On Tuesday 12 April 2005 13:06, JS wrote: > Hi, > > 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? > > Thanks, Hi! The app/paint-funcs/paint-funcs-generic.h. file Bill pointed too is not used anymore - it is there in case someone builds the GIMP disabling aceleration with an option I forgot which is. For the composting functions, take a look in the app/composite directory, in the "gimp-composite-generic.c" file. Some of the functions are acelerated for MMX or SSE in the corresponding files, others are not. As for your question (reading about Porter Duff) wow... comparing 12 kindso oif operations is a lot - but AFAIK the compositing models on the GIMP were not created thinking on these specific Ops. Some may be the same, others certainly are not. http://bugzilla.gnome.org/show 2) There is not a proper Spec. This area of the current Docuemtnation is finding lacking, and there is even a bug openned against the docs. A better description can be found on the older "groking the GIMP" book for some of the modes. Currently, teh best way to know what eachmode does, if the explanation in the above sources does nto suffice, is checking the code in the above file. 3) No. GEGL is not in use yet. As I told, the funciotns are in the app/composite directory. 4) Please, take a look at http://bugzilla.gnome.org/show_bug.cgi?id=161449 for a way to check a cheap way of implementing these new combination modes in a way that would not cluter the GIMP ui. If there is people wanting it working (custom layer modes) , I could go backk to work on it, even making it available to the GIMP if GEGL use is further stalled. 5) Nice name this of yours! Regards, JS -><- João Sebastião de Oliveira Bueno Calligaris
