[Bf-codereview] VIEWER: Add toggle to determine correct glBlendFunc with regards to associated or unassociated alpha (issue 5176042)

[troy.sobotka at gmail.com]

>  From a design perspective i'm not sure how this should work ideally.
Making the
> user select the alpha mode of the image sounds like a cheap way out of
the whole
> alpha premul mess. At least this could be stored per image, so the
user has to
> define that only once when loading an image (reasonable default is
another
> question then).

I thought this originally and then turned around on it.

The reason is artist control.

If we assume artists are manually decomposing and generating alphas and
multiplying / dividing as required via math or other nodes, we would
then put the onus on the artist to correctly flag every instance of
their alpha. Common cases would be rotoscope and matte painting
decomposes and knockouts.

I strongly suspect that, despite initial reactions, this may very well
be the most elegant solution relative to artist simplicity.

http://codereview.appspot.com/5176042/