... 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.
