On Tue, 27 Jan 2004, Sottek, Matthew J wrote:
> > I didn't remove anything. There was never any support for
> >componentAlpha. I just made XAA aware that it didn't support
> >it.
>
> You removed the ability for a driver to support accelerated component
> alpha on a XFree 4.4.0 binary. If this is now the most common case
> then why wouldn't a driver want the opportunity to support that? Seems
> like the driver should be required to punt that rather than Xaa punting
> for them.
There was never a way for the driver to know that componentAlpha
was used. I removed the ambiguity. Now, if you get masks that have
RGB components, the RGB components are to be ignored. It could
have been defined either way: componentAlpha or non-componentAlpha.
I don't know if componentAlpha is the more common case, but I
think that drivers are less likely to be able to accelerate it than
they are non-componentAlpha, so being able to support componentAlpha
seems better suited to the exception rather than the rule.
We can always add to the flags as Thomas and I discussed.
Not sure that we want to squeeze that into 4.4 though.
Mark.
>
> Looking at the XAADoComposite function, it isn't very large so a
> driver could just hook at that level and pull a copy of that function
> into the driver minus the component alpha check and be able to support
> accelerated component alpha. There also seems to be a check that
> punts anything with a transform which also eliminates a large number
> of useful RENDER cases. (Do all stretches have a transform?)
> Seems like a driver that wanted to support RENDER well would have
> to hook at the Composite level currently so it isn't really a big
> deal that component alpha doesn't get passed through to the driver.
>
> There still remains the issue of why would the newer font libs
> use component alpha when that removes all opportunity for
> acceleration. Is there a way for the libs to determine that
> component alpha is an unaccelerated path?
>
> -Matt
>
>
>
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