Multi-screen issues

Multi-screen issues can be caused by multiple parts of the software stack. See also https://notmart.org/blog/2023/02/how-to-report-multiscreen-bugs/.

Screen is not detected or turned on at all

These issues are mostly in KWin; assign them to `kwin - multi-monitor` and triage further:

Possible cause	Information to request to rule it out or confirm it
KWin not noticing it	request the output of `kscreen-doctor -o`
Bad cable (rare)	Try a different cable, or try the same screen/cable combination on another device

After login, wake-from-sleep, or screen connection/disconnection, desktops or panels are on the wrong screen, or a screen has a black background and can't be right-clicked, but the user can move the cursor and app windows there

This means that somehow the mapping of desktop/panel to screen has gotten messed up. Possibilities:

Possible cause	Information to request to rule it out or confirm it
"Primary Screen" assignment has moved to the wrong screen	common` and continue triaging.
Desktops or panels are not following "Primary Screen" or screen priority assignments	desktop containment` and ask them to diff their `~/.config/plasma-org.kde.plasma.desktop-appletsrc` file before and after it happens, and attach the diff
User disabled the Kscreen2 service	Re-enable it if it's been disabled in System Settings > Startup & Shutdown > Background Services

Screen configuration UI does not reflect reality or has a bug in it

These are issues in the KScreen KCM; assign them to `systemsettings | kcm_kscreen`.

App windows don't launch on the expected screen

Possible cause	Information to request to rule it out or confirm it
User is on X11 or the app in question is using XWayland and the window always opens on a specific screen, rather than on the screen with the cursor	The app is either forcing its window to open on the primary screen, or else remembering its prior window position. Not a bug.
Window always opens on the screen with the cursor instead of some other location where the user wants it to open	Window is a native-Wayland window or it's an X11/XWayland window that doesn't implement position memory, and so in either case, it falls back to the KWin window placement setting. Not a bug.

Desktop icon positions get reset

A refactoring of desktop icon positioning code in 2024 resolved a large number of issues related to those icons losing their place after reboots or screen adjustments.

Description of the refactoring work: https://akselmo.dev/posts/plasma-desktop-icons-positioning-refactor/

plasma-desktop Merge Requests related to that work:

Graphical corruption or visual freezes

TODO