Improvements for Extended Morton Codes for Bounding Volume Hierarchy Construction on GPUs in Problematicly Large Scenes

Abstract

We present three new methods to enhance the positional accuracy of Morton Codes in large scenes that have distant or large primitives, which is an essential aspect of many Bounding Volume Hierarchy (BVH) construction algorithms on the GPU. Two methods will use an additional occupation grid to remove unnecessary bits and move splits if considered more beneficial to combat the issue of distant primitives. The other method updates the computation of the scene bounds for scenes with large primitives at the edge of the scene. We show by building linear BVHs on the GPU for different scenes with the improved Morton Codes that there is room for improvement for both distant and large primitives in a scene. The new scene bounds computation shows a performance improvement of 0.41% - 0.93% in two games, a small but significant improvement according to the stakeholder (AMD). However, the other two methods show a potential increase in tracing performance in cases with distant primitives, but it takes too much time to create the occupation grid.