[cross-posting this reply to the mesa-dev list]
On 01/27/2013 09:07 AM, Brian Paul wrote:
On Sun, Jan 27, 2013 at 2:51 AM, Eric Anholt<e...@anholt.net> wrote:
Brian Paul<bri...@vmware.com> writes:
Even if GL_ARB_multisample is advertised, it's OK for the max number of
samples to be zero.
Huh? The EXT_framebuffer_multisample spec says minmax of MAX_SAMPLES is
1.
And GL_ARB_framebuffer_object says it's zero.
It looks like the piglit test is checking the wrong extension. At
line 364 we're calling
piglit_require_extension("GL_ARB_framebuffer_object"). I don't see
any checks for GL_EXT_framebuffer_multisample. I was looking at
GL_MAX_SAMPLES in the former, not the later.
I guess the proper fix is to just check for the proper extension.
There's several things going on here.
First, the piglit test needs a
piglit_require_extension("GL_EXT_framebuffer_multisample") check.
Second, I think we need to disable advertising this extension for
swrast, softpipe and llvmpipe.
Third, I think we need to decide what GL_MAX_SAMPLES=1 really means.
I've been reading the various multisample-related extensions and none
of them really says anything special about GL_MAX_SAMPLES=1. But in
some places (like the GLSL spec) you'll see the phrase
"single-sampling" but it seems to mean the non-multisample /
conventional rasterization case.
My thinking is that it would be theoretically possible to have
single-sample multisampling (perhaps with a different sample position
per pixel).
In any case, regardless of the number of samples per pixel, we still
must obey centroid sampling mode (must interpolate at a point that
lies in both the pixel and in the primitive being
rendered). swrast, softpipe and llvmpipe don't support that so we
really shouldn't advertise GL_MAX_SAMPLES=1 (it should be zero) so
GL_EXT_framebuffer_multisample shouldn't be advertised for those drivers.
Most likely, the user's going to be disappointed if they want
multisampling in their app and the driver only gives him GL_MAX_SAMPLES=1.
Does this sound reasonable?
-Brian
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