
+SU Turn split bounded unions on
-SU Turn split bounded unions off
Early versions of POV-Ray had no system of automatic bounding or spatial
sub-division to speed up ray-object intersection tests. Users had to manually
create bounding boxes to speed up the rendering. POV-Ray 3.0 has more
sophisticated automatic bounding than any previous version. In many cases the
manual bounding on older scenes is slower than the new automatic systems.
Therefore POV-Ray removes manual bounding when it knows it will help. In rare
instances you may want to keep manual bounding. Some older scenes incorrectly
used bounding when they should have used clipping. If POV-Ray removes the
bounds in these scenes the image will not look right. To turn off the
automatic removal of manual bounds you should specify Remove_Bounds =off or
use -UR . The default is Remove_Bounds =on.
One area where the jury is still out is the splitting of manually bounded
unions. Unbounded unions are always split into their component parts so that
automatic bounding works better. Most users do not bound unions because they
know that doing so is usually slower. If you do manually bound a union we
presume you really want it bound. For safety sake we do not presume to remove
such bounds. If you want to remove manual bounds from unions you should
specify Split_Unions =on or use +SU . The default is Split_Unions =off.
6.2.3 Shell-out to Operating System
Pre_Scene_Command=s Set command before entire scene
Pre_Frame_Command=s Set command before each frame
Post_Scene_Command=s Set command after entire scene
Post_Frame_Command=s Set command after each frame
User_Abort_Command=s Set command when user aborts POV-Ray
Fatal_Error_Command=s Set command when POV-Ray has fatal error
Note that no + / - switches are available for these options. They cannot be
used from the command line. They may only be used from INI files.
POV-Ray offers you the opportunity to shell-out to the operating system at
several key points to execute another program or batch file. Usually this is
used to manage files created by the internal animation loop however the shell
commands are available for any scene. The CMD is a single line of text which
is passed to the operating system to execute a program. For example
Post_Scene_Command=tga2gif -d -m myfile
would use the utility tga2gif with the -d and -m parameters to convert
myfile.tga to myfile.gif after the scene had finished rendering.
6.2.3.1 String Substitution in Shell Commands
It could get cumbersome to change the Post_Scene_Command every time you
changed scene names. POV-Ray can substitute various values into a CMD string
for you. For example:
Post_Scene_Command=tga2gif -d -m %s
POV-Ray will substitute the %s with the scene name in the command. The scene
name is the Input_File_Name or +I setting with any drive, directory or
extension removed. For example:
Input_File_Name=c:\povray3\scenes\waycool.pov
is stripped down to the scene name waycool which results in...
Post_Scene_Command=tga2gif -d -m waycool
In an animation it may be necessary to have the exact output file name with
the frame number included. The string %o will substitute the output file
name. Suppose you want to save your output files in a zip archive using pkzip
. You could do...
Post_Frame_Command=pkzip -m %s %o
After rendering frame 12 of myscene.pov POV-Ray would shell to the operating
system with " pkzip -m myscene mysce012.tga ". The -m switch in pkzip moves
mysce012.tga to myscene.zip and removes it from the directory. Note that %o
includes frame numbers only when in an animation loop. During the
Pre_Scene_Command and Post_Scene_Command there is no frame number so the
original, unnumbered Output_File_Name is used. Any User_Abort_Command or
Fatal_Error_Command not inside the loop will similarly give an unnumbered %o
substitution.
Here is the complete list of substitutions available for a common string.
%o Output file name with extension and embedded frame number if any
%s Scene name derived by stripping path and ext from input name
%n Frame number of this frame
%k Clock value of this frame
%h Height of image in pixels
%w Width of image in pixels
%% A single % sign.
6.2.3.2 Shell Command Sequencing
Here is the sequence of events in an animation loop. Non-animated scenes work
the exact same way except there is no loop.
1) Process all INI file keywords and command line switches just once.
2) Open any text output streams and do Create_INI if any.
3) Execute Pre_Scene_Command if any.
4) Loop through frames (or just do once on non-animation).
a) Execute Pre_Frame_Command if any.
b) Parse entire scene file, open output file and read settings,
turn on display, render the frame, destroy all objects,
textures etc., close output file, close display.
c) Execute Post_Frame_Command if any.
d) Go back to 4 a until all frames are done.
5) Execute Post_Scene_Command if any.
6) Exit POV-Ray.
If the user interrupts processing the User_Abort_Command , if any, is
executed. User aborts can only occur during the parsing and rendering parts
of step 4 a above.
If a fatal error occurs that POV-Ray notices the Fatal_Error_Command , if
any, is executed. Sometimes an unforeseen bug or memory error could cause a
total crash of the program in which case there is no chance to shell out.
Fatal errors can occur just about anywhere including during the processing of
switches or INI files. If a fatal error occurs before POV-Ray has read the
Fatal_Error_Command string then obviously no shell can occur.
Note that the entire scene is re-parsed for every frame. Future versions of
POV-Ray may allow you to hold over parts of a scene from one frame to the
next but for now it starts from scratch every time. Note also that the
Pre_Frame_Command occurs before the scene is parsed. You might use this to
call some custom scene generation utility before each frame. This utility
could rewrite your .pov or .inc files if needed. Perhaps you will want to
generate new .gif or .tga files for image maps or height fields on each
frame.
6.2.3.3 Shell Command Return Actions
Pre_Scene_Return=s Set pre scene return actions
Pre_Frame_Return=s Set pre frame return actions
Post_Scene_Return=s Set post scene return actions
Post_Frame_Return=s Set post frame return actions
User_Abort_Return=s Set user abort return actions
Fatal_Error_Return=s Set fatal return actions
Note that no + / - switches are available for these options. They cannot be
used from the command line. They may only be used from INI files.
Most operating systems allow application programs to return an error code if
something goes wrong. When POV-Ray executes a shell command it can make use
of this error code returned from the shell process and take some appropriate
action if the code is zero or non-zero. POV-Ray itself returns such codes. It
returns 0 for success, 1 for fatal error and 2 for user abort.
The actions are designated by a single letter in the different ..._Return =s
options. The possible actions are:
I ignore the code
S skip one step
A all steps skipped
Q quit POV-Ray immediately
U generate a user abort in POV-Ray
F generate a fatal error in POV-Ray
For example if your Pre_Frame_Command calls a program which generates your
height field data and that utility fails then it will return a non-zero code.
We would probably want POV-Ray to abort as well. The option Pre_Frame_Return
=F will cause POV-Ray to do a fatal abort if the Pre_Frame_Command returns a
non-zero code.
Sometimes a non-zero code from the external process is a good thing. Suppose
you want to test if a frame has already been rendered. You could use the S
action to skip this frame if the file is already rendered. Most utilities
report an error if the file is not found. For example the command pkzip -v
myscene mysce012.tga tells pkzip you want to view the catalog of myscene.zip
for the file mysce012.tga . If the file isn't in the archive pkzip returns a
non-zero code.
However we want to skip if the file is found. Therefore we need to reverse
the action so it skips on zero and doesn't skip on non-zero. To reverse the
zero vs. non-zero triggering of an action precede it with a "-" sign (note a
"!" will also work since it is used in many programming languages as a negate
operator).
Pre_Frame_Return= S will skip if the code shows error (non-zero) and will
proceed normally on no error (zero). Pre_Frame_Return =-S will skip if there
is no error (zero) and will proceed normally if there is an error (non-zero).
The default for all shells is I which means that the return action is ignored
no matter what. POV-Ray simply proceeds with whatever it was doing before the
shell command. The other actions depend upon the context. You may want to
refer back to the animation loop sequence chart in the previous section. The
action for each shell is as follows.
On return from any User_Abort_Command if there is an action triggered and you
have specified...
F then turn this user abort into a fatal error. Do the
Fatal_Error_Command, if any. Exit POV-Ray with error code 1.
S, A, Q, or U then proceed with the user abort. Exit POV-Ray with error
code 2.
On return from any Fatal_Error_Command proceed with the fatal error no matter
what. Exit POV-Ray with error code 1. On return from any Pre_Scene_Command ,
Pre_Frame_Command , Post_Frame_Command or Post_Scene_Commands if there is an
action triggered and you have specified...
F then generate a fatal error. Do the Fatal_Error_Command, if any. Exit
POV-Ray with an error code 1.
U then generate a user abort. Do the User_Abort_Command, if any. Exit
POV-Ray with an error code 2.
Q then quit POV-Ray immediately. Acts as though POV-Ray never really ran.
Do no further shells, (not even Post_Scene_Command) and exit POV-Ray with
an error code 0.
On return from a Pre_Scene_Command if there is an action triggered and you
have specified...
S then skip rendering all frames. Acts as though the scene completed all
frames normally. Do not do any Pre_Frame_Command or Post_Frame_Commands.
Do the Post_Scene_Command, if any. Exit POV-Ray with error code 0. On the
earlier chart this means skip step #4.
A then skip all scene activity. Works exactly like Q quit. On the earlier
chart this means skip to step #6.
On return from a Pre_Frame_Command if there is an action triggered and you
have specified...
S then skip only this frame. Acts as though this frame never existed. Do
not do the Post_Frame_Command. Proceed with the next frame. On the
earlier chart this means skip steps #4b and #4c but loop back as needed
in #4d.
A then skip rendering this frame and all remaining frames. Acts as though
the scene completed all frames normally. Do not do any further
Post_Frame_Commands. Do the Post_Scene_Command, if any. Exit POV-Ray with
error code 0. On the earlier chart this means skip the rest of step #4
and proceed at step #5.
On return from a Post_Frame_Command if there is an action triggered and you
have specified...
S then skip rendering all remaining frames. Acts as though the scene
completed all frames normally. Do the Post_Scene_Command, if any. Exit
POV-Ray with error code 0. On the earlier chart this means skip the rest
of step #4 and proceed at step #5.
A same as S for this shell command.
On return from any Post_Scene_Command if there is an action triggered and you
have specified...
6.2.4 Text Output
Text output is an important way that POV-Ray keeps you informed about what it
is going to do, what it is doing and what it did. New to POV-Ray 3.0, the
program splits its text messages into 7 separate streams. Some versions of
POV-Ray color codes the various types of text. Some versions allow you to
scroll back several pages of messages. All versions allow you to turn some of
these text streams off/on or to direct a copy of the text output to one or
several files. This section details the options which give you control over
text output.
6.2.4.1 Text Streams
There are seven distinct text streams that POV-Ray uses for output. On some
versions each stream is designated by a particular color. Text from these
streams are displayed whenever it is appropriate so there is often an
intermixing of the text. The distinction is only important if you choose to
turn some of the streams off or to direct some of the streams to text files.
On some systems you may be able to review the streams separately in their own
scroll-back buffer.
Here is a description of each stream.
BANNER: } This stream displays the program's sign-on banner, copyright,
contributor's list, and some help screens. It cannot be turned off or
directed to a file because most of this text is displayed before any options
or switches are read. Therefore you cannot use an option or switch to control
it. There are switches which display the help screens. They are covered in
section "Help Screen Switches" .
DEBUG: } This stream displays debugging messages. It was primarily designed
for developers but this and other streams may also be used by the user to
display messages from within their scene files. See "Text Message Streams"
for details on this feature. This stream may be turned off and/or directed to
a text file.
FATAL: } This stream displays fatal error messages. After displaying this
text, POV-Ray will terminate. When the error is a scene parsing error, you
may be shown several lines of scene text that leads up to the error. This
stream may be turned off and/or directed to a text file.
RENDER: } This stream displays information about what options you have
specified to render the scene. It includes feedback on all of the major
options such as scene name, resolution, animation settings, anti-aliasing and
others. This stream may be turned off and/or directed to a text file.
STATISTICS: } This stream displays statistics after a frame is rendered. It
includes information about the number of rays traced, the length of time of
the processing and other information. This stream may be turned off and/or
directed to a text file.
STATUS: } This stream displays one-line status messages that explain what
POV-Ray is doing at the moment. On some systems this stream is displayed on a
status line at the bottom of the screen. This stream cannot be directed to a
file because there is generally no need to. The text displayed by the Verbose
option or +V switch is output to this stream so that part of the status
stream may be turned off.
WARNING: } This stream displays warning messages during the parsing of scene
files and other warnings. Despite the warning, POV-Ray can continue to render
the scene. You will be informed if POV-Ray has made any assumptions about
your scene so that it can proceed. In general any time you see a warning, you
should also assume that this means that future versions of POV-Ray will not
allow the warned action. Therefore you should attempt to eliminate warning
messages so your scene will be able to run in future versions of POV-Ray.
This stream may be turned off and/or directed to a text file.
6.2.4.2 Console Text Output
Debug_Console=bool Turn console display of debug info text on/off
+GD Same as Debug_Console=On
-GD Same as Debug_Console=Off
Fatal_Console=bool Turn console display of fatal error text on/off
+GF Same as Fatal_Console=On
-GF Same as Fatal_Console=Off
Render_Console=bool Turn console display of render info text on/off
+GR Same as Render_Console=On
-GR Same as Render_Console=Off
Statistic_Console=bool Turn console display of statistic text on/off
+GS Same as Statistic_Console=On
-GS Same as Statistic_Console=Off
Warning_Console=bool Turn console display of warning text on/off
+GW Same as Warning_Console=On
-GW Same as Warning_Console=Off
All_Console=bool Turn on/off all debug, fatal, render, statistic and
warning text to console.
+GA Same as All_Console=On
-GA Same as All_Console=Off
You may suppress the output to the console of the Debug , Fatal , Render ,
Statistic or Warning text streams. For example the Statistic_Console =off
option or the -GS switch can turn off the Statistic stream. Using on or +GS
you may turn it on again. You may also turn all five of these streams on or
off at once using the All_Console option or +GA switch.
Note that these options take effect immediately when specified. Obviously any
Error or Warning messages that might occur before the option is read are not
be affected.
6.2.4.3 Directing Text Streams to Files
Debug_File=true Echo debug info text to DEBUG.OUT
Debug_File=false Turn off file output of debug info
Debug_File=file Echo debug info text to file
+GDfile Both Debug_Console=On, Debug_File=file
-GDfile Both Debug_Console=Off, Debug_File=file
Fatal_File=true Echo fatal text to FATAL.OUT
Fatal_File=false Turn off file output of fatal
Fatal_File=file Echo fatal info text to file
+GFfile Both Fatal_Console=On, Fatal_File=file
-GFfile Both Fatal_Console=Off, Fatal_File=file
Render_File=true Echo render info text to RENDER.OUT
Render_File=false Turn off file output of render info
Render_File=file Echo render info text to file
+GRfile Both Render_Console=On, Render_File=file
-GRfile Both Render_Console=Off, Render_File=file
Statistic_File=true Echo statistic text to STATS.OUT
Statistic_File=false Turn off file output of statistics
Statistic_File=file Echo statistic text to file
+GSFile Both Statistic_Console=On, Statistic_File=file
-GSFile Both Statistic_Console=Off, Statistic_File=file
Warning_File=true Echo warning info text to WARNING.OUT
Warning_File=false Turn off file output of warning info
Warning_File=file Echo warning info text to file
+GWfile Both Warning_Console=On, Warning_File=file
-GWfile Both Warning_Console=Off, Warning_File=file
All_File=true Echo all debug, fatal, render, statistic and warning
text to ALLTEXT.OUT
All_File=false Turn off file output of all debug, fatal, render,
statistic and warning text
All_File=file Echo all debug, fatal, render, statistic and warning
text to file
+GAfile Both All_Console=On, All_File=file
-GAfile Both All_Console=Off, All_File=file
You may direct a copy of the text streams to a text file for the Debug ,
Fatal , Render , Statistic or Warning text streams. For example the
Statistic_File =s option or the +GS s switch. If the string s is true or any
of the other valid true strings then that stream is redirected to a file with
a default name. Valid true values are true , yes , on or 1 . If the value is
false the direction to a text file is turned off. Valid false values are
false , no , off or 0 . Any other string specified turns on file output and
the string is interpreted as the output file name.
Similarly you may specify such a true, false or file name string after a
switch such as +GS file. You may also direct all five streams to the same
file using the All_File option or +GA switch. You may not specify the same
file for two or more streams because POV-Ray will fail when it tries to open
or close the same file twice.
Note that these options take effect immediately when specified. Obviously any
Error or Warning messages that might occur before the option is read will not
be affected.
6.2.4.4 Help Screen Switches
+H or +? Show help screen 0 if this is the only switch
+H0 to +H8 Show help screen 0 to 8 if this is the only switch
+?0 to +?8 Same as +H0 to +H8
Note that there are no INI style equivalents to these options.
Graphical interface versions of POV-Ray such as Mac or Windows have extensive
online help. Other versions of POV-Ray have only a few quick-reference help
screens. The +? switch, optionally followed by a single digit from 0 to 8,
will display these help screens to the Banner text stream. After displaying
the help screens, POV-Ray terminates. Because some operating systems do not
permit a question mark as a command line switch you may also use the +H
switch. Note however that this switch is also used to specify the height of
the image in pixels. Therefore the +H switch is only interpreted as a help
switch if it is the only switch on the command line and if the value after
the switch is less than or equal to 8.
6.2.5 Tracing Options
There is more than one way to trace a ray. Sometimes there is a trade-off
between quality and speed. Sometimes options designed to make tracing faster
can slow things down. This section covers options that tell POV-Ray how to
trace rays with the appropriate speed and quality settings.
6.2.5.1 Quality Settings
Quality=n Set quality value to n (0 <= n <= 11)
+Qn Same as Quality=n
The Quality =n option or +Q n switch allows you to specify the image
rendering quality. You may choose to lower the quality for test rendering and
raise it for final renders. The quality adjustments are made by eliminating
some of the calculations that are normally performed. For example settings
below 4 do not render shadows. Settings below 8 do not use reflection or
refraction. The values correspond to the following quality levels:
0,1 Just show quick colors. Use full ambient lighting only. Quick colors
are used only at 5 or below.
2,3 Show specified diffuse and ambient light.
4 Render shadows, but no extended lights. 5 Render shadows, including
extended lights.
6,7 Compute texture patterns.
8 Compute reflected, refracted, and transmitted rays.
9 Compute halos.
6.2.5.2 Radiosity Setting
+QR Turns radiosity on -QR Turns radiosity on
Radiosity is an additional calculation which computes diffuse
inter-reflection. It is an extremely slow calculation that is somewhat
experimental. The parameters which control how radiosity calculations are
performed are specified in the global_settings {radiosity {... }} statement.
See "Radiosity" for further details.
6.2.5.3 Automatic Bounding Control
Bounding=bool Turn bounding on/off
+MB Turn bounding on; threshold 25 or prev. amt
-MB Turn bounding off
Bounding_Threshold=n Set bound threshold to n
+MBn Turn bounding on; bound threshold to n
-MBn Turn bounding off; for future threshold to n
Light_Buffer=bool Turn light buffer on/off
+UL Turn light buffer on
-UL Turn light buffer off
Vista_Buffer=bool Turn vista buffer on/off
+UV Turn vista buffer on
-UV Turn vista buffer off
POV-Ray uses a variety of spatial sub-division systems to speed up ray-object
intersection tests. The primary system uses a hierarchy of nested bounding
boxes. This system compartmentalizes all finite objects in a scene into
invisible rectangular boxes that are arranged in a tree-like hierarchy.
Before testing the objects within the bounding boxes the tree is descended
and only those objects are tested whose bounds are hit by a ray. This can
greatly improve rendering speed. However for scenes with only a few objects
the overhead of using a bounding system is not worth the effort. The Bounding
=off option or -MB switch allows you to force bounding off. The default value
is on.
The Bounding_Threshold =n or +MB n switch allows you to set the minimum
number of objects necessary before bounding is used. The default is +MB 25
which means that if your scene has fewer than 25 objects POV-Ray will
automatically turn bounding off because the overhead isn't worth it.
Generally it's a good idea to use a much lower threshold like +MB 5.
Additionally POV-Ray uses systems known as vista buffers and light buffers to
further speed things up. These systems only work when bounding is on and when
there are a sufficient number of objects to meet the bounding threshold. The
vista buffer is created by projecting the bounding box hierarchy onto the
screen and determining the rectangular areas that are covered by each of the
elements in the hierarchy. Only those objects whose rectangles enclose a
given pixel are tested by the primary viewing ray. The vista buffer can only
be used with perspective and orthographic cameras because they rely on a
fixed viewpoint and a reasonable projection (i. e. straight lines have to
stay straight lines after the projection).
The light buffer is created by enclosing each light source in an imaginary
box and projecting the bounding box hierarchy onto each of its six sides.
Since this relies on a fixed light source, light buffers will not be used for
area lights.
Reflected and transmitted rays do not take advantage of the light and vista
buffer.
The default settings are Vista_Buffer =on or +UV and Light_Buffer =on or +UL
. The option to turn these features off is available to demonstrate their
usefulness and as protection against unforeseen bugs which might exist in any
of these bounding systems.
In general, any finite object and many types of CSG of finite objects will
properly respond to this bounding system. In addition blobs and meshes use an
additional internal bounding system. These systems are not affected by the
above switch. They can be switched off using the appropriate syntax in the
scene file (see "Blob" and "Mesh" for details). Text objects are split into
individual letters that are bounded using the bounding box hierarchy. Some
CSG combinations of finite and infinite objects are also automatically bound.
The end result is that you will rarely need to add manual bounding objects as
was necessary in earlier versions of POV-Ray unless you use many infinite
objects.
6.2.5.4 Anti-Aliasing Options
Antialias=bool Turns anti-aliasing on/off
+A Turns aa on with threshold 0.3 or previous amount
-A Turns anti-aliasing off
Sampling_Method=n Sets aa-sampling method (1 or 2)
+AMn Same as Sampling_Method=n
Antialias_Threshold=n.n Sets anti-aliasing threshold
+An.n Sets aa on with aa-threshold at n.n
-An.n Sets aa off (aa-threshold n.n in future)
Jitter=bool Sets aa-jitter on/off
+J Sets aa-jitter on with 1.0 or previous amount
-J Sets aa-jitter off
Jitter_Amount=n.n Sets aa-jitter amount to n.n. If n.n <= 0 aa-jitter
is set off
+Jn.n Sets aa-jitter on; jitter amount to n.n. If n.n <=
0 aa-jitter is set off
-Jn.n Sets aa-jitter off (jitter amount n.n in future)
Antialias_Depth=n Sets aa-depth (1 <= n <= 9)
+Rn Same as Antialias_Depth=n
The ray-tracing process is in effect a discrete, digital sampling of the
image with typically one sample per pixel. Such sampling can introduce a
variety of errors. This includes a jagged, stair-step appearance in sloping
or curved lines, a broken look for thin lines, moire patterns of interference
and lost detail or missing objects, which are so small they reside between
adjacent pixels. The effect that is responsible for those errors is called
aliasing .
Anti-aliasing is any technique used to help eliminate such errors or to
reduce the negative impact they have on the image. In general, anti-aliasing
makes the ray-traced image look smoother . The Antialias =on option or +A
switch turns on POV-Ray's anti-aliasing system.
When anti-aliasing is turned on, POV-Ray attempts to reduce the errors by
shooting more than one viewing ray into each pixel and averaging the results
to determine the pixel's apparent color. This technique is called
super-sampling and can improve the appearance of the final image but it
drastically increases the time required to render a scene since many more
calculations have to be done.
POV-Ray gives you the option to use one of two alternate super-sampling
methods. The Sampling_Method =n option or +AM n switch selects non-adaptive
super-sampling (method 1) or adaptive super-sampling (method 2). Selecting
one of those methods does not turn anti-aliasing on. This has to be done by
using the +A command line switch or Antialias =on option.
} } }
In the default, non-adaptive method ( +AM 1), POV-Ray initially traces one
ray per pixel. If the color of a pixel differs from its neighbors (to the
left or above) by more than a threshold value then the pixel is super-sampled
by shooting a given, fixed number of additional rays. The default threshold
is 0.3 but it may be changed using the Antialias_Threshold =n.n option. When
the switches are used, the threshold may optionally follow the +A . For
example +A 0.1 turns anti-aliasing on and sets the threshold to 0.1.
The threshold comparison is computed as follows. If r_1, g_1, b_1 and r_2,
g_2, b_2 are the rgb components of two pixels then the difference between
pixels is computed by
diff = abs(r1-r2) + abs(g1-g2) + abs(b1-b2).
If this difference is greater than the threshold both pixels are
super-sampled. The rgb values are in the range from 0.0 to 1.0 thus the most
two pixels can differ is 3.0. If the anti-aliasing threshold is 0.0 then
every pixel is super-sampled. If the threshold is 3.0 then no anti-aliasing
is done. Lower threshold means more anti-aliasing and less speed. Use
anti-aliasing for your final version of a picture, not the rough draft. The
lower the contrast, the lower the threshold should be. Higher contrast
pictures can get away with higher tolerance values. Good values seem to be
around 0.2 to 0.4.
When using the non-adaptive method, the default number of super-samples is
nine per pixel, located on a 3*3 grid. The Antialias_Depth =n option or +R n
switch controls the number of rows and columns of samples taken for a
super-sampled pixel. For example +R 4 would give 4*4=16 samples per pixel.
} }
The second, adaptive super-sampling method starts by tracing four rays at the
corners of each pixel. If the resulting colors differ more than the threshold
amount additional samples will be taken. This is done recursively, i. e. the
pixel is divided into four sub-pixels that are separately traced and tested
for further subdivision. The advantage of this method is the reduced number
of rays that have to be traced. Samples that are common among adjacent pixels
and sub-pixels are stored and reused to avoid re-tracing of rays. The
recursive character of this method makes it adaptive, i. e. the
super-sampling concentrates on those parts of the pixel that are more likely
to need super-sampling (see figure below).
Example of how the adpative super-sampling works.
The maximum number of subdivisions is specified by the Antialias_Depth =n
option or +R n switch. This is different from the non-adaptive method were
the total number of super-samples is specified. A maximum number of n
subdivisions results in a maximum number of samples per pixel that is given
by the following table.
Number of samples per Maximum number of samples
super-sampled pixel for per super-sampled pixel for
+Rn the non-adaptive method the adaptive method
1 1 9
2 4 25
3 9 81
4 16 289
5 25 1089
6 36 4225
7 49 16641
8 64 66049
9 81 263169
You should note that the maximum number of samples in the adaptive case is
hardly ever reached for a given pixel. If the adaptive method is used with no
anti-aliasing each pixel will be the average of the rays traced at its
corners. In most cases a recursion level of three is sufficient.
Another way to reduce aliasing artifacts is to introduce noise into the
sampling process. This is called jittering and works because the human visual
system is much more forgiving to noise than it is to regular patterns. The
location of the super-samples is jittered or wiggled a tiny amount when
anti-aliasing is used. Jittering is used by default but it may be turned off
with the Jitter =off option or -J switch. The amount of jittering can be set
with the Jitter_Amount =n.n option. When using switches the jitter scale may
be
specified after the +J switch. For example +J 0.5 uses half the normal
jitter. The default amount of 1.0 is the maximum jitter which will insure
that all super-samples remain inside the original pixel. Note that the
jittering noise is random and non-repeatable so you should avoid using jitter
in animation sequences as the anti-aliased pixels will vary and flicker
annoyingly from frame to frame.
If anti-aliasing is not used one sample per pixel is taken regardless of the
super-sampling method specified.
7 Scene Description Language
The Scene Description Language allows you to describe the world in a readable
and convenient way. Files are created in plain ASCII text using an editor of
your choice. The input file name is specified using the Input_File_Name =
file option or +I file switch. By default the files have the extension .pov .
POV-Ray reads the file, processes it by creating an internal model of the
scene and then renders the scene.
The overall syntax of a scene is a file that contains any number of the
following items in any order.
LANGUAGE_DIRECTIVES
camera{ CAMERA_ITEMS }
OBJECT_STATEMENTS
ATMOSPHERE_STATEMENTS
global_settings { GLOBAL_ITEMS }
See "Language Directives" , "Objects" , "Camera" , "Atmospheric Effects" and
"Global Settings" for details.
7.1 Language Basics
The POV-Ray language consists of identifiers, reserved keywords, floating
point expressions, strings, special symbols and comments. The text of a
POV-Ray scene file is free format. You may put statements on separate lines
or on the same line as you desire. You may add blank lines, spaces or
indentations as long as you do not split any keywords or identifiers.
7.1.1 Identifiers and Keywords
POV-Ray allows you to define identifiers for later use in the scene file. An
identifier may be 1 to 40 characters long. It may consist of upper or lower
case letters, the digits 0 through 9 or an underscore character ("_"). The
first character must be an alphabetic character. The declaration of
identifiers is covered later.
POV-Ray has a number of reserved keywords which are listed below.
aa_level fog_offset reciprocal
aa_threshold fog_type recursion_limit
abs frequency red
acos gif reflection
acosh global_settings refraction
adaptive glowing render
adc_bailout gradient repeat
agate granite rgb
agate_turb gray_threshold rgbf
all green rgbft
alpha halo rgbt
ambient height_field right
ambient_light hexagon ripples
angle hf_gray_16 rotate
aperture hierarchy roughness
arc_angle hollow samples
area_light hypercomplex scale
asc if scallop_wave
asin ifdef scattering
asinh iff seed
assumed_gamma image_map shadowless
atan incidence sin
atan2 include sine_wave
atanh int sinh
atmosphere interpolate sky
atmospheric_attenuation intersection sky_sphere
attenuating inverse slice
average ior slope_map
background irid smooth
bicubic_patch irid_wavelength smooth_triangle
black_hole jitter sor
blob julia_fractal specular
blue lambda sphere
blur_samples lathe spherical_mapping
bounded_by leopard spiral
box light_source spiral1
box_mapping linear spiral2
bozo linear_spline spotlight
break linear_sweep spotted
brick location sqr
brick_size log sqrt
brightness looks_like statistics
brilliance look_at str
bumps low_error_factor strcmp
bumpy1 mandel strength
bumpy2 map_type strlen
bumpy3 marble strlwr
bump_map material_map strupr
bump_size matrix sturm
camera max substr
case max_intersections superellipsoid
caustics max_iteration switch
ceil max_trace_level sys
checker max_value t
chr merge tan
clipped_by mesh tanh
clock metallic test_camera_1
color min test_camera_2
color_map minimum_reuse test_camera_3
colour mod test_camera_4
colour_map mortar text
component nearest_count texture
composite no texture_map
concat normal tga
cone normal_map thickness
confidence no_shadow threshold
conic_sweep number_of_waves tightness
constant object tile2
control0 octaves tiles
control1 off torus
cos offset track
cosh omega transform
count omnimax translate
crackle on transmit
crand once triangle
cube onion triangle_wave
cubic open true
cubic_spline orthographic ttf
cylinder panoramic turbulence
cylindrical_mapping pattern1 turb_depth
debug pattern2 type
declare pattern3 u
default perspective ultra_wide_angle
degrees pgm union
dents phase up
difference phong use_color
diffuse phong_size use_colour
direction pi use_index
disc pigment u_steps
distance pigment_map v
distance_maximum planar_mapping val
div plane variance
dust png vaxis_rotate
dust_type point_at vcross
eccentricity poly vdot
else polygon version
emitting pot vlength
end pow vnormalize
error ppm volume_object
error_bound precision volume_rendered
exp prism vol_with_light
exponent pwr vrotate
fade_distance quadratic_spline v_steps
fade_power quadric warning
falloff quartic warp
falloff_angle quaternion water_level
false quick_color waves
file_exists quick_colour while
filter quilted width
finish radial wood
fisheye radians wrinkles
flatness radiosity x
flip radius y
floor rainbow yes
focal_point ramp_wave z
fog rand
fog_alt range
All reserved words are fully lower case. Therefore it is recommended
that your identifiers contain at least one upper case character so it
is sure to avoid conflict with reserved words.
The following keywords are in the above list of reserved keywords but
are not currently used by POV-Ray however they remain reserved.
bumpy1 test_camera_1
bumpy2 test_camera_2
bumpy3 test_camera_3
incidence test_camera_4
pattern1 track
pattern2 volume_object
pattern3 volume_rendered
spiral vol_with_light
7.1.2 Comments
Comments are text in the scene file included to make the scene file easier to
read or understand. They are ignored by the ray-tracer and are there for your
information. There are two types of comments in POV-Ray.
Two slashes are used for single line comments. Anything on a line after a
double slash ( // ) is ignored by the ray-tracer. For example:
// This line is ignored
You can have scene file information on the line in front of the comment as
in:
object { FooBar } // this is an object
The other type of comment is used for multiple lines. It starts with " /* "
and ends with " */ ". Everything in-between is ignored. For example:
/* These lines
are ignored
by the
ray-tracer */
This can be useful if you want to temporarily remove elements from a scene
file. /* ... */ comments can comment out lines containing other // comments
and thus can be used to temporarily or permanently comment out parts of a
scene. /* ... */ comments can be nested, the following is legal:
/* This is a comment
// This too
/* This also */
*/
Use comments liberally and generously. Well used, they really improve the
readability of scene files.
7.1.3 Float Expressions
Many parts of the POV-Ray language require you to specify one or more
floating point numbers. A floating point number is a number with a decimal
point. Floats may be specified using literals, identifiers or functions which
return float values. You may also create very complex float expressions from
combinations of any of these using various familiar operators.
Where POV-Ray needs an integer value it allows you to specify a float value
and it truncates it to an integer. When POV-Ray needs a logical or boolean
value it interprets any non-zero float as true and zero as false. Because
float comparisons are subject to rounding errors POV-Ray accepts values
extremely close to zero as being false when doing boolean functions.
Typically values whose absolute values are less than a preset value epsilon
are considered false for logical expressions. The value of epsilon is system
dependent but is generally about 1.0e-10. Two floats a and b are considered
to be euqal if abs(a-b) < epsilon. %%% LATEX-ONLY \subsubsection {Float
Literals} \label {Float Literals} %%% END
Float literals are represented by an optional sign ("+" or "-") digits, an
optional decimal point and more digits. If the number is an integer you may
omit the decimal point and trailing zero. If it is all fractional you may
omit the leading zero. POV-Ray supports scientific notation for very large or
very small numbers. The following are all valid float literals:
-2.0 -4 34 3.4e6 2e-5 .3 0.6
7.1.3.1 Float Identifiers
Float identifiers may be declared to make scene files more readable and to
parameterize scenes so that changing a single declaration changes many
values. An identifier is declared as follows.
#declare IDENTIFIER = EXPRESSION
Where IDENTIFIER is the name of the identifier up to 40 characters long and
EXPRESSION is any valid expression which evaluates to a float value. Here are
some examples.
#declare Count = 0
#declare Rows = 5.3
#declare Cols = 6.15
#declare Number = Rows*Cols
#declare Count = Count+1
As the last example shows, you can re-declare a float identifier and may use
previously declared values in that re-declaration. There are several built-in
identifiers which POV-Ray declares for you. See "Built-in Identifiers" for
details.
7.1.3.2 Float Operators
Arithmetic float expressions can be created from float literals, identifiers
or functions using the following operators in this order of precedence...
() expressions in parentheses first
+A -A !A unary minus, unary plus and logical "not"
A*B A/B multiplication and division
A+B A-B addition and subtraction
Relational, logical and conditional expressions may also be created. However
there is a restriction that these types of expressions must be enclosed in
parentheses first. This restriction, which is not imposed by most computer
languages, is necessary because POV-Ray allows mixing of float and vector
expressions. Without the parentheses there is an ambiguity problem.
Parentheses are not required for the unary logical not operator "!" as shown
above. The operators and their precedence are shown here.
Relational expressions: The operands are arithmetic expressions and the
result is always boolean with 1 for true and 0 for false. All relational
operators have the same precedence.
(A < B) A is less than B
(A <= B) A is less than or equal to B
(A = B) A is equal to B (actually abs(A-B)<EPSILON)
(A != B) A is not equal to B (actually abs(A-B)>=EPSILON)
(A >= B) A is greater than or equal to B
(A > B) A is greater than B
Logical expressions: The operands are converted to boolean values of 0 for
false and 1 for true. The result is always boolean. All logical operators
have the same precedence. Note that these are not bitwise operations, they
are logical.
(A & B) true only if both A and B are true, false otherwise
(A | B) true if either A or B or both are true
Conditional expressions: The operand C is boolean while operands A and B are
any expressions. The result is of the same type as A and B.
(C ? A : B) if C then A else B
Assuming the various identifiers have been declared, the following are
examples of valid expressions...
1+2+3 2*5 1/3 Row*3 Col*5
(Offset-5)/2 This/That+Other*Thing
((This<That) & (Other>=Thing)?Foo:Bar)
Expressions are evaluated left to right with innermost parentheses evaluated
first, then unary +, - or !, then multiply or divide, then add or subtract,
then relational, then logical, then conditional.
7.1.4 Vector Expressions
POV-Ray often requires you to specify a vector . A vector is a set of related
float values. Vectors may be specified using literals, identifiers or
functions which return vector values. You may also create very complex vector
expressions from combinations of any of these using various familiar
operators.
POV-Ray vectors may have from two to five components but the vast majority of
vectors have three components. Unless specified otherwise, you should assume
that the word vector means a three component vector. POV-Ray operates in a 3D
x, y, z coordinate system and you will use three component vectors to specify
x, y and z values. In some places POV-Ray needs only two coordinates. These
are often specified by a 2D vector called an UV vector . Fractal objects use
4D vectors. Color expressions use 5D vectors but allow you to specify 3, 4 or
5 components and use default values for the unspecified components. Unless
otherwise noted, all 2, 4 or 5 component vectors work just like 3D vectors
but they have a different number of components.
7.1.4.1 Vector Literals
Vectors consist of two to five float expressions that are bracketed by angle
brackets \langle and > . The terms are separated by commas. For example here
is a typical three component vector:
< 1.0, 3.2, -5.4578 >
The commas between components are necessary to keep the program from thinking
that the 2nd term is the single float expression 3.2-5.4578 and that there is
no 3rd term. If you see an error message such as Float expected but '>' found
instead you probably have missed a comma.
Sometimes POV-Ray requires you to specify floats and vectors side-by-side.
The rules for vector expressions allow for mixing of vectors with vectors or
vectors with floats so commas are required separators whenever an ambiguity
might arise. For example \langle 1,2,3>-4 evaluates as a mixed float and
vector expression where 4 is subtracted from each component resulting in
\langle -3,-2,-1>. However the comma in <1,2,3>,-4 means this is a vector
followed by a float.
Each component may be a full float expression. For example \langle
This+3,That/3,5*Other_Thing> is a valid vector.
7.1.4.2 Vector Identifiers
Vector identifiers may be declared to make scene files more readable and to
parameterize scenes so that changing a single declaration changes many
values. An identifier is declared as follows...
#declare IDENTIFIER = EXPRESSION
Where IDENTIFIER is the name of the identifier up to 40 characters long and
EXPRESSION is any valid expression which evaluates to a vector value. Here
are some examples...
#declare Here = <1,2,3>
#declare There = <3,4,5>
#declare Jump = <Foo*2,Bar-1,Bob/3>
#declare Route = There-Here
#declare Jump = Jump+<1,2,3>
Note that you invoke a vector identifier by using its name without any angle
brackets. As the last example shows, you can re-declare a vector identifier
and may use previously declared values in that re-declaration. There are
several built-in identifiers which POV-Ray declares for you. See "Built-in
Identifiers" for details.
7.1.4.3 Vector Operators
Vector literals, identifiers and functions may also be combined in
expressions the same as float values. Operations are performed on a
component-by-component basis. For example <1,2,3> + <4,5,6> evaluates the
same as \langle 1+4,2+5,3+6> or <5,7,9>. Other operations are done on a
similar component-by-component basis. For example (\langle 1,2,3> = <3,2,1>)
evaluates to \langle 0,1,0> because the middle components are equal but the
others are not. Admittedly this isn't very useful but its consistent with
other vector operations.
Conditional expressions such as (C ? A : B) require that C is a float
expression but A and B may be vector expressions. The result is that the
entire conditional evaluates as a valid vector. For example if Foo and Bar
are floats then
Foo < Bar ? <1,2,3> : <5,6,7>
evaluates as the vector <1,2,3> if Foo is less than Bar and evaluates as
<5,6,7> otherwise.
You may use the dot operator to extract a single component from a vector.
Suppose the identifier Spot was previously defined as a vector. Then Spot.x
is a float value that is the first component of this x, y, z vector.
Similarly Spot.y and Spot.z reference the 2nd and 3rd components. If Spot was
a two component UV vector you could use Spot.u and Spot.v to extract the
first and second component. For a 4D vector use .x , .y , .z and .t to
extract each float component. The dot operator is also used in color
expressions which are covered later.
7.1.4.4 Operator Promotion
You may use a lone float expression to define a vector whose components are
all the same. POV-Ray knows when it needs a vector of a particular type and
will promote a float into a vector if need be. For example the POV-Ray scale
statement requires a three component vector. If you specify scale 5 then
POV-Ray interprets this as scale <5,5,5> which means you want to scale by 5
in every direction.
Versions of POV-Ray prior to 3.0 only allowed such use of a float as a vector
in various limited places such as scale and turbulence. However you may now
use this trick anywhere. For example...
box{0,1} // This is the same as box{<0,0,0>,<1,1,1>}
sphere{0,1} // This is the same as sphere{<0,0,0>,1}
When promoting a float into a vector of 2, 3, 4 or 5 components, all
components are set to the float value, however when promoting a vector of a
lower number of components into a higher order vector, all remaining
components are set to zero. For example if POV-Ray expects a 4D vector and
you specify 9 the result is <9,9,9,9> but if you specify <7,6> the result is
\langle 7,6,0,0>.
7.1.5 Specifying Colors
POV-Ray often requires you to specify a color. Colors consist of five values
or color components. The first three are called red , green and blue. They
specify the intensity of the primary colors red, green and blue using an
additive color system like the one used by the red, green and blue color
phosphors on a color monitor.
The 4th component, called filter , specifies the amount of filtered
transparency of a substance. Some real-world examples of filtered
transparency are stained glass windows or tinted cellophane. The light
passing through such objects is tinted by the appropriate color as the
material selectively absorbs some frequencies of light while allowing others
to pass through. The color of the object is subtracted from the light passing
through so this is called subtractive transparency.
The 5th component, called transmit , specifies the amount of non-filtered
light that is transmitted through a surface. Some real-world examples of
non-filtered transparency are thin see-through cloth, fine mesh netting and
dust on a surface. In these examples, all frequencies of light are allowed to
pass through tiny holes in the surface. Although the amount of light passing
through is diminished, the color of the light passing through is unchanged.
The color of the object is added to the light passing through so this is
called additive transparency.
Note that early versions of POV-Ray used the keyword alpha to specify
filtered transparency. However that word is often used to describe
non-filtered transparency. For this reason alpha is no longer used.
Each of the five components of a color are float values which are normally in
the range between 0.0 and 1.0. However any values, even negatives may be
used.
Colors may be specified using vectors, keywords with floats or identifiers.
You may also create very complex color expressions from combinations of any
of these using various familiar operators. The syntax for specifying a color
has evolved since POV-Ray was first released. We have maintained the original
keyword-based syntax and added a short-cut vector notation. Either the old or
new syntax is acceptable however the vector syntax is easier to use when
creating color expressions.
7.1.5.1 Color Vectors
The syntax for a color vector is any of the following...
color rgb VECTOR3
color rgbf VECTOR4
color rgbt VECTOR4
color rgbft VECTOR5
where VECTOR3 , VECTOR4 or VECTOR5 are any valid vector expressions of 3, 4
or 5 components. For example
color rgb <1.0, 0.5, 0.2>
This specifies a color whose red component is 1.0 or 100% of full intensity.
The green component is 0.5 or 50% of full intensity and the blue component is
0.2 or 20% of full intensity. Although the filter and transmit components are
not explicitly specified, they exist and are set to their default values of 0
or no transparency.
The rgbf keyword requires a four component vector. The 4th component is the
filter component and the transmit component defaults to zero. Similarly the
rgbt keyword requires four components where the 4th value is moved to the 5th
component which is transmit and then the filter component is set to zero.
The rgbft keyword allows you to specify all five components. Internally in
expressions all five are always used.
Under most circumstances the keyword color is optional and may be omitted. We
also support the British or Canadian spelling colour . Under some
circumstances, if the vector expression is a 5 component expression or there
is a color identifier in the expression then the rgbtf keyword is optional.
7.1.5.2 Color Keywords
The older keyword method of specifying a color is still useful and many users
prefer it. Like a color vector, you begin with the optional keyword color .
This is followed by any of five additional keywords red , green , blue ,
filter or transmit . Each of these component keywords is followed by a float
expression. For example
color red 1.0 green 0.5
This specifies a color whose red component is 1.0 or 100% of full intensity
and the green component is 0.5 or 50% of full intensity. Although the blue,
filter and transmit components are not explicitly specified, they exist and
are set to their default values of 0. The component keywords may be given in
any order and if any component is unspecified its value defaults to zero.
7.1.5.3 Color Identifiers
Color identifiers may be declared to make scene files more readable and to
parameterize scenes so that changing a single declaration changes many
values. A color identifier is declared as either of the following...
#declare IDENTIFIER = COLOR_VECTOR
#declare IDENTIFIER = COLOR_KEYWORDS...
Where IDENTIFIER is the name of the identifier up to 40 characters long and
COLOR_VECTOR or COLOR_KEYWORDS are any valid color specifications as
described in the two previous sections of this document. Here are some
examples...
#declare White = rgb <1,1,1>
#declare Cyan = color blue 1.0 green 1.0
#declare Weird = rgb <Foo*2,Bar-1,Bob/3>
#declare LightGray = White*0.8
#declare LightCyan = Cyan red 0.6
As the LightGray example shows you do not need any color keywords when
creating color expressions based on previously declared colors. The last
example shows you may use a color identifier with the keyword style syntax.
