[Mesa-dev] WebGL WG interested in 1.0.1 conformance test results on real drivers

[Eric Anholt]

On Tue, 17 Apr 2012 12:53:12 -0700 (PDT), Benoit Jacob <bjacob at mozilla.com> wrote:
> > > > i965 driver:
> > > > 
> > > > Results: (8866 of 8879 passed)
> > > > 
> > > > > Failures:
> > > > > conformance/context/context-attributes-alpha-depth-stencil-antialias.html:
> > > > > 1 tests failed
> > > > 
> > > > > PASS webGL = getWebGL(2, 2, { depth: false, stencil: false,
> > > > > alpha:
> > > > > false, antialias: true }, [ 0, 0, 0, 1 ], 1, 0) is non-null.
> > > > > PASS contextAttribs = webGL.getContextAttributes() is non-null.
> > > > > FAIL pixel[0] != 255 && pixel[0] != 0 should be true. Was
> > > > > false.
> > > > 
> > > > Is this assuming that MSAA is available?
> > > 
> > > Ouch. Yes, this test is effectively requiring MSAA. It's a bug in
> > > the
> > > test: in WebGL, anti-aliasing is a hint, not a requirement. We'll
> > > fix this very soon in the WebGL conformance tests, but it's too
> > > late
> > > for the 1.0.1 version unfortunately. Very unfortunate that we
> > > didn't
> > > catch this earlier.
> > 
> > Ah no, sorry, this is not a bug in the conformance test, this is
> > purely a Firefox bug. What happens is that this test is checking
> > that the actual context attributes match reality. They should.
> > Firefox's bug is that it's returning the context creation attributes
> > (which have antialias=true) instead of the actual context
> > attributes. Will fix. Nothing to be done or worry about on your end.
> 
> Sorry for ping-ponging on this but looking closer into this, I'm not so sure anymore that it's a Firefox bug:
> 
>  - Firefox does check the actual context format and returns that
> 
>  - I can't reproduce this test failure here on Mesa 7.11, r600g driver.
> 
> So I'm wondering if this could actually be an issue with the Intel driver, or with Mesa 8 ?
> 
> The question is: does Mesa/Intel correctly return 0 for glGetIntegerv(LOCAL_GL_MAX_SAMPLES, &result)?
> 
> An APItrace of this test would give the answer.

GL_MAX_SAMPLES tells you how many samples you can ask for from a
multisample renderbuffer (GL 3.0 spec page 285), while to ask about the
number of samples in a particular GLX visuals you have to check the
GLX_SAMPLE_BUFFERS_ARB of the visual (GL_ARB_multisample spec).  We
currently expose GL_MAX_SAMPLES of 4 (GL 3.0 spec page 391), but that's
a lie and if you ask for a 4-sample renderbuffer we don't actually
multisample it.  We don't expose any GLX visuals with nonzero
GLX_SAMPLE_BUFFERS_ARB, which is conformant but disappointing.
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