Hemi-Cube Ray-Tracing: A Method for Generating Soft Shadows

Abstract

This paper presents a new ray-tracing technique for generating soft shadows. The technique treats scenes consisting of light sources and opaque objects which are polygons or polyhedra of arbitrary shape and size. To determine the intensity at a point on a surface, the hemisphere is sampled extensively through the use of hemi-cubes. So-called item-buffer boxes, a combination of itembuffers and buffer boxes, are used to calculate ray intersections as well as to suppress image aliasing. Several methods for reducing aliasing caused by hemi-cubes are discussed. The uniform treatment of rays allows for a straightforward extension of the algorithm to produce fuzzy reflections. The success of the new technique depends on a fast implementation of a visible surface algorithm as provided by today’s high-end graphics workstations. The results are images of realistically illuminated synthetic environments.