Make sure that the identifier comes first before any other component
keywords.
Like floats and vectors, you may re-define colors throughout a scene but the
need to do so is rare.
7.1.5.4 Color Operators
Color vectors may be combined in expressions the same as float or vector
values. Operations are performed on a component-by-component basis. For
example rgb <1.0, 0.5 0.2> * 0.9 evaluates the same as rgb <1.0, 0.5 0.2> *
<0.9, 0.9, 0.9> or rgb <0.9, 0.45, 0.18> . Other operations are done on a
similar component-by-component basis.
You may use the dot operator to extract a single component from a color.
Suppose the identifier Shade was previously defined as a color. Then
Shade.red is the float value of the red component of Shade . Similarly
Shade.green , Shade.blue , Shade.filter and Shade.transmit extract the float
value of the other color components.
7.1.5.5 Common Color Pitfalls
The variety and complexity of color specification methods can lead to some
common mistakes. Here are some things to consider when specifying a color.
When using filter transparency, the colors which come through are multiplied
by the primary color components. For example if grey light such as rgb
<0.9,0.9,0.9> passes through a filter such as rgbf <1.0,0.5,0.0,1.0> the
result is rgb <0.9,0.45,0.0> with the red let through 100%, the green cut in
half from 0.9 to 0.45 and the blue totally blocked. Often users mistakenly
specify a clear object by
color filter 1.0
but this has implied red, green and blue values of zero. You've just
specified a totally black filter so no light passes through. The correct way
is either
color red 1.0 green 1.0 blue 1.0 filter 1.0
or
color transmit 1.0
In the 2nd example it doesn't matter what the rgb values are. All of the
light passes through untouched.
Another pitfall is the use of color identifiers and expressions with color
keywords. For example...
color My_Color red 0.5
this substitutes whatever was the red component of My_Color with a red
component of 0.5 however...
color My_Color + red 0.5
adds 0.5 to the red component of My_Color and even less obvious...
color My_Color * red 0.5
that cuts the red component in half as you would expect but it also
multiplies the green, blue, filter and transmit components by zero! The part
of the expression after the multiply operator evaluates to rgbft
<0.5,0,0,0,0> as a full 5 component color.
The following example results in no change to My_Color .
color red 0.5 My_Color
This is because the identifier fully overwrites the previous value. When
using identifiers with color keywords, the identifier should be first.
One final issue, some POV-Ray syntax allows full color specifications but
only uses the rgb part. In these cases it is legal to use a float where a
color is needed. For example:
finish { ambient 1 }
The ambient keyword expects a color so the value 1 is promoted to <1,1,1,1,1>
which is no problem. However
pigment { color 0.4 }
is legal but it may or may not be what you intended. The 0.4 is promoted to
<0.4,0.4,0.4,0.4,0.> with the filter and transmit set to 0.4 as well. It is
more likely you wanted...
pigment { color rgb 0.4 }
in which case a 3 component vector is expected. Therefore the 0.4 is promoted
to <0.4,0.4,0.4,0.0,0.0> with default zero for filter and transmit.
7.1.6 Strings
The POV-Ray language requires you to specify a string of characters to be
used as a file name, text for messages or text for a text object. Strings may
be specified using literals, identifiers or functions which return string
values. Although you cannot build string expressions from symbolic operators
such as are used with floats, vectors or colors, you may perform various
string operations using string functions. Some applications of strings in
POV-Ray allow for non-printing formatting characters such as newline or
form-feed.
7.1.6.1 String Literals
String literals begin with a double quote mark '"' which is followed by up to
256 printable ASCII characters and are terminated by another double quote
mark. The following are all valid string literals:
"Here" "There" "myfile.gif" "textures.inc"
7.1.6.2 String Identifiers
String identifiers may be declared to make scene files more readable and to
parameterize scenes so that changing a single declaration changes many
values. An identifier is declared as follows...
#declare IDENTIFIER = STRING
Where IDENTIFIER is the name of the identifier up to 40 characters long and
STRING is a string literal, string identifier or function which returns a
string value. Here are some examples...
#declare Font_Name = "ariel.ttf"
#declare Inc_File = "myfile.inc"
#declare Name = "John"
#declare Name = concat(Name," Doe")
As the last example shows, you can re-declare a string identifier and may use
previously declared values in that re-declaration.
7.1.7 Built-in Identifiers
There are several built-in float and vector identifiers. You can use them to
specify values or to create expressions but you cannot re-declare them to
change their values.
7.1.7.1 Constant Built-in Identifiers
Most built-in identifiers never change value. They are defined as though the
following lines were at the start of every scene.
#declare pi = 3.1415926535897932384626
#declare true = 1
#declare yes = 1
#declare on = 1
#declare false = 0
#declare no = 0
#declare off = 0
#declare u = <1,0>
#declare v = <0,1>
#declare x = <1,0,0>
#declare y = <0,1,0>
#declare z = <0,0,1>
#declare t = <0,0,0,1>
The built-in float identifier pi is obviously useful in math expressions
involving circles.
The built-in float identifiers on , off , yes , no , true and false are
designed for use as boolean constants.
The built-in vector identifiers x , y and z provide much greater readability
for your scene files when used in vector expressions. For example....
plane { y, 1} // The normal vector is obviously "y".
plane { <0,1,0>, 1} // This is harder to read.
translate 5*x // Move 5 units in the "x" direction.
translate <5,0,0> // This is less obvious.
An expression like 5*x evaluates to 5 <1,0,0> or <5,0,0>.
Similarly u and v may be used in 2D vectors. When using 4D vectors you should
use x , y , z , and t and POV-Ray will promote x , y and z to 4D when used
where 4D is required.
7.1.7.2 Built-in Identifier 'clock'
The built-in float identifier clock is used to control animations in POV-Ray.
Unlike some animation packages, the action in POV-Ray animated scenes does
not depend upon the integer frame numbers. Rather you should design your
scenes based upon the float identifier clock . For non-animated scenes its
default value is 0 but you can set it to any float value using the INI file
option Clock=n.n or the command-line switch +Kn.n to pass a single float
value your scene file.
Other INI options and switches may be used to animate scenes by automatically
looping through the rendering of frames using various values for clock . By
default, the clock value is 0 for the initial frame and 1 for the final
frame. All other frames are interpolated between these values. For example if
your object is supposed to rotate one full turn over the course of the
animation you could specify rotate 360*clock*y . Then as clock runs from 0 to
1, the object rotates about the y-axis from 0 to 360 degrees.
Although the value of clock will change from frame-to-frame, it will never
change throughout the parsing of a scene.
7.1.7.3 Built-in Identifier 'version'
The built-in float identifier version contains the current setting of the
version compatibility option. Although this value defaults to 3 which is the
current POV-Ray version number, the initial value of version may be set by
the INI file option Version=n.n or by the +MVn.n command-line switch. This
tells POV-Ray to parse the scene file using syntax from an earlier version of
POV-Ray.
The INI option or switch only affects the initial setting. Unlike other
built-in identifiers, you may change the value of version throughout a scene
file. You do not use #declare to change it though. The #version language
directive is used to change modes. Such changes may occur several times
within scene files.
Together with the built-in version identifier the #version directive allows
you to save and restore the previous values of this compatibility setting.
For example suppose mystuff.inc is in version 1 format. At the top of the
file you could put:
#declare Temp_Vers = version // Save previous value
#version 1.0 // Change to 1.0 mode
... // Version 1.0 stuff goes here...
#version Temp_Vers // Restore previous version
7.1.8 Functions
POV-Ray defines a variety of built-in functions for manipulating floats,
vectors and strings. The functions are listed grouped according to their
usage and not by the type of value they return. For example vdot computes the
dot product of two vectors and is listed as a vector function even though it
returns a single float value.
Function calls consist of a keyword which specifies the name of the function
followed by a parameter list enclosed in parentheses. Parameters are
separated by commas. For example:
keyword(param1,param2)
Functions evaluate to values that are floats, vectors or strings and may be
used in expressions or statements anywhere that literals or identifiers of
that type may be used.
7.1.8.1 Float Functions
The following are the functions which take one or more float parameters and
return float values. Assume that A and B are any valid expression that
evaluates to a float. See "Vector Functions" and "String Functions" for other
functions which return float values but whose primary purpose is more closely
related to vectors and strings.
abs(A): Absolute value of A. If A is negative, returns -A otherwise returns
A. acos(A): Arc-cosine of A. Returns the angle, measured in radians, whose
cosine is A. asin(A): Arc-sine of A. Returns the angle, measured in radians,
whose sine is A. atan2(A,B): Arc-tangent of (A/B). Returns the angle,
measured in radians, whose tangent is (A/B). Returns appropriate value even
if B is zero. Use atan2(A,1) {/EN D/} to compute usual atan(A) function.
ceil(A): Ceiling of A. Returns the smallest integer greater than A. Rounds up
to the next higher integer. cos(A): Cosine of A. Returns the cosine of the
angle A, where A is measured in radians. degrees(A): Convert radians to
degrees. Returns the angle measured in degrees whose value in radians is A.
Formula is degrees=A/pi*180.0. div(A,B): Integer division. The integer part
of (A/B). exp(A): Exponential of A. Returns the value of e raised to the A
power where e is the non-repeating value approximately equal to 2.71828182846
the base of natural logarithms. floor(A): Floor of A. Returns the largest
integer less than A. Rounds down to the next lower integer. int(A): Integer
part of A. Returns the truncated integer part of A. Rounds towards zero.
log(A): Natural logarithm of A. Returns the natural logarithm base e of the
value A wher e e is the non-repeating value approximately equal to
2.71828182846. max(A,B): Maximum of A and B. {/EN D/} Returns A if A larger
than B. Otherwise retu rns B. min(A,B): Minimum of A and B. {/EN D/} Returns
A if A smaller than B. Otherwise returns B. mod(A,B): Value of A modulo A.
{/E ND/} Returns the remainder after the integer division of A/B. Formula is
mod=((A/B)-int(A/B))*B. pow(A,B): Exponentiation. Returns the value of A
raised to the power B. radians(A): Convert degrees to radians. Returns the
angle measured in radians whose value in degrees is A. Formula is
radians=A*pi/180.0. rand(A): Returns the next pseudo-random number from the
stream specified by the positive integer A. You must call seed() to
initialize a random stream before calling rand(). The numbers are uniformly
distributed, and have values between 0.0 and 1.0, inclusively. The numbers
generated by separate streams are independent random variables. seed(A):
Initializes a new pseudo-random stream with the initial seed value A. The
number corresponding to this random stream is returned. Any number of
pseudo-random streams may be used as shown in the example below: #declare R
#declare R2 = seed(12345)
#sphere { <rand(R1), rand(R1), rand(R1)>, rand(R2) }
Multiple random generators are very useful in situations where you use rand()
to place a group of objects, and then decide to use rand() in another
location earlier in the file to set some colors or place another group of
objects. Without separate rand() streams, all of your objects would move when
you added more calls to rand(). This is very annoying. sin(A): Sine of A.
Returns the sine of the angle A, where A is measured in radians. sqrt(A):
Square root of A. Returns the value whose square is A. tan(A): Tangent of A.
Returns the tangent of the angle A, where A is measured in radians.
7.1.8.2 Vector Functions
The following are the functions which take one or more vector and float
parameters and return vector or float values. All of these functions support
only three component vectors. Assume that A and B are any valid expression
that evaluates to a three component vector and that F is any valid expression
that evaluates to a float.
vaxis_rotate(A,B,F): Rotate A about B by F. Given the x,y,z coordinates of a
point in space designated by the vector A, rotate that point about an
arbitrary axis defined by the vector B. Rotate it through an angle specified
in degrees by the float value F. The result is a vector containing the new
x,y,z coordinates of the point. vcross(A,B): Cross product of A and B.
Returns a vector that is the vector cross product of the two vectors. The
resulting vector is perpendicular to the two original vectors and its length
is proportional to the angle between them. See the animated demo scene
VECT2.POV for an illustration. vdot(A,B): Dot product of A and B. Returns a
float value that is the dot product (sometimes called scaler product of A
with B. Formula is vdot=A.x*B.x + A.y*B.y + A.z*B.z. See the animated demo
scene VECT2.POV for an illustration. vlength(A): Length of A. Returns a float
value that is the length of vector A. Can be used to compute the distance
between two points. Dist=vlength(B-A). Formula is vlength=sqrt(vdot(A,A)).
vnormalize(A): Normalize vector A. Returns a unit length vector that is the
same direction as A. Formula is vnormalize=A/vlength(A). vrotate(A,B): Rotate
A about origin by B. Given the x,y,z coordinates of a point in space
designated by the vector A, rotate that point about the origin by an amount
specified by the vector B. Rotate it about the x-axis by an angle specified
in degrees by the float value B.x. Similarly B.y and B.z specify the amount
to rotate in degrees about the y-axis and z-axis. The result is a vector
containing the new x,y,z coordinates of the point.
7.1.8.3 String Functions
The following are the functions which take one or more string and float
parameters and return string or float values. Assume that S1 and S2 are any
valid strings and that A , L and P are any valid expressions that evaluate to
floats.
asc(S1): ASCII value of S1. Returns an integer value in the range 0 to 255
that is the ASCII value of the first character of S1. For example asc("ABC")
is 65 because that is the value of the character "A". chr(A): Character whose
ASCII value is A. Returns a single character string. The ASCII value of the
character is specified by an integer A which must be in the range 0 to 255.
For example chr(70) is the string "F". If you use chr() when rendering text
objects you should be aware that the characters rendered for values of A >
127 are dependent on the (TTF) font being used. Many (TTF) fonts use the
Latin-1 (ISO 8859-1) character set, but not all do. concat(S1,S2,[S3...]):
Concatenate strings S1 and S2. Returns a string that is the concatenation of
all parameter strings. Must have at least 2 parameters but may have more. For
example: concat("Value is ", str(A,3,1), " inches")
If the float value A was 12.34 the result is "Value is 12.3 inches" which is
a string. file_exists(S1): Search for file specified by S1. Attempts to open
the file whose name is specified the string S1. The current directory and all
directories specified in any Library_Path INI options or +L command line
switches are searched. File is immediately closed. Returns a boolean value 1
on success and 0 on failure. str(A,L,P): Convert float A to formatted string.
Returns a formatted string representation of float value A. The float
parameter L specifies the minimum length of the string and the type of left
padding used if the string's representation is shorter than the minimum. If L
is positive then the padding is with blanks. If L is negative then the
padding is with zeros. The overall minimum length of the formatted string is
abs(L). If the string needs to be longer, it will be made as long as
necessary to represent the value. The float parameter P specifies the number
of digits after the decimal point. If P is negative then a compiler-specific
default precision is use. Here are some examples: str(123.456,0,3) "123.4
str(123.456,4,3) "123.456"
str(123.456,9,3) " 123.456"
str(123.456,-9,3) "00123.456"
str(123.456,0,2) "123.46"
str(123.456,0,0) "123"
str(123.456,5,0) " 123"
str(123.000,7,2) " 123.00"
str(123.456,0,-1) "123.456000" (platform specific)
strcmp(S1,S2): Compare string S1 to S2. Returns a float value zero if the
strings are equal, a positive number if S1 comes after S2 in the ASCII
collating sequence, else a negative number. strlen(S1): Length of S1. Returns
an integer value that is the number of characters in the string S1.
strlwr(S1): Lower case of S1. Returns a new string in which all upper case
letters in the string S1 are converted to lower case. The original string is
not affected. For example strlwr("Hello There!") results in "hello there!".
substr(S1,P,L): Sub-string from S1. Returns a string that is a subset of the
characters in parameter S1 starting at the position specified by the integer
value P for a length specified by the integer value L. For example
substr("ABCDEFGHI",4,2) evaluates to the string "EF". If P+L>strlen(S1) an
error occurs. strupr(S1): Upper case of S1. Returns a new string in which all
lower case letters in the string S1 are converted to upper case. The original
string is not affected. For example strupr("Hello There!") results in "HELLO
THERE!". val(S1): Convert string S1 to float. Returns a float value that is
represented by the text in S1. For example val("123.45") is 123.45 as a
float.
7.2 Language Directives
The POV Scene Language contains several statements called language directives
which tell the file parser how to do its job. These directives can appear in
almost any place in the scene file - even in the middle of some other
statements. They are used to include other text files in the stream of
commands, to declare identifiers, to define conditional or looped parsing and
to control other important aspects of scene file processing.
Each directive begins with the hash character # (often called a number sign
or pound sign). It is followed by a keyword and optionally other parameters.
In versions of POV-Ray prior to 3.0, the use of this # character was
optional. Language directives could only be used between objects, camera or
light_source statements and could not appear within those statements. The
exception was the #include which could appear anywhere. Now that all language
directives can be used almost anywhere, the # character is mandatory.
The following keywords introduce language directives.
#break #default #statistics
#case #else #switch
#debug #end #version
#declare #render #warning
Earlier versions of POV-Ray considered #max_intersections and
#max_trace_level to be language directives but they have been
moved to the global_settings statement. Their use as a
directive still works but it generates a warning and may be
discontinued in the future.
7.2.1 Include Files
The language allows include files to be specified by placing the line
#include "filename.inc"
at any point in the input file. The filename may be specified by any valid
string expression but it usually is a literal string enclosed in double
quotes. It may be up to 40 characters long (or your computer's limit),
including the two double-quote characters.
The include file is read in as if it were inserted at that point in the file.
Using include is the same as actually cutting and pasting the entire contents
of this file into your scene.
Include files may be nested. You may have at most 10 nested include files.
There is no limit on un-nested include files.
Generally, include files have data for scenes but are not scenes in
themselves. By convention scene files end in .pov and include files end with
.inc .
It is legal to specify drive and directory information in the file
specification however it is discouraged because it makes scene files less
portable between various platforms.
It is typical to put standard include files in a special sub-directory.
POV-Ray can only read files in the current directory or one referenced by the
Library_Path option (See section "Library Paths" ).
7.2.2 Declare
Identifiers may be declared and later referenced to make scene files more
readable and to parametrize scenes so that changing a single declaration
changes many values. There are several built-in identifiers which POV-Ray
declares for you. See "Built-in Identifiers" for details.
7.2.2.1 Declaring identifiers
An identifier is declared as follows.
#declare IDENTIFIER = ITEM
Where IDENTIFIER is the name of the identifier up to 40 characters long and
ITEM is any of the following
float, vector, color or string expressions
objects (all kinds)
texture, pigment, normal, finish or halo
color_map, pigment_map, slope_map, normal_map
camera, light_source
atmosphere
fog
rainbow
sky_sphere
transform
Here are some examples.
#declare Rows = 5
#declare Count = Count+1
#declare Here = <1,2,3>
#declare White = rgb <1,1,1>
#declare Cyan = color blue 1.0 green 1.0
#declare Font_Name = "ariel.ttf"
#declare Ring = torus {5,1}
#declare Checks = pigment { checker White, Cyan }
object{ Rod scale y*5 } // not "cylinder { Rod }"
object {
Ring
pigment { Checks scale 0.5 }
transform Skew
}
Declarations, like most language directives, can appear anywhere in the file
- even within other statements. For example:
#declare Here=<1,2,3>
#declare Count=0 // initialize Count
union {
object { Rod translate Here*Count }
#declare Count=Count+1 // re-declare inside union
object { Rod translate Here*Count }
#declare Count=Count+1 // re-declare inside union
object { Rod translate Here*Count }
}
As this example shows, you can re-declare an identifier and may use
previously declared values in that re-declaration. However if you attempt to
re-declare an identifier as anything other than its original type, it will
generate a warning message.
Declarations may be nested inside each other within limits. In the example in
the previous section you could declare the entire union as a object. However
for technical reasons you may not use any language directive inside the
declaration of floats, vectors or color expressions.
7.2.3 Default Directive
POV-Ray creates a default texture when it begins processing. You may change
those defaults as described below. Every time you specify a texture {... }
statement, POV-Ray creates a copy of the default texture. Anything you put in
the texture statement overrides the default settings. If you attach a pigment
, normal or finish to an object without any texture statement then POV-Ray
checks to see if a texture has already been attached. If it has a texture
then the pigment, normal or finish will modify the existing texture. If no
texture has yet been attached to the object then the default texture is
copied and the pigment, normal or finish will modify that texture.
You may change the default texture, pigment, normal or finish using the
language directive #default {... } as follows:
#default {
texture {
pigment {...}
normal {...}
finish {...}
}
}
Or you may change just part of it like this:
#default {
pigment {..}.
}
This still changes the pigment of the default texture. At any time there is
only one default texture made from the default pigment, normal and finish.
The example above does not make a separate default for pigments alone. Note
that the special textures tiles and material_map or a texture with a
texture_map may not be used as defaults.
You may change the defaults several times throughout a scene as you wish.
Subsequent #default statements begin with the defaults that were in effect at
the time. If you wish to reset to the original POV-Ray defaults then you
should first save them as follows:
//At top of file
#declare Original_Default = texture {}
later after changing defaults you may restore it with...
#default {texture {Original_Default}}
If you do not specify a texture for an object then the default texture is
attached when the object appears in the scene. It is not attached when an
object is declared. For example:
#declare My_Object =
sphere{ <0,0,0>, 1 } // Default texture not applied
object { My_Object } // Default texture added here
You may force a default texture to be added by using an empty texture
statement as follows:
#declare My_Thing =
sphere { <0,0,0>, 1 texture {} } // Default texture applied
The original POV-Ray defaults for all items are given throughout the
documentation under each appropriate section.
7.2.4 Version Directive
While many language changes have been made for POV-Ray 3.0, all of version
2.0 syntax and most of version 1.0 syntax still works. Whenever possible we
try to maintain backwards compatibility. One feature introduced in 2.0 that
was incompatible with any 1.0 scene files is the parsing of float
expressions. Setting +MV 1.0 command line switch or the Version =1.0 INI
option turns off expression parsing as well as many warning messages so that
nearly all 1.0 files will still work. The changes between 2.0 and 3.0 are not
as extensive. Setting Version =2.0 is only necessary to eliminate some
warning messages. Naturally the default setting for this option is Version
=3.0.
The #version language directive is used to change modes within scene files.
This switch or INI options only affects the initial setting.
Together with the built-in version identifier the #version directive allows
you to save and restore the previous values of this compatibility setting.
For example suppose mystuff.inc is in version 1.0 format. At the top of the
file you could put:
#declare Temp_Vers = version // Save previous value
#version 1.0 // Change to 1.0 mode
... // Version 1.0 stuff goes here ...
#version Temp_Vers // Restore previous version
Previous versions of POV-Ray would not allow you to change versions inside an
object or declaration but that restriction has been lifted for POV-Ray 3.0.
Future versions of POV-Ray may not continue to maintain full backward
compatibility even with the #version directive. We strongly encourage you to
phase in 3.0 syntax as much as possible.
7.2.5 Conditional Directives
POV-Ray 3.0 allows a variety of new language directives to implement
conditional parsing of various sections of your scene file. This is
especially useful in describing the motion for animations but it has other
uses as well. Also available is a #while loop directive. You may nest
conditional directives 200 levels deep.
7.2.5.1 IF ELSE Directives
The simplest conditional directive is a traditional #if directive. It is of
the form...
#if (COND)
// This section is
// parsed if COND is true
#else
// This section is
// parsed if COND is false
#end // End of conditional part
where (COND) is a float expression that evaluates to a boolean value. A value
of 0.0 is false and any non-zero value is true. Note that extremely small
values of about 1e-10 are considered zero in case of round off errors. The
parentheses around the condition are required. The #else directive is
optional. The #end directive is required.
7.2.5.2 IFDEF Directives
The #ifdef directive is similar to the #if directive however it is used to
determine if an identifier has been previously declared. After the #ifdef
directive instead of a boolean expression you put a lone identifier enclosed
in parentheses. For example:
#ifdef (User_Thing)
// This section is parsed if the
// identifier "User_Thing" was
// previously declared
object{User_Thing} // invoke identifier
#else
// This section is parsed if the
// identifier "User_Thing" was not
// previously declared
box{<0,0,0>,<1,1,1>} // use a default
#end
// End of conditional part
7.2.5.3 IFNDEF Directives
The #ifndef directive is similar to the #ifdef directive however it is used
to determine if the given identifier isn't declared yet. For example:
#ifndef (User_Thing)
// This section is parsed if the
// identifier "User_Thing" was not
// previously declared
box{<0,0,0>,<1,1,1>} // use a default
#else
// This section is parsed if the
// identifier "User_Thing" was
// previously declared
object{User_Thing} // invoke identifier
#end
// End of conditional part
7.2.5.4 SWITCH CASE and RANGE Directives
A more powerful conditional is the #switch directive. The syntax is as
follows...
#switch (VALUE)
#case (TEST_1)
// This section is parsed if VALUE=TEST_1
#break //First case ends
#case (TEST_2)
// This section is parsed if VALUE=TEST_2
#break //Second case ends
#range (LOW_1,HIGH_1)
// This section is parsed if (VALUE>=LOW_1)&(VALUE<=HIGH_1)
#break //Third case ends
#range (LOW_2,HIGH_2)
// This section is parsed if (VALUE>=LOW_2)&(VALUE<=HIGH_2)
#break //Fourth case ends
#else
// This section is parsed if no other case or
// range is true.
#end // End of conditional part
The float expression VALUE following the #switch directive is evaluated and
compared to the values in the #case or #range directives. When using #case ,
it is followed by a float expression TEST_1 in parentheses. It is compared to
the VALUE . As usual in POV-Ray, float comparisons are considered equal if
their difference is under 1e-10. If the values are equal, parsing continues
normally until a #break , #else or #end directive is reached. If the
comparison fails POV-Ray skips until another #case or #range is found.
If you use the #range directive it is followed by two float expressions LOW_1
and HIGH_1 which are enclosed in parentheses and separated by a comma. If the
switch VALUE is in the range specified then parsing continues normally until
a #break , #else or #end directive is reached. If the VALUE is outside the
range the comparison fails and POV-Ray skips until another #case or #range is
found.
If no #case or #range succeeds the #else section is parsed. The #else
directive is optional. If no #else is specified and no match succeeds then
parsing resumes after the #end directive.
There may be any number of #case or #range directives in any order you want.
If a segment evaluates true but no #break is specified, the parsing will fall
through to the next #case or #range and will continue until a #break , #else
or #end . Hitting a #break while parsing a successful section causes an
immediate jump to the #end without processing subsequent sections, even if a
subsequent condition would also have been satisfied.
7.2.5.5 WHILE Directive
The #while directive is a looping feature that makes it easy to place
multiple objects in a pattern or other uses. The #while directive is followed
by a float expression that evaluates to a boolean value. A value of 0.0 is
false and any non-zero value is true. Note that extremely small values of
about 1e-10 are considered zero in case of round off errors. The parentheses
around the expression are required. If the condition is true parsing
continues normally until an #end directive is reached. At the end, POV-Ray
loops back to the #while directive and the condition is re-evaluated. Looping
continues until the condition fails. When it fails, parsing continues after
the #end directive. For example:
#declare Count=0
#while (Count < 5)
object{MyObject translate x*3*Count}
#declare Count=Count+1
#end
This example places five copies of MyObject in a row spaced three units apart
in the x-direction.
7.2.6 User Message Directives
With the addition of conditional and loop directives, the POV-Ray language
has the potential to be more like an actual programming language. This means
that it will be necessary to have some way to see what is going on when
trying to debug loops and conditionals. To fulfill this need we have added
the ability to print text messages to the screen. You have a choice of five
different text streams to use including the ability to generate a fatal error
if you find it necessary. Limited formatting is available for strings output
by this method.
7.2.6.1 Text Message Streams
The syntax for a text message is any of the following:
#debug STRING
#error STRING
#error STRING
#render STRING
#statistics STRING
#warning STRING
Where STRING is any valid string of text including string identifiers or
functions which return strings. For example:
#switch (clock*360)
#range (0,180)
#render "Clock in 0 to 180 range\n"
#break
#range (180,360)
#render "Clock in 180 to 360 range\n"
#break
#else
#warning "Clock outside expected range\n"
#warning concat("Value is:",str(clock*360,5,0),"\n")
#end
There are seven distinct text streams that POV-Ray uses for output. You may
output only to five of them. On some versions of POV-Ray, each stream is
designated by a particular color. Text from these streams are displayed
whenever it is appropriate so there is often an intermixing of the text. The
distinction is only important if you choose to turn some of the streams off
or to direct some of the streams to text files. On some systems you may be
able to review the streams separately in their own scroll-back buffer. See
"Console Text Output" for details on re-directing the streams to a text file.
Here is a description of how POV-Ray uses each stream. You may use them for
whatever purpose you want except note that use of the #error stream causes a
fatal error after the text is displayed.
DEBUG: This stream displays debugging messages. It was primarily designed for
developers but this and other streams may also be used by the user to display
messages from within their scene files. FATAL: This stream displays fatal
error messages. After displaying this text, POV-Ray will terminate. When the
error is a scene parsing error, you may be shown several lines of scene text
that leads up to the error. RENDER: This stream displays information about
what options you have specified to render the scene. It includes feedback on
all of the major options such as scene name, resolution, animation settings,
anti-aliasing and others. STATISTICS: This stream displays statistics after a
frame is rendered. It includes information about the number of rays traced,
the length of time of the processing and other information. WARNING: This
stream displays warning messages during the parsing of scene files and other
warnings. Despite the warning, POV-Ray can continue to render the scene.
7.2.6.2 Text Formatting
Some escape sequences are available to include non-printing control
characters in your text. These sequences are similar to those used in string
literals in the C programming language. Note that these control characters
only apply in text message directives. They are not implemented for other
string usage in POV-Ray such as text objects or file names. Depending on what
platform you are using, they may not be fully supported for console output.
However they will appear in any text file if you re-direct a stream to a
file. The sequences are:
"\a" Bell or alarm, 0x07
"\b" Backspace, 0x08
"\f" Form feed, 0x0C
"\n" New line (line feed) 0x0A
"\r" Carriage return 0x0D
"\t" Horizontal tab 0x09
"\v" Vertical tab 0x0B
"\0" Null 0x00
"\\" Backslash 0x5C
"\'" Single quote 0x27
"\"" Double quote 0x22
For example:
#debug "This is one line.\nBut this is another"
7.3 POV-Ray Coordinate System
Objects, lights and the camera are positioned using a typical 3D coordinate
system. The usual coordinate system for POV-Ray has the positive y-axis
pointing up, the positive x-axis pointing to the right and the positive
z-axis pointing into the screen. The negative values of the axes point the
other direction as shown in the images in section "Understanding POV-Ray's
Coordinate System" .
Locations within that coordinate system are usually specified by a three
component vector. The three values correspond to the x, y and z directions
respectively. For example, the vector \langle 1,2,3> means the point that's
one unit to the right, two units up and three units in front of the center of
the universe at <0,0,0>.
Vectors are not always points though. They can also refer to an amount to
size, move or rotate a scene element or to modify the texture pattern applied
to an object.
The supported transformations are rotate , scale and translate . They are
used to turn, size and translate an object or texture. A transformation
matrix may also be used to specify complex transformations directly.
7.3.1 Transformations
The supported transformations are rotate, scale and translate. They are used
to turn, size and translate an object or texture.
rotate <VECTOR>
scale <VECTOR>
translate <VECTOR>
7.3.1.1 Translate
An object or texture pattern may be moved by adding a translate parameter. It
consists of the keyword translate followed by a vector expression. The terms
of the vector specify the number of units to move in each of the x, y and z
directions. Translate moves the element relative to it's current position.
For example
sphere { <10, 10, 10>, 1
pigment { Green }
translate <-5, 2, 1>
}
will move the sphere from <10,10,10> to \langle 5,12,11>. It does not move it
to the absolute location <-5,2,1>. Translating by zero will leave the element
unchanged on that axis. For example:
sphere { <10, 10, 10>, 1
pigment { Green }
translate 3*x // evaluates to <3,0,0> so move 3 units
// in the x direction and none along y or z
}
7.3.1.2 Scale
You may change the size of an object or texture pattern by adding a scale
parameter. It consists of the keyword scale followed by a vector expression.
The 3 terms of the vector specify the amount of scaling in each of the x, y
and z directions.
Scale is used to stretch or squish an element. Values larger than one stretch
the element on that axis while values smaller than one are used to squish it.
Scale is relative to the current element size. If the element has been
previously re-sized using scale then scale will size relative to the new
size. Multiple scale values may used.
For example
sphere { <0,0,0>, 1
scale <2,1,0.5>
}
will stretch and smash the sphere into an ellipsoid shape that is twice the
original size along the x-direction, remains the same size in the y-direction
and is half the original size in the z-direction.
If a lone float expression is specified it is promoted to a three component
vector whose terms are all the same. Thus the item is uniformly scaled by the
same amount in all directions. For example:
object {
MyObject
scale 5 // Evaluates as <5,5,5> so uniformly scale
// by 5 in every direction.
}
7.3.1.3 Rotate
You may change the orientation of an object or texture pattern by adding a
rotate parameter. It consists of the keyword rotate followed by a vector
expression. The three terms of the vector specify the number of degrees to
rotate about each of the x-, y- and z-axes.
Note that the order of the rotations does matter. Rotations occur about the
x-axis first, then the y-axis, then the z-axis. If you are not sure if this
is what you want then you should only rotate on one axis at a time using
multiple rotation statements to get a correct rotation. As in
rotate <0, 30, 0> // 30 degrees around Y axis then,
rotate <-20, 0, 0> // -20 degrees around X axis then,
rotate <0, 0, 10> // 10 degrees around Z axis.
Rotation is always performed relative to the axis. Thus if an object is some
distance from the axis of rotation it will not only rotate but it will orbit
about the axis as though it was swinging around on an invisible string.
To work out the rotation directions you must perform the famous Computer
Graphics Aerobics exercise as explained in the section "Understanding
POV-Ray's Coordinate System" .
7.3.1.4 Matrix Keyword
The matrix keyword can be used to explicitly specify the transformation
matrix to be used for objects or textures. Its syntax is:
matrix < m00, m01, m02,
m10, m11, m12,
m20, m21, m22,
m30, m31, m32 >
%%% PHS-ONLY %%% %%% Where m00 through m32 are float expressions that specify
%%% the elements of a 4*4 matrix with the fourth column implicitly %%% set to
<0,0,0,1>. A point P, P=<px, py, %%% pz>, is transformed into Q, Q=<qx, qy,
qz> by %%% %%% %%% qx = M00 * px + M10 * py + M20 * pz + M30
%%% qy = M01 * px + M11 * py + M21 * pz + M31
%%% qz = M02 * px + M12 * py + M22 * pz + M32
%%% %%% END
Normally you won't use the matrix keyword because it's less descriptive than
the transformation commands and harder to visualize. There is an intersecting
aspect of the matrix command though. It allows more general transformation
like shearing. The following matrix causes an object to be sheared along the
y-axis.
object {
MyObject
matrix < 1, 1, 0,
0, 1, 0,
0, 0, 1,
0, 0, 0 >
}
7.3.2 Transformation Order
Because rotations are always relative to the axis and scaling is relative to
the origin, you will generally want to create an object at the origin and
scale and rotate it first. Then you may translate it into its proper
position. It is a common mistake to carefully position an object and then to
decide to rotate it because a rotation of an object causes it to orbit about
the axis, the position of the object may change so much that it orbits out of
the field of view of the camera!
Similarly scaling after translation also moves an object unexpectedly. If you
scale after you translate the scale will multiply the translate amount. For
example
translate <5, 6, 7>
scale 4
will translate to <20,24,28> instead of \langle 5,6,7>. Be careful when
transforming to get the order correct for your purposes.
7.3.3 Transform Identifiers
At times it is useful to combine together several transformations and apply
them in multiple places. A transform identifier may be used for this purpose.
Transform identifiers are declared as follows:
#declare IDENT = transform { TRANSFORMATION... }
Where IDENT is the identifier to be declared and TRANSFORMATION is one or
more translate , rotate , scale or matrix specifications or a previously
declared transform identifier. A transform identifier is invoked by the
transform keyword without any brackets as shown here:
object {
MyObject // Get a copy of MyObject
transform MyTrans // Apply the transformation
translate -x*5 // Then move it 5 units left
}
object {
MyObject // Get another copy of MyObject
transform MyTrans // Apply the same transformation
translate -x*5 // Then move this one 5 units right
}
On extremely complex CSG objects with lots of components it may speed up
parsing if you apply a declared transformation rather than the individual
translate , rotate , scale or matrix specifications. The transform is
attached just once to each component. Applying each individual translate ,
rotate , scale or matrix specifications takes long. This only affects parsing
- rendering works the same either way.
7.3.4 Transforming Textures and Objects
When an object is transformed all textures attached to the object at that
time are transformed as well. This means that if you have a translate ,
rotate , scale or matrix in an object before a texture the texture will not
be transformed. If the transformation is after the texture then the texture
will be transformed with the object. If the transformation is inside the
texture {... } statement then only the texture is affected. The shape remains
the same. For example:
sphere { 0, 1
texture { Jade } // texture identifier from TEXTURES.INC
scale 3 // this scale affects both the
// shape and texture
}
sphere { 0, 1
scale 3 // this scale affects the shape only
texture { Jade }
}
sphere { 0, 1
texture {
Jade
scale 3 // this scale affects the texture only
}
}
Transformations may also be independently applied to pigment patterns and
surface normal patterns. Note that scaling a normal pattern affects only the
width and spacing. It does not affect the apparent height or depth of the
bumps. For example:
box { <0, 0, 0>, <1, 1, 1>
texture {
pigment {
checker Red, White
scale 0.25 // This affects only the color pattern
}
normal {
bumps 0.3 // This specifies apparent height of bumps
scale 0.2 // Scales diameter and space between bumps
// but not the height. Has no effect on
// color pattern.
}
rotate y*45 // This affects the entire texture but
} // not the object.
}
7.4 Camera
The camera definition describes the position, projection type and properties
of the camera viewing the scene. Its syntax is:
camera {
[ perspective | orthographic | fisheye |
ultra_wide_angle | omnimax | panoramic |
cylinder FLOAT ]
location <VECTOR>
look_at <VECTOR>
right <VECTOR>
up <VECTOR>
direction <VECTOR>
sky <VECTOR>
right <VECTOR>
angle FLOAT
blur_samples FLOAT
aperture FLOAT
focal_point <VECTOR>
normal { NORMAL }
}
Depending on the projection type some of the parameters are required, some
are optional and some aren't used. If no projection type is given the
perspective camera will be used (pinhole camera). If no camera is specified a
default camera is used.
Regardless of the projection type all cameras use the location , look_at ,
right , up , direction and sky keywords to determine the location and
orientation of the camera. Their meaning differs with the projection type
used. A more detailed explanation of the camera placement follows later.
7.4.1 Type of Projection
The following list explains the different projection types that can be used
with the camera. The most common types are the perspective and orthographic
projections.
Perspective projection: This projection represents the classic pinhole
camera. The (horizontal) viewing angle is either determined by the ratio
between the length of the direction vector and the length of the right vector
or by the optional keyword angle, which is the preferred way. The viewing
angle has to be larger than 0 degrees and smaller than 180 degrees. See the
figure below for the geometry of the perspective camera. The perspective
camera.
Orthographic projection: This projection uses parallel camera rays to create
an image of the scene. The size of the image is determined by the lengths of
the right and up vectors. If you add the orthographic keyword after all other
parameters of a perspective camera you'll get an orthographic view with the
same image area, i.e. the size of the image is the same. In this case you
needn't specify the lengths of the right and up vector because they'll be
calculated automatically. You should be aware though that the visible parts
of the scene change when switching from perspective to orthographic view. As
long as all objects of interest are near the look_at location they'll be
still visible if the orthographic camera is used. Objects farer away may get
out of view while nearer objects will stay in view. Fisheye projection: This
is a spherical projection. The viewing angle is specified by the angle
keyword. An angle of 180 degrees creates the "standard" fisheye while an
angle of 360 degrees creates a super-fisheye ("I-see-everything-view"). If
you use this projection you should get a circular image. If this isn't the
case, i.e. you get an elliptical image, you should read "Aspect Ratio" .
Ultra wide angle projection: This projection is somewhat similar to the
fisheye but it projects the image onto a rectangle instead of a circle. The
viewing angle can be specified using the angle keyword. Omnimax projection:
The omnimax projection is a 180 degrees fisheye that has a reduced viewing
angle in the vertical direction. In reality this projection is used to make
movies that can be viewed in the dome-like Omnimax theaters. The image will
look somewhat elliptical. The angle keyword isn't used with this projection.
Panoramic projection: This projection is called "cylindrical equirectangular
projection". It overcomes the degeneration problem of the perspective
projection if the viewing angle approaches 180 degrees. It uses a type of
cylindrical projection to be able to use viewing angles larger than 180
degrees with a tolerable lateral-stretching distortion. The angle keyword is
used to determine the viewing angle. Cylindrical projection: Using this
projection the scene is projected onto a cylinder. There are four different
types of cylindrical projections depending on the orientation of the cylinder
and the position of the viewpoint. The viewing angle and the length of the up
or right vector determine the dimensions of the camera and the visible image.
Th1 vertical cylinder, fixed viewpoint ber. The types are:
2 horizontal cylinder, fixed viewpoint
3 vertical cylinder, viewpoint moves along the cylinder's axis
4 horizontal cylinder, viewpoint moves along the cylinder's axis
If the perspective camera is used the angle keyword overrides the viewing
angle specified by the direction keyword and vice versa. Each time angle is
used the length of the direction vector is adjusted to fit the new viewing
angle.
There is no limitation to the viewing angle except for the perspective
projection. If you choose viewing angles larger than 360 degrees you'll see
repeated images of the scene (the way the repetition takes place depends on
the camera). This might be useful for special effects.
You should note that the vista buffer can only be used with the perspective
and orthographic camera.
7.4.2 Focal Blur
Simulates focal depth-of-field by shooting a number of sample rays from
jittered points within each pixel and averaging the results.
The aperture setting determines the depth of the sharpness zone. Large
apertures give a lot of blurring, while narrow apertures will give a wide
zone of sharpness. Note that, while this behaves as a real camera does, the
values for aperture are purely arbitrary and are not related to f-stops.
The center of the zone of sharpness is the focal_point vector (the default
focal_point is <0,0,0>).
The blur_samples value controls the maximum number of rays to use for each
pixel. More rays give a smoother appearance but is slower, although this is
controlled somewhat by an adaptive mechanism that stops shooting rays when a
certain degree of confidence has been reached that shooting more rays would
not result in a significant change.
The confidence and variance keywords control the adaptive function. The
confidence value is used to determine when the samples seem to be close
enough to the correct color. The variance value specifies an acceptable
tolerance on the variance of the samples taken so far. In other words, the
process of shooting sample rays is terminated when the estimated color value
is very likely (as controlled by the confidence probability) near the real
color value.
Since the confidence is a probability its values can range from 0 to 1 (the
default is 0.9, i. e. 90%). The value for the variance should be in the range
of the smallest displayable color difference (the default is 1/128).
Larger confidence values will lead to more samples, slower traces and better
images. The same holds for smaller variance thresholds.
By default no focal blur is used, i. e. the default aperture is 0 and the
default number of samples is 0.
7.4.3 Camera Ray Perturbation
The optional keyword normal may be used to assign a normal pattern to the
camera. All camera rays will be perturbed using this pattern. This lets you
create special effects. See the animated scene camera2.pov for an example.
7.4.4 Placing the Camera
In the following sections the placing of the camera will be further
explained.
7.4.4.1 Location and Look_At
Under many circumstances just two vectors in the camera statement are all you
need to position the camera: location and look_at . For example:
camera {
location <3,5,-10>
look_at <0,2,1>
}
The location is simply the x, y, z coordinates of the camera. The camera can
be located anywhere in the ray-tracing universe. The default location is <0,
0, 0>. The look_at vector tells POV-Ray to pan and tilt the camera until it
is looking at the specified x, y, z coordinates. By default the camera looks
at a point one unit in the z-direction from the location.
The look_at specification should almost always be the last item in the camera
statement. If other camera items are placed after the look_at vector then the
camera may not continue to look at the specified point.
7.4.4.2 The Sky Vector
Normally POV-Ray pans left or right by rotating about the y-axis until it
lines up with the look_at point and then tilts straight up or down until the
point is met exactly. However you may want to slant the camera sideways like
an airplane making a banked turn. You may change the tilt of the camera using
the sky vector. For example:
camera {
location <3,5,-10>
sky <1,1,0>
look_at <0,2,1>
}
This tells POV-Ray to roll the camera until the top of the camera is in line
with the sky vector. Imagine that the sky vector is an antenna pointing out
of the top of the camera. Then it uses the sky vector as the axis of rotation
left or right and then to tilt up or down in line with the sky vector. In
effect you're telling POV-Ray to assume that the sky isn't straight up. Note
that the sky vector must appear before the look_at vector.
The sky vector does nothing on its own. It only modifies the way the look_at
vector turns the camera. The default value for sky is <0, 1, 0>.
7.4.4.3 The Direction Vector
The direction vector tells POV-Ray the initial direction to point the camera
before moving it with look_at or rotate vectors (the default is direction <0,
0, 1> ). It may also be used to control the (horizontal) field of view with
some types of projection. This should be done using the easier to use angle
keyword though.
If you are using the ultra wide angle, panoramic or cylindrical projection
you should use a unit length direction vector to avoid strange results.
The length of the direction vector doesn't matter if one of the following
projection types is used: orthographic, fisheye or omnimax.
