Subject: Re: bug#77104: 31.0.50; Transparent png image background is ignored in frames with alpha-background

From: Alan Third <[email-masked]>
Date: Wed, 19 Mar 2025 16:23:44 +0000

On Wed, Mar 19, 2025 at 09:06:07PM +0800, Po Lu wrote:
> Eli Zaretskii <[email-masked]> writes:
> 
> > Po Lu and Alan, is this a bug or a missing feature?
> 
> I'm tending towards "bug", but only Alan can be sure.

I'd lean more towards missing feature, but it's a toss up really.

I think the problem is that Emacs has never handled image
transparency, so it sets the transparent pixels of the image to the
frame's background colour. There's quite a bit of fiddling to manage
this with changing backgrounds and so on.

I'm not sure what would be required for drawing transparent images to
the glass. On NS I think it would be near trivial as the toolkit will
handle it for us, but I don't know about others. For example I have a
memory of being told that some terms don't clear under images so
drawing a transparent image might show the previous pixels.
-- 
Alan Third