SAH-Optimized k-DOP Hierarchies for Ray Tracing

We revisit the idea of using hierarchies of k-sided discrete orientation polytopes (k-DOPs) for ray tracing. We propose a method for building a k-DOP-based bounding volume hierarchy while optimizing its topology using the surface area heuristic. The key component of our method is a fast and exact algorithm for evaluating the surface area of a 14-DOP combined with the parallel locally ordered clustering algorithm (PLOC). Our k-DOP PLOC builder has about 40% longer build times than AABB PLOC, but for scenes with oblong slanted objects, the resulting BVH provides up to 2.5x ray tracing speedup over AABB BVH. We also show that k-DOPs can be used in combination with other techniques, such as oriented bounding boxes (OBBs). Transforming k-DOP BVH into OBB BVH is straightforward and provides up to 12% better trace times than the transformation from AABB to OBB BVH.