[cairo] [Fwd: CAIRO_OPERATOR_SOURCE issue]

[Oscar Lazzarino]

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?

Thanks.

O.