DOBB-BVH: Efficient Ray Traversal by Transforming Wide BVHs into Oriented Bounding Box Trees using Discrete Rotations

TL;DR

This paper presents DOBB-BVH, a novel method for transforming wide BVHs into efficient OBB hierarchies using discrete rotations, significantly improving ray tracing performance with manageable build time costs.

Contribution

Introducing a new OBB construction technique with shared transforms from discrete rotations, enabling efficient encoding and improved traversal performance in BVHs.

Findings

18.5% average improvement in primary rays

32.4% average improvement in secondary rays

up to 65% maximum gain in ray intersection performance

Abstract

Oriented bounding box (OBB) bounding volume hierarchies offer a more precise fit than axis-aligned bounding box hierarchies in scenarios with thin elongated and arbitrarily rotated geometry, enhancing intersection test performance in ray tracing. However, determining optimally oriented bounding boxes can be computationally expensive and have high memory requirements. Recent research has shown that pre-built hierarchies can be efficiently converted to OBB hierarchies on the GPU in a bottom-up pass, yielding significant ray tracing traversal improvements. In this paper, we introduce a novel OBB construction technique where all internal node children share a consistent OBB transform, chosen from a fixed set of discrete quantized rotations. This allows for efficient encoding and reduces the computational complexity of OBB transformations. We further extend our approach to hierarchies with multiple children per node by leveraging Discrete Orientation Polytopes (k-DOPs), demonstrating improvements in traversal performance while limiting the build time impact for real-time applications. Our method is applied as a post-processing step, integrating seamlessly into existing hierarchy construction pipelines. Despite a 12.6% increase in build time, our experimental results demonstrate an average improvement of 18.5% in primary, 32.4% in secondary rays, and maximum gain of 65% in ray intersection performance, highlighting its potential for advancing real-time applications.