I'm trying to locate the alpha compositions code in Gimp and cannot find it. I've found C/MMX/Altivec versions of many image-image composition operations but they don't seem to use the alpha channel at all.

For example, I wonder wether the "overlay" composition corresponds to the Porter-Duff "over" operand. I've seen that some of the Porter-Duff operations are now part of GGGL (http://pippin.gimp.org/gggl/). I'm a little lost in all this. So I guess my questions are:

1) Does Gimp implement the 12 Porter-Duff operations (http://www.w3.org/TR/2002/WD-SVG11-20020215/masking.html)? If so, I guess they must have different names.
2) Where are the specifications for the compositing functions found in Gimp (like blend, screen, overlay, etc)? None of these functions seem to make use of the alpha channel, but is there still a link I do not see with the Porter-Duff ops?
3) Where is Gimp heading wrt composition ops? Is GGGL the new standard?


Jean-Sébastien Senécal
Freelance programmer / Programmeur autonome
M. Sc. Computer Sciences / Informatique, Université de Montréal
Web: http://drone.ws

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