Using Hardware Ray Transforms to Accelerate Ray/Primitive Intersections for Long, Thin Primitive Types

Ingo Wald, Nate Morrical, Stefan Zellmann, Lei Ma, Will Usher, Tiejun Huang, Valerio Pascucci
In Proceedings of the ACM on Computer Graphics and Interactive Techniques (Proceedings of High Performance Graphics), 2020
Fig. 1: Three of the models we used for evaluating our method: Left) SciVis2011 contest data set (334.96K rounded cylinders via Quilez-style 'capsules', plus 315.88K triangles). Middle,Right) hair/fur on the Blender Foundation franck and autumn models (2.4M and 3.4M 'phantom' curve segments, plus 249.62K and 904.40K triangles, respectively). For these three models, our method leverages hardware ray transforms to realize a hardware-accelerated OBB culling test, achieving speedup of 1.3×, 2.0×, and 2.1×, respectively, over a traditional (but also hardware-accelerated) AABB-based BVH (both methods use exactly the same primitive intersection codes). Bottom: heat map of number of intersection program evaluations for the two methods, respectively.

Abstract

With the recent addition of hardware ray tracing capabilities, GPUs have become incredibly efficient at ray tracing both triangular geometry, and instances thereof. However, the bounding volume hierarchies that current ray tracing hardware relies on are known to struggle with long, thin primitives like cylinders and curves, because the axis-aligned bounding boxes that these hierarchies rely on cannot tightly bound such primitives. In this paper, we evaluate the use of RTX ray tracing capabilities to accelerate these primitives by tricking the GPU's instancing units into executing a hardware-accelerated oriented bounding box (OBB) rejection test before calling the user’s intersection program. We show that this can be done with minimal changes to the intersection programs and demonstrate speedups of up to 5.9× on a variety of data sets.

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@article{wald_owltubes_20,
journal = {Proceedings of the ACM on Computer Graphics and Interactive Techniques (Proceedings of High Performance Graphics)},
title = {{Using Hardware Ray Transforms to Accelerate Ray/Primitive Intersections for Long, Thin Primitive Types}},
author = {Wald, Ingo and Morrical, Nate and Zellmann, Stefan and Ma, Lei and Usher, Will and Huang, Tiejun and Pascucci, Valerio},
year = {2020},
}