On Sat, Jul 7, 2012 at 9:24 PM, Calculemus wrote:

I am trying to understand the code for the compositor soft-light, in the file /gegl-0.2.0/operations/generated/soft-light.c.

I am not sure about line 25: aD = aA + aB - aA * aB;

What is aD, is it alpha channel? Does gegl assume that the input image buffers are RGBA?

Thanks

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Just above the process function you can see the prepare function which sets input, aux and output buffers to RaGaBaA which is RGBA with premultiplied alpha.

Note the comment at the top of that file:

/* SVG rendering modes; see: * http://www.w3.org/TR/SVG12/rendering.html * http://www.w3.org/TR/2004/WD-SVG12-20041027/rendering.html#comp-op-prop *
* aA = aux(src) alpha aB = in(dst) alpha aD = out alpha * cA = aux(src) colour cB = in(dst) colour cD = out colour */

It's also probably useful to note that these operations are generated by svg-12-blend.rb, so you might be better off looking there for some of the code.

-- drawoc

On Sat, Jul 7, 2012 at 8:20 PM, Calculemus wrote:

What source is used for the math? I see the original Adobe reference uses different math for the compositors like soft-light. Not sure which math to use, the one you guys have in GEGL or the one in the Adobe reference, which is used in Photoshop and After Effects, etc.

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