Wayland GDM add custom monitor resolution

What are the possible ways of adding resolutions to the list of available resolutions in Settings -> Displays?

I have unsuccessfully added my own ~gdm/.config/monitors.xml file, but that does not seem to take effect. (this is probably due to https://gitlab.gnome.org/GNOME/gdm/-/issues/224 - I am basing it on my GDM X11 monitors config).

For X11, I could achieve what I wanted with xrandr, but now I understand that something equivalent is neither planned, nor intended for Wayland.

Running Arch Linux, 5.11.12-arch1-1, GNOME 40.

Any advice would be greatly appreciated!

Here is my initial question, posted on reddit.

custom monitor resolution

Are you really still using a CRT monitor? I can not really believe that. Even in the poorest countries, as power consumption is so high for CRT tubes? You should try to get a used TFT, some people give there working ones to garbage when they buy a larger one.

Or do I misunderstand your question?

Hello StefanSalewski, many thanks for your reply!

I have my laptop with a builtin 15" 3840 x 2160 (16:9) resolution, and my external monitor, a 32" 3440 x 1440 (21:9) resolution. The monitor is connected with HDMI.

My question is how I can force GNOME to set a custom resolution, which I know works with X11, when running Wayland.

So you already have a TFT display. And you want to use a different than the native TFT resolution? That is really a very bad idea for text and other detailed display. Display of a TFT or LCD is a matrix with a fixed resolution, so interpolating to other resolutions gives always a very bad result. I have seen that 20 years ago in the lab, when we had old measurement hardware with windows 3.1 and old VGA cards, but replaced a CRT with a TFT.

But now it is 20 years later, we have Linux, and we can select font sizes free, and can even scale display in Gnome settings. Maybe not really perfect, but much better than do some strange interpolation.

And yes, I know that TV devices scale its image content generally. Even that is a bit sad, but for moving picture content it is ok. So when you only wants to watch youtube videos…

But forget my response, I really thought that you are still using a real CRT tube :slight_smile:

Yeah, no big heavy CRT, but a LED monitor with a VA panel. Its a GIGABYTE G34WQC.

The monitor does support 3440 x 1440, which I know and can manually configure with X11 using xrandr.

The issue arises with Wayland, as in the GNOME settings list of supported resolutions, no 21:9 resolutions are listed at all, and the highest available option is 2560 x 1440 (which is 16:9).

With X11, I can achieve this resolution by lowering the monitor update frequency to ca 35 Hz (instead of standard 60), and forcibly push up the resolution used. With Wayland I have only found one way to adjust the list of available resolutions, through ~gdm/.config/monitors.xml, but that does not seem to have an effect.

So my question is: How can I add an entry to the Resolution dropdown myself? I know for sure that the resolution works, but with Wayland no equivalent low-level tooling is in place and I have to rely on the higher-level configuration: thus as I am using GNOME I am asking here.

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