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Thomas Monk

DX11 Instanced Tessellation in DX10?

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Now that tessellation has arrived under DX11 hardware, will game developers bother to investigate techniques such as Instanced Tessellation (Andrei Tatarinov) or even expose the additional detail the old fashioned "brute force" way under DX9 or DX10? Will DX9/DX10 users have to suffer lower quality mesh detail in games as developers turn increasingly to DX11 tessellation to deliver fine mesh detail? Any opinions from the developing community would be much appreciated.

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At Siggraph 2009 Valve gave a talk about implementing a similar tessellation scheme for their DX9 path. I checked their website and didn't see anything published or any slides that were made available from the talk.

From what I recall, they used the CPU to do the work of the VS-HS-TS chain from DX11. Then the vertex shader became their DS stage to start using the GPU. They reported having very good results.

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Note that it is relatively easy to do any tessellation on the CPU before sending the vertices to the GPU; however, this negates all the benefits of tessellation except storage compression (lowered space consumption on HDD).

It is conceivable that next-generation engines do just this, or the instanced patch approach, to implement tessellation when running on pre-D3D11 hardware. This way, the art pipeline can work in an unified way (and export patches to the engine) regardless of target hardware.

EDIT: Offloading the domain shader duties to the vertex shader while running the rest of tessellation in software sounds like a workable approach too, but it is necessarily still far from being nearly as efficient as true, complete hardware tessellation.

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