[cairo] Component-alpha in compositing operations.

Owen Taylor otaylor at redhat.com
Fri Oct 20 06:34:35 PDT 2006

On Fri, 2006-10-20 at 11:09 +0000, jose_ogp at juno.com wrote:
> 	If I may, I'd like to bring up some observations on the
> the semantics of how the 'component-alpha' attribute is currently
> used in xrender's compositing operations. I thought to bring it up
> here, on the cairo list, since cairo mirrors xrender's compositing
> semantics and as cairo seems more directly concerned with these
> kinds of things than the xorg list.
> 	One fairly common operation that one seems to find in gui
> effects is to 'modulate' an image with some given color prior to
> blending with a destination.. ie. one wants to multiply the image
> channels by the given color's channels, and composite this result.

The component alpha in XRENDER and cairo isn't designed for this;
it's very specific to the particular operating of drawing sub-pixel
anti-aliased text.
					- Owen

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