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

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Alan Third <alan <at> idiocy.org>
Cc: luangruo <at> yahoo.com, dybfysiat <at> 163.com, alan <at> idiocy.org, 77104 <at> debbugs.gnu.org, yantar92 <at> posteo.net
Subject: bug#77104: 31.0.50; Transparent png image background is ignored in frames with alpha-background
Date: Wed, 19 Mar 2025 19:02:44 +0200

> Date: Wed, 19 Mar 2025 16:23:44 +0000
> From: Alan Third <alan <at> idiocy.org>
> Cc: Eli Zaretskii <eliz <at> gnu.org>, Ihor Radchenko <yantar92 <at> posteo.net>,
> 	77104 <at> debbugs.gnu.org, dybfysiat <at> 163.com
> 
> 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.

That's what I thought, indeed.

> 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.

Patches welcome.

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