Display Settings - Mirror Displays

  1 month ago
  Under review

Monitor Mirroring
Monitor mirroring is a display setting which allows for "mirroring" (or duplicating/replicating/etc) the contents of one monitor onto another monitor.
This is a fairly common feature and available in MacOS, Windows, and in the world of Linux, available in KDE and GNOME.
In the latest version of Linux Mint (21), I have searched and can not find any functionality for mirror displays at all, so I am fairly confident it doesn't have this functionality.

Use Cases
One use case is to have two monitors plugged into a PC, one facing the user, and one facing an observer, so they can watch what the other user is doing as part of some demostration. Such as when giving a presentation in a meeting room.
Another use case is to have a small monitor on a desktop, and a large TV, both displaying the output from one PC, for easily switching between regular PC use and gaming on a large TV.

Proposal for how this functionality should work
I propose this functionality be added to Linux Mint's display settings, and that this feature be available per monitor. Not as a global setting, to simply display the same output on all monitors.
Mirroring globally all monitors is a limitation some OSes have in their implementation of monitor mirroring. While this is acceptable for two-screen setups, it is less useful for situations where users have three or four screens plugged into the same PC, and wish to mirror a single main monitor onto just one other display. Such as mirror the central main monitor from a 3 monitor display onto a nearby TV.
Here is a mockup of what this might look like in practice, with an additional option to choose individually per monitor, to mirror the contents of another monitor:


What should the dropdown list display?
A list of choices, including, "Do Not Mirror", and a list of monitors available to mirror.

What prevents someone from mirroring monitor A onto monitor B, and monitor B onto mirror A, creating an infinite loop?
The list of available monitors should only include monitors that are not currently mirroring the contents of another monitor. When a monitor is switched from 'Do Not Mirror' to a choice of monitors, it should be removed from the list of available monitors.

What happens when a monitor mirrors the contents of a monitor with a different resolution or frame rate?
The image to display on the target monitor should be stretched or shrunk to fit. It's up to users to ensure monitor refresh rates and resolutions make sense and to attempt to match them as best as possible between monitors.