7.4.4.4 Angle
The angle keyword specifies the (horizontal) viewing angle in degress of the
camera used. Even though it is possible to use the direction vector to
determine the viewing angle for the perspective camera it is much easier to
use the angle keyword.
The necessary calculations to convert from one method to the other are
described below. These calculations are used to determine the length of the
direction vector whenever the angle keyword is encountered.
The viewing angle is converted to a direction vector length and vice versa
using the formula The viewing angle is given by the formula
angle = 2 * arctan(0.5 * right_length / direction_length)
where right_length and direction_length are the lengths of the right and
direction vector respectively and arctan is the inverse tangens function.
From this the length of the direction vector can be calculated for a given
viewing angle and right vector.
From this the length of the direction vector can be calculated for a given
viewing angle and right vector. direction_length = 0.5 * right_length / tan
7.4.4.5 Up and Right Vectors
The direction of the up and right vectors (together with the direction
vector) determine the orientation of the camera in the scene. They are set
implicitly by their default values of
right 4/3*x
up y
or the look_at parameter (in combination with location) . The directions of
an explicitly specified right and up vector will be overridden by any
following look_at parameter.
While some camera types ignore the length of these vectors others use it to
extract valuable information about the camera settings. The following list
will explain the meaning of the right and up vector for each camera type.
Since the direction the vectors is always used to describe the orientation of
the camera it will not be explained again.
Perspective projection: The lengths of the up and right vectors are used to
set the size of the viewing window and the aspect ratio as described in
detail in section "Aspect Ratio" . Since the field of view depends on the
length of the direction vector (implicitly set by the angle keyword or
explicitly set by the direction keyword) and the lengths of the right and up
vectors you should carefully choose them in order to get the desired results.
Orthographic projection: The lengths of the right and up vector set the size
of the viewing window regardless of the direction vector length, which is not
used by the orthographic camera. Again the relation of the lengths is used to
set the aspect ratio. Fisheye projection: The right and up vectors are used
to set the aspect ratio. Ultra wide angle projection: The up and right
vectors work in a similar way as for the perspective camera. Omnimax
projection: The omnimax projection is a 180 degrees fisheye that has a
reduced viewing angle in the vertical direction. In reality this projection
is used to make movies that can be viewed in the dome-like Omnimax theaters.
The image will look somewhat elliptical. The angle keyword isn't used with
this projection. Panoramic projection: The up and right vectors work in a
similar way as for the perspective camera. Cylindrical projection: In
cylinder type 1 and 3 the axis of the cylinder lies along the up vector and
the width is determined by the length of right vector or it may be overridden
with the angle vector. In type 3 the up vector determines how many units high
the image is. For example if you have up 4*y on a camera at the origin. Only
points from y=2 to y=-2 are visible. All viewing rays are perpendicular to
the y-axis. For type 2 and 4, the cylinder lies along the right vector.
Viewing rays for type 4 are perpendicular to the right vector.
Note that the up, right and direction vectors should always remain
perpendicular to each other or the image will be distorted. If this is not
the case a warning message will be printed. The vista buffer will not work
for non-perpendicular camera vectors.
7.4.4.5.1 Aspect Ratio
Together the right and up vectors define the aspect ratio (height to width
ratio) of the resulting image. The default values up <0, 1, 0rangle and right
<1.33, 0, 0> result in an aspect ratio of 4 to 3. This is the aspect ratio of
a typical computer monitor. If you wanted a tall skinny image or a short wide
panoramic image or a perfectly square image you should adjust the up and
right vectors to the appropriate proportions.
Most computer video modes and graphics printers use perfectly square pixels.
For example Macintosh displays and IBM S-VGA modes 640x480, 800x600 and
1024x768 all use square pixels. When your intended viewing method uses square
pixels then the width and height you set with the +W and +H switches should
also have the same ratio as the right and up vectors. Note that 640/480 = 4/3
so the ratio is proper for this square pixel mode.
Not all display modes use square pixels however. For example IBM VGA mode
320x200 and Amiga 320x400 modes do not use square pixels. These two modes
still produce a 4/3 aspect ratio image. Therefore images intended to be
viewed on such hardware should still use 4/3 ratio on their up and right
vectors but the +W and +H settings will not be 4/3.
For example:
camera {
location <3,5,-10>
up <0,1,0>
right <1,0,0>
look_at <0,2,1>
}
This specifies a perfectly square image. On a square pixel display like SVGA
you would use +W and +H settings such as +W 480 +H 480 or +W 600 +H 600.
However on the non-square pixel Amiga 320x400 mode you would want to use
values of +W 240 +H 400 to render a square image.
7.4.4.5.2 Handedness
The right vector also describes the direction to the right of the camera. It
tells POV-Ray where the right side of your screen is. The sign of the right
vector can be used to determine the handedness of the coordinate system in
use. The default right statement is:
right <1.33, 0, 0>
This means that the +x-direction is to the right. It is called a left-handed
system because you can use your left hand to keep track of the axes. Hold out
your left hand with your palm facing to your right. Stick your thumb up.
Point straight ahead with your index finger. Point your other fingers to the
right. Your bent fingers are pointing to the +x-direction. Your thumb now
points into +y-direction. Your index finger points into the +z-direction.
To use a right-handed coordinate system, as is popular in some CAD programs
and other ray-tracers, make the same shape using your right hand. Your thumb
still points up in the +y-direction and your index finger still points
forward in the +z-direction but your other fingers now say the +x-direction
is to the left. That means that the right side of your screen is now in the
-x-direction. To tell POV-Ray to act like this this you can use a negative x
value in the right vector like this:
right <-1.33, 0, 0>
Since x increasing to the left doesn't make much sense on a 2D screen you now
rotate the whole thing 180 degrees around by using a positive z value in your
camera's location. You end up with something like this.
camera {
location <0,0,10>
up <0,1,0>
right <-1.33,0,0>
look_at <0,0,0>
}
Now when you do your ray-tracer's aerobics, as explained in the section
"Understanding POV-Ray's Coordinate System" , you use your right hand to
determine the direction of rotations.
In a two dimensional grid, x is always to the right and y is up. The two
versions of handedness arise from the question of whether z points into the
screen or out of it and which axis in your computer model relates to up in
the real world.
Architectural CAD systems, like AutoCAD, tend to use the God's Eye
orientation that the z-axis is the elevation and is the model's up direction.
This approach makes sense if you're an architect looking at a building
blueprint on a computer screen. z means up, and it increases towards you,
with x and y still across and up the screen. This is the basic right handed
system.
Stand alone rendering systems, like POV-Ray, tend to consider you as a
participant. You're looking at the screen as if you were a photographer
standing in the scene. Up in the model is now y, the same as up in the real
world and x is still to the right, so z must be depth, which increases away
from you into the screen. This is the basic left handed system.
7.4.4.6 Transforming the Camera
The translate and rotate commands can re-position the camera once you've
defined it. For example:
camera {
location < 0, 0, 0>
direction < 0, 0, 1>
up < 0, 1, 0>
right < 1, 0, 0>
rotate <30, 60, 30>
translate < 5, 3, 4>
}
In this example, the camera is created, then rotated by 30 degrees about the
x-axis, 60 degrees about the y-axis and 30 degrees about the z-axis, then
translated to another point in space.
7.4.5 Camera Identifiers
You may declare several camera identifiers if you wish. This makes it easy to
quickly change cameras. For example:
#declare Long_Lens =
camera {
location -z*100
angle 3
}
#declare Short_Lens =
camera {
location -z*50
angle 15
}
camera {
Long_Lens // edit this line to change lenses
look_at Here
}
7.5 Objects
Objects are the building blocks of your scene. There are a lot of different
types of objects supported by POV-Ray: finite solid primitives, finite patch
primitives, infinite solid polynomial primitives and light sources.
Constructive Solid Geometry (CSG) is also supported.
The basic syntax of an object is a keyword describing its type, some floats,
vectors or other parameters which further define its location and/or shape
and some optional object modifiers such as texture, pigment, normal, finish,
bounding, clipping or transformations.
The texture describes what the object looks like, i. e. its material.
Textures are combinations of pigments, normals, finishes and halos. Pigment
is the color or pattern of colors inherent in the material. Normal is a
method of simulating various patterns of bumps, dents, ripples or waves by
modifying the surface normal vector. Finish describes the reflective and
refractive properties of a material. The halo is used to describe the
interior of the object.
Bounding shapes are finite, invisible shapes which wrap around complex, slow
rendering shapes in order to speed up rendering time. Clipping shapes are
used to cut away parts of shapes to expose a hollow interior. Transformations
tell the ray-tracer how to move, size or rotate the shape and/or the texture
in the scene.
7.5.1 Empty and Solid Objects
It is very important that you know the basic concept behind empty and solid
objects in POV-Ray to fully understand how features like halos and
translucency are used.
Objects in POV-Ray can either be solid, empty or filled with (small)
particles.
A solid object is made from the material specified by its pigment and finish
statements (and to some degree its normal statement). By default all objects
are assumed to be solid. If you assign a stone texture to a sphere you'll get
a ball made completely of stone. It's like you had cut this ball from a block
of stone. A glass ball is a massive sphere made of glass.
You should be aware that solid objects are conceptual things. If you e. g.
clip away parts of the sphere you'll see that the sphere is empty, i. e.
you'll clearly see that the interior is empty and it just has a very thin
surface.
This is not contrary to the concept of a solid object used in POV-Ray. It is
assumed that all space inside the sphere is covered by the sphere's material.
Thus there is no room for any other particles like those used by fog or
halos.
Empty objects are created by adding the hollow keyword (see "Hollow" ) to the
object statement. An empty (or hollow) object is assumed to be made of a very
thin surface which is of the material specified by the pigment, finish and
normal statements. The object's interior is empty, i. e. it normally contains
air molecules.
An empty object can be filled with particles by adding fog or atmosphere to
the scene or by adding a halo to the object. It is very important to
understand that in order to fill an object with any kind of particles it
first has to be made hollow.
7.5.1.1 Halo Pitfall
There is a piftall in the current empty/solid object implementation that you
have to be aware of.
In order to be able to put solid objects inside a halo (this also holds for
fog and atmosphere) a test has to be made for every ray that passes through
the halo. If this ray travels through a solid object the halo will not be
calculated. This is what anyone will expect.
The problem arises when the camera ray is inside any non-hollow object. In
this case the ray is already travelling through a solid object and even if
the halo's container object is hit and it is hollow, the halo will not be
calculated. There is no way of telling between these two cases.
POV-Ray has to determine wether the camera is inside any object prior to
tracing a camera ray in order to be able to correctly render halos when the
camera is inside the container object. There's no way around doing this.
The solution to this problem (that will often happen with infinite objects
like planes) is to make those objects hollow too. Thus the ray will travel
through a hollow object, will hit the container object and the halo will be
calculated.
7.5.1.2 Refraction Pitfall
There is a pitfall in the way refractive (and non-refractive translucent)
objects are handled.
Imagine you want to create an object that's partially made of glass and
stone. You'd use something like the following merge because you don't want to
see any inside surfaces.
merge {
sphere { <-1,0,0>, 2 texture { Stone } }
sphere { <+1,0,0>, 2 texture { Glass } }
}
What's wrong with this, you may ask? The problem is that there is no way of
telling what the interior of the actual object will look like. This is not a
problem of POV-Ray, it's a general problem. You can't define the interior of
any object in a surface based model. You would have to create some (complex)
rules to decide what the interior will look like. Is it made of stone? Is it
made of glass? Is it made of some bizarre mixture between glass and stone? Is
it half stone and half glass? Where is the boundary between the two materials
and what does it look like?
You will not be able to answer any of the above questions by just looking at
the above object. You need more informations.
If you wanted to create an object made half of stone and half of glass you
would have used the following statements.
union {
intersection {
sphere { <-1,0,0>, 2 }
plane { x, 0 }
texture { Stone }
}
intersection {
sphere { <+1,0,0>, 2 }
plane { x, 0 inverse }
texture { Glass }
}
}
This example is correct because there is one object made only of stone and
one made only of glass.
You should never use objects whose interior is not well defined, i. e. there
must not be different textures for the object having different refractive
(and translucent) properties. You should be aware that this holds only for
the lowest layer if you use layered textures.
7.5.2 Finite Solid Primitives
There are twelve different solid finite primitive shapes: blob, box, cone,
cylinder, fractal, height field, lathe, sphere, superellipsoid, surface of
revolution, text object and torus. These have a well-defined inside and can
be used in CSG (see section "Constructive Solid Geometry" ). They are finite
and respond to automatic bounding. As with all shapes they can be translated,
rotated and scaled.
7.5.2.1 Blob
Blobs are an interesting and flexible object type. Mathematically they are
iso-surfaces of scalar fields, i. e. their surface is defined by the strength
of the field in each point. If this strength is equal to a threshold value
you're on the surface otherwise you're not.
Picture each blob component as an object floating in space. This object is
filled with a field that has its maximum at the center of the object and
drops off to zero at the object's surface. The field strength of all those
components are added together to form the field of the blob. Now POV-Ray
looks for points where this field has a given value, the threshold value. All
these points form the surface of the blob object. Points with a greater field
value than the threshold value are considered to be inside while points with
a smaller field value are outside.
There's another, simpler way of looking at blobs. They can be seen as a union
of flexible components that attract or repel each other to form a blobby
organic looking shape. The components' surfaces actually stretch out smoothly
and connect as if they were made of honey or something like that.
A blob is made up of spherical and cylindrical components and is defined as
follows:
blob {
threshold THRESHOLD_VALUE
cylinder { <END1>, <END2>, RADIUS, [ strength ] STRENGTH }
sphere { <CENTER>, RADIUS, [ strength ] STRENGTH }
[ component STRENGTH, RADIUS, <CENTER> ]
[ hierarchy FLAG ]
[ sturm ]
}
The threshold keyword determines the total field strength value that POV-Ray
is looking for. By following the ray out into space and looking at how each
blob component affects the ray, POV-Ray will find the points in space where
the field strength is equal to the threshold value. The following list shows
some things you should know about the threshold value.
1) The threshold value must be positive.
2) A component disappears if the threshold value is greater than its
strength.
3) As the threshold value gets larger the surface you see gets closer to
the centers of the components.
4) As the threshold value gets smaller, the surface you see gets closer to
the surface of the components.
Cylindrical components are specified by the keyword cylinder giving a
cylinder formed by the base <END1>, the apex <END2> and the radius. The
cylinder has hemispherical caps at the base and apex. Spherical components
are specified by the keyword sphere forming a sphere at <CENTER> with the
given radius. Each component can be individually translated, rotated, scaled
and textured. The complete syntax for the cylindrical and spherical
components is:
sphere { <CENTER>, RADIUS, [strength] STRENGTH
[ translate <VECTOR> ]
[ rotate <VECTOR> ]
[ scale <VECTOR> ]
TEXTURE_MODIFIERS
}
cylinder { <END1>, <END2>, RADIUS, [strength] STRENGTH
[ translate <VECTOR> ]
[ rotate <VECTOR> ]
[ scale <VECTOR> ]
TEXTURE_MODIFIERS
}
By unevenly scaling a spherical component you can create ellipsoidal
components. The component keyword gives a spherical component and is only
used for compatibility with earlier POV-Ray versions.
The strength parameter is a float value specifying the field strength at the
center of the object. The strength may be positive or negative. A positive
value will make that component attract other components while a negative
value will make it repel other components. Components in different, separate
blob shapes do not affect each other.
You should keep the following things in mind.
1) The strength value may be positive or negative. Zero is a bad value, as
the net result is that no field was added - you might just as well have
not used this component.
2) If strength is positive, then POV-Ray will add the component's field to
the space around the center of the component. If this adds enough field
strength to be greater than the "threshold" value you will see a
surface.
3) If the strength value is negative, then POV-Ray will subtract the
component's field from the space around the center of the component.
This will only do something if there happen to be positive components
nearby. What happens is that the surface around any nearby positive
components will be dented away from the center of the negative
component.
The components of each blob object are internally bounded by a spherical
bounding hierarchy to speed up blob intersection tests and other operations.
By using the optional keyword hierarchy you can switch this hierarchy off.
An example of a three component blob is:
blob {
threshold 0.6
sphere { <.75, 0, 0>, 1, 1 }
sphere { <-.375, .64952, 0>, 1, 1 }
sphere { <-.375, -.64952, 0>, 1, 1 }
scale 2
}
If you have a single blob component then the surface you see will just look
like the object used, i. e. a sphere or a cylinder, with the surface being
somewhere inside the surface specified for the component. The exact surface
location can be determined from the blob equation listed below (you will
probably never need to know this, blobs are more for visual appeal than for
exact modeling).
For the more mathematically minded, here's the formula used internally by
POV-Ray to create blobs. You don't need to understand this to use blobs. The
formula used for a single blob component is:
density = strength * (1 - radius^2)^2
This formula has the nice property that it is exactly equal to the strength
parameter at the center of the component and drops off to exactly 0 at a
distance from the center of the component that is equal to the radius value.
The density formula for more than one blob component is just the sum of the
individual component densities:
density = density1 + density2 + ...
The calculations for blobs must be very accurate. If this shape renders
improperly you may add the keyword sturm after the last component to use
POV-Ray's slower-yet-more-accurate Sturmian root solver.
7.5.2.2 Box
A simple box can be defined by listing two corners of the box like this:
box { <CORNER1>, <CORNER2> }
The geometry of a box.
Where <CORNER1> and <CORNER2> are vectors defining the x, y, z coordinates of
the opposite corners of the box.
Note that all boxes are defined with their faces parallel to the coordinate
axes. They may later be rotated to any orientation using the rotate keyword.
Each element of <CORNER1> should always be less than the corresponding
element in <CORNER2>. If any elements of <CORNER1> are larger than <CORNER2>
the box will not appear in the scene.
Boxes are calculated efficiently and make good bounding shapes (if manually
bounding seems to be necessary).
7.5.2.3 Cone
A finite length cone or a frustum (a cone with the point cut off) may be
defined by.
cone {
<BASE_POINT>, BASE_RADIUS, <CAP_POINT>, CAP_RADIUS
[ open ]
}
The geometry of a cone.
Where <BASE_POINT> and \langle CAP_POINT> are vectors defining the x, y, z
coordinates of the center of the cone's base and cap and BASE_RADIUS and
CAP_RADIUS are float values for the corresponding radii.
Normally the ends of a cone are closed by flat planes which are parallel to
each other and perpendicular to the length of the cone. Adding the optional
keyword open after CAP_RADIUS will remove the end caps and results in a
tapered hollow tube like a megaphone or funnel.
7.5.2.4 Cylinder
A finite length cylinder with parallel end caps may be defined by.
cylinder {
<BASE_POINT>, <CAP_POINT>, RADIUS
[ open ]
}
The geometry of a cylinder.
Where <BASE_POINT> and \langle CAP_POINT> are vectors defining the x, y, z
coordinates of the cylinder's base and cap and RADIUS is a float value for
the radius.
Normally the ends of a cylinder are closed by flat planes which are parallel
to each other and perpendicular to the length of the cylinder. Adding the
optional keyword open after the radius will remove the end caps and results
in a hollow tube.
7.5.2.5 Height Field
Height fields are fast, efficient objects that are generally used to create
mountains or other raised surfaces out of hundreds of triangles in a mesh.
The height field syntax is:
height_field {
FILE_TYPE "FILENAME"
[ hierarchy BOOL ]
[ smooth BOOL ]
[ water_level FLOAT ]
}
A height field is essentially a one unit wide by one unit long square with a
mountainous surface on top. The height of the mountain at each point is taken
from the color number or palette index of the pixels in a graphic image file.
The maximum height is one, which corresponds to the maximum possible color or
palette index value in the image file.
________ <- image index 255 (or 65535 for 16-bit images)
/ /|
+1y -- |
| | |
| | |+1z <- Image upper-right
| | /
0,0,0-- +1x
^
|____ Image lower-left
The size and orientation of an un-scaled height field.
The mesh of triangles corresponds directly to the pixels in the image file.
Each square formed by four neighboring pixels is divided into two triangles.
An image with a resolution of N*M pixels has (N-1)*(M-1) squares that are
divided into 2*(N-1)\times (M-1) triangles.
The resolution of the height field is influenced by two factors: the
resolution of the image and the resolution of the color/index values. The
size of the image determines the resolution in the x- and z-direction. A
larger image uses more triangles and looks smoother. The resolution of the
color/index value determines the resolution along the y-axis. A height field
made from an 8 bit image can have 256 different height levels while one made
from a 16 bit image can have up to 65536 different height levels. Thus the
second height field will look much smoother in the y-direction if the height
field is created appropriately.
The size/resolution of the image does not affect the size of the height
field. The un-scaled height field size will always be 1\times 1. Higher
resolution image files will create smaller triangles, not larger height
fields.
There are six or possibly seven types of files which can define a
heightfield, as follows:
height_field { gif "filename.gif" }
height_field { pgm "filename.pgm" }
height_field { png "filename.png" }
height_field { pot "filename.pot" }
height_field { ppm "filename.ppm" }
height_field { sys "filename.???" }
height_field { tga "filename.tga" }
The image file used to create a height field can be a GIF, TGA, POT, PNG,
PGM, PPM and possibly a system specific (e. g. Windows BMP or Macintosh Pict)
format file. The GIF, PNG, PGM and possibly system format files are the only
ones that can be created using a standard paint program. Though there are
paint programs for creating TGA image files they won't be of much use for
creating the special 16 bit TGA files used by POV-Ray (see below and
"HF_Gray_16" for more details).
In an image file like GIF that uses a color palette the color number is the
palette index at a given pixel. Use a paint program to look at the palette of
a GIF image. The first color is palette index zero, the second is index one,
the third is index two and so on. The last palette entry is index 255.
Portions of the image that use low palette entries will result in lower parts
of the height field. Portions of the image that use higher palette entries
will result in higher parts of the height field.
Height fields created from GIF files can only have 256 different height
levels because the maximum number of colors in a GIF file is 256.
The color of the palette entry does not affect the height of the pixel. Color
entry 0 could be red, blue, black or orange but the height of any pixel that
uses color entry 0 will always be 0. Color entry 255 could be indigo, hot
pink, white or sky blue but the height of any pixel that uses color entry 255
will always be 1.
You can create height field GIF images with a paint program or a fractal
program like Fractint . You can usually get Fractint from most of the same
sources as POV-Ray.
A POT file is essentially a GIF file with a 16 bit palette. The maximum
number of colors in a POT file is 65536. This means a POT height field can
have up to 65536 possible height values. This makes it possible to have much
smoother height fields. Note that the maximum height of the field is still 1
even though more intermediate values are possible.
At the time of this writing the only program that created POT files was a
freeware IBM-PC program called Fractint . POT files generated with this
fractal program create fantastic landscapes.
The TGA and PPM file formats may be used as a storage device for 16 bit
numbers rather than an image file. These formats use the red and green bytes
of each pixel to store the high and low bytes of a height value. These files
are as smooth as POT files but they must be generated with special
custom-made programs. Several programs can create TGA heightfields in the
format POV uses, such as gforge and Terrain Maker .
PNG format heightfields are usually stored in the form of a grayscale image
with black corresponding to lower and white to higher parts of the height
field. Because PNG files can store up to 16 bits in grayscale images they
will be as smooth as TGA and PPM images. Since they are grayscale images you
will be able to view them with a regular image viewer. gforge can create
16-bit heightfields in PNG format. Color PNG images will be used in the same
way as TGA and PPM images.
SYS format is a platform specific file format. See your platform specific
documentation for details.
An optional water_level parameter may be added after the file name. It
consists of the keyword water_level followed by a float value telling the
program to ignore parts of the height field below that value. The default
value is zero and legal values are between zero and one. For example
water_level .5 tells POV-Ray to only render the top half of the height field.
The other half is below the water and couldn't be seen anyway. This term
comes from the popular use of height fields to render landscapes. A height
field
would be used to create islands and another shape would be used to simulate
water around the islands. A large portion of the height field would be
obscured by the water so the water_level parameter was introduced to allow
the ray-tracer to ignore the unseen parts of the height field. water_level is
also used to cut away unwanted lower values in a height field. For example if
you have an image of a fractal on a solid colored background, where the
background color is palette entry 0, you can remove the background in the
height field by specifying, water_level .001 .
Normally height fields have a rough, jagged look because they are made of
lots of flat triangles. Adding the keyword smooth causes POV-Ray to modify
the surface normal vectors of the triangles in such a way that the lighting
and shading of the triangles will give a smooth look. This may allow you to
use a lower resolution file for your height field than would otherwise be
needed. However, smooth triangles will take longer to render.
In order to speed up the intersection tests an one-level bounding hierarchy
is available. By default it is always used but it can be switched off to
eventually improve the rendering speed for small height fields (i. e. low
resolution images).
7.5.2.6 Julia Fractal
A julia fractal object is a 3-D slice of a 4-D object created by generalizing
the process used to create the classic Julia sets. You can make a wide
variety of strange objects using julia_fractal , including some that look
like bizarre blobs of twisted taffy.
The julia_fractal syntax (with default values listed in comments) is:
julia_fractal {
4DJULIA_PARAMETER // default is <1,0,0,0>
[ quaternion | hypercomplex ] // default is quaternion
[ sqr | cube | exp |
reciprocal | sin | asin |
sinh | asinh | cos | acos |
cosh | acosh | tan | atan |
tanh | atanh | log | pwr(X,Y) ] // default is sqr
[ max_iteration MAX_ITERATION ] // default value 20
[ precision PRECISION ] // default value 20
[ slice 4DNORMAL, DISTANCE ] // default <0,0,0,1>,0
}
The 4-D vector 4DJULIA_PARAMETER is the classic Julia parameter p in the
iterated formula f(h) + p.
The julia fractal object is calculated by using an algorithm that determines
whether an arbitrary point h(0) in 4-D space is inside or outside the object.
The algorithm requires generating the sequence of vectors h(0), h(1), ... by
iterating the formula
h(n+1) = f(h(n)) + p (n = 0, 1, ..., max_iteration-1)
where p is the fixed 4-D vector parameter of the julia fractal and f() is one
of the functions sqr, cube, ... specified by the presence of the
corresponding keyword. The point h(0) that begins the sequence is considered
inside the julia fractal object if none of the vectors in the sequence
escapes a hypersphere of radius 4 about the origin before the iteration
number reaches the max_iteration value. As you increase max_iteration, some
points escape that did not previously escape, forming the julia fractal.
Depending on the JULIA_PARAMETER , the julia fractal object is not
necessarily connected; it may be scattered fractal dust . Using a low
max_iteration can fuse together the dust to make a solid object. A high
max_iteration is more accurate but slows rendering. Even though it is not
accurate, the solid shapes you get with a low_maximum iteration value can be
quite interesting.
Since the mathematical object described by this algorithm is four-dimensional
and POV-Ray renders three dimensional objects, there must be a way to reduce
the number of dimensions of the object from four dimensions to three. This is
accomplished by intersecting the 4-D fractal with a 3-D plane defined by the
slice field and then projecting the intersection to 3-D space. The slice
plane is the 3-D space that is perpendicular to NORMAL4D and is DISTANCE
units from the origin. Zero length NORMAL4D vectors or a NORMAL4D vector with
a zero fourth component are illegal.
You can get a good feel for the four dimensional nature of a julia fractal by
using POV-Ray's animation feature to vary a slice's DISTANCE parameter. You
can make the julia fractal appear from nothing, grow, then shrink to nothing
as DISTANCE changes, much as the cross section of a 3-D object changes as it
passes through a plane.
The precision parameter is a tolerance used in the determination of whether
points are inside or outside the fractal object. Larger values give more
accurate results but slower rendering. Use as low a value as you can without
visibly degrading the fractal object's appearance.
The presence of the keywords quaternion or hypercomplex determine which 4-D
algebra is used to calculate the fractal. Both are 4-D generalizations of the
complex numbers but neither satisfies all the field properties (all the
properties of real and complex numbers that many of us slept through in high
school). Quaternions have non-commutative multiplication and hypercomplex
numbers can fail to have a multiplicative inverse for some non-zero elements
(it has been proved that you cannot successfully generalize complex numbers
to four dimensions with all the field properties intact, so something has to
break). Both of these algebras were discovered in the 19th century. Of the
two, the quaternions are much better known, but one can argue that
hypercomplex numbers are more useful for our purposes, since complex valued
functions such as sin, cos, etc. can be generalized to work for hypercomplex
numbers in a uniform way.
For the mathematically curious, the algebraic properties of these two
algebras can be derived from the multiplication properties of the unit basis
vectors 1 = <1,0,0,0>, i=\langle 0,1,0,0>, j=<0,0,1,0> and k=\langle
0,0,0,1>. In both algebras 1 x = x 1 = x for any x (1 is the multiplicative
identity). The basis vectors 1 and i behave exactly like the familiar complex
numbers 1 and i in both algebras.
Quaternion basis vector multiplication rules:
ij = k; jk = i; ki = j
ji = -k; kj = -i; ik = -j
ii = jj = kk = -1; ijk = -1;
Hypercomplex basis vector multiplication rules:
ij = k; jk = -i; ki = -j
ji = k; kj = -i; ik = -j
ii = jj = kk = -1; ijk = 1;
A distance estimation calculation is used with the quaternion calculations to
speed them up. The proof that this distance estimation formula works does not
generalize from two to four dimensions but the formula seems to work well
anyway, the absence of proof notwithstanding!
The presence of one of the function keywords sqr , cube , etc. determines
which function is used for f(h) in the iteration formula h(n+1) = f(h(n)) +
p. Most of the function keywords work only if the hypercomplex keyword is
present. Only sqr and cube work with quaternions. The functions are all
familiar complex functions generalized to four dimensions.
Function Keyword Maps 4-D value h to:
================================================
sqr h*h
cube h*h*h
exp e raised to the power h
reciprocal 1/h
sin sine of h
asin arcsine of h
sinh hyperbolic sine of h
asinh inverse hyperbolic sine of h
cos cosine of h
acos arccosine of h
cosh hyperbolic cos of h
acosh inverse hyperbolic cosine of h
tan tangent of h
atan arctangent of h
tanh hyperbolic tangent of h
atanh inverse hyperbolic tangent of h
log natural logarithm of h
pwr(x,y) h raised to the complex power x+iy
A simple example of a julia fractal object is:
julia_fractal {
<-0.083,0.0,-0.83,-0.025>
quaternion
sqr
max_iteration 8
precision 15
}
The first renderings of julia fractals using quaternions were done by Alan
Norton and later by John Hart in the '80's. This new POV-Ray implementation
follows Fractint in pushing beyond what is known in the literature by using
hypercomplex numbers and by generalizing the iterating formula to use a
variety of transcendental functions instead of just the classic Mandelbrot
z^2 + c formula. With an extra two dimensions and eighteen functions to work
with, intrepid explorers should be able to locate some new fractal beasties
in hyperspace, so have at it!
7.5.2.7 Lathe
The lathe is an object generated from rotating a two-dimensional curve about
an axis. This curve is defined by a set of points which are connected by
linear, quadratic or cubic spline curves. The syntax is:
lathe {
[ linear_spline | quadratic_spline | cubic_spline ]
NUMBER_OF_POINTS,
<POINT_1>, <POINT_2>, ..., <POINT_n>
[ sturm ]
}
The parameter NUMBER_OF_POINTS determines how many two-dimensional points are
forming the curve. These points are connected by linear, quadratic or cubic
splines as specified by an optional keyword (the default is linear_spline ).
Since the curve is not automatically closed, i. e. the first and last points
are not automatically connected, you'll have to do this by your own if you
want a closed curve. The curve thus defined is rotated about the y-axis to
form the lathe object which is centered at the origin.
The following examples creates a simple lathe object that looks like a thick
cylinder, i. e. a cylinder with a thick wall:
lathe {
linear_spline
5,
<2, 0>, <3, 0>, <3, 5>, <2, 5>, <2, 0>
pigment {Red}
}
The cylinder has an inner radius of 2 and an outer radius of 3, giving a wall
width of 1. It's height is 5 and it's located at the origin pointing up, i.
e. the rotation axis is the y-axis. Note that the first and last point are
equal to get a closed curve.
The splines that are used by the lathe and prism objects are a little bit
difficult to understand. The basic concept of splines is to draw a curve
through a given set of points in a determined way. The linear spline is the
simplest spline because it's nothing more than connecting consecutive points
with a line. This means that the curve that is drawn between two points only
depends on those two points. No additional information is taken into account.
Quadratic and cubic splines are different in that they do not only take other
points into account when connecting two points but they also look smoother
and - in the case of the cubic spline - produce smoother transitions at each
point.
Quadratic splines are made of quadratic curves. Each of them connects two
consecutive points. Since those two points (call them second and third point)
aren't enough to describe a quadratic curve the predecessor of the third
point is taken into account when the curve is drawn. Mathematically the
relationship (their location on the 2-D plane) between the third and fourth
point determines the slope of the curve at the third point. The slope of the
curve at the second point is out of control. Thus quadratic splines look much
smoother than linear splines but the transitions at each point are generally
not smooth because the slopes on both sides of the point are different.
Cubic splines overcome the transition problem of quadratic splines because
they also take the first point into account when drawing the curve between
the second and third point. The slope at the second point is under control
now and allows a smooth transition at each point. Thus cubic splines produce
the most flexible and smooth curves.
You should note that the number of spline segments, i. e. curves between two
points, depends on the spline type used. For linear splines you get n-1
segments connecting the points P[i], i=1,...,n. A quadratic spline gives you
n-2 segments because the last point is only used for determining the slope as
explained above (thus you'll need at least three points to define a quadratic
spline). The same holds for cubic splines where you get n-3 segments with the
first and last point used only for slope calculations (thus needing at least
four points). If you want to get a closed quadratic and cubic spline with
smooth transitions at the end points you have to make sure that in the cubic
case P[n-1] = P[2] (to get a closed curve), P[n] = P[3] and P[n-2] = P[1] (to
smooth the transition). In the quadratic case P[n-1] = P[1] (to close the
curve) and P[n] = P[2]. %%% LATE-ONLY You should note that the number of
spline segments, i. e. curves between two points, depends on the spline type
used. For linear splines you get n-1 segments connecting the points P_i, i=1,
..., n. A quadratic spline gives you n-2 segments because the last point is
only used for determining the slope as explained above (thus you'll need at
least three points to define a quadratic spline). The same holds for cubic
splines where you get n-3 segments with the first and last point used only
for slope calculations (thus needing at least four points). If you want to
get a closed quadratic and cubic spline with smooth transitions at the end
points you have to make sure that in the cubic case P_ {n-1} = P_2 (to get a
closed curve), P_n = P_3 and P_ {n-2} = P_1 (to smooth the transition). In
the quadratic case P_ {n-1} = P_1 (to close the curve) and P_n = P_2 (for a
smooth transition). %%% END
The slower but more accurate Sturmian root solver may be used with the
quadratic spline lathe if the shape does not render properly. Since a
quadratic polynomal has to be solved for the linear spline lathe the Sturmian
root solver is not needed. In case of cubic splines the Sturmian root solver
is always used because a 6th order polynomal has to be solved.
7.5.2.8 Prism
The prism is an object generated from sweeping one or more two-dimensional,
closed curves along an axis. These curves are defined by a set of points
which are connected by linear, quadratic or cubic splines.
The syntax for the prism is:
prism {
[ linear_sweep | conic_sweep ]
[ linear_spline | quadratic_spline | cubic_spline ]
HEIGHT1,
HEIGHT2,
TOTAL_NUMBER_OF_POINTS,
<POINT_1>, <POINT_2>, ..., <POINT_n>
[ open ]
[ sturm ]
}
The prism object allows you to use any number of sub-prisms inside one prism
statement (they are of the same spline and sweep type). Wherever an even
number of sub-prisms overlaps a whole appears.
The syntax of the prism object depends on the type of spline curve used.
Below the syntax of the linear spline prism is given.
prism {
linear_spline
HEIGHT1,
HEIGHT2,
TOTAL_NUMBER_OF_POINTS,
<A_1>, <A_2>, ..., <A_na>, <A_1>,
<B_1>, <B_2>, ..., <B_nb>, <B_1>,
<C_1>, <C_2>, ..., <C_nc>, <C_1>,
...
}
Each of the sub-prisms has to be closed by repeating the first point of a
sub-prism at the end of the sub-prism's point sequence. If this is not the
case a warning is issued and the prism is ignored (with linear splines
automatic closing is used). This implies that all points of a prism are
different (except the first and last of course). This applies to all spline
types though the control points of the quadratic and cubic splines can be
arbitrarily chosen.
The last sub-prism of a linear spline prism is automatically closed - just
like the last sub-polygon in the polygon statement - if the first and last
point of the sub-polygon's point sequence are not the same. This make it very
easy to convert between polygons and prisms. Quadratic and cubic splines are
never automatically closed.
The syntax for quadratic spline prisms is:
prism {
quadratic_spline
HEIGHT1,
HEIGHT2,
TOTAL_NUMBER_OF_POINTS,
<CL_A>, <A_1>, <A_2>, ..., <A_na>, <A_1>,
<CL_B>, <B_1>, <B_2>, ..., <B_nb>, <B_1>,
<CL_C>, <C_1>, <C_2>, ..., <C_nc>, <C_1>,
...
}
Quadratic spline sub-prisms need an additional control point at the beginning
of each sub-prisms' point sequence to determine the slope at the start of the
curve.
Last but not least the syntax for the cubic spline prism.
prism {
cubic_spline
HEIGHT1,
HEIGHT2,
TOTAL_NUMBER_OF_POINTS,
<CL_A1>, <A_1>, <A_2>, ..., <A_na>, <A_1>, <CL_A2>,
<CL_B1>, <B_1>, <B_2>, ..., <B_nb>, <B_1>, <CL_B2>,
<CL_C1>, <C_1>, <C_2>, ..., <C_nc>, <C_1>, <CL_C2>,
...
}
In addition to the closed point sequence each cubic spline sub-prism needs
two control points to determine the slopes at the start and end of the curve.
The parameter TOTAL_NUMBER_OF_POINTS determines how many two-dimensional
points (lying in the x-z-plane) form the curves (this includes all control
points needed for quadratic and cubic splines). The curves are swept along
the y-axis from HEIGHT1 to HEIGHT2 to form the prism object. By default
linear sweeping is used to create the prism, i. e. the prism's walls are
perpendicular to the x-z-plane (the size of the curve does not change during
the sweep). You can also use conic sweeping / conic_sweep that leads to a
prism with cone-like walls by scaling the curve down during the sweep.
Like cylinders the prism is normally closed. You can remove the caps on the
prism by using the open keyword. If you do so you shouldn't use it with CSG
because the results may get wrong.
The following example creates a simple prism object that looks like a piece
of cake:
prism {
linear_sweep
linear_spline
0, 1,
4,
<-1, 0>, <1, 0>, <0, 5>, <-1, 0>
pigment {Red}
}
For an explanation of the spline concept read the description of the lathe
object.
The slower but more accurate Sturmian root solver may be used with the cubic
spline prisms if the shape does not render properly. The linear and quadratic
spline prisms do not need the Sturmian root solver.
7.5.2.9 Sphere
The syntax of the sphere object is:
sphere {
<CENTER>, RADIUS
}
The geometry of a sphere.
Where <CENTER> is a vector specifying the x, y, z coordinates of the center
of the sphere and RADIUS is a float value specifying the radius. Spheres may
be scaled unevenly giving an ellipsoid shape.
Because spheres are highly optimized they make good bounding shapes (if manal
bounding seems to be necessary).
7.5.2.10 Superquadric Ellipsoid
The superquadric ellipsoid is an extension of the quadric ellipsoid. It can
be used to create boxes and cylinders with round edges and other interesting
shapes. Mathematically it is given by the equation:
f(x, y, z) = (|x|^(2/e) + |y|^(2/e)) ^ (e/n) + |z|^(2/n) - 1 = 0
The values of e and n, called the east-west and north-south exponent,
determine the shape of the superquadric ellipsoid. Both have to be greater
than zero. The sphere is e. g. given by e = 1 and n = 1.
The syntax of the superquadric ellipsoid, which is located at the origin, is:
superellipsoid { <e, n> }
Two useful objects are the rounded box and the rounded cylinder. These are
declared in the following way.
#declare Rounded_Box = superellipsoid { <r, r> }
#declare Rounded_Cylinder = superellipsoid { <1, r> }
The roundedness r determines the roundedness of the edges and has to be
greater than zero and smaller than one. The smaller you choose the values of
r the smaller and sharper the edges will get.
Very small values of e and n might cause problems with the root solver (the
Sturmian root solver cannot be used).
7.5.2.11 Surface of Revolution
The surface of revolution (SOR) object is generated by rotating the graph of
a function about an axis. This function describes the dependence of the
radius from the position on the rotation axis. The syntax of the SOR object
is:
sor {
NUMBER_OF_POINTS,
<POINT0>, <POINT1>, ..., <POINTn-1>
[ open ]
[ sturm ]
}
The points <POINT0> through <POINTn-1> are two-dimensional vectors consisting
of the radius and the corresponding height, i. e. the position on the
rotation axis. These points are smoothly connected (the curve is passing
through the specified points) and rotated about the y-axis to form the SOR
object. The first and last points are only used to determine the slopes of
the function at the start and end point. The function used for the SOR object
is similar to the splines used for the lathe object. The difference is that
the SOR object is less flexible because it underlies the restrictions of any
mathematical function, i. e. to any given point y on the rotation axis
belongs at most one function value, i. e. one radius value. You can't rotate
closed curves with the SOR object.
The optional keyword open allows you to remove the caps on the SOR object. If
you do this you shouldn't use it with CSG anymore because the results may be
wrong.
The SOR object is useful for creating bottles, vases, and things like that. A
simple vase could look like this:
#declare Vase = sor {
7,
<0.000000, 0.000000>
<0.118143, 0.000000>
<0.620253, 0.540084>
<0.210970, 0.827004>
<0.194093, 0.962025>
<0.286920, 1.000000>
<0.468354, 1.033755>
open
}
One might ask why there is any need for a SOR object if there is already a
lathe object which is much more flexible. The reason is quite simple. The
intersection test with a SOR object involves solving a cubic polynomial while
the test with a lathe object requires to solve of a 6th order polynomial (you
need a cubic spline for the same smoothness ). Since most SOR and lathe
objects will have several segments this will make a great difference in
speed. The roots of the 3rd order polynomial will also be more accurate and
easier to find.
The slower but more accurate Sturmian root solver may be used with the
surface of revolution object if the shape does not render properly.
The following explanations are for the mathematically interested reader who
wants to know how the surface of revolution is calculated. Though it is not
necessary to read on it might help in understanding the SOR object.
The function that is rotated about the y-axis to get the final SOR object is
given by
r^2 = f(h) = A*h^3 + B*h^2 + C*h + D
%%% PHS-ONLY %%% %%% with radius r and height h. Since this is a cubic
function in h it %%% has enough flexibility to allow smooth curves. %%% %%%
The curve itself is defined by a set of n points P(i), i=0...n-1, %%% which
are interpolated using one function for every segment of %%% the curve. A
segment j, j=1...n-3, goes from point P(j) to %%% point P(j+1) and uses
points P(j-1) and P(j+2) to determine %%% the slopes at the endpoints. If
there are n points we will have %%% n-3 segments. This means that we need at
least four points to get a %%% proper curve. %%% %%% The coefficients A(j),
B(j), C(j) and D(j) are calculated for every %%% segment using the equation
%%% %%% %%% b = M * x, with
%%%
%%% / \
%%% | r(j)^2 |
%%% | |
%%% | r(j+1)^2 |
%%% b = | |
%%% | 2*r(j)*(r(j+1)-r(j-1))/(h(j+1)-h(j-1)) |
%%% | |
%%% | 2*r(j+1)*(r(j+2)-r(j))/(h(j+2)-h(j)) |
%%% /
%%%
%%% / \
%%% | h(j)^3 h(j)^2 h(j) 1 |
%%% | |
%%% | h(j+1)^3 h(j+1)^2 h(j+1) 1 |
%%% M = | |
%%% | 3*h(j)^2 2*h(j) 1 0 |
%%% | |
%%% | 3*h(j+1)^2 2*h(j+1) 1 0 |
%%% /
%%%
%%% / \
%%% | A(j) |
%%% | |
%%% | B(j) |
%%% x = | |
%%% | C(j) |
%%% | |
%%% | D(j) |
%%% /
%%% %%% %%% where r(j) is the radius and h(j) is the height of point P(j).
%%% %%% The figure below shows the configuration of the points P(i), the %%%
location of segment j, and the curve that is defined by this segment. %%% END
Segment j of n-3 segments in a point configuration of n points. The points
describe the curve of a surface of revolution.
7.5.2.12 Text
A text object creates 3-D text as an extruded block letter. Currently only
TrueType fonts are supported but the syntax allows for other font types to be
added in the future. The syntax is:
text {
ttf "FONTNAME.TTF",
"STRING_OF_TEXT",
THICKNESS_FLOAT, OFFSET_VECTOR
}
Where fontname.ttf is the name of the TrueType font file. It is a quoted
string literal or string expression. The string expression which follows is
the actual text of the string object. It too may be a quoted string literal
or string expression. See "Strings" for more on string expressions.
The text will start with the origin at the lower left, front of the first
character and will extend in the +x-direction. The baseline of the text
follows the x-axis and decenders drop into the -y-direction. The front of the
character sits in the x-y-plane and the text is extruded in the +z-direction.
The front-to-back thickness is specified by the required value
THICKNESS_FLOAT.
Characters are generally sized so that 1 unit of vertical spacing is correct.
