[cairo] [Fwd: CAIRO_OPERATOR_SOURCE issue]

Oscar Lazzarino oscar.lazzarino at gmail.com
Sun May 9 12:42:05 PDT 2010

On Sat, May 8, 2010 at 3:15 PM, Jonathan Morton
<jonathan.morton at movial.com> wrote:
> Yes, Cairo uses premultiplied alpha throughout.  Presumably
> cairo_set_source_rgba() is correcting the colour channels of the given
> colour so that they are limited by the alpha channel.

If so, what is the correct way to use Cairo with OpenGL to draw on
screen (with glDrawPixels) or to generate textures (with glTexImage2D
and friends) since OpenGL assumes non-premultiplied alpha? Is there a
fast way to un-premultiply?



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