bug#71162:

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 23 May 2024 21:08:24 -0700
> From: David McCracken <davidm@ixont.com>
> 
> I have developed a library that includes a toolbar with custom icons. It
> works in all versions of Emacs in Windows and in Emacs version 26.3
> under Ubuntu-Mate 20.54 but the toolbar doesn't work in Emacs 27.1 under
> Ubuntu-Mate 22.04. In my preferred configuration I put my icons under
> the user home directory so that this doesn't change if Emacs is
> updated. My library accesses this with e.g.
> (tool-bar-add-item "~/icons/lxa-next"
> to use my lxa-next.xpm icon. In Emacs 26.3 it also works to put my icon
> in /usr/share/emacs/26.3/etc/images and refer to it as simply
> "lxa-next". Emacs 27.1 shows nothing either way. My lxa-next.xpm appears
> similar to the native lock-broken.xpm (4.7kB vs. 4.6kB) so I
> experimented referring to that instead of mine and it worked. I also
> tested left-arrow but instead of left-arrow.xpm or pbm, it showed a very
> plain < image that doesn't exist in the images directory. It should be
> noted that there is a lock-broken.pbm but the xpm version was
> automatically selected. The icon selection mechanism of Emacs 26.3 is
> usable but could be improved by accepting an explicit icon file
> extension. That of 27.1 is unusable and, unless we can fix it, I will
> have to advise users of my library to install an older version of Emacs.

I tried to visit the XPM file you attached, and it displays okay with
both Emacs 27.1 and the current development version, at least on
MS-Windows.  So I don't see a reason why this would not work on a tool
bar.  I suggest that you post some minimal Lisp code that displays
these icons on the Emacs tool bar, starting from "emacs -Q", and then
we could try the code and see if the problem can be reproduced and
debugged.

Btw, to clarify: you are saying that your XPM icons don't work in
Emacs 27.1 both on MS-Windows and on Ubuntu?  Or only on Ubuntu?

Thanks.