The characters are about 0.5 to 0.75 units tall.
The horizontal spacing is handled by POV-Ray internally including any kerning
information stored in the font. The required vector OFFSET_VECTOR defines any
extra translation between each character. Normally you should specify a zero
for this value. Specifing 0.1*x would put additional 0.1 units of space
between each character.
Only printable characters are allowed in text objects. Characters such as
return, line feed, tabs, backspace etc. are not supported.
7.5.2.13 Torus
A torus is a 4th order quartic polynomial shape that looks like a donut or
inner tube. Because this shape is so useful and quartics are difficult to
define, POV-Ray lets you take a short-cut and define a torus by:
torus {
MAJOR, MINOR
[ sturm ]
}
where MAJOR is a float value giving the major radius and MINOR is a float
specifying the minor radius. The major radius extends from the center of the
hole to the mid-line of the rim while the minor radius is the radius of the
cross-section of the rim. The torus is centered at the origin and lies in the
x-z-plane with the y-axis sticking through the hole.
--- - - - - - - - -- +Y
/ / |
/ / |
| | | |<-B->| -X-|-+X
/ / |
__________/_ _ _ _ _ _ _ __________/ |
|<--A-->| -Y
A = Major Radius
B = Minor Radius
Major and minor radius of a torus.
The torus is internally bounded by two cylinders and two rings forming a
thick cylinder. With this bounding cylinder the performance of the torus
intersection test is vastly increased. The test for a valid torus
intersection, i. e. solving a 4th order polynomial, is only performed if the
bounding cylinder is hit. Thus a lot of slow root solving calculations are
avoided.
Calculations for all higher order polynomials must be very accurate. If the
torus renders improperly you may add the keyword sturm after the MINOR value
to use POV-Ray's slower-yet-more-accurate Sturmian root solver.
7.5.3 Finite Patch Primitives
There are six totally thin, finite objects which have no well-defined inside.
They are bicubic patch, disc, smooth triangle, triangle, polygon and mesh.
They may be combined in CSG union but cannot be use in other types of CSG (or
inside a clipped_by statement). Because these types are finite POV-Ray can
use automatic bounding on them to speed up rendering time. As with all shapes
they can be translated, rotated and scaled.
7.5.3.1 Bicubic Patch
{/TARGET 0 'bicubic patch'/} {bicubic patch} A bicubic patch is a 3D curved
surface created from a mesh of triangles. POV-Ray supports a type of bicubic
patch called a Bezier patch. A bicubic patch is defined as follows:
bicubic_patch {
type PATCH_TYPE
flatness FLATNESS_VALUE
u_steps NUM_U_STEPS
v_steps NUM_V_STEPS
<CP1>, <CP2>, <CP3>, <CP4>,
<CP5>, <CP6>, <CP7>, <CP8>,
<CP9>, <CP10>, <CP11>, <CP12>,
<CP13>, <CP14>, <CP15>, <CP16>
}
The keyword type is followed by a float PATCH_TYPE which currently must be
either 0 or 1. For type 0 only the control points are retained within
POV-Ray. This means that a minimal amount of memory is needed but POV-Ray
will need to perform many extra calculations when trying to render the patch.
Type 1 preprocesses the patch into many subpatches. This results in a
significant speedup in rendering at the cost of memory.
The four parameters type , flatness , u_steps and v_steps may appear in any
order. They are followed by 16 vectors that define the x, y, z coordinates of
the 16 control points which define the patch. The patch touches the four
corner points <CP1>, <CP4>, \langle CP13> and <CP16> while the other 12
points pull and stretch the patch into shape. The Bezier surface is enclosed
by the convex hull formed by the 16 control points, this is known as the
convex hull property .
The keywords u_steps and v_steps are each followed by float values which tell
how many rows and columns of triangles are the minimum to use to create the
surface. The maximum number of individual pieces of the patch that are tested
by POV-Ray can be calculated from the following:
sub-pieces = 2^u_steps * 2^v_steps
This means that you really should keep u_steps and v_steps under 4. Most
patches look just fine with u_steps 3 and v_steps 3 , which translates to 64
subpatches (128 smooth triangles).
As POV-Ray processes the Bezier patch it makes a test of the current piece of
the patch to see if it is flat enough to just pretend it is a rectangle. The
statement that controls this test is flatness . Typical flatness values range
from 0 to 1 (the lower the slower).
If the value for flatness is 0 POV-Ray will always subdivide the patch to the
extend specified by u_steps and v_steps . If flatness is greater than 0 then
every time the patch is split, POV-Ray will check to see if there is any need
to split further.
There are both advantages and disadvantages to using a non-zero flatness. The
advantages include:
- If the patch isn't very curved, then this will be detected and POV-Ray
won't waste a lot of time looking at the wrong pieces.
- If the patch is only highly curved in a couple of places, POV-Ray will
keep subdividing there and concentrate it's efforts on the hard part.
The biggest disadvantage is that if POV-Ray stops subdividing at a particular
level on one part of the patch and at a different level on an adjacent part
of the patch there is the potential for cracking . This is typically visible
as spots within the patch where you can see through. How bad this appears
depends very highly on the angle at which you are viewing the patch.
Like triangles, the bicubic patch is not meant to be generated by hand. These
shapes should be created by a special utility. You may be able to acquire
utilities to generate these shapes from the same source from which you
obtained POV-Ray.
bicubic_patch {
type 1
flatness 0.01
u_steps 4
v_steps 4
<0, 0, 2>, <1, 0, 0>, <2, 0, 0>, <3, 0,-2>,
<0, 1 0>, <1, 1, 0>, <2, 1, 0>, <3, 1, 0>,
<0, 2, 0>, <1, 2, 0>, <2, 2, 0>, <3, 2, 0>,
<0, 3, 2>, <1, 3, 0>, <2, 3, 0>, <3, 3, -2>
}
The triangles in a POV-Ray bicubic_patch are automatically smoothed using
normal interpolation but it is up to the user (or the user's utility program)
to create control points which smoothly stitch together groups of patches.
7.5.3.2 Disc
One other flat, finite object available with POV-Ray is the disc. The disc is
infinitely thin, it has no thickness. If you want a disc with true thickness
you should use a very short cylinder. A disc shape may be defined by:
disc {
<CENTER>, <NORMAL>, RADIUS [, HOLE_RADIUS ]
}
The vector <CENTER> defines the x, y, z coordinates of the center of the
disc. The \langle NORMAL> vector describes its orientation by describing its
surface normal vector. This is followed by a float specifying the RADIUS.
This may be optionally followed by another float specifying the radius of a
hole to be cut from the center of the disc.
7.5.3.3 Mesh
The mesh object can be used to efficiently store large numbers of triangles.
Its syntax is:
mesh {
triangle {
<CORNER1>, <CORNER2>, <CORNER3>
[ texture { STRING } ]
}
smooth_triangle {
<CORNER1>, <NORMAL1>,
<CORNER2>, <NORMAL2>,
<CORNER3>, <NORMAL3>
[ texture { STRING } ]
}
[ hierarchy FLAG ]
}
Any number of triangles and/or smooth triangles can be used and each of those
triangles can be individually textured by assigning a texture name to it. The
texture has to be declared before the mesh is parsed. It is not possible to
use texture definitions inside the triangle or smooth triangle statements.
This is a restriction that is necessary for an efficient storage of the
assigned textures.
The mesh's components are internally bounded by a bounding box hierarchy to
speed up intersection testing. The bounding hierarchy can be turned off with
the hierarchy keyword. This should only be done if memory is short or the
mesh consists of only a few triangles.
Copies of a mesh object refer to the same triangle data and thus consume very
little memory. You can easily trace hundred copies of an 10000 triangle mesh
without running out of memory (assuming the first mesh fits into memory).
The mesh object has two advantages over a union of triangles: it needs less
memory and it is transformed faster. The memory requierements are reduced by
efficiently storing the triangles vertices and normals. The parsing time for
transformed meshes is reduced because only the mesh object has to be
transformed and not every single triangle as it is necessary for unions.
The mesh object can currently only include triangle and smooth triangle
components. That restriction is liable to change, allowing polygonal
components, at some point in the future.
7.5.3.4 Polygon
Polygons are useful for creating rectangles, squares and other planar shapes
with more than three edges. Their syntax is:
polygon {
TOTAL_NUMBER_OF_POINTS,
<A_1>, <A_2>, ..., <A_na>, <A_1>,
<B_1>, <B_2>, ..., <B_nb>, <B_1>,
<C_1>, <C_2>, ..., <C_nc>, <C_1>,
...
}
The points <A_1> through <A_na> describe the first sub-polygon, the points
<B_1> through <B_nb> describe the second sub-polygon, and so on. A polygon
can contain any number of sub-polygons, either overlapping or not. In places
where an even number of polygons overlaps a whole appears. You only have to
be sure that each of these polygons is closed. This is insured by repeating
the first point of a sub-polygon at the end of the sub-polygon's point
sequence. This implies that all points of a sub-polygon are different.
If the (last) sub-polygon is not closed a warning is issued and the program
automatically closes the polygon. This is useful because polygons imported
from other programs may not be closed, i. e. their first and last point are
not the same.
All points of a polygon are three-dimensional vectors that have to lay on one
plane. If this is not the case an error occurs. You can also use
two-dimensional vectors to describe the polygon. POV-Ray assumes that the z
value is zero in this case.
A square polygon that matches the default planar imagemap is simply:
polygon {
4,
<0, 0>, <0, 1>, <1, 1>, <1, 0>
texture {
finish { ambient 1 diffuse 0 }
pigment { image_map { gif "test.gif" } }
}
//scale and rotate as needed here
}
The sub-polygon feature can be used to generate complex shapes like the
letter "P", where a whole is cut into another polygon:
#declare P = polygon {
12,
<0, 0>, <0, 6>, <4, 6>, <4, 3>, <1, 3>, <1, 0>, <0, 0>,
<1, 4>, <1, 5>, <3, 5>, <3, 4>, <1, 4>
}
The first sub-polygon (on the first line) describes the outer shape of the
letter "P". The second sub-polygon (on the second line) describes the
rectangular hole that is cut in the top of the letter "P". Both rectangles
are closed, i. e. their first and last points are the same.
The feature of cutting holes into a polygon is based on the polygon
inside/outside test used. A point is considerd to be inside a polygon if a
straight line drawn from this point in an arbitrary direction crosses an odd
number of edges (this is known as Jordan's curve theorem ).
Another very complex example showing one large triangle with three small
holes and three seperate, small triangles is given below:
polygon {
28,
<0, 0> <1, 0> <0, 1> <0, 0> // large outer triangle
<.3, .7> <.4, .7> <.3, .8> <.3, .7> // small outer triangle #1
<.5, .5> <.6, .5> <.5, .6> <.5, .5> // small outer triangle #2
<.7, .3> <.8, .3> <.7, .4> <.7, .3> // small outer triangle #3
<.5, .2> <.6, .2> <.5, .3> <.5, .2> // inner triangle #1
<.2, .5> <.3, .5> <.2, .6> <.2, .5> // inner triangle #2
<.1, .1> <.2, .1> <.1, .2> <.1, .1> // inner triangle #3
}
7.5.3.5 Triangle and Smooth Triangle
The triangle primitive is available in order to make more complex objects
than the built-in shapes will permit. Triangles are usually not created by
hand but are converted from other files or generated by utilities. A triangle
is defined by
triangle {
<CORNER1>, <CORNER2>, <CORNER3>
}
where <CORNERn> is a vector defining the x, y, z coordinates of each corner
of the triangle.
Because triangles are perfectly flat surfaces it would require extremely
large numbers of very small triangles to approximate a smooth, curved
surface. However much of our perception of smooth surfaces is dependent upon
the way light and shading is done. By artificially modifying the surface
normals we can simulate as smooth surface and hide the sharp-edged seams
between individual triangles.
The smooth triangle primitive is used for just such purposes. The smooth
triangles use a formula called Phong normal interpolation to calculate the
surface normal for any point on the triangle based on normal vectors which
you define for the three corners. This makes the triangle appear to be a
smooth curved surface. A smooth triangle is defined by
smooth_triangle {
<CORNER1>, <NORMAL1>,
<CORNER2>, <NORMAL2>,
<CORNER3>, <NORMAL3>
}
where the corners are defined as in regular triangles and \langle NORMALn> is
a vector describing the direction of the surface normal at each corner.
These normal vectors are prohibitively difficult to compute by hand.
Therefore smooth triangles are almost always generated by utility programs.
To achieve smooth results, any triangles which share a common vertex should
have the same normal vector at that vertex. Generally the smoothed normal
should be the average of all the actual normals of the triangles which share
that point.
7.5.4 Infinite Solid Primitives
There are five polynomial primitive shapes that are possibly infinite and do
not respond to automatic bounding. They are plane, cubic, poly, quadric and
quartic. They do have a well defined inside and may be used in CSG and inside
a clipped_by statement. As with all shapes they can be translated, rotated
and scaled..
7.5.4.1 Plane
The plane primitive is a simple way to define an infinite flat surface. The
plane is specified as follows:
plane { <NORMAL>, DISTANCE }
The <NORMAL> vector defines the surface normal of the plane. A surface normal
is a vector which points up from the surface at a 90 degree angle. This is
followed by a float value that gives the distance along the normal that the
plane is from the origin (that is only true if the normal vector has unit
length; see below). For example:
plane { <0, 1, 0>, 4 }
This is a plane where straight up is defined in the positive y-direction. The
plane is 4 units in that direction away from the origin. Because most planes
are defined with surface normals in the direction of an axis you will often
see planes defined using the x , y or z built-in vector identifiers. The
example above could be specified as:
plane { y, 4 }
The plane extends infinitely in the x- and z-directions. It effectively
divides the world into two pieces. By definition the normal vector points to
the outside of the plane while any points away from the vector are defined as
inside. This inside/outside distinction is only important when using planes
in CSG and clipped_by .
A plane is called a polynomial shape because it is defined by a first order
polynomial equation. Given a plane:
plane { <A, B, C>, D }
it can be represented by the equation
A*x + B*y + C*z - D*sqrt(A^2 + B^2 + C^2) = 0.
Therefore our example plane {y,4 } is actually the polynomial equation y=4.
You can think of this as a set of all x, y, z points where all have y values
equal to 4, regardless of the x or z values.
This equation is a first order polynomial because each term contains only
single powers of x, y or z. A second order equation has terms like x^2, y^2,
z^2, xy, xz and yz. Another name for a 2nd order equation is a quadric
equation. Third order polys are called cubics. A 4th order equation is a
quartic. Such shapes are described in the sections below.
7.5.4.2 Poly, Cubic and Quartic
Higher order polynomial surfaces may be defined by the use of a poly shape.
The syntax is
poly { ORDER, <T1, T2, T3, .... Tm> }
where ORDER is a whole number from 2 to 7 inclusively that specifies the
order of the equation. T1, T2, ... Tm are float values for the coefficients
of the equation. There are m such terms where
m = ((ORDER+1)*(ORDER+2)*(ORDER+3))/6.
An alternate way to specify 3rd order polys is:
cubic { <T1, T2,... T20> }
Also 4th order equations may be specified with:
quartic { <T1, T2,... T35> }
Here's a more mathematical description of quartics for those who are
interested. Quartic surfaces are 4th order surfaces and can be used to
describe a large class of shapes including the torus, the lemniscate, etc.
The general equation for a quartic equation in three variables is (hold onto
your hat):
a00 x^4 + a01 x^3 y + a02 x^3 z+ a03 x^3 + a04 x^2 y^2+
a05 x^2 y z+ a06 x^2 y + a07 x^2 z^2+a08 x^2 z+a09 x^2+
a10 x y^3+a11 x y^2 z+ a12 x y^2+a13 x y z^2+a14 x y z+
a15 x y + a16 x z^3 + a17 x z^2 + a18 x z + a19 x+
a20 y^4 + a21 y^3 z + a22 y^3+ a23 y^2 z^2 +a24 y^2 z+
a25 y^2 + a26 y z^3 + a27 y z^2 + a28 y z + a29 y+
a30 z^4 + a31 z^3 + a32 z^2 + a33 z + a34 = 0
To declare a quartic surface requires that each of the coefficients (a0 ...
a34) be placed in order into a single long vector of 35 terms.
As an example let's define a torus the hard way. A Torus can be represented
by the equation:
x^4 + y^4 + z^4 + 2 x^2 y^2 + 2 x^2 z^2 + 2 y^2 z^2 -
2 (r_0^2 + r_1^2) x^2 + 2 (r_0^2 - r_1^2) y^2 -
2 (r_0^2 + r_1^2) z^2 + (r_0^2 - r_1^2)^2 = 0
Where r_0 is the major radius of the torus, the distance from the hole of the
donut to the middle of the ring of the donut, and r_1 is the minor radius of
the torus, the distance from the middle of the ring of the donut to the outer
surface. The following object declaration is for a torus having major radius
6.3 minor radius 3.5 (Making the maximum width just under 20).
// Torus having major radius sqrt(40), minor radius sqrt(12)
quartic {
< 1, 0, 0, 0, 2, 0, 0, 2, 0,
-104, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 1, 0, 0, 2, 0, 56, 0,
0, 0, 0, 1, 0, -104, 0, 784 >
sturm
bounded_by { // bounded_by speeds up the render,
// see bounded_by
// explanation later
// in docs for more info.
sphere { <0, 0, 0>, 10 }
}
}
Poly, cubic and quartics are just like quadrics in that you don't have to
understand what one is to use one. The file shapesq.inc has plenty of
pre-defined quartics for you to play with. The syntax for using a pre-defined
quartic is:
object { Quartic_Name }
Polys use highly complex computations and will not always render perfectly.
If the surface is not smooth, has dropouts, or extra random pixels, try using
the optional keyword sturm in the definition. This will cause a slower but
more accurate calculation method to be used. Usually, but not always, this
will solve the problem. If sturm doesn't work, try rotating or translating
the shape by some small amount. See the sub-directory math in the scene files
directory for examples of polys in scenes.
There are really so many different quartic shapes, we can't even begin to
list or describe them all. If you are interested and mathematically inclined,
an excellent reference book for curves and surfaces where you'll find more
quartic shape formulas is:
"The CRC Handbook of Mathematical Curves and Surfaces"
David von Seggern
CRC Press, 1990
7.5.4.3 Quadric
Quadric surfaces can produce shapes like ellipsoids, spheres, cones,
cylinders, paraboloids (dish shapes) and hyperboloids (saddle or hourglass
shapes). Note that you do not confuse quaDRic with quaRTic . A quadric is a
2nd order polynomial while a quartic is 4th order. Quadrics render much
faster and are less error-prone.
A quadric is defined in POV-Ray by
quadric { <A,B,C>, <D,E,F>, <G,H,I>, J }
where A through J are float expressions that define a surface of x, y, z
points which satisfy the equation
A x^2 + B y^2 + C z^2 +
D xy + E xz + F yz +
G x + H y + I z + J = 0
Different values of A, B, C, ... J will give different shapes. If you take
any three dimensional point and use its x, y and z coordinates in the above
equation the answer will be 0 if the point is on the surface of the object.
The answer will be negative if the point is inside the object and positive if
the point is outside the object. Here are some examples:
X^2 + Y^2 + Z^2 - 1 = 0 Sphere
X^2 + Y^2 - 1 = 0 Infinite cylinder along the Z axis
X^2 + Y^2 - Z^2 = 0 Infinite cone along the Z axis
The easiest way to use these shapes is to include the standard file
shapes.inc into your program. It contains several pre-defined quadrics and
you can transform these pre-defined shapes (using translate, rotate and
scale) into the ones you want. You can invoke them by using the syntax:
object { Quadric_Name }
The pre-defined quadrics are centered about the origin \langle 0,0,0> and
have a radius of 1. Don't confuse radius with width. The radius is half the
diameter or width making the standard quadrics 2 units wide.
Some of the pre-defined quadrics are,
Ellipsoid
Cylinder_X, Cylinder_Y, Cylinder_Z
QCone_X, QCone_Y, QCone_Z
Paraboloid_X, Paraboloid_Y, Paraboloid_Z
7.5.5 Constructive Solid Geometry
POV-Ray supports Constructive Solid Geometry (CSG) with five different
operations: difference, intersection, merge, union and negation (inversion).
While the first four operations represent binary operators, i. e. they need
two arguments, the negation is a unary operator, it takes only one argument.
7.5.5.1 About CSG
Constructive Solid Geometry is a technique for combining two or more objects
to create a new object using the three boolean set operators union ,
intersection , and negation . It only works with solid objects, i. e. objects
that have a well-defined interior. This is the case for all objects described
in the sections "Finite Solid Primitives" and "Infinite Solid Primitives" .
CSG shapes may be used anywhere a standard shape can be used, even inside
other CSG shapes. They can be translated, rotated or scaled in the same way
as any other shape. The shapes making up the CSG shape may be individually
translated, rotated and scaled as well.
7.5.5.2 Inside and Outside
Most shape primitives, like spheres, boxes and blobs divide the world into
two regions. One region is inside the object and one is outside.
Given any point in space you can say it's either inside or outside any
particular primitive object. Well, it could be exactly on the surface but
this case is rather hard to determine due to numerical problems.
Even planes have an inside and an outside. By definition, the surface normal
of the plane points towards the outside of the plane. You should note that
triangles and triangle-based shapes cannot be used as solid objects in CSG
since they have no well defined inside and outside.
CSG uses the concepts of inside and outside to combine shapes together as
explained in the following sections.
Imagine you have to objects that partially overlap like shown in the figure
below. Four different areas of points can be distinguished: points that are
neither in object A nor in object B, points that are in object A but not in
object B, points that are not in object A but in object B and last not least
points that are in object A and object B.
* = Object A
% = Object B
*
* * %
* * % %
* *% %
* %* %
* % * %
* % * %
*******%******* %
% %
%%%%%%%%%%%%%%%%%
Two overlapping objects.
Keeping this in mind it will be quite easy to understand how the CSG
operations work.
7.5.5.3 Inverse
When using CSG it is often useful to invert an object so that it'll be
inside-out. The appearance of the object is not changed, just the way that
POV-Ray perceives it. When the inverse keyword is used the inside of the
shape is flipped to become the outside and vice versa.
Note that the difference operation is performed by intersecting the first
object with the negation of the second object.
7.5.5.4 Union
*
* * %
* * % %
* *% %
* %* %
* % * %
* % * %
*******%******* %
% %
%%%%%%%%%%%%%%%%%
The union of two objects.
Unions are simply glue used to bind two or more shapes into a single entity
that can be manipulated as a single object. The image above shows the union
of A and B. The new object created by the union operation can be scaled,
translated and rotated as a single shape. The entire union can share a single
texture but each object contained in the union may also have its own texture,
which will override any matching texture statements in the parent object.
You should be aware that the surfaces inside the union will not be removed.
As you can see from the figure this may be a problem for transparent unions.
If you want those surfaces to be removed you'll have to use the merge
operations explained in a later section.
The following union will contain a box and a sphere.
union {
box { <-1.5, -1, -1>, <0.5, 1, 1> }
cylinder { <0.5, 0, -1>, <0.5, 0, 1>, 1 }
}
Earlier versions of POV-Ray placed restrictions on unions so you often had to
combine objects with composite statements. Those earlier restrictions have
been lifted so composite is no longer needed. Composite is still supported
for backwards compatibility but it is recommended that union is now used in
it's place since future support for the composite keyword is not guaranteed.
7.5.5.5 Intersection
A point is inside an intersection if it is inside both objects, A and B, as
show in the figure below.
%*
% *
% *
%*******
The intersection between two objects.
For example:
intersection {
box { <-1.5, -1, -1>, <0.5, 1, 1> }
cylinder { <0.5, 0, -1>, <0.5, 0, 1>, 1 }
}
7.5.5.6 Difference
The CSG difference operation takes the intersection between the first object
and the negation of the second object. Thus only points inside object A and
outside object B belong to the difference of both objects.
The results is a subtraction of the 2nd shape from the first shape as shown
in the figure below.
*
* *
* *
* *
* 1 %
* %
* %
*******%
The difference between two objects.
For example:
difference {
box { <-1.5, -1, -1>, <0.5, 1, 1> }
cylinder { <0.5, 0, -1>, <0.5, 0, 1>, 1 }
}
7.5.5.7 Merge
The union operation just glues objects together, it does not remove the
objects' surfaces inside the union. If a transparent union is used those
surface will get visible.
The merge operations can be used to avoid this problem. It works just like
union but it eliminates the inner surfaces like shown in the figure below.
*
* * %
* * % %
* *% %
* %
* %
* %
*******% %
% %
%%%%%%%%%%%%%%%%%
Merge removes inner surfaces.
7.5.6 Light Sources
The last object covered is the light source. Light sources have no visible
shape of their own. They are just points or areas which emit light. Their
full syntax is:
light_source {
<LOCATION>
color <COLOUR>
[ spotlight ]
[ point_at <POINT_AT> ]
[ radius RADIUS ]
[ falloff FALLOFF ]
[ tightness TIGHTNESS ]
[ area_light <AXIS1>, <AXIS2>, SIZE1, SIZE2 ]
[ adaptive ADAPTIVE ]
[ jitter JITTER ]
[ looks_like { OBJECT } ]
[ fade_distance FADE_DISTANCE ]
[ fade_power FADE_POWER ]
[ atmospheric_attenuation BOOL ]
}
The different types of light sources and the optional modifiers are described
in the following sections.
7.5.6.1 Point Lights
A point light source sends light of the specified color uniformly in all
directions. Its location is described by the location keyword and its color
is given by the color keyword. The complete syntax is:
light_source {
<LOCATION>
color <COLOUR>
[ looks_like { OBJECT } ]
[ fade_distance FADE_DISTANCE ]
[ fade_power FADE_POWER ]
[ atmospheric_attenuation BOOL ]
}
7.5.6.2 Spotlights
A spotlight is a point light source where the rays of light are constrained
by a cone. The light is bright in the center of this cone and falls off or
darkens at the edges of the cone. The syntax is:
light_source {
<LOCATION>
color <COLOUR>
spotlight
point_at <POINT_AT>
radius RADIUS
falloff FALLOFF
tightness TIGHTNESS
[ looks_like { OBJECT } ]
[ fade_distance FADE_DISTANCE ]
[ fade_power FADE_POWER ]
[ atmospheric_attenuation BOOL ]
}
The spotlight is identified by the spotlight keyword. It is located at
LOCATION and points at POINT_AT. The following illustration will be helpful
in understanding how these values relate to each other.
(+) location
/ \
/ \
/ \
/ \
/ \
/ \
+--*--+
^ point_at
The geometry of a spotlight.
The spotlight's other parameters are radius , falloff and tightness .
Think of a spotlight as two nested cones as shown in the figure. The inner
cone is specified by the radius parameter and is fully lit. The outer cone is
the falloff cone beyond which there is no light. The values for these two
parameters are half the opening angles of the corresponding cones, both
angles have to be smaller than 90 degrees. The light smoothly falls off
between the radius and the falloff angle like shown in the figures below (as
long as the radius angle is not negative).
Intensity multiplier curve with a fixed falloff angle of 45 degrees.
Intensity multiplier curve with a fixed radius angle of 45 degrees.
The tightness value specifies how quickly the light dims, or falls off, from
the spotlight's center line to the the falloff cone (full darkness outside).
The default value for tightness is 10. Lower tightness values will make the
spotlight brighter, making the spot wider and the edges sharper. Higher
values will dim the spotlight, making the spot tighter and the edges softer.
Values from 1 to 100 are acceptable.
Intensity multiplier curve with fixed angle and falloff angles of 30 and 60
degrees respectively and different thightness values.
You should note from the figures that the radius and falloff angles interact
with the tightness parameter. Only negative radius angles will give the
tightness value full control over the spotlight's appearance as you can see
from the figure below. In that case the falloff angle has no effect and the
lit area is only determined by the tightness parameter.
Intensity multiplier curve with a negative radius angle and different
tightness values.
Spotlights may be used anyplace that a normal light source is used. Like any
light sources, they are invisible. They are treated as shapes and may be
included in CSG shapes. They may also be used in conjunction with area
lights.
7.5.6.3 Cylindrical Lights
Cylindrical light sources work pretty much like spotlights except that the
light rays are constraint by a cylinder and not a cone. The syntax is:
light_source {
<LOCATION>
color <COLOUR>
cylinder
point_at <POINT_AT>
radius RADIUS
falloff FALLOFF
tightness TIGHTNESS
[ looks_like { OBJECT } ]
[ fade_distance FADE_DISTANCE ]
[ fade_power FADE_POWER ]
[ atmospheric_attenuation BOOL ]
}
The radius , falloff and tightness keywords control the same features as with
the spotlight.
You should keep in mind that the cylindrical light source is still a point
light source. The rays are emitted from one point and are only constraint by
a cylinder. The light rays are not parallel.
7.5.6.4 Area Lights
Area light sources occupy a finite, one- or two-dimensional area of space.
They can cast soft shadows because they can partially block light.
The area lights used in POV-Ray are rectangular in shape, sort of like a flat
panel light. Rather than performing the complex calculations that would be
required to model a true area light, it is approximated as an array of point
light sources spread out over the area occupied by the light. The intensity
of each individual point light in the array is dimmed so that the total
amount of light emitted by the light is equal to the light color specified in
the declaration. The syntax is:
light_source {
<LOCATION>
color <COLOUR>
area_light <AXIS1>, <AXIS2>, SIZE1, SIZE2
adaptive ADAPTIVE
jitter JITTER
[ spotlight ]
[ point_at <POINT_AT> ]
[ radius RADIUS ]
[ falloff FALLOFF ]
[ tightness TIGHTNESS ]
[ looks_like { OBJECT } ]
[ fade_distance FADE_DISTANCE ]
[ fade_power FADE_POWER ]
[ atmosphere BOOL ]
[ atmospheric_attenuation BOOL ]
}
The light's location and color are specified in the same way as a for a
regular light source.
The area_light command defines the size and orientation of the area light as
well as the number of lights in the light source array. The vectors AXIS1 and
AXIS2 specify the lengths and directions of the edges of the light. Since the
area lights are rectangular in shape these vectors should be perpendicular to
each other. The larger the size of the light the thicker the soft part of
shadows will be. The numbers SIZE1 and SIZE2 specify the dimensions of the
array of point lights. The more lights you use the smoother your shadows will
be but the longer they will take to render.
The jitter command is optional. When used it causes the positions of the
point lights in the array to be randomly jittered to eliminate any shadow
banding that may occur. The jittering is completely random from render to
render and should not be used when generating animations.
Note that it is possible to specify spotlight parameters along with the area
light parameters to create area spotlights . Using area spotlights is a good
way to speed up scenes that use area lights since you can confine the lengthy
soft shadow calculations to only the parts of your scene that need them.
An interesting effect can be created using a linear light source. Rather than
having a rectangular shape, a linear light stretches along a line sort of
like a thin fluorescent tube. To create a linear light just create an area
light with one of the array dimensions set to 1.
The adaptive command is used to enable adaptive sampling of the light source.
By default POV-Ray calculates the amount of light that reaches a surface from
an area light by shooting a test ray at every point light within the array.
As you can imagine this is very slow. Adaptive sampling on the other hand
attempts to approximate the same calculation by using a minimum number of
test rays. The number specified after the keyword controls how much adaptive
sampling is used. The higher the number the more accurate your shadows will
be but the longer they will take to render. If you're not sure what value to
use a good starting point is adaptive 1 . The adaptive keyword only accepts
integer values and cannot be set lower than 0.
When performing adaptive sampling POV-Ray starts by shooting a test ray at
each of the four corners of the area light. If the amount of light received
from all four corners is approximately the same then the area light is
assumed to be either fully in view or fully blocked. The light intensity is
then calculated as the average intensity of the light received from the four
corners. However, if the light intensity from the four corners differs
significantly then the area light is partially blocked. The area light is
split into four quarters and each section is sampled as described above. This
allows POV-Ray to rapidly approximate how much of the area light is in view
without having to shoot a test ray at every light in the array. Visually the
sampling goes like shown below.
level 0 1 2 3
rays 4 9 25 81
* . . . * x . * . x x * x * x
. . . . . . . . . . * * * * *
. . . . . * . * . * x * x * x etc...
. . . . . . . . . . * * * * *
* . . . * x . * . x x * x * x
* new samples
x reused samples from previous level
Area light adaptive samples.
While the adaptive sampling method is fast (relatively speaking) it can
sometimes produces inaccurate shadows. The solution is to reduce the amount
of adaptive sampling without completely turning it off. The number after the
adaptive keyword adjusts the number of times that the area light will be
split before the adaptive phase begins. For example if you use adaptive 0 a
minimum of 4 rays will be shot at the light. If you use adaptive 1 a minimum
of 9 rays will be shot ( adaptive 2 gives 25 rays, adaptive 3 gives 81 rays,
etc). Obviously the more shadow rays you shoot the slower the rendering will
be so you should use the lowest value that gives acceptable results.
The number of rays never exceeds the values you specify for rows and columns
of points. For example area_light x,y,4,4 specifies a 4 by 4 array of lights.
If you specify adaptive 3 it would mean that you should start with a 9 by 9
array. In this case no adaptive sampling is done. The 4 by 4 array is used.
7.5.6.5 Shadowless Lights
Using the shadowless keyword you can stop a light source from casting
shadows.
7.5.6.6 Looks_like
Normally the light source itself has no visible shape. The light simply
radiates from an invisible point or area. You may give a light source any
shape by adding a looks_like {OBJECT } statement.
There is an implied no_shadow attached to the looks_like object so that light
is not blocked by the object. Without the automatic no_shadow the light
inside the object would not escape. The object would, in effect, cast a
shadow over everything.
If you want the attached object to block light then you should attach it with
a union and not a looks_like as follows:
union {
light_source { <100, 200, -300> color White }
object { My_Lamp_Shape }
}
7.5.6.7 Light Fading
By default POV-Ray does not diminish light from any light source as it
travels through space. In order to get a more realistic effect fade_distance
and fade_power can be used to model the distance based falloff in light
intensity.
The fade_distance keyword is used to specify the distance at which the full
light intensity arrives, i. e. the intensity which was given by the color
keyword. The actual attenuation is described by the fade_power keyword, which
determines the falloff rate. E. g. linear or quadratic falloff can be used by
setting FADE_POWER to 1 or 2 respectively. The complete formula to calculate
the factor by which the light is attenuated is
2
attenuation = -------
1 + (d / FADE_DISTANCE) ^ FADE_POWER
with d being the distance the light has traveled.
Light fading functions for different fading powers.
You should note two important facts: First, for FADE_DISTANCEs larger than
one the light intensity at distances smaller than FADE_DISTANCE actually
increases. This is necessary to get the light source color if the distance
traveled equals the FADE_DISTANCE. Second, only light coming directly from
light sources is attenuated. Reflected or refracted light is not attenuated
by distance.
7.5.6.8 Atmosphere Interaction
By default light sources will interact with an atmosphere added to the scene.
This behaviour can be switched off by using the atmosphere keyword inside the
light source statement.
light_source {
...
atmosphere off
}
7.5.6.9 Atmospheric Attenuation
Normally light coming from light sources is not influenced by fog or
atmosphere. This can be changed by turning the atmospheric attenuation for a
given light source on. All light coming from this light source will now be
diminished as it travels through the fog or atmosphere. This results in an
distance-based, exponential intensity falloff ruled by the used fog or
atmosphere. If there is no fog or atmosphere no change will be seen.
7.5.7 Object Modifiers
A variety of modifiers may be attached to objects. Transformations such as
translate, rotate and scale have already been discussed. Textures are in a
section of their own below. Here are three other important modifiers:
clipped_by , bounded_by and no_shadow . Although the examples below use
object statements and object identifiers, these modifiers may be used on any
type of object such as sphere, box etc.
7.5.7.1 Clipped_By
The clipped_by statement is technically an object modifier but it provides a
type of CSG similar to CSG intersection. You attach a clipping object like
this:
object {
My_Thing
clipped_by{plane{y,0}}
}
Every part of the object My_Thing that is inside the plane is retained while
the remaining part is clipped off and discarded. In an intersection object
the hole is closed off. With clipped_by it leaves an opening. For example the
following figure shows object A being clipped by object B.
* *
* *
* *
***************
An object clipped by another object.
clipped_by may be used to slice off portions of any shape. In many cases it
will also result in faster rendering times than other methods of altering a
shape.
Often you will want to use the clipped_by and bounded_by options with the
same object. The following shortcut saves typing and uses less memory.
object {
My_Thing
bounded_by { box { <0,0,0>, <1,1,1> } }
clipped_by { bounded_by }
}
7.5.7.2 Bounded_By
The calculations necessary to test if a ray hits an object can be quite time
consuming. Each ray has to be tested against every object in the scene.
POV-Ray attempts so speed up the process by building a set of invisible
boxes, called bounding boxes, which cluster the objects together. This way a
ray that travels in one part of the scene doesn't have to be tested against
objects in another, far away part of the scene. When large a number of
objects are present the boxes are nested inside each other. POV-Ray can use
bounding boxes on any finite object and even some clipped or bounded
quadrics. However infinite objects (such as a planes, quartic, cubic and
poly) cannot be automatically bound. CSG objects are automatically bound if
they contain finite (and in some cases even infinite) objects. This works by
applying the CSG set operations to the bounding boxes of all objects used
inside the CSG object. For difference and intersection operations this will
hardly ever lead to an optimal bounding box. It's sometimes better (depending
on the complexity of the CSG object) to use a bounded_by statement with such
shapes.
Normally bounding shapes are not necessary but there are cases where they can
be used to speed up the rendering of complex objects. Bounding shapes tell
the ray-tracer that the object is totally enclosed by a simple shape. When
tracing rays, the ray is first tested against the simple bounding shape. If
it strikes the bounding shape the ray is further tested against the more
complicated object inside. Otherwise the entire complex shape is skipped,
which greatly speeds rendering.
To use bounding shapes, simply include the following lines in the declaration
of your object:
bounded_by {
object { ... }
}
An example of a bounding shape:
intersection {
sphere { <0,0,0>, 2 }
plane { <0,1,0>, 0 }
plane { <1,0,0>, 0 }
bounded_by { sphere { <0,0,0>, 2 } }
}
The best bounding shape is a sphere or a box since these shapes are highly
optimized, although, any shape may be used. If the bounding shape is itself a
finite shape which responds to bounding slabs then the object which it
encloses will also be used in the slab system.
CSG shapes can benefit from bounding slabs without a bounded_by statement
however they may do so inefficiently in intersection, difference and merge.
In these three CSG types the automatic bound used covers all of the component
objects in their entirety. However the result of these intersections may
result in a smaller object. Compare the sizes of the illustrations for union
and intersection in the CSG section above. It is possible to draw a much
smaller box around the intersection of A and B than the union of A and B yet
the automatic bounds are the size of the union of A and B regardless of the
kind of CSG specified.
While it is almost always a good idea to manually add a bounded_by to
intersection, difference and merge, it is often best to not bound a union. If
a union has no bounded_by and no clipped_by POV-Ray can internally split
apart the components of a union and apply automatic bounding slabs to any of
its finite parts. Note that some utilities such as raw2pov may be able to
generate bounds more efficiently than POV-Ray's current system. However most
unions you create yourself can be easily bounded by the automatic system. For
technical reasons POV-Ray cannot split a merge object. It is probably best to
hand bound a merge, especially if it is very complex.
Note that if bounding shape is too small or positioned incorrectly it may
clip the object in undefined ways or the object may not appear at all. To do
true clipping, use clipped_by as explained above. Often you will want to use
the clipped_by and bounded_by options with the same object. The following
shortcut saves typing and uses less memory.
object {
My_Thing
clipped_by{ box { <0,0,0>,<1,1,1 > }}
bounded_by{ clipped_by }
}
7.5.7.3 Hollow
POV-Ray by default assumes that objects are made of a solid material that
completely fills the interior of an object. By adding the hollow keyword to
the object you can make it hollow. That is very useful if you want
atmospheric effects to exist inside an object. It is even required for
objects containing a halo (see "Halo" for details).
In order to get a hollow CSG object you just have to make the top level
object hollow. All children will assume the same hollow state except their
state is explicitly set. The following example will set both spheres inside
the union hollow
union {
sphere { -0.5*x, 1 }
sphere { 0.5*x, 1 }
hollow
}
while the next example will only set the second sphere hollow because the
first sphere was explicitly set to be not hollow.
union {
sphere { -0.5*x, 1 hollow off }
sphere { 0.5*x, 1 }
hollow
}
7.5.7.4 No_Shadow
You may specify the no_shadow keyword in an object to make that object cast
no shadow. This is useful for special effects and for creating the illusion
that a light source actually is visible. This keyword was necessary in
earlier versions of POV-Ray which did not have the looks_like statement. Now
it is useful for creating things like laser beams or other unreal effects.
Simply attach the keyword as follows:
object {
My_Thing
no_shadow
}
7.5.7.5 Sturm
Some of POV-Ray's objects allow you to choose between a fast but sometimes
inaccurate root solver and a slower but more accurate one. This is the case
for all objects that involve the solution of a cubic or quartic polynomial.
There are analytic mathematical solutions for those polynomals that can be
used.
Lower order polynomals are trivial to solve while higher order polynomials
require iterative algorithms to solve them. One of those algorithms is the
Sturmian root solver.
The following list shows all objects for which the Sturmian root solver can
be used.
blob
cubic
lathe (only with quadratic splines)
poly
prism (only with cubic splines)
quartic
sor
7.6 Textures
The texture describes what the object looks like, i. e. its material.
Textures are combinations of pigments, normals, finishes and halos. Pigment
is the color or pattern of colors inherent in the material. Normal is a
method of simulating various patterns of bumps, dents, ripples or waves by
modifying the surface normal vector. Finish describes the reflective and
refractive properties of a material. Halo simulates effects like clouds, fog,
fire etc. by using a density field defined inside the object.
A plain texture consists of a single pigment, an optional normal, a single
finish and optionally one or more halos. A special texture combines two or
more textures using a pattern or blending function. Special textures may be
made quite complex by nesting patterns within patterns. At the innermost
levels however, they are made up from plain textures. Note that allthough we
call a plain texture plain it may be a very complex texture. The term plain
only means that it has a single pigment, normal, finish and halo.
The most complete form for defining a plain texture is as follows:
texture {
TEXTURE_IDENTIFIER
pigment {..}.
normal {..}.
finish {..}.
halo {..}.
TRANSFORMATIONS
}
Each of the items in a texture are optional but if they are present the
identifier must be first and the transformations must be last. The pigment,
normal and finish parameters modify any pigment, normal and finish already
specified in the TEXTURE_IDENTIFIER. Any halos are added to the already
existing halos. If no texture identifier is specified the pigment, normal and
finish statements modify the current default values and any halo is added to
the default halo, if any. TRANSFORMATIONs are translate, rotate, scale and
matrix statements. They should be specified last.
The sections below describe all of the options available in pigments,
normals, finishes and halos. Special textures are covered later.
7.6.1 Pigment
The color or pattern of colors for an object is defined by a pigment
statement. All plain textures must have a pigment. If you do not specify one
the default pigment is used. A pigment statement is part of a texture
specification. However it can be tedious to type texture {pigment {... }}
just to add a color to an object. Therefore you may attach a pigment directly
to an object without explicitly specifying that it as part of a texture. For
example:
//this... //can be shortened to this...
object { object {
My_Object My_Object
texture { pigment {color Red}
pigment {color Red} }
}
}
The color you define is the way you want the object to look if fully
illuminated. You pick the basic color inherent in the object and POV-Ray
brightens or darkens it depending on the lighting in the scene. The parameter
is called pigment because we are defining the basic color the object actually
is rather than how it looks.
The most complete form for defining a pigment is as follows:
pigment {
PIGMENT_IDENTIFIER
PATTERN_TYPE
PIGMENT_MODIFIERS...
}
Each of the items in a pigment are optional but if they are present, they
should be in the order shown above to insure that the results are as
expected. Any items after the PIGMENT_IDENTIFIER modify or override settings
given in the identifier. If no identifier is specified then the items modify
the pigment values in the current default texture. Valid PIGMENT_MODIFIERS
are color_map , pigment_map , image_map and quick_color statements as well as
any of the generic PATTERN_MODIFIERS such as translate , rotate , scale ,
turbulence , wave shape and warp statements. Such modifiers apply only to the
pigment and not to other parts of the texture. Modifiers should be specified
last.
The various pattern types fall into roughly four categories. Each category is
discussed below. They are solid color, color list patterns, color mapped
patterns and image maps.
7.6.1.1 Solid Color Pigments
The simplest type of pigment is a solid color. To specify a solid color you
simply put a color specification inside a pigment. For example:
pigment {color Orange}
A color specification consists of the option keyword color followed by a
color identifier or by a specification of the amount of red, green, blue,
filtered and unfiltered transparency in the surface. See section "Specifying
Colors" for more details about colors. Any pattern modifiers used with a
solid color are ignored because there is no pattern to modify.
7.6.1.2 Color List Pigments
There are three color list patterns: checker , hexagon and brick . The result
is a pattern of solid colors with distinct edges rather than a blending of
colors as with color mapped patterns. Each of these patterns is covered in
more detail in a later section. The syntax for each is:
pigment { brick COLOR1, COLOR2 MODIFIERS ... }
pigment { checker COLOR1, COLOR2 MODIFIERS ... }
pigment { hexagon COLOR1, COLOR2, COLOR3 MODIFIERS ... }
Each COLORn is any valid color specification. There should be a comma between
each color or the color keyword should be used as a separator so that POV-Ray
can determine where each color specification starts and ends.
