[Piglit] [PATCH 2/3] all.tests: remove MSAA integer tests

[Marek Olšák]

On Mon, Oct 8, 2012 at 1:41 AM, Paul Berry <stereotype441 at gmail.com> wrote:
> On 6 October 2012 18:49, Marek Olšák <maraeo at gmail.com> wrote:
>>
>> AFAIK, integer formats cannot be resolved, but only one sample is chosen
>> and
>> copied to the destination. However the chosen sample might not be at the
>> center
>> of the pixel, so the tests might never pass.
>
>
> According to my reading of the spec, integer format MSAA resolves should
> work fine--the samples should be averaged together, just as they are for
> fixed-point and floating-point formats.  So unless I'm misreading the spec,
> these tests should pass.  And in fact, on Intel hardware with Mesa they do.
>
> I'm really interested in keeping these tests around because on Intel
> hardware, the MSAA resolve is performed by a special-purpose shader that's
> generated on the fly by the driver.  That shader has to be subtly different
> when using integer formats (to avoid overflow, it has to use the integer AVG
> instruction, rather than floating point ADDs followed by a division).  These
> piglit tests are, at the moment, the only thing verifying that we've handled
> the integer case correctly.
>
> Integer format MSAA is a rare, but not unheard of, use case (in fact, GL 3.2
> introduced a constant, GL_MAX_INTEGER_SAMPLES, to allow the driver to
> advertise its level of support for it).  So I'd really rather not drop these
> tests if we can avoid it.
>
> I'm guessing that you want to drop the tests because they're failing on a
> particular piece of hardware.  Have we ruled out the possibility of a driver
> bug?  If there's no driver bug (e.g. the tests are failing because of a
> hardware limitation), I'd recommend modifying the driver to report
> FRAMEBUFFER_UNSUPPORTED for those formats that don't work (we currently do
> this on Intel chipsets to work around some hardware bugs).  The multisample
> formats tests will automatically skip any formats that report
> FRAMEBUFFER_UNSUPPORTED.

It's not a driver bug. The tests are failing because my hardware
cannot resolve integer textures. The format must be blendable for MSAA
resolving to work. The hardware can fetch from those textures just
fine though. I guess I can try to set the UNORM format for the source
and destination resources and see what happens. I am sceptic it will
work with the 32-bits-per-channel formats though.

Anyway, I don't plan to implement MSAA resolving in the fragment shader.

Marek