Font scaling in dual monitor setup

Question

Just installed Ubuntu 20.04 on a ThinkPad W451 where the screen resolution on the laptop is 2880x1620 and attached a second monitor with resolution 1920x1080. Sadly there seems Ubuntu either shows tiny fonts on the laptop monitor, or if the fonts on the laptop monitor are OK, the windows and fonts on the second monitor are huge.

In the Displays settings, there is a scale selection for either monitor, but the scale cannot be independently set: if I set it on one, it affects the other.

Is there a way to use dual monitors so that the font sizes would just adapt to the actual DPI for each monitor? I cannot believe that such a fundamental thing is still not solved in 2020: for each monitor, if we know the DPI, we should be able to draw things with the intended size. I tried this with the default window manager, xfce4 and Mate, and all of them get it wrong.

Do you have a Fractional Scaling option in display settings? For me the normal Scale setting (only 100% or 200% options) like you seems to affect all monitors. But if I enable Fractional Scaling I can set different scales on different monitors as well as having 5 scale increment options (100%, 125%, 150%, 175%, 200%). — codlord, Jul 19 '20 at 14:13
Yes, there is a fractional scaling option but it does not work: it remembers the values shown per monitor, but it does not correctly apply them, instead, I still get either tiny fonts on the laptop or huge fonts on the second monitor. I did not try all combinations, but I think the actual scaling used for both monitors is the one specified for the primary (laptop) screen, and the other setting, even if different is ignored. For example, when laptopt is set to 200 and second screen to 100, laptop looks good, second screen much too big. — jpp1, Jul 20 '20 at 15:18
Any updates here ? Running into the same problem on Ubuntu 20.04 . — sbunny, Apr 01 '21 at 08:51

score 4 · Answer 1 · answered Sep 21 '21 at 10:52

Is there a way to use dual monitors so that the font sizes would just adapt to the actual DPI for each monitor?
Yes, with xrandr. I will sketch the solution, and leave the details for you to tinker and find out.

xrandr is an official configuration utility to the RandR (Resize and Rotate) X Window System extension (source).

You need a command line like

$ xrandr --output <output #1> --primary --mode 2880x1620  --pos 0x0 --scale 2x2  --rotate normal --output <output #2> --mode 1920x1080 --pos <other> --scale 1x1 --rotate normal

Whenever you found the right configuration, you can make it permanent by adding the modes and setting the defalts. I leave here relevant links.

Font scaling in dual monitor setup

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