Re: New library wallpaper.el pushed to master

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Wed, 14 Sep 2022 00:13:02 -0700
> Cc: emacs-devel@gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I though that would be considered unclean, given that you deployed the
> > cl-defgeneric machinery there.  At the very least, it would mean w32
> > users will not be able to use external programs to do the job, even if
> > they do have such a program.  Is that acceptable?
> 
> I don't know; I don't use MS-Windows.  But if we can do it natively,
> perhaps it is acceptable to not be able to use an external command.
> 
> If we're fine with that limitation, I see that Po Lu added support for
> Haiku, and I think MS-Windows could do something similar to that.

I added support for this on MS-Windows.  Strangely, it works with some
images, but not with others.  On XP, only BMP images seem to work (and
I think I saw someone on the Internet saying this is all XP supports).
On Windows 10, I can set the wallpaper to JPEG images as well, but
some don't work.  I guess someone more knowledgeable than myself will
have to fix whatever needs fixing here.

Ken, the code is currently enabled only for WINDOWSNT, but if you
think it could work and be useful in the Cygwin w32 build, please
remove the conditionals.