Hi David

David Gowers wrote:
> Ah, so if I want to make the result preserve the alpha of the
> underlying layer, I'll need to do that via layer mask?

Exactly, masking should generally be performed *after* blending with the
new layer mode compositing model.

> FWIW, since you changed the meaning of the layer modes, is this a good
> time to make compositing gamma-correct?

Yes definitely. In fact, layer mode compositing with GEGL _does_ work on
data with gamma = 1.0. That is, the layer mode blending occurs on color
data in the babl format "RaGaBaA float", i.e pre-multiplied, linear
light 32 bit per channel RGBA.

The reason you don't see a difference when toggling Use GEGL is that now
during development the source data, namely the data from the tiles of
the TileManagers of the GimpDrawables, are treated as if containing
color data in the babl format "RGBA u8", i.e. linear light 8 bit per
channel RGBA. A more correct assumption would be "R'G'B'A u8", i.e.
gamma corrected RGBA.

The long term goal is of course to make sure color space conversions are
correct throughout the whole image processing pipeline, taking into
account the current color profile of the image etc.

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