An Improved Multi-Level Raytracing Algorithm

Previous work has used entry point search (EP search) to accelerate raytracing by avoiding redundant traversal of nodes in a KD tree. EP search works by identifying a node which may be used as a starting point for tracing a particular group of coherent rays, thus bypassing all nodes above it. This is most effective when all rays can be shown to be occluded, since a leaf or low inner node can often be used as the entry point. Unfortunately, occlusion detection is difficult in scenes with complex geometry, and is particularly difficult for BVH data structures, for which ordered traversal cannot be guaranteed. If occlusion cannot be considered, EP search alone becomes considerably less effective. We present an alternative to EP search which eliminates traversals above and below the entry point node. Compared to EP search, our method has a similar runtime cost, generally eliminates more nodes, never eliminates fewer nodes, and is more effective in the absence of occlusion. Although designed for BVHs, our algorithm can be easily applied to other tree structures. CR Categories: I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism, Ray Tracing—; I.3.3 [Graphics Systems]: Picture/Image Generation Display algorithms—;