Microsoft’s analysis division has been arduous at work attempting to make ray tracing a extra accessible characteristic for video games of the longer term. A brand new patent from one of many group’s senior architects describes how the reminiscence and cache load for bounding quantity hierarchies (BVH)— buildings used to hurry up ray tracing—might be lowered by utilizing the same strategy to texture Degree of Element (LOD) software.
Whereas Microsoft’s Xbox consoles could be the primary beneficiary of this method, AMD’s historically ray tracing weak GPUs, and graphics playing cards that are not blessed with a ton of VRAM are additionally a possible winners.
As with all such patents, the small print inside it are complicated but in addition broad when it comes to the place they might be used. Its writer, Mark Grossman, is a senior architect in Microsoft’s analysis division, specialising in chip growth, and he has an extended and distinguished profession in GPUs (beginning with Silicon Graphics, earlier than transferring to ATI Applied sciences, then AMD, and at last Microsoft).
Final 12 months, he had a patent permitted for lowering the reminiscence footprint of meshlets, small teams of polygons as utilized in mesh shaders. His newest patent (by way of Tom’s {Hardware}) follows a near-identical format. To hurry up the method of ray tracing, video games use BVH buildings, that are somewhat like a flowchart of the volumes that objects in a 3D world take up. BVHs are break up into a big total map, known as a top-level acceleration construction (TLAS), and a number of smaller bottom-level ones (BLAS).
In Cyberpunk 2077, the common dimension of the TLAS is round 15 to 20MB, however the complete BLAS is many occasions bigger than this, operating into lots of or 1000’s of megabytes. In case your graphics card has 16GB or extra of VRAM, it is probably not an issue however in case you have 8GB or much less, then it is not arduous to see why it will possibly grow to be a difficulty. And that is very true of consoles with shared reminiscence swimming pools.
Microsoft’s method avoids utilizing your complete BVH in a single go. As an alternative, small chunks of it are used at a time, and the small print of this utilization and the a part of the BVH in query (known as a node) are saved in two lists within the GPU’s reminiscence. With every successive body, the ray tracing algorithm updates these lists, making certain that solely the nodes required for use within the scene (the remaining simply not being seen or value utilizing) are saved within the VRAM.
Be aware that this technique not solely reduces the load on the graphics card’s reminiscence and the GPU’s cache, however it additionally lowers the quantity of ray tracing checks that must be carried out. Slightly than having to continually traverse throughout your complete BVH construction to see what rays are interacting with which objects, solely these within the lists (known as a residency and recording map) must be checked.
That is vital for AMD’s graphics processors as a result of not like Nvidia’s GPUs, they have no devoted {hardware} for accelerating the traversal course of. As an alternative, it is all dealt with by way of compute shaders. Each distributors do have specialised items for testing ray-box and ray-triangle intersections, in order that they each verify these items off in a short time, however RDNA 2 and newer GPUs spend fairly a little bit of time working by the BVH.
So whereas all of this work is to the advantage of the Xbox, it could even be a boon to any gaming PC sporting a Radeon graphics card, powered by a RDNA 2 or RDNA 3 GPU.
Yeah, that is all very difficult, and I am virtually definitely over-simplifying it, however the one factor that the very best gaming PCs and consoles have in abundance is compute energy. So it is sensible to leverage one thing that, whereas involving a lot of further however primary calculations, reduces reminiscence and ray tracing masses.
Though Microsoft’s patent is primarily focused in direction of enhancing ray tracing efficiency on its Xbox Sequence X consoles, the method might be carried out on any platform, as it is not particular towards any explicit {hardware}. So in case you have a mainstream graphics card, like a GeForce RTX 4060 or Radeon RX 7600, then you would effectively have the possibility to get pleasure from ray tracing in a sport within the not-too-distant future.
