Re: alpha support for colors

[Stefan Monnier]

> I think a good use case is things like flymake error faces.  I want my
> error lines to be more "reddish" while still retaining the original
> font lock highlighting.

I was sold on your idea long before you suggested it (actually, I've
been wishing for it mostly to automatically create "lighter/darker"
faces and I'm not completely sure if alpha-blending can do that well).

I think to do it you'll want to look at the face merging code in
src/xfaces.c.  There's already code to merge heights (where faces can
specify relative sizes or even an Elisp function that computes the new
height from the height of underlying faces), so it really shouldn't be
that hard.

There's a secondary alpha-blending issue, which I think is orthogonal,
which is how to blend foreground and background.  This part would not be
handled in src/xfaces.c.

And then again there's the alpha-blending of the Emacs window with the
windows that might appear underneath, but this is yet another
orthogonal issue.


        Stefan