[Software] Plasma on Debian 12 not using HiDPI on SDDM

[jfabernathy]

On a lot of distros with KDE Plasma 5.27 if you have a 4K UHD monitor with 3840x2160 display using 200% scaling, you can apply this scaling to your SDDM login screen by using the System Settings -> Startup and Shutdown -> Login Screen (SDDM) -> Apply Plasma Settings to make your login screen's font more like the fonts on your normal desktop.

This is not working on Debian 12. Is there something missing or a way to workaround this?

[Random_Troll]

Does https://wiki.archlinux.org/title/SDDM#Enable_HiDPI work? I don't use SDDM so I can't test (sorry).

[jfabernathy]

Does https://wiki.archlinux.org/title/SDDM#Enable_HiDPI work? I don't use SDDM so I can't test (sorry).

I'd say this is a marginal workaround. The KDE Plasma "Apply Plasma Settings" is support to work.
After creating the HIDPI file that the archlinux wiki referenced I had to reboot. At first the SDDM screen was still too small. I then selected X11 at login and once there, I setup scaling to 200%. rebooted again and now SDDM screen was in HiDPI mode. Now logging in showed the Task Manager panel too small so I had to double it's Panel height. I rebooted and with SDDM in HiDPI mode, I tried Wayland. This time the scaling was pack to 100%, so I changed it to 200% and rebooted. SDDM was still HiDPI and I logged in with Wayland and I was at 200% scaling but the the Task Manager was way too large so I had to put its height back to normal (44).

I'm hoping to stay on Wayland and if I do then I have things working but. This really needs to be fixed to work as cleanly as other Plasma distros.

[jfabernathy]

Hey! That's odd. Have you tried checking if the necessary packages are installed on Debian 12?

How do you ever know if you have all the packages installed? Where is that list?

[bw123]

...
I then selected X11 at login and once there, I setup scaling to 200%. rebooted again and now SDDM screen was in HiDPI mode. Now logging in showed the Task Manager panel too small so I had to double it's Panel height. I rebooted and with SDDM in HiDPI mode, I tried Wayland. This time the scaling was pack to 100%
...

Yeah switching between X11 and wayland seems problematic, supposedly fixed, but way upstream somewhere?

I don't understand kscreen, I've been using plasma-desktop on bullseye with kscreen2 disabled/notRunning for a long time now. If you don't have multiple monitors that you need to remember placement for or custom resolutions, is there a point to have it running? You can (still?) disable it in Startup>backgroundServices. That's something that I think is different about the debian release, just about everything is on and enabled by default, and finding out how to disable things changes every release. Same problem, different day.

https://community.kde.org/Plasma/Wayland_Showstoppers
https://bugs.kde.org/show_bug.cgi?id=433460

oh yeh, I ditched SDDM, tried LightDM it sucked too, so noDM is the way to go here. Do you have multiple users, do you need a display manager?

This really needs to be fixed to work as cleanly as other Plasma distros.

I think it should, but really how often are you going to switch the setting?