7.6.1.3 Color Maps
Most of the color patterns do not use abrupt color changes of just two or
three colors like those in the brick, checker or hexagon patterns. They
instead use smooth transitions of many colors that gradually change from one
point to the next. The colors are defined in a pigment modifier called a
color map that describes how the pattern blends from one color to the next.
Each of the various pattern types available is in fact a mathematical
function that takes any x, y, z location and turns it into a number between
0.0 and 1.0 inclusive. That number is used to specify what mix of colors to
use from the color map.
A color map is specified by...
pigment{
PATTERN_TYPE
color_map {
[ NUM_1 COLOR_1]
[ NUM_2 COLOR_2]
[ NUM_3 COLOR_3]
...
}
PIGMENT_MODIFIERS...
}
Where NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive.
COLOR_1, COLOR_2, ... are color specifications. Note that the [] brackets are
part of the actual statement. They are not notational symbols denoting
optional parts. The brackets surround each entry in the color map. There may
be from 2 to 256 entries in the map. The alternate spelling colour_map may be
used.
For example
sphere {
<0,1,2>, 2
pigment {
gradient x //this is the PATTERN_TYPE
color_map {
[0.1 color Red]
[0.3 color Yellow]
[0.6 color Blue]
[0.6 color Green]
[0.8 color Cyan]
}
}
}
The pattern function is evaluated and the result is a value from 0.0 to 1.0.
If the value is less than the first entry (in this case 0.1) then the first
color (red) is used. Values from 0.1 to 0.3 use a blend of red and yellow
using linear interpolation of the two colors. Similarly values from 0.3 to
0.6 blend from yellow to blue. Note that the 3rd and 4th entries both have
values of 0.6. This causes an immediate abrupt shift of color from blue to
green. Specifically a value that is less than 0.6 will be blue but exactly
equal to 0.6 will be green. Moving along, values from 0.6 to 0.8 will be a
blend of green and cyan. Finally any value greater than or equal to 0.8 will
be cyan.
If you want areas of unchanging color you simply specify the same color for
two adjacent entries. For example:
color_map {
[0.1 color Red]
[0.3 color Yellow]
[0.6 color Yellow]
[0.8 color Green]
}
In this case any value from 0.3 to 0.6 will be pure yellow.
The color_map keyword may be used with any pattern except brick , checker ,
hexagon and image_map . You may declare and use color_map identifiers. For
example:
#declare Rainbow_Colors=
color_map {
[0.0 color Magenta]
[0.33 color Yellow]
[0.67 color Cyan]
[1.0 color Magenta]
}
object{My_Object
pigment{
gradient x
color_map{Rainbow_Colors}
}
}
7.6.1.4 Pigment Maps
In addition to specifying blended colors with a color map you may create a
blend of pigments using a pigment map . The syntax for a pigment map is
identical to a color map except you specify a pigment in each map entry (and
not a color).
A pigment map is specified by...
pigment{
PATTERN_TYPE
pigment_map {
[ NUM_1 PIGMENT_BODY_1]
[ NUM_2 PIGMENT_BODY_2]
[ NUM_3 PIGMENT_BODY_3]
...
}
PIGMENT_MODIFIERS...
}
Where NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive. A
PIGMENT_BODY is anything that would normally appear inside a pigment {... }
statement but the pigment keyword and {} braces are not needed. Note that the
[] brackets are part of the actual statement. They are not notational symbols
denoting optional parts. The brackets surround each entry in the map. There
may be from 2 to 256 entries in the map.
For example
sphere {
<0,1,2>, 2
pigment {
gradient x //this is the PATTERN_TYPE
pigment_map {
[0.3 wood scale 0.2]
[0.3 Jade] //this is a pigment identifier
[0.6 Jade]
[0.9 marble turbulence 1]
}
}
}
When the gradient x function returns values from 0.0 to 0.3 the scaled wood
pigment is used. From 0.3 to 0.6 the pigment identifier Jade is used. From
0.6 up to 0.9 a blend of Jade and a turbulent marble is used. From 0.9 on up
only the turbulent marble is used.
Pigment maps may be nested to any level of complexity you desire. The
pigments in a map may have color maps or pigment maps or any type of pigment
you want. Any entry of a pigment map may be a solid color however if all
entries are solid colors you should use a color map which will render
slightly faster.
Entire pigments may also be used with the block patterns such as checker,
hexagon and brick. For example...
pigment {
checker
pigment { Jade scale .8 }
pigment { White_Marble scale .5 }
}
Note that in the case of block patterns the pigment {... } wrapping is
required around the pigment information.
A pigment map is also used with the average pigment type. See "Average" for
details.
You may not use pigment_map or individual pigments with an image_map . See
"texture_map" for an alternative way to do this.
7.6.1.5 Image Maps
When all else fails and none of the above pigment pattern types meets your
needs you can use an image map to wrap a 2-D bit-mapped image around your 3-D
objects.
7.6.1.5.1 Specifying an Image Map
The syntax for an image map is...
pigment {
image_map {
FILE_TYPE "filename"
MODIFIERS...
}
}
Where FILE_TYPE is one of the following keywords gif , tga , iff , ppm , pgm
, png or sys . This is followed by the name of the file in quotes. Several
optional modifiers may follow the file specification. The modifiers are
described below. Note that earlier versions of POV-Ray allowed some modifiers
before the FILE_TYPE but that syntax is being phased out in favor of the
syntax described here.
Filenames specified in the image_map statements will be searched for in the
home (current) directory first and, if not found, will then be searched for
in directories specified by any -L (library path) options active. This would
facilitate keeping all your image maps files in a separate subdirectory and
giving an -L option on the command line to where your library of image maps
are.
By default, the image is mapped onto the x-y-plane. The image is projected
onto the object as though there were a slide projector somewhere in the
-z-direction. The image exactly fills the square area from (x,y) coordinates
(0,0) to (1,1) regardless of the image's original size in pixels. If you
would like to change this default you may translate, rotate or scale the
pigment or texture to map it onto the object's surface as desired.
In section "Checker" the checker pigment pattern is explained. The checks are
described as solid cubes of colored clay from which objects are carved. With
image maps you should imagine that each pixel is a long, thin, square,
colored rod that extends parallel to the z-axis. The image is made from rows
and columns of these rods bundled together and the object is then carved from
the bundle.
If you would like to change this default orientation you may translate,
rotate or scale the pigment or texture to map it onto the object's surface as
desired.
7.6.1.5.2 The map_type Option
The default projection of the image onto the x-y-plane is called a planar map
type . This option may be changed by adding the map_type keyword followed by
a number specifying the way to wrap the image around the object.
A map_type 0 gives the default planar mapping already described.
A map_type 1 gives a spherical mapping. It assumes that the object is a
sphere of any size sitting at the origin. The y-axis is the north/south pole
of the spherical mapping. The top and bottom edges of the image just touch
the pole regardless of any scaling. The left edge of the image begins at the
positive x-axis and wraps the image around the sphere from west to east in a
-y-rotation. The image covers the sphere exactly once. The once keyword has
no meaning for this mapping type.
With map_type 2 you get a cylindrical mapping. It assumes that a cylinder of
any diameter lies along the y-axis. The image wraps around the cylinder just
like the spherical map but the image remains one unit tall from y=0 to y=1.
This band of color is repeated at all heights unless the once keyword is
applied.
Finally map_type 5 is a torus or donut shaped mapping. It assumes that a
torus of major radius one sits at the origin in the x-z-plane. The image is
wrapped around similar to spherical or cylindrical maps. However the top and
bottom edges of the map wrap over and under the torus where they meet each
other on the inner rim.
Types 3 and 4 are still under development.
Note that the map_type option may also be applied to bump_map and
material_map statements.
7.6.1.5.3 The Filter and Transmit Bitmap Modifiers
To make all or part of an image map transparent you can specify filter and/or
transmit values for the color palette/registers of PNG, GIF or IFF pictures
(at least for the modes that use palettes). You can do this by adding the
keyword filter or transmit following the filename. The keyword is followed by
two numbers. The first number is the palette number value and the second is
the amount of transparency. The values should be separated by a comma. For
example:
image_map {
gif "mypic.gif"
filter 0, 0.5 // Make color 0 50% filtered transparent
filter 5, 1.0 // Make color 5 100% filtered transparent
transmit 8, 0.3 // Make color 8 30% non-filtered transparent
}
You can give the entire image a filter or transmit value using filter all
VALUE or transmit all VALUE . For example:
image_map {
gif "stnglass.gif"
filter all 0.9
}
Note that early versions of POV-Ray used the keyword alpha to specify
filtered transparency however that word is often used to describe
non-filtered transparency. For this reason alpha is no longer used.
See "filter" and "transmit" for details on the differences between filtered
and non-filtered transparency.
7.6.1.5.4 Using the Alpha Channel
Another way to specify non-filtered transmit transparency in an image map is
by using the alpha channel .
PNG allows you to store a different transparency for each color index in the
PNG file, if desired. If your paint programs support this feature of PNG you
can do the transparency editing within your paint program rather than
specifying transmit values for each color in the POV file. Since PNG and TGA
image formats can also store full alpha channel (transparency) information
you can generate image maps that have transparency which isn't dependent on
the color of a pixel but rather its location in the image.
Although POV uses transmit 0.0 to specify no transparency and 1.0 to specify
full transparency, the alpha data ranges from 0 to 255 in the opposite
direction. Alpha data 0 means the same as transmit 1.0 and alpha data 255
produces transmit 0.0.
7.6.1.6 Quick Color
When developing POV-Ray scenes its often useful to do low quality test runs
that render faster. The +Q command line switch can be used to turn off some
time consuming color pattern and lighting calculations to speed things up.
However all settings of +Q5 or lower turns off pigment calculations and
creates gray objects.
By adding a quick_color to a pigment you tell POV-Ray what solid color to use
for quick renders instead of a patterned pigment. For example:
pigment {
gradient x
color_map{
[0.0 color Yellow]
[0.3 color Cyan]
[0.6 color Magenta]
[1.0 color Cyan]
}
turbulence 0.5
lambda 1.5
omega 0.75
octaves 8
quick_color Neon_Pink
}
This tells POV-Ray to use solid Neon_Pink for test runs at quality +Q 5 or
lower but to use the turbulent gradient pattern for rendering at +Q 6 and
higher.
Note that solid color pigments such as
pigment {color Magenta}
automatically set the quick_color to that value. You may override this if you
want. Suppose you have 10 spheres on the screen and all are yellow. If you
want to identify them individually you could give each a different
quick_color like this:
sphere {
<1,2,3>,4
pigment { color Yellow quick_color Red }
}
sphere {
<-1,-2,-3>,4
pigment { color Yellow quick_color Blue }
}
and so on. At +Q 6 or higher they will all be yellow but at +Q 5 or lower
each would be different colors so you could identify them.
7.6.2 Normal
Ray-tracing is known for the dramatic way it depicts reflection, refraction
and lighting effects. Much of our perception depends on the reflective
properties of an object. Ray tracing can exploit this by playing tricks on
our perception to make us see complex details that aren't really there.
Suppose you wanted a very bumpy surface on the object. It would be very
difficult to mathematically model lots of bumps. We can however simulate the
way bumps look by altering the way light reflects off of the surface.
Reflection calculations depend on a vector called a surface normal vector.
This is a vector which points away from the surface and is perpendicular to
it. By artificially modifying (or perturbing) this normal vector you can
simulate bumps.
The normal {... } statement is the part of a texture which defines the
pattern of normal perturbations to be applied to an object. Like the pigment
statement, you can omit the surrounding texture block to save typing. Do not
forget however that there is a texture implied. For example...
//this... //can be shortened to this...
object { object {
My_Object My_Object
texture { pigment {color Purple}
pigment {color Purple} normal {bumps 0.3}
normal {bumps 0.3} }
}
}
Note that attaching a normal pattern does not really modify the surface. It
only affects the way light reflects or refracts at the surface so that it
looks bumpy.
The most complete form for defining a normal is as follows:
normal {
NORMAL_IDENTIFIER
PATTERN_TYPE FloatValue
NORMAL_MODIFIERS
TRANSFORMATIONS...
}
Each of the items in a normal are optional but if they are present they
should be in the order shown above to insure that the results are as
expected. Any items after the NORMAL_IDENTIFIER modify or override settings
given in the identifier. If no identifier is specified then the items modify
the normal values in the current default texture. The PATTERN_TYPE may
optionally be followed by a float value that controls the apparent depth of
the bumps. Typical values range from 0.0 to 1.0 but any value may be used.
Negative values invert the pattern. The default value if none is specified is
0.5.
Valid NORMAL_MODIFIERS are slope_map , normal_map , bump_map and bump_size
statements as well as any of the generic PATTERN_MODIFIERS such as translate,
rotate, scale, turbulence, wave shape and warp statements. Such modifiers
apply only to the normal and not to other parts of the texture. Modifiers
should be specified last.
There are three basic types of NORMAL_PATTERN_TYPEs. They are pattern
normals, specialized normals and bump maps. They differ in the types of
modifiers you may use with them. Originally POV-Ray had some patterns which
were exclusively used for pigments while others were exclusively used for
normals. Since POV-Ray 3.0 you can use any pattern for either pigments or
normals. For example it is now valid to use ripples as a pigment or wood as a
normal type. The patterns bumps , dents , ripples , waves , wrinkles and
bump_map were once exclusively normal patterns which could not be used as
pigments. Because these six types use specialized normal modification
calculations they cannot have slope_map , normal_map or wave shape modifiers.
All other normal pattern types may use them.
7.6.2.1 Slope Maps
A slope map is a normal pattern modifier which gives the user a great deal of
control over the exact shape of the bumpy features. It is best illustrated
with a gradient normal pattern. Suppose you have...
plane{ z, 0
pigment{ White }
normal { gradient x }
}
This gives a ramp wave pattern that looks like small linear ramps that climb
from the points at x=0 to x=1 and then abruptly drops to 0 again to repeat
the ramp from x=1 to x=2. A slope map turns this simple linear ramp into
almost any wave shape you want. The syntax is as follows...
normal{
PATTERN_TYPE Value
slope_map {
[ NUM_1 POINT_SLOPE_1]
[ NUM_2 POINT_SLOPE_2]
[ NUM_3 POINT_SLOPE_3]
...
}
NORMAL_MODIFIERS...
}
Note that the [] brackets are part of the actual statement. They are not
notational symbols denoting optional parts. The brackets surround each entry
in the slope map. There may be from 2 to 256 entries in the map.
The NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive.
POINT_SLOPE_1, POINT_SLOPE_2, ... are 2 component vectors such as <0,1> where
the first value represents the apparent height of the wave and the second
value represents the slope of the wave at that point. The height should range
between 0.0 and 1.0 but any value could be used.
The slope value is the change in height per unit of distance. For example a
slope of zero means flat, a slope of 1.0 means slope upwards at a 45 degree
angle and a slope of -1 means slope down at 45 degrees. Theoretically a slope
straight up would have infinite slope. In practice, slope values should be
kept in the range -3.0 to +3.0. Keep in mind that this is only the visually
apparent slope. A normal does not actually change the surface.
For example here is how to make the ramp slope up for the first half and back
down on the second half creating a triangle wave with a sharp peak in the
center.
normal {
gradient x // this is the PATTERN_TYPE
slope_map {
[0 <0, 1>] // start at bottom and slope up
[0.5 <1, 1>] // halfway through reach top still climbing
[0.5 <1,-1>] // abruptly slope down
[1 <0,-1>] // finish on down slope at bottom
}
}
The pattern function is evaluated and the result is a value from 0.0 to 1.0.
The first entry says that at x=0 the apparent height is 0 and the slope is 1.
At x=0.5 we are at height 1 and slope is still up at 1. The third entry also
specifies that at x=0.5 (actually at some tiny fraction above 0.5) we have
height 1 but slope -1 which is downwards. Finally at x=1 we are at height 0
again and still sloping down with slope -1.
Although this example connects the points using straight lines the shape is
actually a cubic spline. This example creates a smooth sine wave.
normal {
gradient x // this is the PATTERN_TYPE
slope_map {
[0 <0.5, 1>] // start in middle and slope up
[0.25 <1.0, 0>] // flat slope at top of wave
[0.5 <0.5,-1>] // slope down at mid point
[0.75 <0.0, 0>] // flat slope at bottom
[1 <0.5, 1>] // finish in middle and slope up
}
}
This example starts at height 0.5 sloping up at slope 1. At a fourth of the
way through we are at the top of the curve at height 1 with slope 0 which is
flat. The space between these two is a gentle curve because the start and end
slopes are different. At half way we are at half height sloping down to
bottom out at 3/4ths. By the end we are climbing at slope 1 again to complete
the cycle. There are more examples in slopemap.pov in the sample scenes.
A slope_map may be used with any pattern except brick , checker , hexagon ,
bumps , dents , ripples , waves , wrinkles and bump_map .
You may declare and use slope map identifiers. For example:
#declare Fancy_Wave =
slope_map { // Now let's get fancy
[0.0 <0, 1>] // Do tiny triangle here
[0.2 <1, 1>] // down
[0.2 <1,-1>] // to
[0.4 <0,-1>] // here.
[0.4 <0, 0>] // Flat area
[0.5 <0, 0>] // through here.
[0.5 <1, 0>] // Square wave leading edge
[0.6 <1, 0>] // trailing edge
[0.6 <0, 0>] // Flat again
[0.7 <0, 0>] // through here.
[0.7 <0, 3>] // Start scallop
[0.8 <1, 0>] // flat on top
[0.9 <0,-3>] // finish here.
[0.9 <0, 0>] // Flat remaining through 1.0
}
object{ My_Object
pigment { White }
normal {
wood
slope_map { Fancy_Wave }
}
}
7.6.2.2 Normal Maps
Most of the time you will apply single normal pattern to an entire surface
but you may also create a pattern or blend of normals using a normal map .
The syntax for a normal map is identical to a pigment map except you specify
a normal in each map entry.
A normal map is specified by...
normal{
PATTERN_TYPE
normal_map {
[ NUM_1 NORMAL_BODY_1]
[ NUM_2 NORMAL_BODY_2]
[ NUM_3 NORMAL_BODY_3]
...
}
NORMAL_MODIFIERS...
}
Where NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive. A
NORMAL_BODY is anything that would normally appear inside a normal {... }
statement but the normal keyword and {} braces are not needed. Note that the
[] brackets are part of the actual statement. They are not notational symbols
denoting optional parts. The brackets surround each entry in the map. There
may be from 2 to 256 entries in the map.
For example
normal {
gradient x //this is the PATTERN_TYPE
normal_map {
[0.3 bumps scale 2]
[0.3 dents]
[0.6 dents]
[0.9 marble turbulence 1]
}
}
When the gradient x function returns values from 0.0 to 0.3 then the scaled
bumps normal is used. From 0.3 to 0.6 dents are From 0.6 up to 0.9 a blend of
dents and a turbulent marble is used. From 0.9 on up only the turbulent
marble is used.
Normal maps may be nested to any level of complexity you desire. The normals
in a map may have slope maps or normal maps or any type of normal you want.
A normal map is also used with the average normal type. See "Average" for
details.
Entire normals may also be used with the block patterns such as checker,
hexagon and brick. For example...
normal {
checker
normal { gradient x scale .2 }
normal { gradient y scale .2 }
}
}
Note that in the case of block patterns the normal {... } wrapping is
required around the normal information.
You may not use normal_map or individual normals with a bump_map . See
"texture_map" for an alternative way to do this.
7.6.2.3 Bump Maps
When all else fails and none of the above normal pattern types meets your
needs you can use a bump map to wrap a 2-D bit-mapped bump pattern around
your 3-D objects.
Instead of placing the color of the image on the shape like an image map a
bump map perturbs the surface normal based on the color of the image at that
point. The result looks like the image has been embossed into the surface. By
default, a bump map uses the brightness of the actual color of the pixel.
Colors are converted to gray scale internally before calculating height.
Black is a low spot, white is a high spot. The image's index values may be
used instead (see section "Use_Index and Use_Color" below).
7.6.2.3.1 Specifying a Bump Map
The syntax for bump_map is...
normal {
bump_map {
FILE_TYPE "filename"
BITMAP_MODIFIERS...
}
NORMAL_MODIFIERS...
}
Where FILE_TYPE is one of the following keywords gif , tga , iff , ppm , pgm
, png or sys . This is followed by the name of the file using any valid
string expression. Several optional modifiers may follow the file
specification. The modifiers are described below. Note that earlier versions
of POV-Ray allowed some modifiers before the FILE_TYPE but that syntax is
being phased out in favor of the syntax described here.
Filenames specified in the bump_map statement will be searched for in the
home (current) directory first and, if not found, will then be searched for
in directories specified by any +L switches or Library_Path options. This
would facilitate keeping all your bump maps files in a separate subdirectory,
and specifying a library path to them. Note that any operating system default
paths are not searched unless you also specify them as a Library_Path .
By default, the bump pattern is mapped onto the x-y-plane. The bumps are
projected onto the object as though there were a slide projector somewhere in
the -z-direction. The bump pattern exactly fills the square area from (x,y)
coordinates (0,0) to (1,1) regardless of the bitmaps's original size in
pixels. If you would like to change this default, you may translate, rotate
or scale the normal or texture to map it onto the object's surface as
desired.
The file name is optionally followed by one or more BITMAP_MODIFIERS. The
bump_size , use_color and use_index modifiers are specific to bump maps and
are discussed in the following sections. See "Bitmap Modifiers" for other
general bitmap modifiers.
After a bump_map statement but still inside the normal statement you may
apply any legal normal modifiers except slope_map and pattern wave forms.
7.6.2.3.2 Bump_Size
The relative bump size can be scaled using the bump_size modifier. The bump
size number can be any number other than 0 but typical values are from about
0.1 to as high as 4.0 or 5.0.
normal {
bump_map {
gif "stuff.gif"
bump_size 5.0
}
}
Originally bump_size could only be used inside a bump map but it can now be
used with any normal. Typically it is used to override a previously defined
size. For example:
normal {
My_Normal //this is a previously defined normal identifier
bump_size 2.0
}
7.6.2.3.3 Use_Index and Use_Color
Usually the bump map converts the color of the pixel in the map to a gray
scale intensity value in the range 0.0 to 1.0 and calculates the bumps based
on that value. If you specify use_index , the bump map uses the color's
palette number to compute as the height of the bump at that point. So, color
number 0 would be low and color number 255 would be high (if the image has
256 palette entries). The actual color of the pixels doesn't matter when
using the index. This option is only available on palette based formats. The
use_color keyword may be specified to explicitly note that the color methods
should be used instead. The alternate spelling use_colour is also valid.
These modifiers may only be used inside the bump_map statement.
7.6.3 Finish
The finish properties of a surface can greatly affect its appearance. How
does light reflect? What happens when light passes through? What kind of
highlights are visible. To answer these questions you need a finish
statement.
The finish {... } statement is the part of a texture which defines the
various finish properties to be applied to an object. Like the pigment or
normal statement you can omit the surrounding texture block to save typing.
Do not forget however that there is a texture implied. For example...
this... can be shortened to this...
object { object {
My_Object My_Object
texture { pigment {color Purple}
pigment {color Purple} finish {phong 0.3}
finish {phong 0.3} }
}
}
The most complete form for defining a finish is as follows:
finish {
FINISH_IDENTIFIER
[ ambient COLOR ]
[ diffuse FLOAT ]
[ brilliance FLOAT ]
[ phong FLOAT ]
[ phong_size FLOAT ]
[ specular FLOAT ]
[ roughness FLOAT ]
[ metallic [ FLOAT ] ]
[ reflection COLOR ]
[ refraction FLOAT ]
[ ior FLOAT ]
[ caustics FLOAT ]
[ fade_distance FLOAT ]
[ fade_power FLOAT ]
[ irid { thickness FLOAT turbulence VECTOR } ]
[ crand FLOAT ]
}
The FINISH_IDENTIFIER is optional but should proceed all other items. Any
items after the FINISH_IDENTIFIER modify or override settings given in the
IDENTIFIER. If no identifier is specified then the items modify the finish
values in the current default texture. Note that transformations are not
allowed inside a finish because finish items cover the entire surface
uniformly.
7.6.3.1 Ambient
The light you see in dark shadowed areas comes from diffuse reflection off of
other objects. This light cannot be directly modeled using ray-tracing.
However we can use a trick called ambient lighting to simulate the light
inside a shadowed area.
Ambient light is light that is scattered everywhere in the room. It bounces
all over the place and manages to light objects up a bit even where no light
is directly shining. Computing real ambient light would take far too much
time, so we simulate ambient light by adding a small amount of white light to
each texture whether or not a light is actually shining on that texture.
This means that the portions of a shape that are completely in shadow will
still have a little bit of their surface color. It's almost as if the texture
glows, though the ambient light in a texture only affects the shape it is
used on.
Usually a single float value is specified even though the syntax calls for a
color. For example a float value of 0.3 gets promoted to the full color
vector <0.3,0.3,0.3,0.3,0.3> which is acceptible because only the red, green
and blue parts are used.
The default value is very little ambient light (0.1). The value can range
from 0.0 to 1.0. Ambient light affects both shadowed and non-shadowed areas
so if you turn up the ambient value you may want to turn down the diffuse
value.
Note that this method doesn't account for the color of surrounding objects.
If you walk into a room that has red walls, floor and ceiling then your white
clothing will look pink from the reflected light. POV-Ray's ambient shortcut
doesn't account for this. There is also no way to model specular reflected
indirect illumination such as the flashlight shining in a mirror.
You may color the ambient light using one of two methods. You may specify a
color rather than a float after the ambient keyword in each finish statement.
For example
finish { ambient rgb <0.3,0.1,0.1> } //a pink ambient
You may also specify the overall ambient light source used when calculating
the ambient lighting of an object using the global ambient_light setting. The
formula is given by
AMBIENT = FINISH_AMBIENT * GLOBAL_AMBIENT_LIGHT_SOURCE
7.6.3.2 Diffuse Reflection Items
When light reflects off of a surface the laws of physics say that it should
leave the surface at the exact same angle it came in. This is similar to the
way a billiard ball bounces off a bumper of a pool table. This perfect
reflection is called specular reflection. However only very smooth polished
surfaces reflect light in this way. Most of the time, light reflects and is
scattered in all directions by the roughness of the surface. This scattering
is called diffuse reflection because the light diffuses or spreads in a
variety of directions. It accounts for the majority of the reflected light we
see.
POV-Ray and most other ray-tracers can only simulate directly one of these
three types of illumination. That is the light which comes directly from
actual light sources. Light coming from other objects such as mirrors via
specular reflection (shine a flashlight onto a mirror for example). And last
not least light coming from other objects via diffuse reflections (look at
some dark area under a desk or in a corner: even though a lamp may not
directly illuminate that spot you can still see a little bit because light
comes from diffuse reflection off of nearby objects).
7.6.3.2.1 Diffuse
The keyword diffuse is used in a finish statement to control how much of the
light coming directly from any light sources is reflected via diffuse
reflection. For example
finish {diffuse 0.7}
means that 70% of the light seen comes from direct illumination from light
sources. The default value is diffuse 0.6.
7.6.3.2.2 Brilliance
The amount of direct light that diffuses from an object depends upon the
angle at which it hits the surface. When light hits at a shallow angle it
illuminates less. When it is directly above a surface it illuminates more.
The brilliance keyword can be used in a finish statement to vary the way
light falls off depending upon the angle of incidence. This controls the
tightness of the basic diffuse illumination on objects and slightly adjusts
the appearance of surface shininess. Objects may appear more metallic by
increasing their brilliance. The default value is 1.0. Higher values from to
about 10.0 cause the light to fall off less at medium to low angles. There
are no limits to the brilliance value. Experiment to see what works best for
a particular situation. This is best used in concert with highlighting.
7.6.3.2.3 Crand Graininess
Very rough surfaces, such as concrete or sand, exhibit a dark graininess in
their apparent color. This is caused by the shadows of the pits or holes in
the surface. The crand keyword can be added to cause a minor random darkening
in the diffuse reflection of direct illumination. Typical values range from
crand 0.01 to crand 0.5 or higher. The default value is 0. For example:
finish { crand 0.05 }
The grain or noise introduced by this feature is applied on a pixel-by-pixel
basis. This means that it will look the same on far away objects as on close
objects. The effect also looks different depending upon the resolution you
are using for the rendering. For these reasons it is not a very accurate way
to model the rough surface effect but some objects still look better with a
little crand thrown in.
Note that this should not be used when rendering animations. This is the one
of a few truly random features in POV-Ray and will produce an annoying
flicker of flying pixels on any textures animated with a crand value.
7.6.3.3 Highlights
Highlights are the bright spots that appear when a light source reflects off
of a smooth object. They are a blend of specular reflection and diffuse
reflection. They are specular-like because they depend upon viewing angle and
illumination angle. However they are diffuse-like because some scattering
occurs. In order to exactly model a highlight you would have to calculate
specular reflection off of thousands of microscopic bumps called micro
facets. The more that micro facets are facing the viewer the shinier the
object appears and the tighter the highlights become. POV-Ray uses two
different models to simulate highlights without calculating micro facets.
They are the specular and Phong models.
Note that specular and Phong highlights are not mutually exclusive. It is
possible to specify both and they will both take effect. Normally, however,
you will only specify one or the other.
7.6.3.3.1 Phong Highlights
The phong keyword controls the amount of Phong highlighting on the object. It
causes bright shiny spots on the object that are the color of the light
source being reflected.
The Phong method measures the average of the facets facing in the mirror
direction from the light sources to the viewer.
Phong's value is typically from 0.0 to 1.0, where 1.0 causes complete
saturation to the light source's color at the brightest area (center) of the
highlight. The default phong 0.0 gives no highlight.
The size of the highlight spot is defined by the phong_size value. The larger
the phong size the tighter, or smaller, the highlight and the shinier the
appearance. The smaller the phong size the looser, or larger, the highlight
and the less glossy the appearance.
Typical values range from 1.0 (very dull) to 250 (highly polished) though any
values may be used. Default phong size is 40 (plastic) if phong_size is not
specified. For example:
finish { phong 0.9 phong_size 60 }
7.6.3.3.2 Specular Highlight
A specular highlight is very similar to Phong highlighting but it uses
slightly different model. The specular model more closely resembles real
specular reflection and provides a more credible spreading of the highlights
occuring near the object horizons.
The specular value is typically from 0.0 to 1.0, where 1.0 causes complete
saturation to the light source's color at the brightest area (center) of the
highlight. The default specular 0.0 gives no highlight.
The size of the spot is defined by the value given for roughness . Typical
values range from 1.0 (very rough - large highlight) to 0.0005 (very smooth -
small highlight). The default value, if roughness is not specified, is 0.05
(plastic).
It is possible to specify wrong values for roughness that will generate an
error when you try to render the file. Don't use 0 and if you get errors
check to see if you are using a very, very small roughness value that may be
causing the error. For example:
finish {specular 0.9 roughness 0.02}
7.6.3.3.3 Metallic Highlight Modifier
The keyword metallic may be used with Phong or specular highlights. This
keyword indicates that the color of the highlights will be calculated by an
empirical function that models the reflectivity of metallic surfaces.
White light relfected specularly from a metallic surface takes the color of
the surface, except then the incidence angle approaches 90 degrees, where it
becomes white again.
The metallic keyword may be follow by a numeric value to specify the
influence the above effect has (the default value is one). For example:
finish {
phong 0.9
phong_size 60
metallic
}
7.6.3.4 Specular Reflection
When light does not diffuse and it does reflect at the same angle as it hits
an object, it is called specular reflection . Such mirror-like reflection is
controlled by the reflection keyword in a finish statement. For example:
finish { reflection 1.0 ambient 0 diffuse 0 }
This gives the object a mirrored finish. It will reflect all other elements
in the scene. Usually a single float value is specified after the keyword
even though the syntax calls for a color. For example a float value of 0.3
gets promoted to the full color vector \langle 0.3,0.3,0.3,0.3,0.3> which is
acceptible because only the red, green and blue parts are used.
The value can range from 0.0 to 1.0. By default there is no reflection.
Adding reflection to a texture makes it take longer to render because an
additional ray must be traced. The reflected light may be tinted by
specifying a color rather than a float. For example
finish { reflection rgb <1,0,0> }
gives a real red mirror that only reflects red light.
Note that although such reflection is called specular it is not controlled by
the specular keyword. That keyword controls a specular highlight .
7.6.3.5 Refraction
When light passes through a surface either into or out of a dense medium the
path of the ray of light is bent. Such bending is called refraction .
Normally transparent or semi-transparent surfaces in POV-Ray do not refract
light. Adding refraction 1.0 to the finish statement turns on refraction.
Note that it is recommended that you only use refraction 0 or refraction 1
(or even better refraction off and refraction on ). Values in between will
darken the refracted light in ways that do not correspond to any physical
property. Many POV-Ray scenes were created with intermediate refraction
values before this bug was discovered so the feature has been maintained. A
more appropriate way to reduce the brightness of refracted light is to change
the filter or transmit value in the colors specified in the pigment
statement. Note also that refraction does not cause the object to be
transparent. Transparency only occurs if there is a non-zero filter or
transmit value in the color.
The amount of bending or refracting of light depends upon the density of the
material. Air, water, crystal and diamonds all have different densities and
thus refract differently. The index of refraction or ior value is used by
scientists to describe the relative density of substances. The ior keyword is
used in POV-Ray to specify the value. For example:
texture {
pigment { White filter 0.9 }
finish {
refraction 1
ior 1.5
}
}
The default ior value of 1.0 will give no refraction. The index of refraction
for air is 1.0, water is 1.33, glass is 1.5 and diamond is 2.4. The file
consts.inc pre-defines several useful values for ior.
Note that if a texture has a filter component and no value for refraction and
ior are supplied the renderer will simply transmit the ray through the
surface with no bending. In layered textures, the refraction and ior keywords
must be in the last texture, otherwise they will not take effect.
7.6.3.5.1 Light Attenuation
Light attenuation is used to model the decrease in light intensity as the
light travels through a translucent object. Its syntax is:
finish {
fade_distance FADE_DISTANCE
fade_power FADE_POWER
}
The fade_distance keyword determines the distance the light has to travel to
reach half intensity while the fade_power keyword describes how fast the
light will fall off. For realistic effects a fade power of 1 to 2 should be
used.
The attenuation is calculated by a formula similar to that used for light
source attenuation.
1
attenuation = -------
1 + (d / FADE_DISTANCE) ^ FADE_POWER
7.6.3.5.2 Faked Caustics
The syntax is:
finish {
caustics POWER
}
7.6.3.6 Iridescence
Iridescence , or Newton's thin film interference, simulates the effect of
light on surfaces with a microscopic transparent film overlay. The effect is
like an oil slick on a puddle of water or the rainbow hues of a soap bubble
(see also "irid_wavelength" ).
The syntax is:
finish {
irid {
AMOUNT
thickness FLOAT
turbulence VECTOR
}
}
This finish modifies the surface color as a function of the angle between the
light source and the surface. Since the effect works in conjunction with the
position and angle of the light sources to the surface it does not behave in
the same ways as a procedural pigment pattern.
The AMOUNT parameter is the contribution of the iridescence effect to the
overall surface color. As a rule of thumb keep to around 0.25 (25%
contribution) or less, but experiment. If the surface is coming out too white
, try lowering the diffuse and possibly the ambient values of the surface.
The thickness keyword represents the film's thickness. This is an awkward
parameter to set, since the thickness value has no relationship to the
object's scale. Changing it affects the scale or busy-ness of the effect. A
very thin film will have a high frequency of color changes while a thick film
will have large areas of color.
The thickness of the film can be varied with the turbulence keyword. You can
only specify the amount of turbulence with iridescence. The octaves, lambda,
and omega values are internally set and are not adjustable by the user at
this time.
In addition, perturbing the object's surface normal through the use of bump
patterns will affect iridescence.
For the curious, thin film interference occurs because, when the ray hits the
surface of the film, part of the light is reflected from that surface, while
a portion is transmitted into the film. This subsurface ray travels through
the film and eventually reflects off the opaque substrate. The light emerges
from the film slightly out of phase with the ray that was reflected from the
surface.
This phase shift creates interference, which varies with the wavelength of
the component colors, resulting in some wavelengths being reinforced, while
others are cancelled out. When these components are recombined, the result is
iridescence.
The concept used for this feature came from the book Fundamentals of
Three-Dimensional Computer Graphics by Alan Watt (Addison-Wesley).
7.6.4 Halo
A halo is used to simulate some of the atmospheric effects that occur when
small particles interact with light or radiate on their own. Those effects
include clouds, fogs, fire, etc.
Halos are attached to an object, the so called container object , which they
completely fill. If the object is partially or completely translucent and the
object is specified to be hollow (see section "Hollow" for more details) the
halo will be visible. Thus the halo effects are limited to the space that the
object covers. This should always be kept in mind.
What the halo actually will look like depends on a lot of parameters. First
of all you have to specify which kind of effect you want to simulate. After
this you need to define the distribution of the particles. This is basically
done in two steps: a mapping function is selected and a density function is
chosen. The first function maps world coordinates onto a one-dimensional
interval while the later describes how this linear interval is mapped onto
the final density values.
The properties of the particles, such as their color and their translucency,
are given by a color map. The density values calculated by the mapping
processes are used to determine the appropriate color using this color map.
A ray marching process is used to volume sample the halo and to accumulate
the intensities and opacity of each interval.
The following sections will describe all of the halo parameters in more
detail. The complete halo syntax is given by:
halo {
attenuating | emitting | glowing | dust
[ constant | linear | cubic | poly ]
[ planar_mapping | spherical_mapping |
cylindrical_mapping | box_mapping ]
[ dust_type DUST_TYPE ]
[ eccentricity ECCENTRICITY ]
[ max_value MAX_VALUE ]
[ exponent EXPONENT ]
[ samples SAMPLES ]
[ aa_level AA_LEVEL ]
[ aa_threshold AA_THRESHOLD ]
[ jitter JITTER ]
[ turbulence <TURBULENCE> ]
[ octaves OCTAVES ]
[ omega OMEGA ]
[ lambda LAMBDA ]
[ colour_map COLOUR_MAP ]
[ frequency FREQUENCY ]
[ phase PHASE ]
[ scale <VECTOR> ]
[ rotate <VECTOR> ]
[ translate <VECTOR> ]
}
7.6.4.1 Halo Mapping
As described above the actual particle distribution and halo appearance is
influenced by a lot of parameters. The steps that are performed during the
halo calculation will be explained below. It will also be noted where the
different halo keywords will have an effect on the calculations.
1. Depending on the current sampling position along the ray, point P
(coordinates x, y, z) inside the halo container object is calculated.
The actual location is influenced by the jitter keyword, the number of
samples and the use of anti-aliasing ( aa_level and aa_threshold).
2. Point P is transformed into point Q using the (current) halo's
transformation. Here all local halo transformations come into play, i.e.
all transformations specified inside the (current) halo statement.
3. Turbulence is added to point Q. The amount of turbulence is given by the
urbulence keyword. The turbulence calculation is influenced by the
octaves, omega and lambda keywords.
4. Radius r is calculated depending on the specified density mapping (
planar_mapping, spherical_mapping, cylindrical_mapping, box_mapping).
The radius is clipped to the range from 0 to 1, i.e. 0 <= r <= 1.
5. The density d is calculated from the radius r using the specified
density function ( constant, linear, cubic, poly) and the maximum value
given by max_value. The density will be in the range from 0 to
max_value.
6. The density d is first multiplied by the frequency value, added to the
phase value and clipped to the range from 0 to 1 before it is used to
get the color from the color_map . If an attenuating halo is used the
color will be determined by the total density along the ray and not by
the sum of the colors for each sample.
All steps are repeated for each sample point along the ray that is inside the
halo container object. Steps 2 through 6 are repeated for all halos attached
to the halo container object.
It should be noted that in order to get a finite particle distribution, i. e.
a particle distribution that vanishes outside a finite area, a finite density
mapping and a finite density function has to be used.
A finite density mapping gives the constant value one for all points outside
a finite area. The box and spherical mappings are the only finite mapping
types.
A finite density function vanishes for all parameter values above one (there
are no negative parameter values). The only infinte density function is the
constant function.
Finite particle distributions are especially useful because they can always
be transformed to stay inside the halo container object. If particles leave
the container object they become invisible and the surface of the container
will be visible due to the density discontiniuty at the surface.
7.6.4.2 Multiple Halos
It is possible to put more than one halo inside a container object. This is
simply done by putting more than one halo statement inside the container
object statement like:
sphere { 0, 1
pigment { Clear }
halo { here comes halo nr. 1 }
halo { here comes halo nr. 2 }
halo { here comes halo nr. 3 }
...
}
The effects of the different halos are added. This is in fact similar to the
CSG union operation.
You should note that currently multiple attenuating halos will use the color
map of the last halo only. It is not possible to use different color maps for
multiple attenuating halos.
7.6.4.3 Halo Type
The type of the halo is defined by one of the following mutually exclusive
keywords (if more than one is specified the last will be used). The default
is attenuating .
halo {
attenuating | emitting | glowing | dust
}
The halo type determines how the light will interact with the particles
inside the container object. There are two basic categories of light
interaction: self-illuminated and illuminated. The first type includes the
attenuating , emitting and glowing effects while the dust effect is of the
second type.
7.6.4.3.1 Attenuating
The attenuating halo that only absorbs light passing through it is rendered
by accumulating the particle density along a ray. The total halo color is
determined from the total, accumulated density and the specified color map
(see section "Halo Color Map" for details about the color map). The
background light, i. e. the light passing through the halo, is attenuated by
the total density and added to the total halo color to get the final color of
the halo.
This model is suited to render particle distributions with a high albedo
because the final color does not depend on the transparency of single volume
elements but only on the total transparency along the ray. The albedo of a
particle is given by the amount of light scattered by this particle in all
directions in relation to the amount of incoming light. If the particle
doesn't absorb any light the albedo is one.
Clouds and steams are two of the effects that can be rendered quite realistic
by adding enough turbulence.
7.6.4.3.2 Dust
The dust halo consists of particles that do not emit any light. They only
reflect and absorb incoming light. Its syntax is:
halo {
dust
[ dust_type DUST_TYPE ]
[ eccentricity ECCENTRICITY ]
}
As the ray marches through the dust all light coming from any light sources
is accumulated and scattered according to the dust type and the current dust
density. Since this light accumulation includes a test for occlusion, other
objects may cast shadows into the dust.
The same scattering types that are used with the atmosphere in section
"Atmosphere" can be used with the dust (the default type is isotropic
scattering). They are:
#declare ISOTROPIC_SCATTERING = 1
#declare MIE_HAZY_SCATTERING = 2
#declare MIE_MURKY_SCATTERING = 3
#declare RAYLEIGH_SCATTERING = 4
#declare HENYEY_GREENSTEIN_SCATTERING = 5
The Henyey-Greenstein function needs the additional parameter eccentricity
that is described in the section about atmosphere. This keyword only applies
to dust type 5, the Henyey-Greenstein scattering.
7.6.4.3.3 Emitting
Emitting halos only emit light. Every particle is a small light source that
emits some light. This light is not attenuated by the other particles because
they are assumed to be very small.
As the ray travels through the density field of an emitting halo the color of
the particles in each volume element and their differential transparency is
determined from the color map. These intensities are accumulated to get the
total color of the density field. This total intensity is added to the light
passing through the halo. The background light is attenuated by the total
density of the halo.
Since the emitted light is not attenuated it can be used to model effects
like fire, explosions, light beams, etc. By choosing a well suited color map
those effects can be rendered with a high degree of realism.
Fire is best modeled using planar mapping. Spherical mapping and high
turbulence values can be used to create explosions (it's best to use a
periodic color map and frequencies larger than one).
Emitting halos do not cast any light on other objects like light sources do,
even though they are made up of small, light-emitting particles. In order to
make them actually emit light hundreds or thousands of small light sources
would have to be used. This would slow down tracing by a degree that would
make it useless.
7.6.4.3.4 Glowing
The glowing halo is similar to the emitting halo. The difference is that the
light emitted by the particles is attenuated by the other particles. This can
be seen as a combination of the attenuating and the emitting model.
7.6.4.4 Density Mapping
The density mapping is used to map points in space onto a linear,
one-dimensional interval between 0.0 and 1.0, thus describing the appearance
of the three-dimensional particle distribution. The different mapping types
are specified by:
halo {
planar_mapping | spherical_mapping |
cylindrical_mapping | box_mapping
}
The default mapping type is planar mapping.
Since the mapping takes place in relation to the origin of the world
coordinate system the following rule must always be kept in mind: Halo
container objects ought to be unit sized objects centered at the origin .
They can be transformed later to suit the individuals needs.
The different mapping types are explained in more detail in the following
sections.
7.6.4.4.1 Box Mapping
The box mapping can be used to create a box-shaped particle distribution. The
mapping is calculated by getting the maximum of the absolute values of each
coordinate as given by the formula:
r(x, y, z) = max(abs(x), abs(y), abs(z))
7.6.4.4.2 Cylindrical Mapping
The distance r(x,y,z) from the y-axis given by
r(x, y, z) = sqrt(x*x + z*z)
is used to get the interval values. Values larger than one are clipped to
one.
7.6.4.4.3 Planar Mapping
The distance r(x,y,z) from the x-z-plane given by
r(x, y, z) = abs(y)
is used to get the interval values. Values larger than one are clipped to
one.
7.6.4.4.4 Spherical Mapping
The distance r(x,y,z) from the origin given by
r(x, y, z) = sqrt(x*x + y*y + z*z)
is used to get the interval values. Values larger than one are clipped to
one.
