AFAICT the hardware doesn't provide any way to retrieve the primitive ID without a geometry shader, so we'd probably need to use a passthrough geometry shader for this. Any volunteers?

Alright, I can create 3 geometry shaders for all primitives, but I am not sure if that is the right way for mesa. Thanks

Just to be clear, I'm talking about doing this transparently in the driver, not in the application.

I do not have radeonsi supported device. How does Intel driver support this? I think this is really useful for picking algorithm.

(In reply to pavol from comment #4)
> I do not have radeonsi supported device. How does Intel driver support this?
> I think this is really useful for picking algorithm.

The piglit test tests/spec/glsl-1.50/execution/primitive-id-no-gs.shader_test is for this very case.  That test passes at least on my Ivybridge.  I don't know what we do in the driver to make this work... or if the hardware just sorts it out.

The hw GS mode A should be able to do this, which is basically a VS which gets PrimitiveID on the input.

FYI I've posted patches to mesa-dev to address this for evergreen and later.

fix for this pushed to mesa master

Thank you, it works great.