Depth buffer shadow algorithms

The depth buffer (also called z-buffer) visible surface algorithm is frequently used for shadow simulation. This shadow algorithm is very powerful, but it suffers from several problems such as aliasing and incorrect self-shadowing of simple surfaces. New algorithms are presented which solve these problems for most cases without much additional computation. A family of depth buffer shadow algorithms is defined. Three main improvements are presented. First, replacing the z-buffer with a p-buffer (plane buffer) gives a more accurate representation of the visible surface across a pixel. Second, storing two surface in the shadow buffer the closest and the second surfaces to the light source, and averaging them to form an intermediate surface yields a much better defined illumination test. Third, considering the values of adjacent pixels in the shadow buffer helps to reduce some aliasing artifacts. These techniques preserve all the desirable properties of the depth buffer visible surface algorithm while yielding more accurate shadows. 12 refs., 17 figs.