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MergeTree: A Fast Hardware HLBVH Constructor for Animated Ray Tracing

Research output: Contribution to journalArticleScientificpeer-review


Original languageEnglish
Article number169
Number of pages14
JournalACM Transactions on Graphics
Issue number5
Early online date12 Oct 2017
Publication statusPublished - Oct 2017
Publication typeA1 Journal article-refereed


Ray tracing is a computationally intensive rendering technique traditionally used in offline high-quality rendering. Powerful hardware accelerators have been recently developed that put real-time ray tracing even in the reach of mobile devices. However, rendering animated scenes remains difficult, as updating the acceleration trees for each frame is a memory-intensive process. This article proposes MergeTree, the first hardware architecture for Hierarchical Linear Bounding Volume Hierarchy (HLBVH) construction, designed to minimize memory traffic. For evaluation, the hardware constructor is synthesized on a 28nm process technology. Compared to a state-of-the-art binned surface area heuristic sweep (SAH) builder, the present work speeds up construction by a factor of 5, reduces build energy by a factor of 3.2, and memory traffic by a factor of 3. A software HLBVH builder on a graphics processing unit (GPU) requires 3.3 times more memory traffic. To take tree quality into account, a rendering accelerator is modeled alongside the builder. Given the use of a toplevel build to improve tree quality, the proposed builder reduces system energy per frame by an average 41% with primary rays and 13% with diffuse rays. In large ( > 500K triangles) scenes, the difference is more pronounced, 62% and 35%, respectively.

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Field of science, Statistics Finland

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