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DirectCompute

ATI Radeon HD 5870: DirectX 11, Eyefinity, And Serious Speed
By , Fedy Abi-Chahla

Of course, the big-daddy feature of DirectX 11 is DirectCompute, an API that facilitates more general purpose GPU computing across the latest DX11 cards, in addition to DX10 and DX10.1 boards. As you ascend the DirectX hierarchy, you get more and more features enabled through DirectCompute. Applications of DirectCompute include image/post-processing, physics, ray-tracing, AI, order-independent transparency, and shadow rendering—in addition to the video transcoding stuff we’ve already seen from Stream and CUDA.

DirectX 11 pipeline, from Allison Klein's Gamefest 2008 presentation.DirectX 11 pipeline, from Allison Klein's Gamefest 2008 presentation.

This is interesting, since most of the examples of GPGPU computing have centered on video transcoding and post-processing through titles like CyberLink MediaShow Espresso and ArcSoft’s SimHD. Now we’re seeing the technology folded into gaming. Indeed, this is a result of game developers getting access to ATI’s Stream technology through a standardized interface, which we’ve long-maintained would be a requisite for widespread adoption.

Take order-independent transparency, for example. In the past, rendering multiple overlapping alpha-blended objects involved heavy sorting, from back to front, of each object. Pre-DX11, this would have involved a lot of host processor computation, and even then you won’t necessarily get a visually-accurate result. In DirectX 11, transparent pixels are sorted using atomic operations and append buffers in just one pass. Check out the screenshots from the demo below.

Simple alpha-blendingSimple alpha-blendingOrder-Independent Transparency via DX11Order-Independent Transparency via DX11

There’s plenty more that can be done with DirectCompute, from high definition ambient occlusion to contact-hardened shadows and depth of field post-processing. ATI even showed off a demo of drag-and-drop transcoding through Windows 7. But when we asked ATI about tests we could use to put DirectCompute to the test, it responded that there’s nothing available yet. So, we’ll wait for third-party ISVs to utilize DirectCompute before going into more depth on it. On tap: Aliens Vs. Predator, S.T.A.L.K.E.R. Call of Pripyat, and Colin McRae: Dirt 2—all to be enabled with DirectCompute functionality in the next few months.

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