[Mesa-dev] [PATCH 4/9] r200: Enable extensions by just setting the flags

[Eric Anholt]

On Thu, 08 Sep 2011 10:53:45 -0700, Ian Romanick <idr at freedesktop.org> wrote:
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> On 09/06/2011 03:21 PM, Roland Scheidegger wrote:
> > EXT_blend_equation_separate allows some unholy combinations which the
> > r200 (possibly other hw too) can't handle correctly. Namely this
> > combination makes it possible to have logic ops on rgb or alpha channels
> > and color blending on the other channels.
> > I know that at least sometime in the past this driver did not advertize
> > EXT_blend_logic_op, since OpenGL 1.1 style logic ops do not have that
> > problem and EXT_blend_logic_op wasn't really all that important. I guess
> > though it's not exactly a severe problem since surely apps old enough to
> > use EXT_blend_logic_op wouldn't try to use EXT_blend_equation_separate
> > (though in theory some app could be clever and really want to do that...).
> 
> That's a good point.  I suspect that no hardware actually handles this
> case correctly.  I seem to recall that this is the reason NVIDIA doesn't
> support GL_EXT_blend_logic_op in their drivers.  I know the non-Quadro
> cards don't support it, anyway.
> 
> Does this work on later chips in the Radeon family?
> 
> I don't think anyone will miss GL_EXT_blend_logic_op if we just remove
> it altogether.

Sadly, for the purpose of doing X on top of GL, we actually do want
logic ops.
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