GNOME Display Scale Resetter

A lightweight Python utility to watch and automatically reset GNOME display scaling when running under Wayland.

Why

Resizing the window of a GNOME desktop environment running inside a VM on Wayland triggers a display reconfiguration. GNOME's Wayland compositor (Mutter) frequently defaults these new resolutions to a 100% scale regardless of the existing display scale setting.

This tool is irrelevant when running under X11, which doesn't support generic display scaling.

How

This script serves as a watchdog for display configurations. It listens for MonitorsChanged signals via the GNOME Mutter DBus API. When a change is detected, such as a VM window resize or physical display hotplug, it checks the current scale and resets to the specified target scale upon a mismatch.

Features

• Reacts instantly to VM window resizes and display hotplugs.
• Can specify:
  • Separate scaling factors for each display.
  • A default scaling factor for any display not listed by name.
• Automatically "snaps" the preferred scale to the closest value supported by Mutter for each display's current resolution.
  • Specifying a display in a mirror group will scale the entire group based on the supported scales of the first display in that group.
• Runs as a user systemd service that automatically starts on login.
  • Named displays do not need to be present when the service starts.

Prerequisites

• GNOME Desktop Environment (Wayland)
• Python 3
• python3-gi (GObject Introspection)

Installation

1. Install the script: The provided service config will look for the script in ~/libexec.

   mkdir -p ~/libexec
   cp display-scale-reset.py ~/libexec/

2. Configure the systemd service: Open display-scale-reset.service for editing and replace {{SCALE}} with the preferred scale configuration.

   Examples:

   • Global scale: --scale 1.25
   • Per-display: --scale eDP-1:1.25 --scale HDMI-1:1.0

3. Install and start the service:

   mkdir -p ~/.config/systemd/user/
   cp display-scale-reset.service ~/.config/systemd/user/
   systemctl --user daemon-reload
   systemctl --user enable display-scale-reset.service
   systemctl --user start display-scale-reset.service

Usage

Listing Displays

Identify connected displays:

~/libexec/display-scale-reset.py --list-displays

Example output:

CONNECTOR       SCALE      PRIMARY
----------------------------------
eDP-1           1.25       Yes
HDMI-1          1.0        No
Virtual-1       1.25       No

Running Once Manually

Force apply a scale configuration and exit:

~/libexec/display-scale-reset.py --force-once --scale 1.25

Watching for Changes

Watch for scale changes on all displays and set all to 150%:

~/libexec/display-scale-reset.py --scale 1.5

Targeting a Single Display

Operate on only one display:

~/libexec/display-scale-reset.py --scale HDMI-1:1.25

Multiple Displays

Custom scale for two displays with a default of 150% for any other display.

~/libexec/display-scale-reset.py --scale 1.5 --scale eDP-1:1.25 --scale HDMI-1:1.0

License

This project is licensed under the MIT License - see the LICENSE file for details.