The xfce4 metapackage depends on desktop-base, which provides a bunch of theme-based update-alternatives, such as "desktop-background". But it doesn't seem to use this mechanism by default, instead falling back to /usr/share/backgrounds/xfce/xfce-x.svg.

This makes it difficult to ship a customised, themed image. But also, it means that by default the Debian themes are not used, which I presume we want the Debian packaging to do by default?

Steps to reproduce:

I used the Trixie RC 2 netinst iso from https://www.debian.org/devel/debian-installer/

Select XFCE during installation

Log in and observe the default wallpaper.

Expected results: a Debian-themed wallpaper from desktop-base

Actual results: the wallpaper is non-Debian-specific and seems to use /usr/share/backgrounds/xfce/xfce-x.svg

Further, I expect to be able to use update-alternatives to change the default wallpaper for new users, and that doesn't seem to work either.

Here's a patch that fixes this for me:
--- xfdesktop4-4.20.1/debian/rules	2025-03-03 01:34:50.000000000 +0000
+++ xfdesktop4-4.20.1/debian/rules	2025-07-29 13:48:35.000000000 +0100
@@ -8,7 +8,8 @@

 override_dh_auto_configure:
 	dh_auto_configure -- --enable-thunarx \
-		--docdir=\$${prefix}/share/doc/xfdesktop4-data
+		--docdir=\$${prefix}/share/doc/xfdesktop4-data \
+		--with-default-backdrop-filename=/usr/share/images/desktop-base/desktop-background

 override_dh_install:
 	dh_install

Hi Robie,

thanks for the bug and the patch. I need to take a deeper look at this. We
definitely want to use the Debian theme and we did have some specific stuff in
place for the previous Xfce versions (in libxfce4util iirc). Some stuff might
have changed in between.

I'm not taking the patch as is but hopefully we won't forget it completely…

Regards,

Hi Robie, I just upgraded a standard Bookworm to Trixie and the wallpaper was
successfully updated to the Trixie theme so I'm unsure about this.

Regards,

Control: forwarded -1 https://gitlab.xfce.org/xfce/xfdesktop/-/issues/364

So, I know I had stumbled upon this earlier this year and I found it:

https://gitlab.xfce.org/xfce/xfdesktop/-/issues/364#note_106405

The default-backdrop is kind of a red herring, the real issue is that
xfdesktop lost the ability to read the relevant property.

I think this should be fixed upstream but as you can see there's no answer on
the bug, unfortunately.

Regards,