[cairo] Problems blending with different platforms

M Joonas Pihlaja jpihlaja at cc.helsinki.fi
Fri Dec 11 04:43:12 PST 2009


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.



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