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USERMAN.DOC
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QRT Users Manual
INTRODUCTION
QRT (Quick Ray Tracer) is an easy to use image generation system
that uses a ray tracing algorithm for image rendering. Versions
exist for the Amiga personal computer and Data General MV10000.
QRT overcomes many of the problems of other ray tracing packages,
and is designed to operate nicely in a multi-tasking environment.
COMPARISON TO OTHER SYSTEMS
QRT was developed on the Amiga personal computer, so it will be
compared to other Amiga ray tracers. There are, to my knowledge,
five other Amiga ray tracers, each with its own strengths and
weaknesses. I will describe each system briefly, and compare it
to QRT. All the Amiga ray tracers can operate in HAM (4096
color) mode.
RT: RT was the first ray tracer written for the Amiga, by Eric
Graham. It will model a universe made of only spheres, a
sky, and a checkered or solid ground. It is relatively
fast, but not generally useful for realistic modeling
because of the sphere limitation. The input language is
cryptic, although some error checking is done. The system
will only generate low resolution images.
SILVER: I have never seen SILVER, so I cannot say much about
this system.
SCULPT-3D: This package incorporates an interactive editor for
creating objects, and is capable of quickly generating a
preliminary image of the scene by using hidden surface
techniques. However, every primitive is made of polygons,
and some primitives such as spheres require hundreds of
polygons for a smooth texture, so the ray tracing is very
slow. Also, the package takes a large amount of memory to
run, and is prone to system crashes. Its chief feature is
the ability to create arbitrary shaped objects using a
series of triangles. Mirrored, dull, or shiny objects are
supported.
CLIGHT: This ray tracer also has an interactive editor, but
produces very poor quality images. It is not capable of
any patterning or reflection characteristics.
QRT Ray Tracer Page 1 User Manual
DBW: This is possibly the most complete ray tracer for the
Amiga. It will support objects with arbitrary degrees of
reflection and gloss, depth of field effects, some
texturing, wavy surfaces, fractals, transparent surfaces,
diffuse propagation of light from object to object, and 5
primitive types (sphere, triangle, parallelogram, fractal,
and ring). The input language, however, is so cryptic as
to be nearly incomprehensible, and if there is any error
in the input file, it will crash the system. It is also
painfully slow; some images take 16 to 24 hours to
complete.
QRT is meant to be a compromise between the fast, simple ray
tracers and the slow powerful systems. It compares favorably in
speed to RT, and in power to Sculpt-3d or DBW. It has a very
friendly input language with extensive error checking. Here are
some features of QRT:
o Multiple primitive types, including user defined quadratic
surfaces
o Arbitrary levels of diffuse reflection, spectral
reflection, transmission, ambient lighting, and gloss
o User defined pattern information for objects
o Bounding boxes for groups of objects
o Shadows
o Multiple light sources with different characteristics
o Arbitrary Phong spectral reflection coefficients
o Color dithering to increase the apparent number of colors
o Easy to use, free format input language with error
checking. Parameters are by keyword and may appear in any
order.
o Supports medium resolution (128k dots/screen)
Each of these features of QRT will be discussed is greater detail
in this document.
THE QRT WORLD
QRT constructs an image of the world by performing certain
manipulations on an internal representation of a group of
QRT Ray Tracer Page 2 User Manual
objects. You must provide a description of these objects to QRT
through the QRT input language.
QRT writes a machine independent bitmap file which can be read by
a computer specific post processor. The post processor either
displays the image or converts it into the proper form for
display by system programs. (See the Machine Dependent
Information section of this manual for details).
QRT is capable of dealing with 5 types of primitive objects:
spheres, parallelograms, triangles, rings (annulus), and
quadratic surfaces. The latter can be used to model cones,
oblong spheroids, and other interesting surfaces. Each of these
objects can have an arbitrary orientation in space, and arbitrary
surface characteristics.
QRT INPUT LANGUAGE
The QRT input language is free format, in that commands may be
placed anywhere on a line, and newlines may be placed at any
point. This makes it easy to use indentation. Comments are also
supported by surrounding text with curly braces '{' and '}'.
Comments may span lines.
Once a file with QRT commands is built (using any available text
editor), qrt can be made to process these commands:
QRT <commands.qrt
where "commands.qrt" is the file containing the input. QRT also
produces some statistics, so this output can also be redirected.
Since QRT runs for a long time, you will probably want to run it
as a background task with a low priority. So, the full set of
commands to run QRT would be:
SetTaskPriority -5
run QRT <commands.qrt >qrt.out
SetTaskPriority 0
This set of commands is specific to the Commodore Amiga; see the
Machine Dependent Information section of the manual for other
operating systems.
QRT will write a very large file, which may be anywhere from 400K
to 4 megabytes depending on the specific computer display
resolution. (See the Machine Dependent Information section of
this manual for the exact file size). There should be at least
enough room on your disk to accommodate this file. I recommend
sending the output to a RAM disk, so that the physical disk does
QRT Ray Tracer Page 3 User Manual
not get used for 60 minutes while QRT computes the image.
A typical QRT command to create a sphere using the default
surface attributes would, be:
SPHERE ( loc = (5,10,100) { this is a white sphere }
radius = 12.5
)
For comparison, the sphere command for DBW looks like this:
s 0 0 0 1 0 0 0 .2 .2 .2 .8 .8 .8 5 10 100 12.5
Or, in R