On Monday 19 October 2009 08:58:22 Michel Dänzer wrote:
> On Fri, 2009-10-16 at 00:29 +0100, ja...@vmware.com wrote:
> > From: Zack Rusin <za...@vmware.com>
> >
> > This fixes the component alpha fallback in exa. I'm not sure which
> > branches this should go into. Also before committing this patch make sure
> > that we get a Tested-by by somebody with a radeon card as this turns on
> > new and wonderful paths not tested in the drivers.
>
> This shouldn't make any difference for sub-pixel AA text with the radeon
> driver, as it doesn't simply check for pMask->componentAlpha but:
>
> if (pMaskPicture->componentAlpha) {
> /* Check if it's component alpha that relies on a source alpha and
> * on the source value. We can only get one of those into the
> * single source value that we get to blend with.
> */
> if (RadeonBlendOp[op].src_alpha &&
> (RadeonBlendOp[op].blend_cntl & RADEON_SRC_BLEND_MASK) !=
> RADEON_SRC_BLEND_GL_ZERO) {
> RADEON_FALLBACK(("Component alpha not supported with source "
> "alpha and source value blending.\n"));
> }
> }
>
> I'm not sure offhand if the proposed change is necessary or even
> sensible given this, or if the Gallium Xorg state tracker shouldn't just
> use similar checks, and I may not find the time to build a firmer
> opinion before I'm back from vacation next month.
Well, the question we're asking the driver is: do you support the following
operation, we expect an answer based on its own capabilities not on the
capabilities of the acceleration architecture.
So the question: do you support component alpha when the driver doesn't should
always be a no, not a conditional maybe that depends on code it has no control
over.
IMO if Exa decomposes PictOpOver component alpha into two non-compoment-alpha
passes, it should actually do that and not depend on driver being able to
figure out what it's trying to do.
z
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