Ray Specialized Contraction on Bounding Volume Hierarchies

Abstract

In this paper we propose a simple but effective method to modify a BVH based on ray distribution for improved ray tracing performance. Our method starts with an initial BVH generated by any state-of-the-art offline algorithm. Then by traversing a small set of sample rays we collect statistics at each node of the BVH. Finally, a simple but ultra-fast BVH contraction algorithm modifies the initial binary BVH to a multi-way BVH. The overall acceleration for ray-primitive testing is about 25% for incoherent diffuse rays and 30% for shadow rays, which is significant as a data structure optimization. Similar results are also presented for packet ray tracing, and for Quad-BVHs the improvement is 10% to 15%. The approach has the advantages of being simple, and compatible with almost any existing BVH and ray tracing techniques, and it require very little extra work to generate the modified tree.