Po Lu <luangruo@yahoo.com> writes:

> Neither approach is easy or exceptionally challenging, so interested
> individuals are invited to chose whichever they should find more to
> their liking.

Hi Po,

I have written a patch for this for the pgtk backend and went with the
first route - supporting an alpha channel in face colors. I figured it's
nicer since we get alpha channels for all other text decorations as
well.

The way it works is that when painting a background color (one which
respects alpha-background), we instead compose it with the frame
background color via a re-implementation of CAIRO_OPERATOR_OVER. I
didn't find a way to do this with cairo itself without painting the
surface inbetween.

I also made sure that this patch integrates with alpha-background, which
is also my primary use case - fully hiding faces which don't respect
alpha-background.

The only syntax supported for transparency is gtk_parse_rgba's
`rgba(255,255,255,1.0)`. Maybe we would want support for `#ff00ff00` too?

One interesting quirk is that when changing the opacity of the `default`
face to less than 1, the whole background is fully transparent again. I
am not sure whether this is a fault in my code or because of some extra
logic regarding the `default` face.

Attached are a screenshot and the patch. I'd very much appreciate
feedback. If necessary I could also try to implement this for X and/or
terminals, however I don't have access to other platforms.

Best
Nate