[cairo] Problems blending with different platforms

[M Joonas Pihlaja]

Hey,

On Thu, 10 Dec 2009, Some Guy wrote:

> I found that if the alpha value of an image in the pixel is 0, but RGB data
> is not, I would get the proper blending behavior on the x86 but the MIPS
> would produce a destination pixel with 0 alpha.
[...]

Pixman assumes that the incoming ARGB data is in premultiplied format, 
so that the r,g,b pixel components actually contain the value 
a/255*{red or green or blue}.  In premultiplied format the r,g,b 
values ought to therefore always be <= a.

Cheers,

Joonas