README for fastshadows
shad demonstrates the real-time shadow casting capability
of the IRIS-4D RealityEngine (RE).
NOTE: THIS PROGRAM ONLY COMPILES ON 4.0.5G OR LATER REALITY ENGINE
MODELS. THE BINARY ON THE CD SEEMS TO WORK ON 4.0.5F AS WELL.
A man page for using shad exists. See shad(6) (ascii version below).
`!' indicates new or updated as of version 4.2
! shadows+light.ps "Fast Shadows and Lighting Effects Using Texture Mapping"
(This paper is a companion to the software
implementation included in this directory.)
ABSTRACT: Generating images of texture mapped geometry requires
projecting surfaces onto a two-dimensional screen. If this projection
involves perspective, then a division must be performed at each pixel
of the projected surface in order to correctly calculate texture map
coordinates.
We show how a simple extension to perspective-correct texture mapping
can be used to create various lighting effects. These include arbitrary
projection of two-dimensional images onto geometry, realistic
spotlights, and generation of shadows using shadow maps. These effects
are obtained in real time using hardware that performs correct texture
mapping.
CR Categories and Subject Descriptors: I.3.3 [Computer Graphics]:
Picture/Image generation; I.3.7 [Computer Graphics]: Three-dimensional
Graphics and Realism - color, shading, shadowing, and texture
Additional Key Words and Phrases: lighting, texture mapping
Shadows have been done before with the Iris GL. Examples of shadows
cast onto flat surfaces are found in jello, insect, and flight.
The RE uses a technique based on shadow maps, which allow casting
shadows onto curved surfaces and self-shadowing.
A good reference for this is "Rendering Antialiased Shadows with
Depth Maps" by Reeves, Salesin and Cook from the 1987 SIGGRAPH
Proceedings. Also, some of the mathematical basis for why it works
is described in "Fast Shadows and Lighting Effects Using Texture
Mapping" by Segal, Korobkin, van Widenfelt, Foran and Haeberli from
1992 SIGGRAPH Proceedings.
The Iris GL support for shadows includes:
- new arguments to texdef
- TX_I_16
- TX_BILINEAR_LEQUAL, TX_BILINEAR_GEQUAL
- new argument to tevdef
- TV_ALPHA
- new GL call
- displacepolygon(float scalefactor)
-rolf (rolf@sgi.com, 415/390-3669)
SHAD(6D) Silicon Graphics SHAD(6D)
NAME
shad - A demonstration of real-time shadows
SYNOPSIS
shad obj1.sgo [obj2.sgo ...]
DESCRIPTION
shad is a simple demonstration of the real-time shadowing capability of
Reality Engine Graphics. Multiple colored lights cast shadows on an ob-
ject or objects.
CONTROLS
The left and middle mouse buttons control the viewer position. The
viewer position is a point on a hemisphere looking in at the object.
When pressing the left mouse button, horizontal mouse motion controls the
position around the hemisphere (longitude), while vertical mouse motion
controls the height on the hemisphere (latitude). When pressing the mid-
dle mouse button, vertical motion controls the distance from the object.
Pressing the right mouse button selects a pop up menu.
Pressing the ESC key exits the program.
While in the Eye View, simultaneously pressing the left shift key and
holding the left mouse button causes the mouse position to control the
placement of one of the lights. This allows a shadow to be moved in
real-time.
NOTES
shad only runs on a Reality Engine, although newer graphics options may
also support real-time shadows.
BUGS
If the Light View clips incorrect shadows may result. Avoid clipping in
the Light Views.
AUTHOR
Paul Haeberli and Rolf van Widenfelt, August 1992
Page 1 Release 4.0.5G August 1992
Source
Documentation
Reference
OR, ...