[cairo] Applying to a surface the alpha of other

Krzysztof Kosiński tweenk.pl at gmail.com
Mon Oct 22 07:02:20 PDT 2012

2012/10/22 Bill Spitzak <spitzak at gmail.com>:
> He does not want to un-premultiply.

I'm not so sure about this. Without un-premultiplication, the result
is equivalent to painting the image with CAIRO_OPERATOR_OVER onto a
black surface. With un-premultiplication, the result is as if the
alpha was reset to zero while keeping the color intact.

Regards, Krzysztof

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