Question Multi draw support when using RenderMeshIndirect

https://docs.unity3d.com/ScriptReference/Graphics.RenderMeshIndirect.html

The new RenderMeshIndirect mentions SV_DrawId for multi-draw support. However, i have been unable to read out this shader semantic at all. I cant find much information on this either, how can i get the draw id in dx11 or 12?

 

There is no SV_DrawID in D3D11/D3D12. I think this is some cross reference from gl_DrawId and its multi-draw rendering. Corresponding functionality exists in D3D12 by using indirect drawing. But approach taken by D3D API will get correct data in buffers based on resurce views used during ID3D12CommandSignature creation. So it is mystery how to correctly use InitIndirectDrawArgs(drawId) function in shader with non-zero drawId parameter.

 

I think i did figure it out. Im implementing this tutorial in Unity: https://vkguide.dev/docs/gpudriven

In the case of doing gpu driven rendering, and culling in a compute shader. The compute shader passes data to the vertex shader, e.g. the visible indices. It also needs to know the drawID.

We can therefore also pass along the drawid. If you get your vertex data by using the instanceId, you can make another structuredbuffer with drawids.

 

https://ubm-twvideo01.s3.amazonaws....ons/Wihlidal_Graham_OptimizingTheGraphics.pdf
Here on page 23 this is mentioned.