7.6.4.5 Density Function
The density function determines how the actual density values are calculated
from the linear, one-dimensional interval that resulted from the density
mapping.
The density function is specified by the following keywords:
halo {
[ constant | linear | cubic | poly ]
[ max_value MAX_VALUE ]
[ exponent EXPONENT ]
}
The exponent keyword is only used together with the poly density function.
The individual functions f(r) are described in the following sections. They
all map the value r(x,y,z) calculated by the density mapping onto a suitable
density range between 0 and MAX_VALUE (specified with the keyword max_value)
.
7.6.4.5.1 Constant
The constant function gives the constant value MAX_VALUE regardless of the
interval value and the type of density mapping. It is calculated by the
trivial formula f(r) = MAX_VALUE.
The constant density function.
The constant density function can be used to create a constant particle
distribution that is only constrained by the container object.
7.6.4.5.2 Linear
A linear falloff from MAX_VALUE at r=0 to zero at r=1 is created with the
linear density function. It is given by:
f(r) = MAX_VALUE * (1 - r)
7.6.4.5.3 Cubic
The cubic function gives a smooth blend between the maximum value MAX_VALUE
at r=0 and 0 at r=1. It is given by:
f(r) = MAX_VALUE * (2 * r - 3) * r * r + 1
The cubic density function.
7.6.4.5.4 Poly
A polynomial function can be used to get a large variety of density
functions. All have the maximum value MAX_VALUE at r=0 and the minimum value
0 at r=1. It is given by:
f(r) = MAX_VALUE * (1 - r) ^ EXPONENT
The polynomial density function for different exponent values.
The exponent is given by the exponent keyword. In case of EXPONENT=0 you'll
get a linear falloff.
7.6.4.6 Halo Color Map
The density f(r), which ranges from 0 to MAX_VALUE, is mapped onto the color
map to get the color and differential translucency for each volume element as
the ray marches through the density field (the final color of attenuating
halos is calculated from the total density; see section "Halo Mapping" and
section "Attenuating" ). The differential translucency determines for each
value of f(r) how much the total opacity has to be increased (or decreased).
The color map is specified by:
halo {
[ colour_map COLOUR_MAP ]
}
The differential translucency is stored in the transmittance channel of the
map's color entries. A simple example is given by
colour_map {
[0 rgbt<1, 1, 1, 1>]
[1 rgbt<1, 1, 1, 0>]
}
In this example areas with a low density (small f(r)) will be translucent
(large differential translucency of 1=100%) and areas with a high density
(large f(r)) will be opaque (small differential translucency of 0=0%). You
should note that negative transmittance values can be used to create very
dense fields.
In the case of the dust halo the filter channels of the colors in the color
map are used to specify the amount of light that will be filtered by the
corresponding color map entry. For all other halo types the filter value is
ignored.
7.6.4.7 Halo Sampling
The halo effects are calculated by marching through the density field along a
ray. At discrete steps samples are taken from the density field and evaluated
according to the color map and all other parameters. The effects of all
volume elements are accumulated to get the total effect.
The following parameters are used to tune the sampling process:
halo {
[ samples SAMPLES ]
[ aa_level AA_LEVEL ]
[ aa_threshold AA_THRESHOLD ]
[ jitter JITTER ]
}
7.6.4.7.1 Number of Samples
The number of samples that are taken along the ray inside the halo container
object is specified by the samples keyword. The greater the number of samples
the more denser the density field is sampled and the more accurate but slower
the result will be.
The default number of samples is 10. This is sufficient for simple density
fields that don't use turbulence.
High turbulence values and dust halos normally need a large number of samples
to avoid aliasing artifacts.
7.6.4.7.2 Super-Sampling
The sampling is prone to alias (like the atmosphere sampling in section
"Atmosphere" ). One way to reduce possible aliasing artifacts is to use
super-sampling. If two neighboring samples differ too much an additional
sampling is taken in-between. This process recurses until the values of the
samples are close too each other or the maximum recursion level given by
AA_LEVEL is reached. The threshold to kick super-sampling in is given by
AA_THRESHOLD .
By default super-sampling is not used. The default values for AA_THRESHOLD
and AA_LEVEL are 0.3 and 3 respectively.
7.6.4.7.3 Jitter
Jitter can be used to introduce some noise to the sampling locations. This
may help to reduce aliasing artifacts at the cost of an increased noise level
in the image. Since the human visual system is much more forgiving to noise
than it is to regular patterns this is not much of a problem.
By default jittering is not used. The values should be smaller than 1.0.
7.6.4.8 Halo Modifiers
This section covers all general halo modifiers. They are:
halo {
[ turbulence <TURBULENCE> ]
[ octaves OCTAVES ]
[ omega OMEGA ]
[ lambda LAMBDA ]
[ frequency FREQUENCY ]
[ phase PHASE ]
[ scale <VECTOR> ]
[ rotate <VECTOR> ]
[ translate <VECTOR> ]
}
7.6.4.8.1 Turbulence Modifier
7.6.4.8.2 Octaves Modifier
7.6.4.8.3 Omega Modifier
7.6.4.8.4 Lambda Modifier
7.6.4.8.5 Frequency Modifier
The frequency parameter adjusts the number of times the density interval is
mapped onto itself, i. e. the range from 0.0 to 1.0, before it is mapped onto
the color map. The formula doing this is:
f_new(r) = (f(r) * FREQUENCY + PHASE) modulo 1.0
7.6.4.8.6 Phase Modifier
The phase parameter determines the offset at which the mapping of the density
field onto itself starts. See the formula in the previous section for how the
pahse is used.
7.6.4.8.7 Transformation Modifiers
Halos can be transformed using the rotate, scale and translate keywords. You
have to be careful that you don't move the density field out of the container
object though.
7.6.5 Special Textures
Special textures are complex textures made up of multiple textures. The
component textures may be plain textures or may be made up of special
textures. A plain texture has just one pigment, normal and finish statement
(and maby some halo statements). Even a pigment with a pigment map is still
one pigment and thus considered a plain texture as are normals with normal
map statements.
Special textures use either a texture_map keyword to specify a blend or
pattern of textures or they use a bitmap similar to an image map called a
material map (specified with the material_map keyword).
There are restrictions on using special textures. A special texture may not
be used as a default texture (see section "Default Directive" ). A special
texture cannot be used as a layer in a layered texture however you may use
layered textures as any of the textures contained within a special texture.
7.6.5.1 Texture Maps
In addition to specifying blended color with a color map or a pigment map you
may create a blend of textures using texture_map . The syntax for a texture
map is identical to the pigment map except you specify a texture in each map
entry.
A texture map is specified by...
texture{
PATTERN_TYPE
texture_map {
[ NUM_1 TEXTURE_BODY_1]
[ NUM_2 TEXTURE_BODY_2]
[ NUM_3 TEXTURE_BODY_3]
...
}
TEXTURE_MODIFIERS...
}
Where NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive. A
TEXTURE_BODY is anything that would normally appear inside a texture {... }
statement but the texture keyword and {} braces are not needed. Note that the
[] brackets are part of the actual statement. They are not notational symbols
denoting optional parts. The brackets surround each entry in the map. There
may be from 2 to 256 entries in the map.
For example:
texture {
gradient x //this is the PATTERN_TYPE
texture_map {
[0.3 pigment{Red} finish{phong 1}]
[0.3 T_Wood11] //this is a texture identifier
[0.6 T_Wood11]
[0.9 pigment{DMFWood4} finish{Shiny}]
}
}
When the gradient x function returns values from 0.0 to 0.3 the red
highlighted texture is used. From 0.3 to 0.6 the texture identifier T_Wood11
is used. From 0.6 up to 0.9 a blend of T_Wood11 and a shiny DMFWood4 is used.
From 0.9 on up only the shiny wood is used.
Texture maps may be nested to any level of complexity you desire. The
textures in a map may have color maps or texture maps or any type of texture
you want.
The blended area of a texture map works by fully calculating both
contributing textures in their entirety and then linearly interpolating the
apparent colors. This means that reflection, refraction and lighting
calculations are done twice for every point. This is in contrast to using a
pigment map and a normal map in a plain texture, where the pigment is
computed, then the normal, then reflection, refraction and lighting are
calculated once for that point.
Entire textures may also be used with the block patterns such as checker,
hexagon and brick. For example...
texture {
checker
texture { T_Wood12 scale .8 }
texture { pigment { White_Marble } finish { Shiny } scale .5 }
}
}
Note that in the case of block patterns the texture {... } wrapping is
required around the texture information. Also note that this syntax prohibits
the use of a layered texture however you can work around this by declaring a
texture identifier for the layered texture and referencing the identifier.
A texture map is also used with the average pattern type. See "Average" for
details.
7.6.5.2 Tiles
Earlier versions of POV-Ray had a special texture called tiles texture that
created a checkered pattern of textures. Although it is still supported for
backwards computability you should use a checker block texture pattern
described in section "Texture Maps" rather than tiles textures.
7.6.5.3 Material Maps
The material map special texture extends the concept of image maps to apply
to entire textures rather than solid colors. A material map allows you to
wrap a 2-D bit-mapped texture pattern around your 3-D objects.
Instead of placing a solid color of the image on the shape like an image map,
an entire texture is specified based on the index or color of the image at
that point. You must specify a list of textures to be used like a texture
palette rather than the usual color palette.
When used with mapped file types such as GIF, and some PNG and TGA images,
the index of the pixel is used as an index into the list of textures you
supply. For unmapped file types such as some PNG and TGA images the 8 bit
value of the red component in the range 0-255 is used as an index.
If the index of a pixel is greater than the number of textures in your list
then the index is taken modulo N where N is the length of your list of
textures.
7.6.5.3.1 Specifying a Material Map
The syntax of a material map is...
texture {
material_map {
FILE_TYPE "filename"
BITMAP_MODIFIERS...
texture {..}. // First used for index 0
texture {..}. // Second texture used for index 1
texture {..}. // Third texture used for index 2
texture {..}. // Fourth texture used for index 3
// and so on for however many used.
}
TRANSFORMATION...
}
Where FILE_TYPE is one of the following keywords gif , tga , iff , ppm , pgm
, png or sys . This is followed by the name of the file using any valid
string expression. Several optional modifiers may follow the file
specification. The modifiers are described below. Note that earlier versions
of POV-Ray allowed some modifiers before the FILE_TYPE but that syntax is
being phased out in favor of the syntax described here.
Filenames specified in the material_map statements will be searched for in
the home (current) directory first and, if not found, will then be searched
for in directories specified by any +L switches or Library_Path options. This
would facilitate keeping all your material map files in a separate
subdirectory and specifying a library path to them. Note that any operating
system default paths are not searched unless you also specify them as a
Library_Path .
By default, the material is mapped onto the x-y-plane. The material is
projected onto the object as though there were a slide projector somewhere in
the -z-direction. The material exactly fills the square area from (x,y)
coordinates (0,0) to (1,1) regardless of the bitmap's original size in
pixels. If you would like to change this default you may translate, rotate or
scale the texture to map it onto the object's surface as desired.
The file name is optionally followed by one or more BITMAP_MODIFIERS. See
"Bitmap Modifiers" for other details.
After a material_map statement but still inside the texture statement you may
apply any legal texture modifiers. Note that no other pigment, normal, finish
or halo statements may be added to the texture outside the material map. The
following is illegal:
texture {
material_map {
gif "matmap.gif"
texture {T1}
texture {T2}
texture {T3}
}
finish {phong 1.0}
}
The finish must be individually added to each texture.
Note that earlier versions of POV-Ray allowed such specifications but they
were ignored. The above restrictions on syntax were necessary for various bug
fixes. This means some POV-Ray 1.0 scenes using material maps many need minor
modifications that cannot be done automatically with the version
compatibility mode.
If particular index values are not used in an image then it may be necessary
to supply dummy textures. It may be necessary to use a paint program or other
utility to examine the map file's palette to determine how to arrange the
texture list.
The textures within a material map texture may be layered but material map
textures do not work as part of a layered texture. To use a layered texture
inside a material map you must declare it as a texture identifier and invoke
it in the texture list.
7.6.6 Layered Textures
It is possible to create a variety of special effects using layered textures.
A layered texture consists of several textures that are partially transparent
and are laid one on top of the other to create a more complex texture. The
different texture layers show through the transparent portions to create the
appearance of one texture that is a combination of several textures.
You create layered textures by listing two or more textures one right after
the other. The last texture listed will be the top layer, the first one
listed will be the bottom layer. All textures in a layered texture other than
the bottom layer should have some transparency. For example:
object {
My_Object
texture {T1} // the bottom layer
texture {T2} // a semi-transparent layer
texture {T3} // the top semi-transparent layer
}
In this example T2 shows only where T3 is transparent and T1 shows only where
T2 and T3 are transparent.
The color of underlying layers is filtered by upper layers but the results do
not look exactly like a series of transparent surfaces. If you had a stack of
surfaces with the textures applied to each, the light would be filtered
twice: once on the way in as the lower layers are illuminated by filtered
light and once on the way out. Layered textures do not filter the
illumination on the way in. Other parts of the lighting calculations work
differently as well. The results look great and allow for fantastic looking
textures but they are simply different from multiple surfaces. See stones.inc
in the standard include files directory for some magnificent layered
textures.
Note layered textures must use the texture {... } wrapped around any pigment,
normal or finish statements. Do not use multiple pigment, normal or finish
statements without putting them inside the texture statement.
Layered textures may be declared. For example
#declare Layered_Examp =
texture {T1}
texture {T2}
texture {T3}
may be invoked as follows:
object {
My_Object
texture {
Layer_Examp
// Any pigment, normal or finish here
// modifies the bottom layer only.
}
}
If you wish to use a layered texture in a block pattern, such as checker,
hexagon, or brick, or in a material map, you must declare it first and then
reference it inside a single texture statement. A special texture cannot be
used as a layer in a layered texture however you may use layered textures as
any of the textures contained within a special texture.
7.6.7 Patterns
POV-Ray uses a method called three-dimensional solid texturing to define the
color, bumpiness and other properties of a surface. You specify the way that
the texture varies over a surface by specifying a pattern . Patterns are used
in pigments, normals and texture maps.
All patterns in POV-Ray are three dimensional. For every point in space, each
pattern has a unique value. Patterns do not wrap around a surface like
putting wallpaper on an object. The patterns exist in 3d and the objects are
carved from them like carving an object from a solid block of wood or stone.
Consider a block of wood. It contains light and dark bands that are
concentric cylinders being the growth rings of the wood. On the end of the
block you see these concentric circles. Along its length you see lines that
are the veins. However the pattern exists throughout the entire block. If you
cut or carve the wood it reveals the pattern inside. Similarly an onion
consists of concentric spheres that are visible only when you slice it.
Marble stone consists of wavy layers of colored sediments that harden into
rock.
These solid patterns can be simulated using mathematical functions. Other
random patterns such as granite or bumps and dents can be generated using a
random number system and a noise function.
In each case, the x, y, z coordinate of a point on a surface is used to
compute some mathematical function that returns a float value. When used with
color maps or pigment maps, that value looks up the color of the pigment to
be used. In normal statements the pattern function result modifies or
perturbs the surface normal vector to give a bumpy appearance. Used with a
texture map, the function result determines which combinations of entire
textures to be used.
The following sections describe each pattern. See the sections "Pigment" and
"Normal" for more details on how to use patterns.
7.6.7.1 Agate
The agate pattern is a banded pattern similar to marble but it uses a
specialized built-in turbulence function that is different from the
traditional turbulence. The traditional turbulence can be used as well but it
is generally not necessary because agate is already very turbulent. You may
control the amount of the built-in turbulence by adding the agate_turb
keyword followed by a float value. For example: pigment {
agate
agate_turb 0.5
color_map {
...
}
}
The agate pattern uses the ramp_wave wave type by default but may use any
wave type. The pattern may be used with color_map , pigment_map , normal_map
, slope_map and texture_map .
7.6.7.2 Average
Technically average is not a pattern type but it is listed here because the
syntax is similar to other patterns. Typically a pattern type specifies how
colors or normals are chosen from a pigment map or normal map, however
average tells POV-Ray to average together all of the patterns you specify.
Average was originally designed to be used in a normal statement with a
normal map as a method of specifying more than one normal pattern on the same
surface. However average may be used in a pigment statement with a pigment
map or in a texture statement with a texture map to average colors too.
When used with pigments, the syntax is:
pigment {
average
pigment_map
{
[WEIGHT_1 PIGMENT_BODY_1]
[WEIGHT_2 PIGMENT_BODY_2]
...
[WEIGHT_n PIGMENT_BODY_n]
}
PIGMENT_MODIFIER
}
Similarly you may use a texture map in a texture statement. All textures are
fully computed. The resulting colors are then weighted and averaged.
When used with a normal map in a normal statement, multiple copies of the
original surface normal are created and are perturbed by each pattern. The
perturbed normals are then weighted, added and normalized.
See the sections "Pigment Maps" , "Normal Maps" and "Texture Maps" for more
information.
7.6.7.3 Bozo
The bozo pattern is a very smooth, random noise function that is
traditionally used with some turbulence to create clouds. The spotted pattern
is identical to bozo but in early versions of POV-Ray spotted did not allow
turbulence to be added. Turbulence can now be added to any pattern so these
are redundant but both are retained for backwards compatibility. The bumps
pattern is also identical to bozo when used anywhere except in a normal
statement. When used as a normal, bumps uses a slightly different method to
perturb the normal with a similar noise function.
The bozo noise function has the following properties:
1. It's defined over 3D space i.e., it takes x, y, and z and returns the
noise value there.
2. If two points are far apart, the noise values at those points are
relatively random.
3. If two points are close together, the noise values at those points are
close to each other.
You can visualize this as having a large room and a thermometer that ranges
from 0.0 to 1.0. Each point in the room has a temperature. Points that are
far apart have relatively random temperatures. Points that are close together
have close temperatures. The temperature changes smoothly but randomly as we
move through the room.
Now let's place an object into this room along with an artist. The artist
measures the temperature at each point on the object and paints that point a
different color depending on the temperature. What do we get? A POV-Ray bozo
texture!
The bozo pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.4 Brick
The brick pattern generates a pattern of bricks. The bricks are offset by
half a brick length on every other row in the x- and z-directions. A layer of
mortar surrounds each brick. The syntax is given by
pigment {
brick COLOR_1, COLOR_2
brick_size VECTOR
mortar FLOAT
}
where COLOR_1 is the color of the mortar and COLOR_2 is the color of the
brick itself. If no colors are specified a default deep red and dark gray are
used. The default size of the brick and mortar together is <8, 3, 4.5> units.
The default thickness of the mortar is 0.5 units. These values may be changed
using the optional brick_size and mortar pattern modifiers. You may also use
pigment statements in place of the colors. For example:
pigment {
brick pigment{Jade}, pigment{Black_Marble}
}
When used with normals, the syntax is normal {
brick BUMP_FLOAT
}
Where BUMP_FLOAT is an optional bump size float value. You may also use full
normal statements. For example:
normal {
brick normal{bumps 0.2}, normal{granite 0.3}
}
When used with textures, the syntax is %%% texture {
brick texture{T_Gold_1A}, texture{Stone12}
}
This is a block pattern which cannot use wave types, color map, or slope map
modifiers.
7.6.7.5 Bumps
The bumps pattern was originally designed only to be used as a normal
pattern. It uses a very smooth, random noise function that creates the look
of rolling hills when scaled large or a bumpy orange peal when scaled small.
Usually the bumps are about 1 unit apart.
When used as a normal, bumps uses a specialized normal perturbation function.
This means that the bumps pattern cannot be used with normal map, slope map
or wave type modifiers in a normal statement.
When used as a pigment pattern or texture pattern, the bumps pattern is
identical to bozo or spotted and is similar to normal bumps but is not
identical as are most normals when compared to pigments. When used as pigment
or texture statements the bumps pattern uses the ramp_wave wave type by
default but may use any wave type. The pattern may be used with color_map ,
pigment_map , and texture_map .
7.6.7.6 Checker
The checker pattern produces a checkered pattern consisting of alternating
squares of COLOR_1 and COLOR_2. If no colors are specified then default blue
and green colors are used.
pigment { checker COLOR_1, COLOR_2 }
The checker pattern is actually a series of cubes that are one unit in size.
Imagine a bunch of 1 inch cubes made from two different colors of modeling
clay. Now imagine arranging the cubes in an alternating check pattern and
stacking them in layer after layer so that the colors still alternate in
every direction. Eventually you would have a larger cube. The pattern of
checks on each side is what the POV-Ray checker pattern produces when applied
to a box object. Finally imagine cutting away at the cube until it is carved
into a smooth sphere or any other shape. This is what the checker pattern
would look like on an object of any kind.
You may also use pigment statements in place of the colors. For example:
pigment { checker pigment{Jade}, pigment{Black_Marble} }
When used with normals, the syntax is
normal { checker BUMP_FLOAT }
Where BUMP_FLOAT is an optional bump size float value. You may also use full
normal statements. For example:
normal {
checker normal{gradient x scale .2}, normal{gradient y scale .2}
}
When used with textures, the syntax is...
texture { checker texture{T_Wood_3A},texture{Stone12} }
This use of checker as a texture pattern replaces the special tiles texture
in previous versions of POV-Ray. You may still use tiles but it may be phased
out in future versions so checker textures are best.
This is a block pattern which cannot use wave types, color map, or slope map
modifiers.
7.6.7.7 Crackle
The crackle pattern is a set of random tiled polygons. With a large scale and
no turbulence it makes a pretty good stone wall or floor. With a small scale
and no turbulence it makes a pretty good crackle ceramic glaze. Using high
turbulence it makes a good marble that avoids the problem of apparent
parallel layers in traditional marble.
Mathematically, the set crackle(p)=0 is a 3D Voronoi diagram of a field of
semi random points and crackle(p) < 0 is the distance from the set along the
shortest path (a Voronoi diagram is the locus of points equidistant from
their two nearest neighbors from a set of disjoint points, like the membranes
in suds are to the centers of the bubbles).
The crackle pattern uses the ramp_wave wave type by default but may use any
wave type. The pattern may be used with color_map , pigment_map , normal_map
, slope_map and texture_map .
7.6.7.8 Dents
The dents pattern was originally designed only to be used as a normal
pattern. It is especially interesting when used with metallic textures. It
gives impressions into the metal surface that look like dents have been
beaten into the surface with a hammer. Usually the dents are about 1 unit
apart.
When used as a normal pattern, dents uses a specialized normal perturbation
function. This means that the dents pattern cannot be used with normal map,
slope map or wave type modifiers in a normal statement.
When used as a pigment pattern or texture pattern, the dents pattern is
similar to normal dents but is not identical as are most normals when
compared to pigments. When used in pigment or texture statements the dents
pattern uses the ramp_wave wave type by default but may use any wave type.
The pattern may be used with color_map , pigment_map and texture_map .
7.6.7.9 Gradient
{/TARGET 0 'gradientpatterns is the gradient pattern. It is specified as
pigment {gradient VECTOR}
where VECTOR is a vector pointing in the direction that the colors blend. For
example pigment { gradient x } // bands of color vary as you move
// along the "x" direction.
produces a series of smooth bands of color that look like layers of colors
next to each other. Points at x=0 are the first color in the color map. As
the x location increases it smoothly turns to the last color at x=1. Then it
starts over with the first again and gradually turns into the last color at
x=2. The pattern reverses for negative values of x. Using gradient y or
gradient z makes the colors blend along the y- or z-axis. Any vector may be
used but x, y and z are most common.
As a normal pattern, gradient generates a saw-tooth or ramped wave
appearance. The syntax is
normal { gradient VECTOR, BUMP_FLOAT}
where the VECTOR giving the orientation is a required parameter but the
BUMP_FLOAT bump size which follows is optional.
The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.10 Granite
This pattern uses a simple 1/f fractal noise function to give a good granite
pattern. This pattern is used with creative color maps in stones.inc to
create some gorgeous layered stone textures.
As a normal pattern it creates an extremely bumpy surface that looks like a
gravel driveway or rough stone.
The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.11 Hexagon
The hexagon pattern is a block pattern that generates a repeating pattern of
hexagons in the x-y-plane. In this instance imagine tall rods that are
hexagonal in shape and are parallel to the y-axis and grouped in bundles like
shown in the example image. Three separate colors should be specified as
follows:
pigment { hexagon COLOR_1, COLOR_2, COLOR_3 }
_____
/ \
/ C2 _____
| / \
| _____/ C3 \
| / /|
/ C1 _____/ |
| /| | |
| _____/ | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | |
| | | | |
| |
| |
The hexagon pattern.
The three colors will repeat the hexagonal pattern with hexagon COLOR_1
centered at the origin, COLOR_2 in the +z-direction and COLOR_3 to either
side. Each side of the hexagon is one unit long. The hexagonal rods of color
extend infinitely in the +y- and -y-directions. If no colors are specified
then default blue, green and red colors are used.
You may also use pigment statements in place of the colors. For example:
pigment {
hexagon pigment { Jade },
pigment { White_Marble },
pigment { Black_Marble }
}
When used with normals, the syntax is
normal { hexagon BUMP_FLOAT }
Where BUMP_FLOAT is an optional bump size float value. You may also use full
normal statements. For example:
normal {
hexagon
normal { gradient x scale .2 },
normal { gradient y scale .2 },
normal { bumps scale .2 }
}
When used with textures, the syntax is...
texture {
hexagon
texture { T_Gold_3A },
texture { T_Wood_3A },
texture { Stone12 }
}
This is a block pattern which cannot use wave types, color map, or slope map
modifiers.
7.6.7.12 Leopard
Leopard creates regular geometric pattern of circular spots.
The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.13 Mandel
The mandel pattern computes the standard Mandelbrot fractal pattern and
projects it onto the x-y-plane. It uses the x and y coordinates to compute
the Mandelbrot set. The pattern is specified with the keyword mandel followed
by an integer number. This number is the maximum number of iterations to be
used to compute the set. Typical values range from 10 up to 256 but any
positive integer may be used. For example:
pigment {
mandel 25
color_map {
[0.0 color Cyan]
[0.3 color Yellow]
[0.6 color Magenta]
[1.0 color Cyan]
}
scale .5
}
The value passed to the color map is computed by the formula:
value = number_of_iterations / max_iterations
When used as a normal pattern, the syntax is...
normal {
mandel ITER, BUMP_AMOUNT
}
where the required integer ITER value is optionally followed by a float bump
size.
The pattern extends infinitely in the z-direction similar to a planar image
map. The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.14 Marble
The marble pattern is very similar to the gradient x pattern. The gradient
pattern uses a default ramp_wave wave type which means it uses colors from
the color map from 0.0 up to 1.0 at location x=1 but then jumps back to the
first color for x > 1 and repeats the pattern again and again. However the
marble pattern uses the triangle_wave wave type in which it uses the color
map from 0 to 1 but then it reverses the map and blends from 1 back to zero.
For example:
pigment {
gradient x
color_map {
[0.0 color Yellow]
[1.0 color Cyan]
}
}
This blends from yellow to cyan and then it abruptly changes back to yellow
and repeats. However replacing gradient x with marble smoothly blends from
yellow to cyan as the x coordinate goes from 0.0 to 0.5 and then smoothly
blends back from cyan to yellow by x=1.0.
Earlier versions of POV-Ray did not allow you to change wave types. Now that
wave types can be changed for most any pattern, the distinction between
marble and gradient x is only a matter of default wave types.
When used with turbulence and an appropriate color map, this pattern looks
like veins of color of real marble, jade or other types of stone. By default,
marble has no turbulence.
The pattern may be used with color_map , pigment_map , normal_map , slope_map
and texture_map .
7.6.7.15 Onion
Onion is a pattern of concentric spheres like the layers of an onion. Each
layer is one unit thick.
The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.16 Quilted
The quilted pattern was originally designed only to be used as a normal
pattern. The quilted pattern is so named because it can create a pattern
somewhat like a quilt or a tiled surface. The squares are actually 3-D cubes
that are 1 unit in size.
When used as a normal pattern it uses a specialized normal perturbation
function. This means that the quilted pattern cannot be used with normal map,
slope map or wave type modifiers in a normal statement.
When used as a pigment pattern or texture pattern, the quilted pattern is
similar to normal quilted but is not identical as are most normals when
compared to pigments. When used in pigment or texture statements the quilted
pattern uses the ramp_wave wave type by default but may use any wave type.
The pattern may be used with color_map , pigment_map and texture_map .
The two parameters control0 and control1 are used to adjust the curvature of
the seam or gouge area between the quilts . The syntax is:
normal {
quilted AMOUNT
control0 C0
control1 C1
}
The values should generally be kept to around the 0.0 to 1.0 range. The
default value is 1.0 if none is specified. Think of this gouge between the
tiles in cross-section as a sloped line.
Quilted pattern with c0=0 and different values for c1.
Quilted pattern with c0=0.33 and different values for c1.
Quilted pattern with c0=0.67 and different values for c1.
Quilted pattern with c0=1 and different values for c1.
This straight slope can be made to curve by adjusting the two control values.
The control values adjust the slope at the top and bottom of the curve. A
control values of 0 at both ends will give a linear slope, as shown above,
yielding a hard edge. A control value of 1 at both ends will give an "s"
shaped curve, resulting in a softer, more rounded edge.
7.6.7.17 Radial
The radial pattern is a radial blend that wraps around the +y-axis. The color
for value 0.0 starts at the +x-direction and wraps the color map around from
east to west with 0.25 in the -z-direction, 0.5 in -x, 0.75 at +z and back to
1.0 at +x. Typically the pattern is used with a frequency modifier to create
multiple bands that radiate from the y-axis.
The pattern uses the ramp_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.18 Ripples
The ripples pattern was originally designed only to be used as a normal
pattern. It makes the surface look like ripples of water. The ripples radiate
from 10 random locations inside the unit cube area <0,0,0> to <1,1,1>. Scale
the pattern to make the centers closer or farther apart.
Usually the ripples from any given center are about 1 unit apart. The
frequency keyword changes the spacing between ripples. The phase keyword can
be used to move the ripples outwards for realistic animation.
The number of ripple centers can be changed with the global parameter
global_settings {number_of_waves FLOAT } somewhere in the scene. This affects
the entire scene. You cannot change the number of wave centers on individual
patterns. See "Number_Of_Waves" for details.
When used as a normal pattern, ripples uses a specialized normal perturbation
function. This means that the ripples pattern cannot be used with normal map,
slope map or wave type modifiers in a normal statement.
When used in pigment or texture statements the ripples pattern uses the
ramp_wave wave type by default but may use any wave type. The pattern may be
used with color_map , pigment_map and texture_map .
7.6.7.19 Spiral1
The spiral1 pattern creates a spiral that winds around the y-axis similar to
a screw. Its syntax is:
pigment {
spiral1 NUMBER_OF_ARMS
}
The NUMBER_OF_ARMS value determins how may arms are winding around the
y-axis.
The pattern uses the triangle_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.20 Spiral2
The spiral2 pattern is a modification of the spiral1 pattern with an
extraordinary look.
The pattern uses the triangle_wave wave type by default but may use any wave
type. The pattern may be used with color_map , pigment_map , normal_map ,
slope_map and texture_map .
7.6.7.21 Spotted
The spotted pattern is identical to the bozo pattern. Early versions of
POV-Ray did not allow turbulence to be used with spotted. Now that any
pattern can use turbulence there is no difference between bozo and spotted.
See "Bozo" for details.
7.6.7.22 Waves
The waves pattern was originally designed only to be used as a normal
pattern. The waves pattern looks similar to the ripples pattern except the
features are rounder and broader. The effect is to make waves that look more
like deep ocean waves. The waves radiate from ten random locations inside the
unit cube area <0,0,0> to <1,1,1>. Scale the pattern to make the centers
closer or farther apart.
Usually the waves from any given center are about 1 unit apart. The frequency
keyword changes the spacing between waves. The phase keyword can be used to
move the waves outwards for realistic animation.
The number of ripple centers can be changed with the global parameter
global_settings {number_of_waves FLOAT } somewhere in the scene. This affects
the entire scene. You cannot change the number of wave centers on individual
patterns. See "Number_Of_Waves" for details.
When used as a normal pattern, waves uses a specialized normal perturbation
function. This means that the waves pattern cannot be used with normal map,
slope map or wave type modifiers in a normal statement.
When used in pigment or texture statements the waves pattern uses the
ramp_wave wave type by default but may use any wave type. The pattern may be
used with color_map , pigment_map and texture_map .
7.6.7.23 Wood
The wood pattern consists of concentric cylinders centered on the z-axis.
When appropriately colored, the bands look like the growth rings and veins in
real wood. Small amounts of turbulence should be added to make it look more
realistic. By default, wood has no turbulence.
Unlike most patterns, the wood pattern uses the triangle_wave wave type by
default. This means that like marble, wood uses color map values 0.0 to 1.0
then repeats the colors in reverse order from 1.0 to 0.0. However you may use
any wave type. The pattern may be used with color_map , pigment_map ,
normal_map , slope_map and texture_map .
7.6.7.24 Wrinkles
The wrinkles pattern was originally designed only to be used as a normal
pattern. It uses a 1/f noise pattern similar to granite but the features in
wrinkles are sharper. The pattern can be used to simulate wrinkled cellophane
or foil. It also makes an excellent stucco texture.
When used as a normal pattern it uses a specialized normal perturbation
function. This means that the wrinkles pattern cannot be used with normal
map, slope map or wave type modifiers in a normal statement.
When used as a pigment pattern or texture pattern, the wrinkles pattern is
similar to normal wrinkles but is not identical as are most normals when
compared to pigments. When used in pigment or texture statements the wrinkles
pattern uses the ramp_wave wave type by default but may use any wave type.
The pattern may be used with color_map , pigment_map and texture_map .
7.6.8 Pattern Modifiers
Pattern modifiers are statements or parameters which modify how a pattern is
evaluated or tells what to do with the pattern. The modifiers color_map and
pigment_map apply only to pigments. See section "Pigment" . The modifiers
bump_size , slope_map and normal_map apply only to normals. See section
"Normal" . The texture_map modifier can only be used with textures. See
section "Texture Maps" .
The pattern modifiers in the following section can be used with pigment,
normal or texture patterns.
7.6.8.1 Transforming Patterns
The most common pattern modifiers are the transformation modifiers translate
, rotate , scale and matrix . For details on these commands see
"Transformations" .
These modifiers may be placed inside pigment, normal and texture statements
to change the position, size and orientation of the patterns.
In general the order of transformations relative to other pattern modifiers
such as turbulence , color_map and other maps is not important. For example
scaling before or after turbulence makes no difference. The turbulence is
done first, then the scaling regardless of which is specified first. However
the order in which transformations are performed relative to warp statements
is important. See "Warps" for details.
7.6.8.2 Frequency and Phase
The frequency and phase modifiers act as a type of scale and translate
modifiers for color_map , pigment_map , normal_map , slope_map and
texture_map . This discussion uses a color map as an example but the same
principles apply to pigment maps, normal maps, slope maps and texture maps.
The frequency keyword adjusts the number of times that a color map repeats
over one cycle of a pattern. For example gradient covers color map values 0
to 1 over the range from x=0 to x=1. By adding frequency 2.0 the color map
repeats twice over that same range. The same effect can be achieved using
scale 0.5*x so the frequency keyword isn't that useful for patterns like
gradient.
However the radial pattern wraps the color map around the +y-axis once. If
you wanted two copies of the map (or 3 or 10 or 100) you'd have to build a
bigger map. Adding frequency 2.0 causes the color map to be used twice per
revolution. Try this:
pigment {
radial
color_map{[0.5 color Red][0.5 color White]}
frequency 6
}
The result is six sets of red and white radial stripes evenly spaced around
the object.
The float after frequency can be any value. Values greater than 1.0 causes
more than one copy of the map to be used. Values from 0.0 to 1.0 cause a
fraction of the map to be used. Negative values reverses the map.
The phase value causes the map entries to be shifted so that the map starts
and ends at a different place. In the example above if you render successive
frames at phase 0 then phase 0.1, phase 0.2 etc you could create an animation
that rotates the stripes. The same effect can be easily achieved by rotating
the radial pigment using rotate y*Angle but there are other uses where phase
can be handy.
Sometimes you create a great looking gradient or wood color map but you want
the grain slightly adjusted in or out. You could re-order the color map
entries but that's a pain. A phase adjustment will shift everything but keep
the same scale. Try animating a mandel pigment for a color palette rotation
effect.
Frequency and phase have no effect on block patterns checker, brick and
hexagon nor do they effect image maps, bump maps or material maps. They also
have no effect in normal statements when used with bumps, dents, quilted or
wrinkles because these normal patterns cannot use normal_map or slope_map .
They can be used with normal patterns ripples and waves even though these two
patterns cannot use normal_map or slope_map either. When used with ripples or
waves, frequency adjusts the space between features and phase can be adjusted
from 0.0 to 1.0 to cause the ripple or waves to move relative to their center
for animating the features.
These values work by applying the following formula
NEW_VALUE = fmod ( OLD_VALUE * FREQUENCY + PHASE, 1.0 ).
7.6.8.3 Waveform
Most patterns that take color_map , pigment_map , slope_map , normal_map or
texture_map use the entries in the map in order from 0.0 to 1.0. The wood and
marble patterns use the map from 0.0 to 1.0 and then reverses it and runs it
from 1.0 to 0.0. The difference can easily be seen when these patterns are
used as normal patterns with no maps.
Patterns such as gradient or onion generate a grove or slot that looks like a
ramp that drops off sharply. This is called a ramp_wave wave type. However
wood and marble slope upwards to a peak, then slope down again in a
triangle_wave . In previous versions of POV-Ray there was no way to change
the wave types. You could simulate a triangle wave on a ramp wave pattern by
duplicating the map entries in reverse, however there was no way to use a
ramp wave on wood or marble.
Now any pattern that takes a map can have the default wave type overridden.
For example:
pigment { wood color_map { MyMap } ramp_wave }
Also available are sine_wave and scallop_wave types. These types are of most
use in normal patterns as a type of built-in slope map. The sine_wave takes
the zig-zag of a ramp wave and turns it into a gentle rolling wave with
smooth transitions. The scallop_wave uses the absolute value of the sine wave
which looks like corduroy when scaled small or like a stack of cylinders when
scaled larger.
Although any of these wave types can be used for pigments, normals or
textures, the sine_wave and scallop_wave types are not as noticeable on
pigments or textures as they are for normals.
Wave types have no effect on block patterns checker, brick and hexagon nor do
they effect image maps, bump maps or material maps. They also have no effect
in normal statements when used with bumps, dents, quilted or wrinkles because
these normal patterns cannot use normal_map or slope_map .
7.6.8.4 Turbulence
followed by a float or vector may be used to stir up any pigment, normal,
texture, irid or halo. A number of optional parameters may be used with
turbulence to control how it is computed. For example:
pigment {
wood color_map { MyMap }
turbulence TURB_VECTOR
octaves FLOAT
omega FLOAT
lambda FLOAT
}
Typical turbulence values range from the default 0.0, which is no turbulence,
to 1.0 or more, which is very turbulent. If a vector is specified different
amounts of turbulence are applied in the x-, y- and z-direction. For example
turbulence <1.0, 0.6, 0.1>
has much turbulence in the x-direction, a moderate amount in the y-direction
and a small amount in the z-direction.
Turbulence uses a random noise function called DNoise . This is similar to
the noise used in the bozo pattern except that instead of giving a single
value it gives a direction. You can think of it as the direction that the
wind is blowing at that spot. Points close together generate almost the same
value but points far apart are randomly different.
In general the order of turbulence parameters relative to other pattern
modifiers such as transformations, color maps and other maps is not
important. For example scaling before or after turbulence makes no
difference. The turbulence is done first, then the scaling regardless of
which is specified first. See "Warps" for a way to work around this behavior.
Turbulence uses DNoise to push a point around in several steps called octaves
. We locate the point we want to evaluate, then push it around a bit using
turbulence to get to a different point then look up the color or pattern of
the new point.
It says in effect Don't give me the color at this spot... take a few random
steps in different directions and give me that color . Each step is typically
half as long as the one before. For example:
P ----->
First Move /
/
/
/Second
/ Move
/
______/
\
\
Q - Final point.
Turbulence random walk.
The magnitude of these steps is controlled by the turbulence value. There are
three additional parameters which control how turbulence is computed. They
are octaves , lambda and omega . Each is optional. Each is followed by a
single float value. Each has no effect when there is no turbulence.
7.6.8.5 Octaves
value controls the number of steps of turbulence that are computed. Legal
values range from 1 to 10. The default value of 6 is a fairly high value; you
won't see much change by setting it to a higher value because the extra steps
are too small. Float values are truncated to integer. Smaller numbers of
octaves give a gentler, wavy turbulence and computes faster. Higher octaves
create more jagged or fuzzy turbulence and takes longer to compute.
7.6.8.6 Lambda
parameter controls how statistically different the random move of an octave
is compared to its previous octave. The default value is 2.0 which is quite
random. Values close to lambda 1.0 will straighten out the randomness of the
path in the diagram above. The zig-zag steps in the calculation are in nearly
the same direction. Higher values can look more swirly under some
circumstances.
7.6.8.7 Omega
value controls how large each successive octave step is compared to the
previous value. Each successive octave of turbulence is multiplied by the
omega value. The default omega 0.5 means that each octave is 1/2 the size of
the previous one. Higher omega values mean that 2nd, 3rd, 4th and up octaves
contribute more turbulence giving a sharper, crinkly look while smaller
omegas give a fuzzy kind of turbulence that gets blurry in places.
7.6.8.8 Warps
The warp statement is a pattern modifier that is similar to turbulence.
Turbulence works by taking the pattern evaluation point and pushing it about
in a series of random steps. However warps push the point in very
well-defined, non-random, geometric ways. The warp statement also overcomes
some limitations of traditional turbulence and transformations by giving the
user more control over the order in which turbulence, transformation and warp
modifiers are applied to the pattern.
Currently there are three types of warps but the syntax was designed to allow
future expansion. The first two, the repeat warp and the black_hole warp are
new features for POV-Ray that modify the pattern in geometric ways. The other
warp provides an alternative way to specify turbulence.
The syntax for using a warp statement in a pigment is
pigment {
PATTERN_TYPE
PIGMENT_MODIFIERS...
warp { WARP_ITEMS..}.
OTHER_PIGMENT_MODIFIERS...
}
Similarly warps may be used in normals and textures. You may have as many
separate warp statements as you like in each pattern. The placement of warp
statements relative to other modifiers such as color_map or turbulence is not
important. However placement of warp statements relative to each other and to
transformations is significant. Multiple warps and transformations are
evaluated in the order in which you specify them. For example if you
translate, then warp or warp, then translate, the results can be different.
7.6.8.8.1 Black Hole Warp
A black hole is so named because of its similarity to real black holes. Just
like the real thing, you cannot actually see a black hole. The only way to
detect its presence is by the effect it has on things that surround it.
Unlike the real thing, however, it won't swallow you up and compress your
entire body to a volume of, say, 2.0 10-10 microns in diameter if you get too
close (We're working on that part).
Take, for example, a woodgrain. Using POV-Ray's normal turbulence and other
texture modifier functions, you can get a nice, random appearance to the
grain. But in its randomness it is regular - it is regularly random! Adding a
black hole allows you to create a localised disturbance in a woodgrain in
either one or multiple locations. The black hole can have the effect of
either sucking the surrounding texture into itself (like the real thing) or
pushing it away. In the latter case, applied to a woodgrain, it would look to
the viewer as if there were a knothole in the wood. In this text we use a
woodgrain regularly as an example, because it is ideally suitable to
explaining black holes. However, black holes may in fact be used with any
texture.
The effect that the black hole has on the texture can be specified. By
default, it sucks with the strength calculated expotentially
(inverse-square). You can change this if you like.
Black holes may be used anywhere a Warp is permitted. The syntax is:
warp
{
black_hole <CENTER>, RADIUS
[falloff VALUE]
[strength VALUE]
[repeat <VECTOR>]
[turbulence <VECTOR>]
[inverse]
}
Some examples are given by
warp
{
black_hole <0, 0, 0>, 0.5
}
warp
{
black_hole <0.15, 0.125, 0>, 0.5
falloff 7
strength 1.0
repeat <1.25, 1.25, 0>
turbulence <0.25, 0.25, 0>
inverse
}
warp
{
black_hole <0, 0, 0>, 1.0
falloff 2
strength 2
inverse
}
In order to fully understand how a black hole works, it is important to know
the theory behind it. A black hole (or any warp) works by taking a point and
perturbing it to another location. The amount of perturbation depends on the
strength of the black hole at the original point passed in to it. The amount
of perturbation directly relates to the amount of visual movement that you
can see occur in a texture. The stronger the black hole at the input
co-ordinate the more that original co-ordinate is moved to another location
(either closer to or further away from the center of the black hole.)
Movement always occurs on the vector that exists between the input point and
the center of the black hole.
Black holes are considered to be spheres. For a point to be affected by a
black hole, it must be within the sphere's volume.
Suppose you have a black hole at <1,1,1> and a point at <1,2,1>. If this
point is perturbed by a total amount of +1 units its new location is <1,3,1>,
which is on a direct line extrapolated from the vector between <1,1,1> and
<1,2,1>. In this case the point is pushed away from the black hole, which is
not normal behaviour but is good for demonstration purposes.
The internal properties of a black hole are as follows.
Center The center of the black hole.
Radius Its radius.
Falloff The power of two by which the effect falls off (default
2.)
Strength The magnitude of the transformation effect (see below.)
Inverted If set, 'push' points away instead of 'pulling' them in.
Repeat If set, we have many black holes instead of one.
