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Variable Rate Compute Shaders on Xbox Series X|S

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Today we are pleased to present a talk from Martin Fuller, Principal Graphics Engineer at Microsoft's Advanced Technology Group.

The talk is on Variable Rate Compute Shaders (VRCS) with a focus on Xbox Series consoles. A basic understanding of Variable Rate Shading is assumed. We provide details of an early variable rate compute shader implementation that shipped with Gears5. We then present a new algorithm than can halve deferred lighting time by exploiting the duplication of g-buffer values, and with only a very small overhead, particularly on Xbox Series consoles. We compute whether to light 1,2,3 or 4 pixels per 2x2 pixel block for the required quality level per screen tile, and perfectly respecting triangle coverage. This same technique is applicable to any deferred or post process pass, including: SSAO, SSGI, SSR, fog, clouds, atmospheric scattering & etc.. Perhaps most significantly, VRCS can be used to reduce the number of rays required to ray trace various graphical effects with minimal or zero perceptible quality loss.

View this talk here on YouTube.

Registered Xbox developers can download the accompany sample code. This sample achieves a ~50% reduction in the time taken for ray marched shadows and atmospheric scattering in a deferred lighting pass.

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