[cairo] Pixel packing mismatch on XRender glyph rendering

Soeren Sandmann sandmann at daimi.au.dk
Thu Jun 7 10:50:11 PDT 2007

"Matt Hoosier" <matt.hoosier at gmail.com> writes:

> Okay, thanks for the background. I wonder: does XRender allow a way to
> send the alpha channel in a separate data structure (e.g. 565 text + 8
> alpha) rather than re-packed into the 8888 image? Probably not,
> because that seems like the sort of optimization you'd already have
> done. :)

XRender does have the concept of "alpha map" which is a way of sending
the alpha channel in a separate data structure.

Caveat: The render implementation always falls back to the slow
general compositing code whenever alpha maps are involved instead of
the various fast paths that have been developed, so the performance
may disappoint you. Also, as far as I know nobody has ever used this
feature for anything, so the implementation may be buggy.


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