Coherent ray tracing via stream filtering

We introduce an approach to coherent ray tracing based on a new stream filtering algorithm. This algorithm, which is motivated by breadth-first ray traversal and elimination of inactive ray elements, exploits the coherence exhibited by processing arbitrarily-sized groups of rays in SIMD fashion. These groups are processed by a series of filters that partition rays into active and inactive subsets throughout the various stages of the rendering process. We present results obtained with a detailed cycle-accurate simulation of a hardware architecture that supports wider-than-four SIMD processing and efficient scatter/gather memory and stream partitioning operations. In this context, stream filtering achieves frame rates of 15-25 fps for scenes of high geometric complexity rendered with path tracing and a variety of advanced visual effects.