xrandr multiple displays showing different areas of the same virtual screen

Question

Background: I have a PC with two HDMI1.4 outputs and 4k monitor that allows Picture-By-Picture display from two HDMI sources. A single HDMI1.4 connection between the computer and the monitor is limited to 30hz. With 2x 1920x2160 outputs it is possible to get 4k at 60hz

When doing this, there are two outputs and each is treated as its own monitor. This causes problems:

• Fullscreen applications, e.g. games or video players are only “fullscreen” on half the screen because it looks like two physical monitors (from the computers point of view)
• maximizing windows only maximizes on one (½) monitor

Is it possible to set up xrandr so that there is a virtual 3840x2160 screen, and then set up each monitor to show a part of it. E.g. monitor 1 displays the left half and monitor 2 displays the right half. Applications would only see the virtual screen and "see" a resolution of 3840x2160, even for maximized windows.

I'm using KDE if it makes any difference.

Answer 1

I guess KDE may have something in it's settings to control this behavior. But if not, then you might try this

xrandr --output HDMI-0 --auto --output HDMI-1 --auto --{right,left}-of HDMI-0

Answer 2

I managed to work it out, xrandr has a VIRTUAL1 output. Through trial and error i worked out how to use it:

1. Generate the modeline:

   cvt 3840 2160
   Modeline "3840x2160_60.00"  712.75  3840 4160 4576 5312  2160 2163 2168 2237 -hsync +vsync
   

2. Add the mode to xrandr:

   xrandr --newmode "3840x2160_60.00"  712.75  3840 4160 4576 5312  2160 2163 2168 2237 -hsync +vsync
   

3. Set the mode on VIRTUAL1:

   xrandr --addmode VIRTUAL1 3840x2160_60.00
   

4. Set display1 to clone VIRTUAL1 (in my case HDMI1):

   xrandr --output HDMI1 --same-as VIRTUAL1
   

5. Then place HDMI2 right of HDMI1:

   xrandr --output HDMI2 --right-of HDMI1