Fractional scaling switch doesn't work in Wayland sessions

[Chris Halse Rogers]

Hitting the “fractional scaling” toggle in the “Screen Display” tab in gnome-control-centre page doesn't work - although the toggle changes to the “enabled” state there's no visible effect, and if I switch to a different page (or close g-c-c) and then switch back (or reopen g-c-c) then the toggle is back in the disabled state.

Running from the command line, I see;
(gnome-control-center:171131): display-cc-panel-WARNING **: 13:34:19.407: no sunset data, using 16.00

(gnome-control-center:171131): display-cc-panel-WARNING **: 13:34:19.407: no sunrise data, using 8.00

(gnome-control-center:171131): display-cc-panel-CRITICAL **: 13:34:21.972: file ../panels/display/cc-display-config.c: line 452 (get_fractional_scaling_key): should not be reached

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: gnome-control-center 1:3.37.90-1ubuntu2
ProcVersionSignature: Ubuntu 5.8.0+bcachefs.git20200701.7e04f345-1-generic 5.8.4
Uname: Linux 5.8.0+bcachefs.git20200701.7e04f345-1-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu45
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon Sep 7 13:34:44 2020
SourcePackage: gnome-control-center
UpgradeStatus: Upgraded to groovy on 2020-06-22 (76 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Kai Mast (kai-mast)]

Any progress on this? Is there an upstream bug report?

[Daniel van Vugt (vanvugt)]

It seems to work in Xorg sessions at least.

An upstream bug report is not appropriate because the switch does not exist upstream. A simple workaround is to toggle the setting manually by running:

gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer']"

[Kai Mast (kai-mast)]

Thanks Daniel. I was not aware this switch isn't available upstream.

[Launchpad Janitor (janitor)]

This bug was fixed in the package gnome-control-center - 1:3.38.3-1ubuntu3

---------------
gnome-control-center (1:3.38.3-1ubuntu3) hirsute; urgency=medium

  * d/p/0024-display-Allow-fractional-scaling-to-be-enabled.patch:
    - Support kms renderer in fractional scaling toggle (LP: #1894593)
    - Change logical layout mode when switching mode in wayland

 -- Marco Trevisan (Treviño) <email address hidden> Wed, 10 Feb 2021 13:43:55 +0100

[corrado venturini (corradoventu)]

Toggle “fractional scaling” and select 125% and 'Apply' the screen start blinking and part of it is full of noise. To have screen again clean I unchecked "fractional scaling” selected 'scale 200%' and then again 'scale 100%'

corrado@corrado-x7-hh-0212:~$ apt policy gnome-control-center
gnome-control-center:
  Installed: 1:3.38.3-1ubuntu3
  Candidate: 1:3.38.3-1ubuntu3
  Version table:
 *** 1:3.38.3-1ubuntu3 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
        100 /var/lib/dpkg/status
corrado@corrado-x7-hh-0212:~$ inxi -Gx
Graphics:
  Device-1: Intel HD Graphics 630 vendor: ASRock driver: i915 v: kernel
  bus ID: 00:02.0
  Device-2: ARC USB 2.0 Camera type: USB driver: uvcvideo bus ID: 3-1.3:4
  Display: wayland server: X.Org 1.20.9 compositor: gnome-shell driver:
  loaded: modesetting unloaded: fbdev,vesa resolution: 1920x1080~60Hz
  OpenGL: renderer: Mesa Intel HD Graphics 630 (KBL GT2) v: 4.6 Mesa 20.3.4
  direct render: Yes
corrado@corrado-x7-hh-0212:~$

[Daniel van Vugt (vanvugt)]

This bug is closed. Please open a new bug by running:

  ubuntu-bug mutter

or

  ubuntu-bug gnome-control-center