[Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Ilia Mirkin]

On Tue, Sep 15, 2015 at 1:09 PM, Erik Faye-Lund <kusmabite at gmail.com> wrote:
> On Tue, Sep 15, 2015 at 6:49 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> However having a piglit test that covers this would be neat... I guess
>> you could clip a pixel in half and make sure that the resolved result
>> is some in-between color? Lots of implementation-dependent stuff going
>> on in there though.
>
> I think this would simply be a matter of drawing a white triangle on a
> black background both with clipping and pre-clipped, and verify that
> the result is the same. Perhaps even using a few differently sub-pixel
> jittered triangles.

Right, but sample positions are implementation-defined. Although I
guess you could retrieve those positions and pre-clip yourself...
However the resolve is also implementation-defined I think, so there's
no good way to know what the resulting color would be. However you
could ensure that it was neither white nor black.