Stuff like passing "input" directly if "aux"'s opacity is 0, etc.
Used to be partly handled by normal mode, even though it applies
to other modes too.
Adjust the logic for the new compositing modes.
Add a GimpLayerModeAffectMask enum, and a corresponding
get_affect_mask() function to GimpOperationLayerMode, which
specifies which of the op's inputs, if any, are affected by the
mode, apart from the overlapping regions. Most modes affect only
the overlapping regions, but dissolve and replace also affect the
rest of the input. This information is used for determining if
the optimizations are applicable.
These variations on darken only and lighten only have the advantage over the
componentvise versions that they always use the full triplet of either original
or new layer - meaning no new colors/hues will be introduced. This is similar
to how these modes operated/operates in picture publisher and photo-paint.
... is fully transparent, instead of just src.
The blend func results only affect the intersection of dest and src.
Run time is currently dominated by the compositing step for most modes,
so the difference in performance is pretty negligible, but it does make
a difference for the more expensive modes, like the HSV ones.
For operations needing to override default behavior sub-classes should still be
used.
This commit also enables pinligh, vividlight and linearlight blend mode modes
Since CIE Lab is one of the supported color spaces for doing the blending -
this enum is not only about transfer functions/curves or gamma. This finishes
already started cleanups.
