Compressed Opacity Maps for Ray Tracing

Abstract

Recently, schemes have been proposed for accelerating 'alpha-tested' triangles in ray-tracing through the use of precomputed, three-level Opacity Masks/Maps that can significantly reduce the need for expensive of 'Any-Hit shader' invocations. We propose and compare two related schemes, VQ2 and VQ4, of compressing such maps that provide both random access and low-cost decompression. Each compressed opacity map, however, relates to a pair of adjacent triangles, taking advantage of correlation across the shared edge and matching likely underlying hardware primitive models.