Turbulence If set, each new repeated black hole's position is
uncertain.
Repeat_Vector The <x,y,z> factor to repeat by.
Turbulence_Vector The maximum <x,y,z> factor for turbulence randomness.
Each of these are discussed below.
Center : A vector defining the center of the sphere that represents the black
hole. If the black hole has Repeat set it is the offset within each block.
Radius : A number giving the length, in units, of the radius of the sphere
that represents the black hole.
If a point is not within radius units of <center> it cannot be affected by
the black hole and will not be perturbed.
Falloff : The power by which the effect of the black hole falls off. The
default is two. The force of the black hole at any given point, before
applying the Strength modifier, is as follows.
First, convert the distance from the point to the center to a proportion (0
to 1) that the point is from the edge of the black hole. A point on the
perimeter of the black hole will be 0.0; a point at the centre will be 1.0; a
point exactly halfway will be 0.5, and so forth.
Mentally you can consider this to be a closeness factor. A closeness of 1.0
is as close as you can get to the center (i. e. at the center), a closeness
of 0.0 is as far away as you can get from the center and still be inside the
black hole and a closeness of 0.5 means the point is exactly halfway between
the two.
Call
this value c. Raise c to the power specified in Falloff . By default Falloff
is 2, so this is c^2 or c squared. The resulting value is the force of the
black hole at that exact location and is used, after applying the Strength
scaling factor as described below, to determine how much the point is
perturbed in space.
For example, if c is 0.5 the force is 0.5^2 or 0.25. If c is 0.25 the force
is 0.125. But if c is exactly 1.0 the force is 1.0.
Recall that as c gets smaller the point is farther from the center of the
black hole. Using the default power of 2, you can see that as c reduces, the
force reduces expotentially in an inverse-square relationship. Put in plain
english, it means that the force is much stronger (by a power of two) towards
the center than it is at the outside.
By increasing Falloff , you can increase the magnitude of the falloff. A
large value will mean points towards the perimeter will hardly be affected at
all and points towards the center will be affected strongly.
A value of 1.0 for Falloff will mean that the effect is linear. A point that
is exactly halfway to the center of the black hole will be affected by a
force of exactly 0.5.
A value of Falloff of less than one but greater than zero means that as you
get closer to the outside, the force increases rather than decreases. This
can have some uses but there is a side effect. Recall that the effect of a
black hole ceases outside its perimiter. This means that points just within
the permiter will be affected strongly and those just outside not at all.
This would lead to a visible border, shaped as a sphere.
A value for Falloff of 0 would mean that the force would be 1.0 for all
points within the black hole, since any number larger 0 raised to the power
of 0 is 1.0.
The magnitude of the movement of the point is determined basically by the
value of force after scaling. We'll consider scaling later. Lets take an
example.
Suppose we have a black hole of radius 2.0 and a point that is exactly 1.0
units from the center. That means it is exactly half-way to the center and
that c would be 0.5. If we use the default falloff of 2 the force at that
point is 0.5^2 or 0.25. What this means is that we must move the point by
0.25 of its distance from the center. In this case it is 1.0 units from the
center, so we move it by 1.0*0.25 or 0.25 units. This gives a final distance
of 1.0-(1.0*0.25) or 0.75 units from the center, on a direct line in 3D space
between the original position and the center.
If the point were part of, say, a wood grain, the wood grain would appear to
bend towards the (invisible) center of the black hole. If the Inverse flag
were set, however, it would be pushed away, meaning its final position would
be 1.0+(1.0*0.25) or 1.25 units from the center.
Strength : The Strength gives you a bit more control over how much a point is
perturbed by the black hole. Basically, the force of the black hole (as
determined above) is multipled by the value of Strength , which defaults to
1.0. If you set Strength to 0.5, for example, all points within the black
hole will be moved by only half as much as they would have been. If you set
it to 2.0 they will be moved twice as much.
There is a rider to the latter example, though - the movement is clipped to a
maximum of the original distance from the center. That is to say, a point
that is 0.75 units from the center may only be moved by a maximum of 0.75
units either towards the center or away from it, regardless of the value of
Strength . The result of this clipping is that you will have an exclusion
area near the centre of the black hole where all points whose final force
value exceeded or equalled 1.0 were moved by a fixed amount.
Inverted : If Inverted is set points are pushed away from the center instead
of being pulled in.
Repeat : Repeat allows you to simulate the effect of many black holes without
having to explicitly declare them. Repeat is a vector that tells POV-Ray to
use this black hole at multiple locations.
If you're not interested in the theory behind all this, just skip the
following text and use the values given in the summary below.
Using Repeat logically divides your scene up into cubes, the first being
located at <0,0,0> and going to \langle repeat>. Suppose your repeat vector
was <1,5,2>. The first cube would be from <0,0,0> to \langle 1,5,2>. This
cube repeats, so there would be one at \langle -1,-5,-2>, <1,5,2>, <2,10,4>
and so forth in all directions, ad infinitum.
When you use Repeat , the center of the black hole does not specify an
absolute location in your scene but an offset into each block. It is only
possible to use positive offsets. Negative values will produce undefined
results.
Suppose your center was <0.5,1,0.25> and the repeat vector is <2,2,2>. This
gives us a block at \langle 0,0,0> and <2,2,2>, etc. The centers of the black
hole's for these blocks would be <0,0,0> + \langle 0.5,1.0,0.25>, i. e.
<0.5,1.0,0.25>, and \langle 2,2,2> + <0.5,1.0,0.25>, i. e. \langle
2,5,3.0,2.25>.
Due to the way repeats are calculated internally, there is a restriction on
the values you specify for the repeat vector. Basically, each black hole must
be totally enclosed within each block (or cube), with no part crossing into a
neighbouring one. This means that, for each of the x, y and z dimensions, the
offset of the center may not be less than the radius, and the repeat value
for that dimension must be >=the center plus the radius since any other
values would allow the black hole to cross a boundary. Put another way, for
each of x, y and z
radius <= offset or center <= repeat - radius.
If the repeat vector in any dimension is too small to fit this criteria, it
will be increased and a warning message issued. If the center is less than
the radius it will also be moved but no message will be issued.
Note that none of the above should be read to mean that you can't overlap
black holes. You most certainly can and in fact this can produce some most
useful effects. The restriction only applies to elements of the same black
hole which is repeating. You can declare a second black hole that also
repeats and its elements can quite happily overlap the first and causing the
appropriate interactions.
It is legal for the repeat value for any dimension to be 0, meaning that
POV-Ray will not repeat the black hole in that direction.
Turbulence : Turbulence can only be used with Repeat . It allows an element
of randomness to be inserted into the way the black holes repeat, to cause a
more natural look. A good example would be an array of knotholes in wood - it
would look rather artificial if each knothole were an exact distance from the
previous.
The turbulence vector is a measurement that is added to each individual back
hole
in an array, after each axis of the vector is multipled by a different random
amount ranging from 0 to 1.
For example, suppose you have a repeating element of a black hole that is
supposed to be at <2,2,2>. You have specified a turbulence vector of <4,5,3>,
meaning you want the position to be able to vary by no more than 1.0 units in
the X direction, 3.0 units in the Y direction and 2.0 in Z. This means that
the valid ranges of the new position are as follows
X can be from 2 to 6.
Y can be from 2 to 7.
Z can be from 2 to 5.
The resulting actual position of the black hole's center for that particular
repeat element is random (but consistent, so renders will be repeatable) and
somewhere within the above co-ordinates.
There is a rider on the use of turbulence, which basically is the same as
that of the repeat vector. Yyou can't specify a value which would cause a
black hole to potentially cross outside of its particular block.
Since POV-Ray doesn't know in advance how much a position will be changed due
to the random nature of the changes, it enforces a rule that is similar to
the one for Repeat , except it adds the maximum possible variation for each
axis to the center. For example, suppose you had a black hole with a center
of <1.0, 1.0, 1.0>, radius of 0.5 and a turbulence of <0.5, 0.25, 0> -
normally, the mimimum repeat would be <1.5, 1.5, 1.5>. However, now we take
into account the turbulence, meaning the minimum repeat vector is actually
<2.0, 1.75, 1.5>.
Repeat summarized : For each of x, y and z the offset of the center must be
>=radius and the value of the repeat must be \ge center + radius +
turbulence. The exception being that repeat may be 0 for any dimension, which
means do not repeat in that direction.
7.6.8.8.2 Repeat Warp
The repeat warp causes a section of the pattern to be repeated over and over.
It takes a slice out of the pattern and makes multiple copies of it
side-by-side. The warp has many uses but was originally designed to make it
easy to model wood veneer textures. Veneer is made by taking very thin slices
from a log and placing them side-by-side on some other backing material. You
see side-by-side nearly identical ring patterns but each will be a slice
perhaps 1/32th of an inch deeper.
The syntax for a repeat warp is
warp { repeat VECTOR offset VECTOR flip VECTOR }
The repeat vector specifies the direction in which the pattern repeats and
the width of the repeated area. This vector must lie entirely along an axis.
In other words, two of its three components must be 0. For example
pigment {
wood
warp {repeat 2*x}
}
which means that from x=0 to x=2 you get whatever the pattern usually is. But
from x=2 to x=4 you get the same thing exactly shifted two units over in the
x-direction. To evaluate it you simply take the x-coordinate modulo 2.
Unfortunately you get exact duplicates which isn't very realistic. The
optional offset vector tells how much to translate the pattern each time it
repeats. For example
pigment {
wood
warp {repeat x*2 offset z*0.05}
}
means that we slice the first copy from x=0 to x=2 at z=0 but at x=2 to x=4
we offset to z=0.05. In the 4 to 6 interval we slice at z=0.10. At the n-th
copy we slice at 0.05 n z. Thus each copy is slightly different. There are no
restrictions on the offset vector.
Finally the flip vector causes the pattern to be flipped or mirrored every
other copy of the pattern. The first copy of the pattern in the positive
direction from the axis is not flipped. The next farther is, the next is not,
etc. The flip vector is a three component x, y, z vector but each component
is treated as a boolean value that tells if you should or should not flip
along a given axis. For example
pigment {
wood
warp {repeat 2*x flip <1,1,0>}
}
means that every other copy of the pattern will be mirrored about the x- and
y- axis but not the z-axis. A non-zero value means flip and zero means do not
flip about that axis. The magnitude of the values in the flip vector doesn't
matter.
7.6.8.8.3 Turbulence Warp
The POV-Ray language contains an ambiguity and limitation on the way you
specify turbulence and transformations such as translate, rotate, scale and
matrix transforms. Usually the turbulence is done first. Then all translate,
rotate, scale and matrix operations are always done after turbulence
regardless of the order in which you specify them. For example this
pigment {
wood
scale .5
turbulence .2
}
works exactly the same as
pigment {
wood
turbulence .2
scale .5
}
The turbulence is always first. A better example of this limitation is with
uneven turbulence and rotations.
pigment {
wood
turbulence 0.5*y
rotate z*60
}
// as compared to
pigment {
wood
rotate z*60
turbulence 0.5*y
}
The results will be the same either way even though you'd think it should
look different.
We cannot change this basic behavior in POV-Ray now because lots of scenes
would potentially render differently if suddenly the order transformation vs
turbulence suddenly mattered when in the past, it didn't.
However, by specifying our turbulence inside warp statement you tell POV-Ray
that the order in which turbulence, transformations and other warps are
applied is significant. Here's an example of a turbulence warp.
warp { turbulence <0,1,1> octaves 3 lambda 1.5 omega 0.3 }
The significance is that this
pigment {
wood
translate <1,2,3> rotate x*45 scale 2
warp { turbulence <0,1,1> octaves 3 lambda 1.5 omega 0.3 }
}
produces different results than this...
pigment {
wood
warp { turbulence <0,1,1> octaves 3 lambda 1.5 omega 0.3 }
translate <1,2,3> rotate x*45 scale 2
}
You may specify turbulence without using a warp statement. However you cannot
control the order in which they are evaluated unless you put them in a warp.
The evaluation rules are as follows:
1) First any turbulence not inside a warp statement is applied regardless
of the order in which it appears relative to warps or transformations.
2) Next each warp statement, translate, rotate, scale or matrix one-by-one,
is applied in the order the user specifies. If you want turbulence done
in a specific order, you simply specify it inside a warp in the proper
place.
7.6.8.9 Bitmap Modifiers
A bitmap modifier is a modifier used inside an "image_map" , "bump_map" or
"material_map" to specify how the 2-D bitmap is to be applied to the 3-D
surface. Several bitmap modifiers apply to specific kinds of maps and they
are covered in the appropriate sections. The bitmap modifiers discussed in
the following sections are applicable to all three types of bitmaps.
7.6.8.9.1 The once Option
Normally there are an infinite number of repeating image maps, bump maps or
material maps created over every unit square of the x-y-plane like tiles. By
adding the once keyword after a file name you can eliminate all other copies
of the map except the one at (0,0) to (1,1). In image maps, areas outside
this unit square are treated as fully transparent. In bump maps, areas
outside this unit square are left flat with no normal modification. In
material maps, areas outside this unit square are textured with the first
texture of the texture list.
For example:
image_map {
gif "mypic.gif"
once
}
7.6.8.9.2 The "map_type" Option
The default projection of the bump onto the x-y-plane is called a planar map
type . This option may be changed by adding the map_type keyword followed by
a number specifying the way to wrap the bump around the object.
A map_type 0 gives the default planar mapping already described.
A map_type 1 gives a spherical mapping. It assumes that the object is a
sphere of any size sitting at the origin. The y-axis is the north/south pole
of the spherical mapping. The top and bottom edges of the bitmap just touch
the pole regardless of any scaling. The left edge of the bitmap begins at the
positive x-axis and wraps the pattern around the sphere from west to east in
a -y-rotation. The pattern covers the sphere exactly once. The once keyword
has no meaning for this type.
With map_type 2 you get a cylindrical mapping. It assumes that a cylinder of
any diameter lies along the y-axis. The bump pattern wraps around the
cylinder just like the spherical map but remains one unit tall from y=0 to
y=1. This band of the pattern is repeated at all heights unless the once
keyword is applied.
Finally map_type 5 is a torus or donut shaped mapping. It assumes that a
torus of major radius 1 sits at the origin in the x-z-plane. The pattern is
wrapped around similar to spherical or cylindrical maps. However the top and
bottom edges of the map wrap over and under the torus where they meet each
other on the inner rim.
Types 3 and 4 are still under development.
For example:
sphere{<0,0,0>,1
pigment{
image_map {
gif "world.gif"
map_type 1
}
}
}
7.6.8.9.3 The interpolate Option
Adding the interpolate keyword can smooth the jagged look of a bitmap. When
POV-Ray asks an image map color or a bump amount for a bump map, it often
asks for a point that is not directly on top of one pixel but sort of between
several differently colored pixels. Interpolations returns an in-between
value so that the steps between the pixels in the map will look smoother.
Although interpolate is legal in material maps the color index is
interpolated before the texture is chosen. It does not interpolate the final
color as you might hope it would. In general, interpolation of material maps
serves no useful purpose but this may be fixed in future versions.
There are currently two types of interpolation:
Bilinear - interpolate 2
Normalized Distance - interpolate 4
For example:
image_map {
gif "mypic.gif"
interpolate 2
}
Default is no interpolation. Normalized distance is the slightly faster of
the two, bilinear does a better job of picking the between color. Normally
bilinear is used.
If your map looks jaggy, try using interpolation instead of going to a higher
resolution image. The results can be very good.
7.7 Atmospheric Effects
Atmospheric effects are a loosely-knit group of features that affect the
background and/or the atmosphere enclosing the scene. POV-Ray includes the
ability to render a number of atmospheric effects, such as fog, haze, mist,
rainbows and skies.
7.7.1 Atmosphere
Computer generated images normally assume a vacuum space that does not allow
the rendering of natural phenomena like smoke, light beams, etc. A very
simple approach to add fog to a scene is explained in section "Fog" . This
kind of fog does not interact with any light sources though. It will not show
light beams or other effects and is therefore not very realistic.
The atmosphere effect overcomes some of the fog's limitations by calculating
the interaction between light and the particles in the atmosphere using
volume sampling. Thus shaft of light beams will become visible and objects
will cast shadows onto smoke or fog.
The syntax of the atmosphere is:
atmosphere {
type TYPE
distance DISTANCE
[ scattering SCATTERING ]
[ eccentricity ECCENTRICITY ]
[ samples SAMPLES ]
[ jitter JITTER ]
[ aa_threshold AA_THRESHOLD ]
[ aa_level AA_LEVEL ]
[ colour <COLOUR> ]
}
The type keyword determines the type of scattering model to be used. There
are five different phase functions representing the different models:
isotropic, Rayleigh, Mie (haze and murky atmosphere) and Henyey-Greenstein.
Isotropic scattering is the simplest form of scattering because it is
independent of direction. The amount of light scattered by particles in the
atmosphere does not depend on the angle between the viewing direction and the
incoming light.
Rayleigh scattering models the scattering for extremely small particles such
as molecules of the air. The amount of scattered light depends on the
incident light angle. It is largest when the incident light is parallel or
anti-parallel to the viewing direction and smallest when the incident light
is perpendicular to the viewing direction. You should note that the Rayleigh
model used in POV-Ray does not take the dependency of scattering on the
wavelength into account.
The Rayleigh scattering function.
Mie scattering is used for relatively small particles such as miniscule water
droplets of fog, cloud particles, and particles responsible for the polluted
sky. In this model the scattering is extremely directional in the forward
direction i. e. the amount of scattered light is largest when the incident
light is anti-parallel to the viewing direction (the light goes directly to
the viewer). It is smallest when the incident light is parallel to the
viewing direction. The haze and murky atmosphere models differ in their
scattering characteristics. The murky model is much more directional than the
haze model.
The Mie "haze" scattering function.
The Mie "murky" scattering function.
The Henyey-Greenstein scattering is based on an analytical function and can
be used to model a large variety of different scattering types. The function
models an ellipse with a given eccentricity e. This eccentricity is specified
by the optional keyword eccentricity which is only used for scattering type
five. An eccentricity value of zero defines isotropic scattering while
positive values lead to scattering in the direction of the light and negative
values lead to scattering in the opposite direction of the light. Larger
values of e (or smaller values in the negative case) increase the directional
property of the scattering.
The Heyney-Greenstein scattering function for different eccentricity values.
The easiest way to use the different scattering types will be to declare some
constants and use those in your atmosphere definition:
#declare ISOTROPIC_SCATTERING = 1
#declare MIE_HAZY_SCATTERING = 2
#declare MIE_MURKY_SCATTERING = 3
#declare RAYLEIGH_SCATTERING = 4
#declare HENYEY_GREENSTEIN_SCATTERING = 5
The distance keyword is used to determine the density of the particles in the
atmosphere. This density is constant for the whole atmosphere. The distance
parameter works in the same way as the fog distance.
With the scattering keyword you can change the amount of light that is
scattered by the atmosphere, thus increasing or decreasing the brightness of
the atmosphere. Smaller scattering values decrease the brightness while
larger values increase it.
The colour or color keyword can be used to create a colored atsosphere, i. e.
it can be used to get particles that filter the light passing through. The
default color is black.
The light passing through the atmosphere (either coming from light sources or
the background) is filtered by the atmosphere's color if the specified color
has a non-zero filter value. In other words, the amount by which the light is
filtered by the atmosphere's color is given by the filter value (pretty much
in the same way as it is done for the fog). Using a color of rgbf
<1,0,0,0.25> will result in a slightly reddish atmosphere because 25% of the
light passing through the atmosphere is filtered by (multiplied with) the
color of the atmosphere, i. e. rgb <1,0,0> (and that's red).
The transmittance channel of the atmosphere's color is used to specify a
minimum translucency. If a value larger than zero is used you'll always see
that amount of the background through the atmosphere, regardless of how dense
the atmosphere is. This works in the same way as it does for fogs.
Since the atmosphere is calculated by sampling along the viewing ray and
looking for contributions from light sources, it is prone to aliasing (just
like any sampling technique). There are four parameters to minimize the
artifacts that may be visible: samples , jitter , aa_level and aa_threshold .
The samples keyword determines how many samples are calculated in one
interval along the viewing ray. The length of the interval is either the
distance as given by the distance keyword or the length of the lit part of
the viewing ray, whichever is smaller. This lit part is a section of the ray
that is most likely lit by a light source. In the case of a spotlight it is
the part of the ray that lies in the cone of light. In other cases it becomes
more difficult. The only thing you should keep in mind is that the actual
sampling interval length is variable but there will never be fewer than the
specified samples in the specified distance.
One
technique to reduce the visibility of sampling artifacts is to jitter the
sample points, i. e. to add random noise to their location. This can be done
with the jitter keyword.
Another technique is super-sampling (an anti-aliasing method). This helps to
avoid missing features by adding additional samples in places were high
intensity changes occur (e. g. the edge of a shadow). The anti-aliasing is
turned on by the aa_level keyword. If this is larger than zero super-sampling
will be used. The additional samples will be recursively placed between two
samples with a high intensity change. The level to which subdivision takes
places is specified by the aa_level keyword. Level one means one subdivision
(one additional sample), level two means two subdivisions (up to three
additional samples), etc.
The threshold for the intensity change is given by the aa_threshold keyword.
If the intensity change is greater than this threshold anti-aliasing will be
used for those two samples.
With spotlights you'll be able to create the best results because their cone
of light will become visible. Pointlights can be used to create effects like
street lights in fog. Lights can be made to not interact with the atmosphere
by adding atmosphere off to the light source. They can be used to increase
the overall light level off the scene to make it look more realistic.
You should note that the atmosphere feature will not work if the camera is
inside a non-hollow object (see "Empty and Solid Objects" for a detailed
explanation).
7.7.2 Background
A background color can be specified if desired. Any ray that doesn't hit an
object will be colored with this color. The default background is black. The
syntax for background is:
background { colour <COLOUR> }
7.7.3 Fog
Fog is defined by the following statement:
fog {
fog_type FOG_TYPE
distance DISTANCE
colour <COLOUR>
[ turbulence <TURBULENCE> ]
[ turb_depth TURB_DEPTH ]
[ omega OMEGA ]
[ lambda LAMBDA ]
[ octaves OCTAVES ]
[ fog_offset FOG_OFFSET ]
[ fog_alt FOG_ALT ]
[ up <FOG_UP> ]
[ TRANSFORMATION ]
}
The optional up vector specifies a direction pointing up, generally the same
as the camera's up vector. All calculations done during the ground fog
evaluation are done relative to this up vector, i. e. the actual heights are
calculated along this vector.
The up vector can also be modified using any of the known transformations
described in "Transformations" . Though it may not be a good idea to scale
the up vector - the results are hardly predictable - it is quite useful to be
able to rotate it. You should also note that translations do not affect the
up direction (and thus don't affect the fog).
Currently there are two fog types, constant fog and ground fog . The constant
fog has a constant density everywhere while the ground fog has a constant
density for all heights below a given point on the up axis and thins out
along this axis. The height below which the fog has constant density is
specified by the fog_offset keyword. The fog_alt keyword is used to specify
the rate by which the fog fades away. At an altitude of fog_offset+fog_alt
the fog has a density of 25%. The density of the fog at a given height y is
calculated by the formula:
/
| 1
| -------, y > fog_alt
| (1 + (y - fog_offset) / fog_alt) ^2
density = -|
|
| 1, y <= fog_alt
|
\
The total density along a ray is calculated by integrating from the height of
the starting point to the height of the end point.
Two constants are defined for easy use of the fog types in the file const.inc
:
// FOG TYPE CONSTANTS
#declare Constant_Fog = 1
#declare Ground_Fog = 2
The color of a pixel with an intersection depth d is calculated by
C_pixel = exp(-d/D) * C_object + (1-exp(-d/D)) * C_fog
where D is the fog distance. At depth 0 the final color is the object's
color. If the intersection depth equals the fog distance the final color
consists of 64% of the object's color and 36% of the fog's color.
The fog color that is given by the color keyword has three purposes. First it
defines the color to be used in blending the fog and the background. Second
it is used to specify a translucency threshold. By using a transmittance
larger than zero one can make sure that at least that amount of light will be
seen through the fog. With a transmittance of 0.3 you'll see at least 30% of
the background. Third it can be used to make a filtering fog. With a filter
value larger than zero the amount of background light given by the filer
value will be multiplied with the fog color. A filter value of 0.7 will lead
to a fog that filters 70% of the background light and leaves 30% unfiltered.
Fogs may be layered . That is, you can apply as many layers of fog as you
like. Generally this is most effective if each layer is a ground fog of
different color, altitude and with different turbulence values. To use
multiple layers of fogs, just add all of them to the scene.
You may optionally stir up the fog by adding turbulence. The turbulence
keyword may be followed by a float or vector to specify an amount of
turbulence to be used. The omega , lambda and octaves turbulence parameters
may also be specified. See section "Pattern Modifiers" for details on all of
these turbulence parameters.
Additionally the fog turbulence may be scaled along the direction of the
viewing ray using the turb_depth amount. Typical values are from 0.0 to 1.0
or more. The default value is 0.5 but any float value may be used.
You should note that the fog feature will not work if the camera is inside a
non-hollow object (see "Empty and Solid Objects" for a detailed explanation).
7.7.4 Sky Sphere
The sky sphere is used create a realistic sky background without the need of
an additional sphere to simulate the sky. Its syntax is:
sky_sphere {
pigment { PIGMENT1 }
pigment { PIGMENT2 }
pigment { PIGMENT3 }
...
[ TRANSFORMATION ]
}
The sky sphere can contain several pigment layers with the last pigment being
at the top, i. e. it is evaluated last, and the first pigment being at the
bottom, i. e. it is evaluated first. If the upper layers contain filtering
and/or transmitting components lower layers will shine through. If not lower
layers will be invisible.
The sky sphere is calculated by using the direction vector as the parameter
for evaluating the pigment patterns. This leads to results independent from
the view point which pretty good models a real sky where the distance to the
sky is much larger than the distances between visible objects.
If you want to add a nice color blend to your background you can easily do
this by using the following example.
sky_sphere {
pigment {
gradient y
color_map {
[ 0.5 color CornflowerBlue ]
[ 1.0 color MidnightBlue ]
}
scale 2
translate -1
}
}
This gives a soft blend from CornflowerBlue at the horizon to MidnightBlue at
the zenith. The scale and translate operations are used to map the direction
vector values, which lie in the range from <-1, -1, -1> to <1, 1, 1>, onto
the range from <0, 0, 0> to <1, 1, 1>. Thus a repetition of the color blend
is avoided for parts of the sky below the horizon.
In order to easily animate a sky sphere you can transform it using the known
transformations described in "Transformations" . Though it may not be a good
idea to translate or scale a sky sphere - the results are hardly predictable
- it is quite useful to be able to rotate it. In an animation the color
blendings of the sky can be made to follow the rising sun for example.
You should note that only one sky sphere can be used in any scene. It also
will not work as you might expect if you use camera types like the
orthographic or cylindrical camera. The orthographic camera uses parallel
rays and thus you'll only see a very small part of the sky sphere (you'll get
one color skies in most cases). Reflections in curved surface will work
though, e. g. you will clearly see the sky in a mirrored ball.
7.7.5 Rainbow
The rainbow is a fog-like, circular arc that can be used to create rainbows.
The syntax is:
rainbow {
direction <DIR>
angle ANGLE
width WIDTH
distance DISTANCE
color_map { COLOUR_MAP }
[ jitter JITTER ]
[ up <UP> ]
[ arc_angle ARC_ANGLE ]
[ falloff_angle FALLOFF_ANGLE ]
}
The direction vector determines the direction of the (virtual) light that is
responsible for the rainbow. Ideally this is an infinitely far away light
source like the sun that emits parallel light rays. The position and size of
the rainbow are specified by the angle and width keywords. To understand how
they work you should first know how the rainbow is calculated.
For each ray the angle between the rainbow's direction vector and the ray's
direction vector is calculated. If this angle lies in the interval from
ANGLE-WIDTH/2 to ANGLE+WIDTH/2 the rainbow is hit by the ray. The color is
then determined by using the angle as an index into the rainbow's colormap.
After the color has been determined it will be mixed with the background
color in the same way like it is done for fogs.
Thus the angle and width parameters determine the angles under which the
rainbow will be seen. The optional jitter keyword can be used to add random
noise to the index. This adds some irregularity to the rainbow that makes it
look more realistic.
The distance keyword is the same like the one used with fogs. Since the
rainbow is a fog-like effect it's possible that the rainbow is noticeable on
objects. If this effect is not wanted it can be avoided by using a large
distance value. By default a sufficiently large value is used to make sure
that this effect does not occure.
The color_map keyword is used to assign a color map that will be mapped onto
the rainbow. To be able to create realistic rainbows it is important to know
that the index into the color map increases with the angle between the ray's
and rainbow's direction vector. The index is zero at the innermost ring and
one at the outermost ring . The filter and transmittance values of the colors
in the color map have the same meaning as the ones used with fogs (see
section "Fog" ).
The default rainbow is a 360 degree arc that looks like a circle. This is no
problem as long as you have a ground plane that hides the lower, non-visible
part of the rainbow. If this isn't the case or if you don't want the full arc
to be visible you can use the optional keywords up , arc_angle and
falloff_angle to specify a smaller arc.
The arc_angle keyword determines the size of the arc in degrees (from 0 to
360 degrees). A value smaller than 360 degrees results in an arc that
abruptly vanishes. Since this doesn't look nice you can use the falloff_angle
keyword to specify a region in which the rainbow will smoothly blend into the
background making it vanish softly. The falloff angle has to be smaller or
equal to the arc angle.
The up keyword determines were the zero angle position is. By changing this
vector you can rotate the rainbow about its direction. You should note that
the arc goes from -ARC_ANGLE/2 to +ARC_ANGLE/2. The soft regions go from
-ARC_ANGLE/2 to -FALLOFF_ANGLE/2 and from +FALLOFF_ANGLE/2 to +ARC_ANGLE/2.
The following example generates a 120 degrees rainbow arc that has a falloff
region of 30 degrees at both ends:
rainbow {
direction <0, 0, 1>
angle 42.5
width 5
distance 1000
jitter 0.01
color_map { Rainbow_Color_Map }
up <0, 1, 0>
arc_angle 240
falloff_angle 60
}
It is possible to use any number of rainbows and to combine them with other
atmospheric effects.
7.8 Global Settings
The global_settings statement is a catch-all statement that gathers together
a number of global parameters. The statement may appear anywhere in a scene
as long as its not inside any other statement. You may have multiple
global_settings statements in a scene. Whatever values were specified in the
last global_settings statement override any previous settings. Regardless of
where you specify the statement, the feature applies to the entire scene.
Note that some items which were language directives in previous versions of
POV-Ray have been moved inside the global_settings statement so that it is
more obvious to the user that their effect is global. The old syntax is
permitted but generates a warning.
global_settings {
adc_bailout FLOAT
ambient_light COLOR
assumed_gamma FLOAT
hf_gray_16 BOOLEAN
irid_wavelength COLOR
max_intersections INTEGER
max_trace_level INTEGER
number_of_waves INTEGER
radiosity { RADIOSITY_ITEMS... }
}
Each item is optional and may appear in and order. If an item is specified
more than once, the last setting overrides previous values. Details on each
item are given in the following sections.
7.8.1 ADC_Bailout
In scenes with many reflective and transparent surfaces, POV-Ray can get
bogged down tracing multiple reflections and refractions that contribute very
little to the color of a particular pixel. The program uses a system called
Adaptive Depth Control (ADC) to stop computing additional reflected or
refracted rays when their contribution is insignificant.
You may use the global setting adc_bailout keyword followed by float value to
specify the point at which a ray's contribution is considered insignificant.
global_settings { adc_bailout FLOAT }
The default value is 1/255, or approximately 0.0039, since a change smaller
than that could not be visible in a 24 bit image. Generally this setting is
perfectly adequate and should be left alone. Setting adc_bailout to 0 will
disable ADC, relying completely on max_trace_level to set an upper limit on
the number of rays spawned.
7.8.2 Ambient Light
Ambient light is used to simulate the effect of interdiffuse reflection that
is responsible for lighting areas that partially or completely lie in shadow.
POV-Ray provides an ambient light source to let you easily change the
brightness of the ambient lighting without changing every ambient value in
all finish statements. It also lets you create interesting effects by
changing the color of the ambient light source. The syntax is:
global_settings { ambient_light COLOR }
The default is a white ambient light source set at rgb\langle 1,1,1> . The
actual ambient used is: AMBIENT = FINISH_AMBIENT * GLOBAL_AMBIENT
7.8.3 Assumed_Gamma
Many people may have noticed at one time or another that some images are too
bright or dim when displayed on their system. As a rule, Macintosh users find
that images created on a PC are too bright, while PC users find that images
created on a Macintosh are too dim.
The assumed_gamma global setting works in conjunction with the Display_Gamma
INI setting (see section "Display Hardware Settings" ) to ensure that scene
files render the same way across the wide variety of hardware platforms that
POV-Ray is used on. The assumed gamma setting is used in a scene file by
adding
global_settings { assumed_gamma FLOAT }
where the assumed gamma value is the correction factor to be applied before
the pixels are displayed and/or saved to disk. For scenes created in older
versions of POV-Ray, the assumed gamma value will be the same as the display
gamma value of the system the scene was created on. For PC systems, the most
common display gamma is 2.2, while for scenes created on Macintosh systems
should use a scene gamma of 1.8. Another gamma value that sometimes occurs in
scenes is 1.0.
Scenes that do not have an assumed_gamma global setting will not have any
gamma correction performed on them, for compatibility reasons. If you are
creating new scenes or rendering old scenes, it is strongly recommended that
you put in an appropriate assumed_gamma global setting. For new scenes, you
should use an assumed gamma value of 1.0 as this models how light appears in
the real world more realistically.
The following sections explain more thoroughly what gamma is and why it is
important.
7.8.3.1 Monitor Gamma
The differences in how images are displayed is a result of how a computer
actually takes an image and displays it on the monitor. In the process of
rendering an image and displaying it on the screen, several gamma values are
important, including the POV scene file or image file gamma and the monitor
gamma.
Most image files generated by POV-Ray store numbers in the range from 0 to
255 for each of the red, green and blue components of a pixel. These numbers
represent the intensity of each color component, with 0 being black and 255
being the brightest color (either 100% red, 100% green or 100% blue). When an
image is displayed, the graphics card converts each color component into a
voltage which is sent to the monitor to light up the red, green and blue
phosphors on the screen. The voltage is usually proportional to the value of
each color component.
Gamma becomes important when displaying intensities that aren't the maximum
or minimum possible values. For example, 127 should represent 50% of the
maximum intensity for pixels stored as numbers between 0 and 255. On systems
that don't do gamma correction, 127 will be converted to 50% of the maximum
voltage, but because of the way the phosphors and the electron guns in a
monitor work, this may be only 22% of the maximum color intensity on a
monitor with a gamma of 2.2. To display a pixel which is 50% of the maximum
intensity on this monitor, we would need a voltage of 73% of the maximum
voltage, which translates to storing a pixel value of 186.
The relationship between the input pixel value and the displayed intensity
can be approximated by an exponential function
obright = ibright ^ display_gamma
where obright is the output intensity and ibright is the input pixel
intensity. Both values are in the range from 0 to 1 (0% to 100%). Most
monitors have a fixed gamma value in the range from 1.8 to 2.6. Using the
above formula with display_gamma values greater than 1 means that the output
brightness will be less than the input brightness. In order to have the
output and input brightness be equal an overall system gamma of 1 is needed.
To do this, we need to gamma correct the input brightness in the same manner
as above but with a gamma value of 1/display_gamma before it is sent to the
monitor. To correct for a display gamma of 2.2, this pre-monitor gamma
correction uses a gamma value of 1.0/2.2 or approximately 0.45.
How the pre-monitor gamma correction is done depends on what hardware and
software is being used. On Macintosh systems, the operating system has taken
it upon itself to insulate applications from the differences in display
hardware. Through a gamma control panel the user may be able to set the
actual monitor gamma and MacOS will then convert all pixel intensities so
that the monitor will appear to have the specified gamma value. On Silicon
Graphics machines, the display adapter has built-in gamma correction
calibrated to the monitor which gives the desired overall gamma (the default
is 1.7). Unfortunately, on PCs and most UNIX systems, it is up to the
application to do any gamma correction needed.
7.8.3.2 Image File Gamma
Since most PC and UNIX applications and image file formats don't understand
display gamma, they don't do anything to correct for it. As a result, users
creating images on these systems adjust the image in such a way that it has
the correct brightness when displayed. This means that the data values stored
in the files are made brighter to compensate for the darkening effect of the
monitor. In essence, the 0.45 gamma correction is built in to the image files
created and stored on these systems. When these files are displayed on a
Macintosh system, the gamma correction built in to the file, in addition to
gamma correction built into MacOS, means that the image will be too bright.
Similarly, files that look correct on Macintosh or SGI systems because of the
built-in gamma correction will be too dark when displayed on a PC.
The new PNG format files generated by POV-Ray 3.0 overcome the problem of too
much or not enough gamma correction by storing the image file gamma (which is
1.0/display_gamma) inside the PNG file when it is generated by POV-Ray. When
the PNG file is later displayed by a program that has been set up correctly,
it uses this gamma value as well as the current display gamma to correct for
the potentially different display gamma used when originally creating the
image.
Unfortunately, of all the image file formats POV-Ray supports, PNG is the
only one that has any gamma correction features and is therefore preferred
for images that will be displayed on a wide variety of platforms.
7.8.3.3 Scene File Gamma
The image file gamma problem itself is just a result of how scenes themselves
are generated in POV-Ray. When you start out with a new scene and are placing
light sources and adjusting surface textures and colors, you generally make
several attempts before the lighting is how you like it. How you choose these
settings depends upon the preview image or the image file stored to disk,
which in turn is dependent upon the overall gamma of the display hardware
being used.
This means that as the artist you are doing gamma correction in the POV-Ray
scene file for your particular hardware. This scene file will generate an
image file that is also gamma corrected for your hardware and will display
correctly on systems similar to your own. However, when this scene is
rendered on another platform, it may be too bright or too dim, regardless of
the output file format used. Rather than have you change all the scene files
to have a single fixed gamma value (heaven forbid!), POV-Ray 3.0 allows you
to specify in the scene file the display gamma of the system that the scene
was created on.
The assumed_gamma global setting, in conjunction with the Display_Gamma INI
setting lets POV-Ray know how to do gamma correction on a given scene so that
the preview and output image files will appear the correct brightness on any
system. Since the gamma correction is done internally to POV-Ray, it will
produce output image files that are the correct brightness for the current
display, regardless of what output format is used. As well, since the gamma
correction is performed in the high-precision data format that POV-Ray uses
internally, it produces better results than gamma correction done after the
file is written to disk.
Although you may not notice any difference in the output on your system with
and without an assumed_gamma setting, the assumed gamma is important if the
scene is ever rendered on another platform.
7.8.4 HF_Gray_16
The hf_gray_16 setting is useful when using POV-Ray to generate heightfields
for use in other POV-Ray scenes. The syntax is...
global_settings { hf_gray_16 BOOLEAN }
The boolean value turns the option on or off. If the keyword is specified
without the boolean value then the option is turned on. If hf_gray_16 is not
specified in any global_settings statement in the entire scene then the
default is off.
When hf_gray_16 is on, the output file will be in the form of a heightfield,
with the height at any point being dependent on the brightness of the pixel.
The brightness of a pixel is calculated in the same way that color images are
converted to grayscale images:
height = 0.3 * red + 0.59 * green + 0.11 * blue
Setting the hf_gray_16 option will cause the preview display, if used, to be
grayscale rather than color. This is to allow you to see how the heightfield
will look because some file formats store heightfields in a way that is
difficult to understand afterwards. See section "Height Field" for a
description of how POV-Ray heightfields are stored for each file type.
7.8.5 Irid_Wavelength
Iridescence calculations depend upon the dominant wavelengths of the primary
colors of red, green and blue light. You may adjust the values using the
global setting irid_wavelength as follows... global_settings { irid_wavelen
The default value is rgb<0.25,0.18,0.14> and any filter or transmit values
are ignored. These values are proportional to the wavelength of light but
they represent no real world units.
In general, the default values should prove adequate but we provide this
option as a means to experiment with other values.
7.8.6 Max_Trace_Level
In scenes with many reflective and transparent surfaces POV-Ray can get
bogged down tracing multiple reflections and refractions that contribute very
little to the color of a particular pixel. The global setting max_trace_level
defines the maximum number of recursive levels that POV-Ray will trace a ray.
global_settings { max_trace_level INTEGER }
This is used when a ray is reflected or is passing through a transparent
object and when shadow rays are cast. When a ray hits a reflective surface,
it spawns another ray to see what that point reflects. That is trace level
one. If it hits another reflective surface another ray is spawned and it goes
to trace level two. The maximum level by default is five.
One speed enhancement added to POV-Ray in version 3.0 is Adaptive Depth
Control (ADC). Each time a new ray is spawned as a result of reflection or
refraction its contribution to the overall color of the pixel is reduced by
the amount of reflection or the filter value of the refractive surface. At
some point this contribution can be considered to be insignificant and there
is no point in tracing any more rays. Adaptive depth control is what tracks
this contribution and makes the decision of when to bail out. On scenes that
use a lot of partially reflective or refractive surfaces this can result in a
considerable reduction in the number of rays fired and makes it safer to use
much higher max_trace_level values.
This reduction in color contribution is a result of scaling by the reflection
amount and/or the filter values of each surface, so a perfect mirror or
perfectly clear surface will not be optimizable by ADC. You can see the
results of ADC by watching the Rays Saved and Highest Trace Level displays on
the statistics screen.
The point at which a ray's contribution is considered insignificant is
controlled by the adc_bailout value. The default is 1/255 or approximately
0.0039 since a change smaller than that could not be visible in a 24 bit
image. Generally this setting is perfectly adequate and should be left alone.
Setting adc_bailout to 0 will disable ADC, relying completely on
max_trace_level to set an upper limit on the number of rays spawned.
If max_trace_level is reached before a non-reflecting surface is found and if
ADC hasn't allowed an early exit from the ray tree the color is returned as
black. Raise max_trace_level if you see black areas in a reflective surface
where there should be a color.
The other symptom you could see is with transparent objects. For instance,
try making a union of concentric spheres with a clear texture on them. Make
ten of them in the union with radius's from 1 to 10 and render the scene. The
image will show the first few spheres correctly, then black. This is because
a new level is used every time you pass through a transparent surface. Raise
max_trace_level to fix this problem.
Note that raising max_trace_level will use more memory and time and it could
cause the program to crash with a stack overflow error, although ADC will
alleviate this to a large extent. Values for max_trace_level are not
restricted, so it can be set to any number as long as you have the time and
memory. However, increasing its setting does not necessarily equate to
increased image quality unless such depths are really needed by the scene.
7.8.7 Max_Intersections
POV-Ray uses a set of internal stacks to collect ray/object intersection
points. The usual maximum number of entries in these I-Stacks is 64. Complex
scenes may cause these stacks to overflow. POV-Ray doesn't stop but it may
incorrectly render your scene. When POV-Ray finishes rendering, a number of
statistics are displayed. If you see I-Stack Overflows reported in the
statistics you should increase the stack size. Add a global setting to your
scene as follows:
global_settings { max_intersections INTEGER }
7.8.8 Number_Of_Waves
The wave and ripples pattern are generated by summing a series of waves, each
with a slightly different center and size. By default, ten waves are summed
but this amount can be globally controlled by changing the number_of_waves
setting.
global_settings { number_of_waves INTEGER }
Changing this value affects both waves and ripples alike on all patterns in
the scene.
7.8.9 Radiosity
Radiosity is an extra calculation that more realistically computes the
diffuse interreflection of light. This diffuse interreflection can be seen if
you place a white chair in a room full of blue carpet, blue walls and blue
curtains. The chair will pick up a blue tint from light reflecting off of
other parts of the room. Also notice that the shadowed areas of your
surroundings are not totally dark even if no light source shines directly on
the surface. Diffuse light reflecting off of other objects fills in the
shadows. Typically ray-tracing uses a trick called ambient light to simulate
such effects but it is not very accurate.
Radiosity is more accurate than simplistic ambient light but it takes much
longer to compute. For this reason, POV-Ray does not use radiosity by
default. Radiosity is turned on using the Radiosity INI file option or the
+QR command line switch.
The following sections describes how radiosity works, how to control it with
various global settings and tips on trading quality vs. speed.
7.8.9.1 How Radiosity Works
The problem of ray-tracing is to figure out what the light level is at each
point that you can see in a scene. Traditionally, in ray tracing, this is
broken into the sum of these components:
- Diffuse, the effect that makes the side of things facing the light
brighter;
- Specular, the effect that makes shiny things have dings or sparkles on
them;
- Reflection, the effect that mirrors give; and
- Ambient, the general all-over light level that any scene has, which keeps
things in shadow from being pure black.
POV's radiosity system, based on a method by Greg Ward, provides a way to
replace the last term - the constant ambient light value - with a light level
which is based on what surfaces are nearby and how bright in turn they are.
The first thing you might notice about this definition is that it is
circular: the light of everything is dependent on everything else and vice
versa. This is true in real life but in the world of ray-tracing, we can make
an approximation. The approximation that is used is: the objects you are
looking at have their ambient values calculated for you by checking the other
objects nearby. When those objects are checked during this process, however,
a traditional constant ambient term is used.
How does POV-Ray calculate the ambient term for each point? By sending out
more rays, in many different directions, and averaging the results. A typical
point might use 200 or more rays to calculate its ambient light level
correctly.
