I have a (pretty cheap) laptop happily running Debian 12 with KDE Plasma 5.27.5. Its display is set to 1920x1080 and it works well. I originally opened this query on the Debian forum:
It was recommended that I ask on a dedicated KDE Forum which is why I’m here.
Recently I acquired a (also pretty cheap) flatscreen TV with an HDMI port. I bought the correct Mini HDMI C to HDMI A cable, plugged in the TV and it popped to life with no effort. Debian detected it and KDE started to display. I can move the cursor between the screens and drag-and-drop windows between the two. So far so good.
Now, from looking around the Net (and on this site), I know that KDE Plasma 5 doesn’t play well with multiple monitors. I’m left with some issues that I can’t get my head around, so I thought I’d ask here.
The laptop’s built-in screen is set to 1920x1080 and it’s the Primary display. The TV is capable of 1920x1080 but when I set this resolution, it’s as if the setting is too big to fit the physical display size of the TV screen. This means the KDE panels are “stretched” outside of the screen. They are too long to fit in the horizontal axis (so icons like the Application Launcher are not visible) and are half-hidden off the bottom of the screen.
If I set the TV’s resolution to 1280x1024, then KDE starts to display correctly (if somewhat enlarged). All well and good. The Primary display has seven virtual workspaces. If I then add an Empty Panel to the TV, with no other widgets added, it seems the TV workspace switches when I change workspaces on the Primary display. This also happens when there are no panels (Application Menu Bar, Default or Empty) configured on the TV monitor.
I’m not sure what to look for other than the commands in the previous thread.
I initially used X11, experimented with Wayland (which seemed somewhat more temperamental), then moved back to X11. With xrandr and arandr, I created an x11.sh script:
9 colin@kuu> cat x11.sh
xrandr --verbose --output eDP-1 --primary --mode 1920x1080 --pos 1920x0 --rotate normal --output HDMI-1 --mode 1920x1080i --pos 0x0 --rotate normal --output DP-1 --off --output HDMI-2 --off
I added the --verbose option manually. and the output is:
10 colin@kuu> pwd
11 colin@kuu> ./x11.sh
crtc 0: 1920x1080 60.00 +1920+0 “eDP-1”
crtc 1: 1920x1080i 60.00 +0+0 “HDMI-1”
The problems described above still persist. In summary:
- The resolution of the TV monitor (HDMI-1), set to 1920x1080i, seems to ‘stretch’ the panel beyond the edges of the screen. In practice this means the Application Menu and Peek at Desktop icons can’t be seen. They are definitely present because I can push the mouse to the edge of the screen and see the tooltip pop-ups. Further, the lower half of the panel is off the bottom of the screen and can’t be seen.
- I use seven virtual desktops. When I switch between them on the Primary display (the laptop’s built in screen), the TV monitor switches to the same virtual desktop.
Should I be using X11 or Wayland with dual monitors? In my experience, Wayland has other problems which are even worse than the screen resolution. (For instance, if I have a file open in Kate on one virtual desktop, switch to another virtual desktop and open another file in Kate, the display switches back to the original virtual desktop and opens the file in the first instance of Kate.)
Please let me know if there’s any more information I can provide.