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#
Fast computation of shadow boundaries using

spatial coherence and backprojections

##
A. James Stewart
and
Sherif Ghali

### Abstract

This paper describes a fast, practical algorithm to compute the
shadow boundaries in a polyhedral scene illuminated by a polygonal
light source. The shadow boundaries divide the faces of the scene
into regions such that the structure or ``aspect'' of the visible area
of the light source is constant within each region. The paper also
describes a fast, practical algorithm to compute the structure of the
visible light source in each region. Both algorithms exploit spatial
coherence and are the most efficient yet developed.

Given the structure of the visible light source in a region,
queries of the form ``What specific areas of the light source are
visible?'' can be answered almost instantly from any point in the
region. This speeds up by several orders of magnitude the accurate
computation of first level diffuse reflections due to an area light
source. Furthermore, the shadow boundaries form a good initial
decomposition of the scene for global illumination computations.

### The Paper

77 Kb compressed Postscript file

@inproceedings{SG-siggraph94,
author = "A. James Stewart and Sherif Ghali",
title = "Fast computation of shadow boundaries using spatial coherence
and backprojections",
booktitle = "Computer Graphics (SIGGRAPH)",
year = "1994",
month = "August",
pages = "231--238"
}