[Piglit] Patch to test for ARB_clip_control v2

[Mathias Fröhlich]

Hi,

On Friday, October 24, 2014 17:17:34 Ilia Mirkin wrote:
> Can you verify that your test fails with an incorrect implementation?
> I just set nvc0 so that it always acts as if clip_halfz == 0, and the
> test passed...
That's interesting.

I can't test with the nvc0, but when I hard set clip_halfz to zero in
st_atom_rasterizer.c, then I get a failing clip-control test with llvmpipe
and radeonsi.

Also interrestingly softpipe does not fail either.
Probably nvc0 and softpipe are clipping based on the final depth buffer
values in [0, 1] instead of the clip space z values either in [-1, 1]
or [0, 1] depending on clip control depth state?
The unclipped NV_depth_buffer_float extension would have made this much
more sensitive to what is clipped exactly when.
Without the unclipped depth buffer values from NV_... I would think it's not
important which of the above variants is taken for clipping or clamping.

The clip-control-depth-precision test is supposed to be independent
of clip_halfz. This tests if the roundoff characteristics are preserved
as targeted in the spec.

> Also, you sent the patches inline just fine for mesa... can you do it
> here as well? It enables people to review your patches...
Will do ...

Greetings

Mathias