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Measuring Acceleration Structures

Hardware accelerated raytracing, as supported by DirectX 12 and Vulkan, relies on an abstract data structure that stores scene geometry, known as “acceleration structure” and often referred to as “BVH” or “BLAS”. Unlike geometry representation for rasterization, rendering engines can not customize the data layout; unlike texture formats, the layout is not standardized across vendors. It may seem like a trivial matter - surely, by 2025 all implementations are close to each other in memory consumption, and the main competition is over ray traversal performance and new ray tracing features? Let’s find out.

So for the purpose of this post, we will just look at a single scene - Amazon Lumberyard Bistro, or more specifically a somewhat customized variant by Nvidia which uses more instancing than the default FBX download. Running this on the latest (as of end of March) drivers of all respective vendors, on a host of different GPUs, we get the following results; the total BLAS size is presented alongside approximate “bytes/triangle” number - which is not really correct to compute but we will do this anyway. Between these factors, it’s hard to estimate the realistic expected memory consumption - but it seems plausible that we will see continued reduction of BVH sizes with future driver updates.

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