[Mesa-dev] gallium/st: add texture gather support

[Dave Airlie]

This adds support to gallium, and also to the state tracker
for ARB_texture_gather and also the gather features of ARB_gpu_shader5.

It adds a single CAP for the ARB_texture_gather max components query,
then another CAP to denote the GPU is capable of SM5 gather.

This doesn't add native support for textureGatherOffsets yet, I don't
have hw that can do this, so instead I just moved the i965 glsl lowering
pass to a generic place and reused it. If you have native support for
this feature, then you need to add another CAP + modify the state tracker
at the appropriate places. I can help with it, if you are sure your hw
can do it. You'd also need to modify the TG4 instruction under the new
CAP to accept 4 offsets.

I have r600g patches on top of this to add support to r600g, r600/700
can only do ARB_texture_gather, whereas evergreen->cayman can do the SM5
stuff, but not native tGOs.

Dave.