GNU bug report logs - #77104
31.0.50; Transparent png image background is ignored in frames with alpha-background

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Message #14 received at 77104 <at> debbugs.gnu.org (full text, mbox):

From: Alan Third <alan <at> idiocy.org>
To: Po Lu <luangruo <at> yahoo.com>
Cc: dybfysiat <at> 163.com, Eli Zaretskii <eliz <at> gnu.org>, 77104 <at> debbugs.gnu.org,
 Ihor Radchenko <yantar92 <at> posteo.net>
Subject: Re: bug#77104: 31.0.50; Transparent png image background is ignored
 in frames with alpha-background
Date: Wed, 19 Mar 2025 16:23:44 +0000

On Wed, Mar 19, 2025 at 09:06:07PM +0800, Po Lu wrote:
> Eli Zaretskii <eliz <at> gnu.org> 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

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