[CREATE] ORA spec: adding additional layer effects

[Martin Renold]

On Fri, Feb 24, 2012 at 10:19:12PM +0000, Andrew Chadwick wrote:
> 
> MyPaint could of course just do its own thing here, or copy Krita.
> I've had a quick poke around the Krita and GIMP implementations of
> these layer modes, but they seem to use HSV only, which seems
> limiting. [...]

I have some code in the cooking that might provide an alternative.  It
converts any layer to normal blending mode (over), such that the alpha
channel is minimized and the composited result does not change.

When saving ORA, layers with non-standard blending modes can be converted. 
This is a one-way conversion, but it ensures that the image can be
"finalized" in any existing ORA application.  We could also save the
original layer alongside with a new attribute such that existing ORA loaders
ignore it.

As we all know, MyPaint depends heavily on other applications for the final
steps of the painting workflow.  It would be sad if users had to limit
themselves to the "smallest common denominator" blending modes because of
that.

On a related note, I realized that we run into the same problem if we want
to composite in linear light.  The solution may be a bit different because I
expect at least GIMP and Krita would like to support linear light
compositing in ORA properly.  I don't remember the spec in detail, maybe
there was a solution there already?  I think Krita handles this concept as
per-image color space choice and not per-layer composite op?

-- 
Martin Renold