Efficient Light Transport Using Precomputed Visibility

Visibility computations are the most time-consuming part of global illumination algorithms. The cost is amplified by the fact that quite often identical or similar information is recomputed multiple times. In particular this is the case when multiple images of the same scene are to be generated under varying lighting conditions and/or viewpoints. But even for a single image with static illumination, the computations could be accelerated by reusing visibility information for many different light paths. In this paper we describe a general method of precomputing, storing, and reusing visibility information for light transport in a number of different types of scenes. In particular, we consider general parametric surfaces, triangle meshes without a global parameterization, and participating media. We also reorder the light transport in such a way that the visibility information is accessed in structured memory access patterns. This yields a method that is well suited for SIMD-style parallelization of the light transport, and can efficiently be implemented both in software and using graphics hardware. We finally demonstrate applications of the method to highly efficient precomputation of BRDFs, bidirectional texture functions, light fields, as well as near-interactive volume lighting