Fractional scaling stopped working on GDM

[pesader]

Describe the bug

Until base commit 214d961525566049d92e1f9299c88a81bc0c9a59af831b711358c13c41da43e9, fractional scaling worked on the login screen, which is GDM (gnome-display-manager) as expected. From the next deployment onward, though, it stopped working.

To Reproduce

1. Boot your computer and login to your user
2. Set a fractional scaling resolution using GNOME Settings
3. Set the same fractional scaling resolution on GDM (I recommend using Login Manager Settings)
4. Log out and see that fractional scaling is not working on GDM

Expected behavior Fractional scaling should keep working on GDM.

OS version:

This is my current deployment:

State: idle
AutomaticUpdates: stage; rpm-ostreed-automatic.timer: last run 52min ago
Deployments:
  fedora:fedora/39/x86_64/silverblue
                  Version: 39.20230930.n.0 (2023-09-30T08:05:33Z)
               BaseCommit: d8d801dd148f55b5bb24b4e4cdd7141a41a843a6c026425bfc17d6aaab6a4770
             GPGSignature: Valid signature by E8F23996F23218640CB44CBE75CF5AC418B8E74C
                     Diff: 25 upgraded, 1 removed
          LayeredPackages: firefoxpwa gocryptfs guake intel-media-driver libavcodec-freeworld libcamera libcamera-gstreamer libcamera-ipa
                           libcamera-qcam libcamera-tools nautilus-python neovim openssl podman-remote rpmfusion-free-release
                           rpmfusion-nonfree-release seahorse-nautilus steam-devices zsh

This is the last deployment that GDM worked properly:

State: idle
AutomaticUpdates: stage; rpm-ostreed-automatic.timer: no runs since boot
Deployments:
  fedora:fedora/39/x86_64/silverblue
                  Version: 39.20230926.n.1 (2023-09-26T17:06:23Z)
               BaseCommit: 214d961525566049d92e1f9299c88a81bc0c9a59af831b711358c13c41da43e9
             GPGSignature: Valid signature by E8F23996F23218640CB44CBE75CF5AC418B8E74C
          LayeredPackages: firefoxpwa gocryptfs guake intel-media-driver
                           libavcodec-freeworld libcamera libcamera-gstreamer libcamera-ipa
                           libcamera-qcam libcamera-tools nautilus-python neovim openssl
                           podman-remote rpmfusion-free-release rpmfusion-nonfree-release
                           seahorse-nautilus steam-devices zsh
                   Pinned: yes

Additional context

My suspicion is that this has to do with an update to mutter. Running rpm-ostree db diff in comparison to my current deployment I got:

Upgraded:
  emacs-filesystem 1:29.1-1.fc39 -> 1:29.1-2.fc39
  ethtool 2:6.4-2.fc39 -> 2:6.5-1.fc39
  firefox 117.0.1-2.fc39 -> 118.0-1.fc39
  firefox-langpacks 117.0.1-2.fc39 -> 118.0-1.fc39
  giflib 5.2.1-16.fc39 -> 5.2.1-17.fc39
  glib2 2.78.0-2.fc39 -> 2.78.0-3.fc39
  harfbuzz 8.1.1-1.fc39 -> 8.2.0-1.fc39
  harfbuzz-icu 8.1.1-1.fc39 -> 8.2.0-1.fc39
  libppd 1:2.0~rc2-3.fc39 -> 1:2.0~rc2-4.fc39
  mutter 45.0-2.fc39 -> 45.0-3.fc39
  mutter-common 45.0-2.fc39 -> 45.0-3.fc39
  ostree 2023.5-3.fc39 -> 2023.6-1.fc39
  ostree-grub2 2023.5-3.fc39 -> 2023.6-1.fc39
  ostree-libs 2023.5-3.fc39 -> 2023.6-1.fc39
  python3-pillow 10.0.0-2.fc39 -> 10.0.1-1.fc39
  python3-setuptools 67.7.2-5.fc39 -> 67.7.2-7.fc39
  python3-urllib3 1.26.16-2.fc39 -> 1.26.16-3.fc39
  python3-urllib3+socks 1.26.16-2.fc39 -> 1.26.16-3.fc39
  qt5-qtbase 5.15.10-8.fc39 -> 5.15.10-9.fc39
  qt5-qtbase-common 5.15.10-8.fc39 -> 5.15.10-9.fc39
  qt5-qtbase-gui 5.15.10-8.fc39 -> 5.15.10-9.fc39
  xdg-desktop-portal 1.18.0-1.fc39 -> 1.18.0-2.fc39

[tpopela]

This is on purpose as the functionality was disabled for Fedora 39 final - see https://src.fedoraproject.org/rpms/mutter/c/13e136bb336b391db726b2aadf3a4c89f6a98765?branch=f39

[pesader]

Thanks for the info :)