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

Paul Berry stereotype441 at gmail.com
Sun Oct 7 17:58:03 PDT 2012

On 7 October 2012 17:10, Marek Olšák <maraeo at gmail.com> wrote:

> 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
> > 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
> 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.

Ah, ok.  I wondered whether your hardware (r600, right?) had dedicated MSAA
resolving logic built into it.  I'm envious :)  I'll be curious to hear if
the UNORM idea works out.

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

I don't blame you--I wouldn't have done MSAA resolving in the fragment
shader on Intel chips if there had been an alternative.

Assuming the UNORM idea doesn't work, are you ok with NAKing this patch and
instead reporting FRAMEBUFFER_UNSUPPORTED for the formats where r600 can't
do an MSAA resolve?  That would be best from my perspective, because it
would allow the Intel logic to still be tested.
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