Now this sounds like it would make the ray-tracer 200 times slower. This is
true, except that the software takes advantage of the fact that ambient light
levels change quite slowly (remember, shadows are calculated separately, so
sharp shadow edges are not a problem). Therefore, these extra rays are sent
out only once in a while (about 1 time in 50), then these calculated values
are saved and reused for nearby pixels in the image when possible.
This process of saving and reusing values is what causes the need for a
variety of tuning parameters, so you can get the scene to look just the way
you want.
7.8.9.2 Adjusting Radiosity
As described earlier, radiosity is turned on by using the Radiosity INI file
option or the +QR command line switch. However radiosity has many parameters
that are specified in a radiosity {... } statement inside a global_settings
{... } statement as follows:
global_settings {
radiosity {
brightness FLOAT
count INTEGER
distance_maximum FLOAT
error_bound FLOAT
gray_threshold FLOAT
low_error_factor FLOAT
minimum_reuse FLOAT
nearest_count INTEGER
recursion_limit INTEGER
}
}
Each item is optional and may appear in and order. If an item is specified
more than once the last setting overrides previous values. Details on each
item is given in the following sections.
7.8.9.2.1 brightness
This is the degree to which ambient values are brightened before being
returned upwards to the rest of the system. If an object is red \langle 1, 0,
0>, with an ambient value of 0.3, in normal situations a red component of 0.3
will be added in. With radiosity on, assume it was surrounded by an object of
gra color <0.6, 0.6, 0.6>. The average color returned by the gathering
process will be the same. This will be multiplied by the texture's ambient
weight value of 0.3, returning <0.18, 0.18, 0.18>. This is much darker than
the 0.3 which would be added in normally. Therefore, all returned values are
brightened by the inverse of the average of the calculated values, so the
average ambient added in does not change. Some will be higher than specified
(higher than 0.3 in this example) and some will be lower but the overall
scene brightness will be unchanged.
7.8.9.2.2 count
The number of rays that are sent out whenever a new radiosity value has to be
calculated is given by count . Values of 100 to 150 make most scenes look
good. Higher values might be needed for scenes with high contrast between
light levels or small patches of light causing the illumination. This would
be used only for a final rendering on an image because it is very compute
intensive. Since most scenes calculate the ambient value at 1% to 2% of
pixels, as a rough estimate, your rendering will take 1% to 2% of this number
times as long. If you set it to 300 your rendering might take 3 to 6 times as
long to complete (1% to 2% times 300).
When this value is too low, the light level will tend to look a little bit
blotchy, as if the surfaces you're looking at were slightly warped. If this
is not important to your scene (as in the case that you have a bump map or if
you have a strong texture) then by all means use a lower number.
7.8.9.2.3 distance_maximum
The distance_maximum is the only tuning value that depends upon the size of
the objects in the scene. This one must be set for scenes to render
properly... the rest can be ignored for a first try. It is difficult to
describe the meaning simply but it sets the distance in model units from a
sample at which the error is guaranteed to hit 100% ( radiosity_error_bound
>=1): no samples are reused at a distance larger than this from their
original calculation point.
Imagine an apple at the left edge of a table. The goal is to make sure that
samples on the surface of the table at the right are not used too close to
the apple and definitely not underneath the apple. If you had enough rays
there wouldn't be a problem since one of them would be guaranteed to hit the
apple and set the reuse radius properly for you. In practice, you must limit
this.
We use this technique: find the object in your scene which might have the
following problem: a small object on a larger flatter surface that you want
good ambient light near. Now, how far from this would you have to get to be
sure that one of your rays had a good chance of hitting it? In the
apple-on-the-table example, assuming I used one POV-Ray unit as one inch, I
might use 30 inches. A theoretically sound way (when you are running lots of
rays) is the distance at which this object's top is 5 degrees above the
horizon of the sample point you are considering. This corresponds to about 11
times the height of the object. So, for a 3-inch apple, 33 inches makes some
sense. For good behavior under and around a 1/3 inch pea, use 3 inches etc.
Another VERY rough estimate is one third the distance from your eye position
to the point you are looking at. The reasoning is that you are probably no
more than 90 inches from the apple on the table, if you care about the
shading underneath it.
7.8.9.2.4 error_bound
The error_bound is one of the two main speed/quality tuning values (the other
is of course the number of rays shot). In an ideal world, this would be the
only value needed. It is intended to mean the fraction of error tolerated.
For example, if it were set to 1 the algorithm would not calculate a new
value until the error on the last one was estimated at as high as 100%.
Ignoring the error introduced by rotation for the moment, on flat surfaces
this is equal to the fraction of the reuse distance, which in turn is the
distance to the closest item hit. If you have an old sample on the floor 10
inches from a wall, an error bound of 0.5 will get you a new sample at a
distance of about 5 inches from the wall. 0.5 is a little rough and ready,
0.33 is good for final renderings. Values much lower than 0.3 take forever .
7.8.9.2.5 gray_threshold
Diffusely interreflected light is a function of the objects around the point
in question. Since this is recursively defined to millions of levels of
recursion, in any real life scene, every point is illuminated at least in
part by every other part of the scene. Since we can't afford to compute this,
we only do one bounce and the calculated ambient light is very strongly
affected by the colors of the objects near it. This is known as color bleed
and it really happens but not as much as this calculation method would have
you believe. The gray_threshold variable grays it down a little, to make your
scene more believable. A value of .6 means to calculate the ambient value as
60% of the equivalent grey value calculated, plus 40% of the actual value
calculated. At 0%, this feature does nothing. At 100%, you always get
white/grey ambient light, with no hue. Note that this does not change the
lightness/darkness, only the strength of hue/grayness (in HLS terms, it
changes H only).
7.8.9.2.6 low_error_factor
If you calculate just enough samples, but no more, you will get an image
which has slightly blotchy lighting. What you want is just a few extra
interspersed, so that the blending will be nice and smooth. The solution to
this is the mosaic preview: it goes over the image one or more times
beforehand, calculating radiosity values. To ensure that you get a few extra,
the radiosity algorithm lowers the error bound during the pre-final passes,
then sets it back just before the final pass. This tuning value sets the
amount that the error bound is dropped during the preliminary image passes.
If your low error factor is 0.8 and your error bound is set to 0.4 it will
really use an error bound of 0.32 during the first passes and 0.4 on the
final pass.
7.8.9.2.7 minimum_reuse
The minimum effective radius ratio is set by minimum_reuse . This is the
fraction of the screen width which sets the minimum radius of reuse for each
sample point (actually, it is the fraction of the distance from the eye but
the two are roughly equal). For example, if the value is 0.02 the radius of
maximum reuse for every sample is set to whatever ground distance corresponds
to 2% of the width of the screen. Imagine you sent a ray off to the horizon
and it hits the ground at a distance of 100 miles from your eyepoint. The
reuse distance for that sample will be set to 2 miles. At a resolution of
300*400 this will correspond to (very roughly) 8 pixels. The theory is that
you don't want to calculate values for every pixel into every crevice
everywhere in the scene, it will take too long. This sets a minimum bound for
the reuse. If this value is too low, (which is should be in theory) rendering
gets slow, and inside corners can get a little grainy. If it is set too high,
you don't get the natural darkening of illumination near inside edges, since
it reuses. At values higher than 2% you start getting more just plain errors,
like reusing the illumination of the open table underneath the apple.
Remember that this is a unitless ratio.
7.8.9.2.8 nearest_count
The nearest_count value is the maximum number of old ambient values blended
together to create a new interpolated value. It will always be the n
geometrically closest reusable points that get used. If you go lower than 4,
things can get pretty patchy. This can be good for debugging, though. Must be
no more than 10, since that is the size of the array allocated.
7.8.9.2.9 radiosity_quality
7.8.9.2.10 recursion_limit
This value determines how many recursion levels are used to calculate the
diffuse inter-reflection. Valid values are one and two.
7.8.9.3 Tips on Radiosity
If you want to see where your values are being calculated set radiosity_count
down to about 20, set radiosity_nearest_count to 1 and set radiosity_grey to
0. This will make everything maximally patchy, so you'll be able to see the
borders between patches. There will have been a radiosity calculation at the
center of most patches. As a bonus, this is quick to run. You can then change
the radiosity_error_bound up and down to see how it changes things. Likewise
modify radiosity_reuse_dist_min and max .
One way to get extra smooth results: crank up the sample count (we've gone as
high as 1300) and drop the low_error_factor to something small like 0.6. Bump
up the reuse_count to 7 or 8. This will get better values, and more of them,
then interpolate among more of them on the last pass. This is not for people
with a lack of patience since it is like a squared function. If your
blotchiness is only in certain corners or near certain objects try tuning the
error bound instead. Never drop it by more than a little at a time, since the
run time will get very long.
If your scene looks good but right near some objects you get spots of the
right (usually darker) color showing on a flat surface of the wrong color
(same as far away from the object), then try dropping reuse_dist_max . If
that still doesn't work well increase your ray count by 100 and drop the
error bound just a bit. If you still have problems, drop reuse_nearest_count
to about 4.
APPENDIX A Copyright
The following sections contain the legal information and license for the
Persistence of Vision(tm) Ray-Tracer, also called POV-Ray(tm).
APPENDIX A.1 General License Agreement
THIS NOTICE MUST ACCOMPANY ALL OFFICIAL OR CUSTOM PERSISTENCE OF VISION
FILES. IT MAY NOT BE REMOVED OR MODIFIED. THIS INFORMATION PERTAINS TO ALL
USE OF THE PACKAGE WORLDWIDE. THIS DOCUMENT SUPERSEDES ALL PREVIOUS GENERAL
LICENSES OR DISTRIBUTION POLICIES. ANY INDIVIDUALS, COMPANIES OR GROUPS WHO
HAVE BEEN GRANTED SPECIAL LICENSES MAY CONTINUE TO DISTRIBUTE VERSION 2.x BUT
MUST RE-APPLY FOR VERSION 3.00 OR LATER .
This document pertains to the use and distribution of the Persistence of
Vision(tm) Ray-Tracer a. k. a POV-Ray(tm). It applies to all POV-Ray program
source files, executable (binary) files, scene files, documentation files,
help file, bitmaps and INI files contained in official POV-Ray Team(tm)
archives. All of these are referred to here as the software .
All of this software is Copyright 1991,1996 by the POV-Ray Team(tm). Although
it is distributed as freeware, it is NOT Public Domain.
The copyrighted package may ONLY be distributed and/or modified according to
the license granted herein. The spirit of the license is to promote POV-Ray
as a standard ray-tracer, provide the full POV-Ray package freely to as many
users as possible, prevent POV-Ray users and developers from being taken
advantage of, enhance the life quality of those who come in contact with
POV-Ray. This license was created so these goals could be realized. You are
legally bound to follow these rules, but we hope you will follow them as a
matter of ethics, rather than fear of litigation.
APPENDIX A.2 Usage Provisions
Permission is granted to the user to use the software and associated files in
this package to create and render images. The use of this software for the
purpose of creating images is completely free. The creator of a scene file
and the image created from the scene file, retains all rights to the image
and scene file they created and may use them for any purpose commercial or
noncommercial.
The user is also granted the right to use the scenes files, fonts, bitmaps,
and include files distributed in the include , texsamps and pov3demo sub-
directories in their own scenes. Such permission does not extend to files in
the povscn sub-directory. povscn files are for your enjoyment and education
but may not be the basis of any derivative works.
APPENDIX A.3 General Rules for All Distributions
The permission to distribute this package under certain very specific
conditions is granted in advance, provided that the following conditions are
met.
These archives must not be re-archived using a different method without the
explicit permission of the POV-Team. You may rename the archives only to meet
the file name conventions of your system or to avoid file name duplications
but we ask that you try to keep file names as similar to the originals as
possible (for example: povsrc.zip to povsrc30.zip )
Ready-to-run unarchived distribution on CD-ROM is also permitted if the files
are arranged in our standard directory or folder structure as though it had
been properly installed on a hard disk.
You must distribute a full package of files as described in the next section.
No portion of this package may be separated from the package and distributed
separately other than under the conditions specified in the provisions given
below.
Non-commercial distribution in which no money or compensation is charged
(such as a user copying the software for a personal friend or colleague) is
permitted with no other restrictions.
Teachers and educational institutions may also distribute the material to
students and may charge minimal copying costs if the software is to be used
in a course.
APPENDIX A.4 Definition of "Full Package"
POV-Ray is contained in two sets of archives for each hardware platform. A
full package consists of either:
1) End user executable archives containing an executable program,
documentation, and sample scenes but no source. - or - 2) Programmer archives
containing full source code but no executable. Also you must include an
archive containing documentation, and sample scenes. On some platforms, the
documentation and sample scenes are archived separately from the source.
Source alone is not sufficient. You must have docs and scenes.
POV-Ray is officially distributed for MS-Dos; Windows 32-bit; Linux for Intel
x86 series; Apple Macintosh; Apple PowerPC; SunOS; and Amiga. Other systems
may be added in the future.
Distributors need not support all platforms but for each platform you support
you must distribute a full package. For example a Macintosh only BBS need not
distribute the Windows versions.
This software may only be bundled with other software packages according to
the conditions specified in the provisions below.
{/HEADER 1 Conditions for Shareware/Freeware Distribution Companies/}
Shareware and freeware distribution companies may distribute the software
included in software-only compilations using media such as, but not limited
to, floppy disk, CD-ROM, tape backup, optical disks, hard disks, or memory
cards. This section only applies to distributors of collected programs.
Anyone wishing to bundle the package with a shareware product must use the
commercial bundling rules. Any bundling with books, magazines or other print
media should also use the commercial rules.
You must notify us that you are distributing POV-Ray and must provide us with
information on how to contact you should any support issues arise.
No more than five dollars U.S. ($5) can be charged per disk for the copying
of this software and the media it is provided on. Space on each disk must be
used as fully as possible. You may not spread the files over more disks than
are necessary.
Distribution on high volume media such as backup tape or CD-ROM is permitted
if the total cost to the user is no more than $0.08 U.S. dollars per megabyte
of data. For example a CD-ROM with 600 meg could cost no more than $48.00.
APPENDIX A.5 Conditions for On-Line Services and BBS's Including Internet
On-line services, BBS's and internet sites may distribute the POV-Ray
software under the conditions in this section. Sites which allow users to run
POV-Ray from remote locations must use separate provisions in the section
below.
The archives must all be easily available on the service and should be
grouped together in a similar on-line area.
It is strongly requested that sites remove prior versions of POV-Ray to avoid
user confusion and simplify or minimize our support efforts.
The site may only charge standard usage rates for the downloading of this
software. A premium may not be charged for this package. I. e. CompuServe or
America On-Line may make these archives available to their users, but they
may only charge regular usage rates for the time required to download.
APPENDIX A.6 Online or Remote Execution of POV-Ray
Some internet sites have been set up so that remote users can actually run
POV-Ray software on the internet server. Other companies sell CPU time for
running POV-Ray software on workstations or high-speed computers. Such use of
POV-Ray software is permitted under the following conditions.
Fees or charges, if any, for such services must be for connect time, storage
or processor usage ONLY. No premium charges may be assessed for use of
POV-Ray beyond that charged for use of other software. Users must be clearly
notified that they are being charged for use of the computer and not for use
of POV-Ray software.
Users must be prominently informed that they are using POV-Ray software, that
such software is free, and where they can find official POV-Ray software. Any
attempt to obscure the fact that the user is running POV-Ray is expressly
prohibited.
All files normally available in a full package distribution, especially a
copy of this license and full documentation must be available for download or
readable online so that users of an online executable have access to all of
the material of a full user package.
If the POV-Ray software has been modified in any way, it must also follow the
provisions for custom versions below.
APPENDIX A.7 Conditions for Distribution of Custom Versions
The user is granted the privilege to modify and compile the source code for
their own personal use in any fashion they see fit. What you do with the
software in your own home is your business.
If the user wishes to distribute a modified version of the software,
documentation or other parts of the package (here after referred to as a
custom version ) they must follow the provisions given below. This includes
any translation of the documentation into other languages or other file
formats. These license provisions have been established to promote the growth
of POV-Ray and prevent difficulties for users and developers alike. Please
follow them carefully for the benefit of all concerned when creating a custom
version.
No portion of the POV-Ray source code may be incorporated into another
program unless it is clearly a custom version of POV-Ray that includes all of
the basic functions of POV-Ray.
All executables, documentation, modified files and descriptions of the same
must clearly identify themselves as a modified and unofficial version of
POV-Ray. Any attempt to obscure the fact that the user is running POV-Ray or
to obscure that this is an unofficial version expressly prohibited.
You must provide all POV-Ray support for all users who use your custom
version. You must provide information so that user may contact you for
support for your custom version. The POV-Ray Team is not obligated to provide
you or your users any technical support.
Include contact information in the DISTRIBUTION_MESSAGE macros in the source
file optout.h and insure that the program prominently displays this
information. Display all copyright notices and credit screens for the
official version.
Custom versions may only be distributed as freeware. You must make all of
your modifications to POV-Ray freely and publicly available with full source
code to the modified portions of POV-Ray and must freely distribute full
source to any new parts of the custom version. The goal is that users must be
able to re-compile the program themselves and to be able to further improve
the program with their own modifications.
You must provide documentation for any and all modifications that you have
made to the program that you are distributing. Include clear and obvious
information on how to obtain the official POV-Ray.
The user is encouraged to send enhancements and bug fixes to the POV-Ray
Team, but the team is in no way required to utilize these enhancements or
fixes. By sending material to the team, the contributor asserts that he owns
the materials or has the right to distribute these materials. He authorizes
the team to use the materials any way they like. The contributor still
retains rights to the donated material, but by donating, grants unrestricted,
irrevocable usage and distribution rights to the POV-Ray Team. The team
doesn't have to use the material, but if we do, you do not acquire any rights
related to POV-Ray. The team will give you credit as the creator of new code
if applicable.
APPENDIX A.8 Conditions for Commercial Bundling
Vendors wishing to bundle POV-Ray with commercial software (including
shareware) or with publications must first obtain explicit permission from
the POV-Ray Team. This includes any commercial software or publications, such
as, but not limited to, magazines, cover-disk distribution, books,
newspapers, or newsletters in print or machine readable form.
The POV-Ray Team will decide if such distribution will be allowed on a
case-by-case basis and may impose certain restrictions as it sees fit. The
minimum terms are given below. Other conditions may be imposed.
* Purchasers of your product must not be led to believe that they are
paying for POV-Ray. Any mention of the POV-Ray bundle on the box, in
advertising or in instruction manuals must be clearly marked with a
disclaimer that POV-Ray is free software and can be obtained for free or
nominal cost from various sources.
* Include clear and obvious information on how to obtain the official
POV-Ray.
* You must provide all POV-Ray support for all users who acquired POV-Ray
through your product. The POV-Ray Development Team is not obligated to
provide you or your customers any technical support.
* Include a credit page or pages in your documentation for POV-Ray.
* If you modify any portion POV-Ray for use with your hardware or software,
you must follow the custom version rules in addition to these rules.
* Include contact and support information for your product.
* Include a full user package as described above.
APPENDIX A.9 Other Provisions
The team permits and encourages the creation of programs, including
commercial packages, which import, export or translate files in the POV-Ray
Scene Description Language. There are no restrictions on use of the language
itself. We reserve the right to add or remove or change any part of the
language.
"POV-Ray", "Persistence of Vision", "POV-Ray Team" and "POV-Help" are
trademarks of the POV-Ray Team.
While we do not claim any restrictions on the letters "POV" alone, we humbly
request that you not use POV in the name of your product. Such use tends to
imply it is a product of the POV-Ray Team. Existing programs which used "POV"
prior to the publication of this document need not feel guilty for doing so
provided that you make it clear that the program is not the work of the team
nor endorsed by us.
APPENDIX A.10 Revocation of License
VIOLATION OF THIS LICENSE IS A VIOLATION OF COPYRIGHT LAWS. IT WILL RESULT IN
REVOCATION OF ALL DISTRIBUTION PRIVILEGES AND MAY RESULT IN CIVIL OR CRIMINAL
PENALTY .
Such violators who are prohibited from distribution will be identified in
this document.
In this regard, "PC Format", a magazine published by Future Publishing, Ltd.
in the United Kingdom, distributed incomplete versions of POV-Ray 1.0 in
violation the license which was effect at the time. They later attempted to
distribute POV-Ray 2.2 without prior permission of the POV-Ray Team in
violation the license which was in effect at the time. There is evidence that
other Future Publishing companies have also violated our terms. Therefore "PC
Format", and any other magazine, book or CD-ROM publication owned by Future
Publishing is expressly prohibited from any distribution of POV-Ray software
until further notice.
APPENDIX A.11 Disclaimer
This software is provided as is without any guarantees or warranty. Although
the authors have attempted to find and correct any bugs in the package, they
are not responsible for any damage or losses of any kind caused by the use or
misuse of the package. The authors are under no obligation to provide
service, corrections, or upgrades to this package.
APPENDIX A.12 Technical Support
We sincerely hope you have fun with our program. If you have any problems
with the program, the team would like to hear about them. Also, if you have
any comments, questions or enhancements, please contact the POV-Ray Team on
the CompuServe Information Service in the GO GRAPHICS forums, GRAPHDEV forum.
Also check us out on the internet at http://www.povray.org or ftp.povray.org
. The USENET group comp.graphics.rendering.raytracing is a great source of
information on POV-Ray and related topics.
License enquiries should be made via email and limited technical support is
available via email to:
Chris Young
POV-Ray Team Coordinator
CIS: 76702,1655
Internet 76702.1655@compuserve.com
The following postal address is only for official license business and only
if email is impossible.
We do not provide technical support via regular mail, only email. We don't
care if you don't have a modem or online access. We will not mail you disks
with updated versions. Do not send money.
Chris Young
3119 Cossell Drive
Indianapolis, IN 46224 U.S.A.
The other authors' contact information may be found in section "Authors" (see
also "Postcards for POV-Ray Team Members" ).
APPENDIX B Authors
Following is a list in alphabetic order of all people who have ever worked on
the POV-Ray Team or who have made a note-worthy contribution. If you want to
contact or thank the authors read the sections "Contacting the Authors" and
"Postcards for POV-Ray Team Members" .
Steve Anger
(POV-Ray 2.0/3.0 developer)
CIS: 70714,3113
Internet: sanger@hookup.net
Randy Antler
(IBM-PC display code enhancements)
John Baily
(RLE targa code)
Eric Barish
(Ground fog code)
Dieter Bayer
(POV-Ray 3.0 developer and docs coordinator)
CIS: 100255,3074
Kendall Bennett
(PMODE library support)
Steve Bennett
(GIF support)
Jeff Bowermaster
(Beta test)
David Buck
(Original author of DKBTrace)
(POV-Ray 1.0 developer)
Chris Cason
(POV-Ray 2.0/3.0 developer, POV-Help, Windows port)
Internet (preferred): Chris.Cason@oaks.com.au or Chris.Cason@povray.org
CIS: 100032,1644
Aaron Collins
(Co-author of DKBTrace 2.12)
(POV-Ray 1.0 developer)
Chris Dailey
(POV-Ray 3.0 developer)
CIS:
Steve Demlow
(POV-Ray 3.0 developer)
CIS:
Andreas Dilger
(POV-Ray 3.0 developer)
Internet: adilger@enel.ucalgary.ca
Http://www-mddsp.enel.ucalgary.ca/People/adilger/
Joris van Drunen Littel
(Mac beta tester)
Alexander Enzmann
(POV-Ray 1.0/2.0/3.0 developer)
CIS: 70323,2461
Internet: xander@mitre.com
Dan Farmer
(POV-Ray 1.0/2.0/3.0 developer)
CIS: 74431,1075
David Harr
(Mac balloon help and palette code)
Jimmy Hoeks
(Help file for Windows user interface)
Terry Kanakis
(Camera fix)
Kari Juharvi Kivisalo
(Ground fog code)
Adam Knight
(Mac beta tester, Mac Apple Guide developer)
CIS:
Lutz Kretzschmar
(IBM-PC display code [SS24 truecolor], part of the anti-aliasing code)
CIS: 100023,2006
Charles Marslett
(IBM-PC display code)
Pascal Massimino
(Fractal objects)
Jim McElhiney
(POV-Ray 3.0 developer)
CIS:
Robert A. Mickelsen
(POV-Ray 3.0 docs)
CIS:
Mike Miller
(Artist, scene files, stones.inc)
CIS: 70353,100
Douglas Muir
(Bump maps, height fields)
Joel NewKirk
(Amiga Version)
CIS: 102627,1152
Jim Nitchals
(Mac version, scene files)
Paul Novak
(Texture contributions)
Dave Park
(Amiga support, AGA video code)
David Payne
(RLE targa code)
Bill Pulver
(Time code, IBM-PC compile)
Anton Raves
(Beta tester, helping out on several Mac thingies)
CIS: 100022,2603
Dan Richardson
(Docs)
CIS:
Tim Rowley
(PPM and Windows-specific BMP image format support)
Internet: trowley@geom.umn.edu
Robert Schadewald
(Beta tester)
CIS:
Eduard Schwan
(Mac version, mosaic preview, docs)
CIS: 71513,2161
Robert Skinner
(Noise functions)
Erkki Sondergaard
(Scene files)
CIS:
Zsolt Szalavari
(Halo code)
Internet: zsolt@cg.tuwien.ac.at
Scott Taylor
(Leopard and onion textures)
Timothy Wegner
(Fractal objects, PNG support)
CIS: 71320,675
Internet: twegner@phoenix.net
Drew Wells
(POV-Ray 1.0 developer, POV-Ray 1.0 team coordinator)
Chris Young
(POV-Ray 1.0/2.0/3.0 developer, POV-Ray 2.0/3.0 team coordinator)
CIS: 76702,1655
APPENDIX C Contacting the Authors
The POV-Team is a collection of volunteer programmers, designers, animators
and artists meeting via electronic mail on Compuserve's GRAPHDEV forum (GO
GRAPHDEV). The POV-Team's goal is to create freely distributable, high
quality rendering and animation software written in C that can be easily
ported to many different computers. If you have any questions about POV-Ray,
please contact Chris Young
POV-Team Coordinator
CIS: 76702,1655
Internet: 76702.1655@compuserve.com
We love to hear about how you're using and enjoying the program. We also will
do our best try to solve any problems you have with POV-Ray and incorporate
good suggestions into the program. If you have a question regarding
commercial use of, distribution of, or anything particularly sticky, please
contact Chris Young, the development team coordinator. Otherwise, spread the
mail around. We all love to hear from you! The best method of contact is
e-mail through CompuServe for most of us. America On-Line and Internet can
now send mail to CompuServe, also, just use the Internet address and the mail
will be sent through to CompuServe where we read our mail daily. Please do
not send large files to us through the e-mail without asking first. We pay
for each minute on CompuServe and large files can get expensive. Send a query
before you send the file, thanks!
APPENDIX D Postcards for POV-Ray Team Members
If you want to personally thank some of the POV-Ray Team members you can send
them a postcard from wherever you are. To avoid invalid addresses from
floating around (in case some of us move) the addresses listed below (in
alphabetical order) are only valid until the given date. Dieter Bayer
Taeublingstr. 26
91058 Erlangen
Germany (until 31. July 1997)
Chris Cason (Windows version)
PO Box 407
Williamstown
Victoria 3016
Australia (until 31. December 1998)
Joel NewKirk
255-9 Echelon Rd
Voorhees, NJ, USA, 08043 (until -)
Eduard Schwan (Macintosh version)
1112 Oceanic Drive
Encinitas, California, USA, 92024-4007 (until 30. June 1998)
You should also be aware that we do not answer any questions asked by regular
mail or phone, we only reply to e-mails. Send any questions you have to the
e-mail address mentioned in section "Contacting the Authors" .
APPENDIX E POV-Ray Output Messages
APPENDIX E.1 Options in Use
APPENDIX E.2 Warning Messages
APPENDIX E.2.1 Warnings during the Parsing Stage
APPENDIX E.2.2 Other Warnings
APPENDIX E.3 Error Messages
APPENDIX E.3.1 Scene File Errors
APPENDIX E.3.2 Other Errors
APPENDIX E.4 Statistics
APPENDIX F Tips and Hints
APPENDIX F.1 Scene Design Tips
There are a number of excellent shareware CAD style modelers available on the
DOS platform now that will create POV-Ray scene files. The online systems
mentioned elsewhere in this document are the best places to find these.
Hundreds of special-purpose utilities have been written for POV-Ray: data
conversion programs, object generators, shell-style launchers and more. It
would not be possible to list them all here, but again, the online systems
listed will carry most of them. Most, following the POV-Ray spirit, are
freeware or inexpensive shareware. Some extremely elaborate scenes have been
designed by drafting on graph paper. Raytracer Mike Miller recommends graph
paper with a grid divided in tenths, allowing natural decimal conversions.
Start out with a boilerplate scene file, such as a copy of basicvue.pov , and
edit that. In general, place your objects near and around the origin with the
camera in the negative z-direction, looking at the origin. Naturally, you
will break from this rule many times, but when starting out, keep things
simple. For basic, boring, but dependable lighting, place a light source at
or near the position of the camera. Objects will look flat, but at least you
will see them. From there, you can move it slowly into a better position.
APPENDIX F.2 Scene Debugging Tips
To see a quick version of your picture, render it very small. With fewer
pixels to calculate the ray-tracer can finish more quickly. -W 160 -H 100 is
a good size. Use the +Q quality switch when appropriate. If there is a
particular area of your picture that you need to see in high resolution,
perhaps with anti-aliasing on (perhaps a fine-grained wood texture), use the
+SC , +EC , +SR and +ER switches to isolate a window . If your image contains
a lot of inter-reflections, set max_trace_level to a low value such as 1 or
2. Don't forget to put it back up when you're finished! Turn off any
unnecessary lights. Comment out extended light keywords when not needed for
debugging. Again, don't forget to put them back in before you retire for the
night with a final render running! If you've run into an error that is
eluding you by visual examination it's time to start bracketing your file.
Use the block comment characters /* ... */ to disable most of your scene and
try to render again. If you no longer get an error the problem naturally lies
somewhere within the disabled area. Slow and methodical testing like this
will eventually get you to a point where you will either be able to spot the
bug, or go quietly insane. Maybe both. If you seem to have lost yourself or
an object (a common experience for beginners) there are a few tricks that can
sometimes help:
1) Move your camera way back to provide a long range view. This may not
help with very small objects which tend to be less visible at a
distance, but it's a nice trick to keep up your sleeve.
2) Try setting the ambient value to 1.0 if you suspect that the object may
simply be hidden from the lights. This will make it self-illuminated and
you'll be able to see it even with no lights in the scene.
3) Replace the object with a larger, more obvious "stand-in" object like a
large sphere or box. Be sure that all the same transformations are
applied to this new shape so that it ends up in the same spot.
APPENDIX F.3 Animation Tips
When animating objects with solid textures, the textures must move with the
object, i. e. apply the same rotate or translate functions to the texture as
to the object itself. This is now done automatically if the transformations
are placed after the texture block like the following example
shape { ...
pigment { ... }
scale < ... >
}
will scale the shape and pigment texture by the same amount.
shape { ...
scale < ... >
pigment { ... }
}
will scale the shape but not the pigment. Constants can be declared for most
of the data types in the program including floats and vectors. By writing
these to include files you can easily separate the parameters for an
animation into a separate file. Some examples of declared constants would be:
#declare Y_Rotation = 5.0 * clock
#declare ObjectRotation = <0, Y_Rotation, 0>
#declare MySphere = sphere { <0, 0, 0>, 1.1234 }
Other examples can be found scattered throughout the sample scene files. A
tip for MS-Dos users: Get ahold of dta.exe (Dave's Targa Animator) for
creating .FLI/.FLC animations. aaplay.exe and play.exe are common viewers for
this type of file. When moving the camera in an animation (or placing one in
a still image, for that matter) avoid placing the camera directly over the
origin. This will cause very strange errors. Instead, move off center
slightly and avoid hovering directly over the scene.
APPENDIX F.4 Texture Tips
Wood is designed like a log with growth rings aligned along the z-axis.
Generally these will look best when scaled down by about a tenth (to a
unit-sized object). Start out with rather small value for the turbulence too
(around 0.05 is good for starters). The marble texture is designed around a
pigment primitive that is much like an x-gradient. When turbulated, the
effect is different when viewed from the side or from the end . Try rotating
it by 90 degrees on the y-axis to see the difference. You cannot get specular
highlights on a totally black object. Try using a very dark gray, say Gray10
or Gray15 (from colors.in ), instead.
APPENDIX F.5 Height Field Tips
Try using POV-Ray itself to create images for height fields: camera { locat
plane { z, 0
finish { ambient 1 } // needs no light sources
pigment { bozo } // or whatever. Experiment.
}
That's all you'll need to create a .tga file that can then be used as a
height field in another image!
APPENDIX F.6 Converting "Handedness"
If you are importing images from other systems you may find that the shapes
are backwards (left-to-right inverted) and no rotation can make them correct.
Often, all you have to do is negate the terms in the right vector of the
camera to flip the camera left-to-right (use the right-hand coordinate
system). Some programs seem to interpret the coordinate systems differently,
however, so you may need to experiment with other camera transformations if
you want the y- and z-vectors to work as POV-Ray does.
APPENDIX G Frequently Asked Questions
This is a collection of frequently asked questions and their answers taken
directly from messages posted in the Graphic Developer's Forum on Compuserve
and the comp.graphics.raytracing newsgroup. This version of the FAQ is
heavily biased towards the CompuServe user of the IBM PC version of POV-Ray.
Hopefully later revisions will remove some of this bias, but at present time,
that is the largest audience.
APPENDIX G.1 General Questions
Q: When will POV-Ray 3.0 be released? A: It is already available. Q: When
will the source code be released? A: The soruce code available too.
APPENDIX G.2 POV-Ray Option Questions
Q: How can I set mosaic preview to go from 8*straight to final render without
going to 4*and then t*first? \\ A: Use the +SP n or Preview_Start_Size option
to set the starting resolution and the +EP n or Preview_End_Size option to
set the ending resolution. With +SP 8 and +EP 8 it will go from 8*8 down to
8*8 (just one pass) then immediately drop into the final pass at 1*1. Q:
Should the +MB switch be used in very small scenes, i. e. with a low number
of objects. \\ A: That depends on the number of objects and their type.
Normally it doesn't hurt to always use the bounding box hierarchy ( +MB 0).
If you have just one or two objects it may be better to not use automatic
bounding. Q: Does the +MB switch affect the quality of the image? A: No. It
only affects the speed of the intersection tests.
APPENDIX G.3 Atmosphere Questions
Q: Why is the atmosphere I added not visible? \ A: The most common error made
when adding an atmosphere to a scene is the missing hollow keyword in all
objects the camera currently is in. If you are inside a box that is used to
model a room you'll have to add the hollow keyword to the box statement. If a
plane is used to model the ground you'll have to make it hollow (only if you
are inside the plane, but to be sure you can always do it). If this doesn't
help there may be other problems you'll have to verify. The distance and
scattering values of the atmosphere have to be larger than zero. Light
sources that shall interact with the atmosphere mustn't contain an atmosphere
off statement.
Q: Why can't I see any atmosphere through my translucent object? \\ A: If you
have a translucent object you (almost) always have to make it hollow by
adding the hollow keyword. Whenever an intersection is found and the ray is
inside a solid object no atmospheric effects will be calculated.
If you have a partially transparent plane for example the atmosphere on the
other side of the plane will only be visible through the plane if this plane
is hollow.
Q: Why do the lit parts of the atmosphere amplify the background? \\
A: First, they don't.
Second, whenever parts of the background are visible through the atmosphere
and those areas of the atmosphere are lit by any light source, the scattered
light is added to the light coming from the background. This is the reason
why the background seems to be amplified by the atmosphere. Just imagine the
followoing example: you have a blue background that is attenuated be the
atmosphere in a way that the color reaching the viewer is <0,0,0.2>. Now some
light coming from a light source is attenuated and scattered by the
atmosphere and finally reaches the viewer with a color of <0.5,0.5,0.5>.
Since we already have light coming from the background, both colors are added
to give <0.5,0.5,0.7>. Thus the light gets a blue hue. As a result you think
that the background light is amplified but it isn't as the following scene
clearly shows.
#version 3.0
camera {
location <0, 6, -20>
look_at <0, 6, 0>
angle 48
}
atmosphere {
type 1
samples 10
distance 20
scattering 0.3
aa_level 3
aa_threshold 0.1
jitter 0.2
}
light_source { <0, 15, 0> color red .7 green .7 blue .7 shadowless }
light_source {
<-5, 15, 0> color rgb <1, 0, 0>
spotlight
point_at <-5, 0, 0>
radius 10
falloff 15
tightness 1
atmospheric_attenuation on
}
light_source {
<0, 15, 0> color rgb <0, 1, 0>
spotlight
point_at <0, 0, 0>
radius 10
falloff 15
tightness 1
atmospheric_attenuation on
}
light_source {
<5, 15, 0> color rgb <0, 0, 1>
spotlight
point_at <5, 0, 0>
radius 10
falloff 15
tightness 1
atmospheric_attenuation on
}
plane { z, 10
pigment { checker color rgb<1, 0, 0> color rgb<0, 1, 0> }
hollow
}
The atmosphere seems to amplify what is seen in the background.
In the background you see a red/green checkered plane. The background color
visible through the atmosphere is added to the light scattered from the
spotlights. You'll notice that even though the red squares behind the red
spotlight's cone are brighter than those outside the cone the green ones are
not. For the green spotlight the situation is turned around: the green
squares seem to be amplified while the red are not. The blue spotlight
doesn't show this effect at all.
APPENDIX H Suggested Reading
Beside the POV-Ray specific books mentioned in "POV-Ray Related Books and
CD-ROMs" there are several good books or periodicals that you should be able
to locate in your local computer book store or your local university library.
"An Introduction to Ray tracing"
Andrew S. Glassner (editor)
ISBN 0-12-286160-4
Academic Press
1989
"3D Artist" Newsletter
"The Only Newsletter about Affordable
PC 3D Tools and Techniques")
Publisher: Bill Allen
P.O. Box 4787
Santa Fe, NM 87502-4787
(505) 982-3532
"Image Synthesis: Theory and Practice"
Nadia Magnenat-Thalman and Daniel Thalmann
Springer-Verlag
1987
"The RenderMan Companion"
Steve Upstill
Addison Wesley
1989
"Graphics Gems"
Andrew S. Glassner (editor)
Academic Press
1990
"Fundamentals of Interactive Computer Graphics"
J. D. Foley and A. Van Dam
ISBN 0-201-14468-9
Addison-Wesley
1983
"Computer Graphics: Principles and Practice (2nd Ed.)"
J. D. Foley, A. van Dam, J. F. Hughes
ISBN 0-201-12110-7
Addison-Wesley,
1990
"Computers, Pattern, Chaos, and Beauty"
Clifford Pickover
St. Martin's Press
"SIGGRAPH Conference Proceedings"
Association for Computing Machinery
Special Interest Group on Computer Graphics
"IEEE Computer Graphics and Applications"
The Computer Society
10662, Los Vaqueros Circle
Los Alamitos, CA 90720
"The CRC Handbook of Mathematical Curves and Surfaces"
David von Seggern
CRC Press
1990
"The CRC Handbook of Standard Mathematical Tables"
CRC Press
The Beginning of Time
APPENDIX I Help on Help
Using the Help Reader (POVHELP.EXE)
KNOWN INCOMPATIBILITIES
See after the Quick Intro.
Quick Intro
Use the +E option to make the help reader a pop-up program.
Use Space to go to the next section.
Use Ctrl-PgUp and Ctrl-PgDn to move between sections also.
Use Tab to highlight hypertext links.
Use Alt-Tab to highlight code fragments.
Use Enter to jump to a highlighted hypertext link.
Use +/- to jump to relevant sections once link jumping has started.
Use BACKSPACE to return to the last place you were before a search/jump.
Use 'S' to search on a keyword.
Use 'J' to toggle text justification when reading a section.
Use 'P' to paste code into your application via the keyboard buffer.
POV-Help will handle non-standard page widths provided the BIOS column count
is correctly updated by whatever program is being used to alter it from 80
columns.
If you use POV-Help as a pop-up program, it will attempt to search on the
word under your cursor when you pop it up. Note that if you exit pop-up mode
by using the hot-key (the default is ALT-ESC), POV-Help takes this to mean
that you want to return to the same place next time and will not perform a
search. A search is only performed if you exited using ESCAPE (meaning you
have finished with the current subject.)
The history stack activated by using Backspace holds 32 entries.
KNOWN INCOMPATIBILITIES
POV-Help does not work with MS-DOS's EDIT program. [In fact, EDIT.COM is
really QBASIC.EXE with a few add ons ; EDIT needs QBASIC to run.]
If it won't work with your editor, try this (assuming you have macro
facilities) -
o write a macro to get the word under the cursor
o have it call POVHELP.EXE with the word as a parameter
o bind the macro to your key-sequence of choice.
Command Line (case insensitive)
+Iname use alternate file name (default HELP.PHE)
+N123 go to the 123rd section (NOT section 123!)
+S4.5.6 go to section '4.5.6'
+Tsphere or "+Tsphere" go straight to the first section found with 'sphere'
in its title.
+W50 window width 40 characters (max 127)
+H15 window height 15 lines (max 21)
+J[-] justify ON (default), -J- to turn off
+PH[n] send 'n' HOME keys after each CR when pasting.
default is -ph1.
+KALT-ESC hot key sequence. can be CTRL|ALT|CTRL-ALT+[Any
character]|[ESC]. e.g. +KCTRL-ALT-P, +KCTRL-1,
+KALT-CTL-'. CTL is also acceptable.
+Eabc d e run program 'abc' with parameters 'd' and 'e'. all
parameters after the '+e' are passed to the program.
text same as +T unless collecting +E parameters, where it
is a parameter
Viewer Commands
Top Menu
Up, Down move highlight bar
Enter view selected item
Escape exit help viewer
Authors, Copyright
Up, Down scroll screen
PgUp, PgDn scroll screen
Left, Right scroll screen
Escape return to top menu
Section
Up, Down scroll screen
PgUp, PgDn scroll screen
Left, Right scroll screen
Escape return to top menu
Space or CtrlPgDn view next section
CtrlPgUp view previous section
"+", Enter jump to first/next hypertext link
"-" jump to previous link/original section
"B" jump back to original section (from before link jumping)
Tab select next visible link, wraps from last to first
ShiftTab select previous visible hypertext link
AltTab select code fragment for pasting.
"P" paste highlighted code fragment via keyboard buffer.
General
The help reader wraps most text. Excluded are specified portions, lists, and
a few others. Use the left and right arrow keys to scroll these if need be.
The help reader is intended to be a 'shell' around an editor program. Some
people may prefer the term 'shim'.
Using EMS for most memory requirements, it loads itself and then runs your
editor for you, providing pop-up help facilities. It will also be able to
paste code fragments into your source. If your editor was, for example, 'ME',
you would place a batch file called 'ME.BAT' in your scene development
directory. If you use 'VI', you'd create 'VI.BAT', and so on.
(YOUR-EDITOR-NAME.BAT)
desired key sequence -
|
--- --- ---
povhelp |+W50 +H15³ |+KCTRL-ALT-H| |+Ed:\me\me.exe| %1 %2 %3 %4 %5
--- --- ---
| |
size of window - |
|
place path to your editor here --
For example -
povhelp +W50 +H15 +KALT-H +Ed:\me\me.exe %1 %2 %3 %4 %5
This command line will yield a version of POV-Help with a 50x15 window,
popped-up with the ALT-H key sequence, over the editor 'd:\me\me.exe'. If you
don't specify a key sequence, POV-Help defaults to using ALT-ESC.
This would load the help reader. which would then load ME.EXE, and things
would proceed as normal. When you exit your editor, the help reader
automatically unloads. You can use the ALT-ESC key sequence to pop up
POVHELP. This is the default ; there is a way to set it. Note that no other
parameters may appear after the +E parameter as they will just be passed to
the program being run.
If you use the hotkey to pop-up, POVHELP performs a simplistic search of
sections and titles based on the word under the cursor. If found, you are
taken to that. Otherwise, you are taken to the main menu, unless you
hot-keyed out.
You can hot-key out of the actual section text, by using the same hot key
that got you in. If you press escape, you are taken back up to the top menu.
But if you hotkey out, you go back to your program. Next time you press the
hot key, you will be taken back to the same place. No search is performed in
this case.
POVHELP needs EMS if it is running as a shell program.
If you don't specify the +E parameter, POVHELP will come up as a stand-alone
program, in which case it does not use EMS.
If you highlight a section of code using Alt-Tab, and you are using POV-Help
in pop-up mode, then you may paste the code via the keyboard buffer using
'P'.
As many editors today use auto-indentation, this may cause some problems with
column alignment. For that reason, POV-Help by default inserts a HOME key
code into the keyboard buffer after each CR. Some editors require more than
one HOME key operation to get to the left column. For this reason, the number
of HOME's sent may be adjusted from 0 (none) to 9 using the +PH[n]
command-line parameter. 'n' is any value from 0 to 9 and defaults to 1.
POV-Help was written by Christopher J. Cason.
CIS : 100032,1644.
Internet : cjcason@yarrow.wt.uwa.edu.au.
Converters will be available which translate POV-Help databases to other
formats such as Postscript, LaTeX, RTF, Windows Help, HTML, etc.
The format of the POV-Help database is documented and freely available.
POV-Help is free. It may not be sold. See POVLEGAL.DOC for details. The
POV-Help suite of programs is copyright (c) 1994 C.J. Cason and the POV-Team.
