Mixed HiDPI / LoDPI screens - how does X11 handle them?

Attila Kinali attila at kinali.ch
Sun May 10 11:48:12 UTC 2020


I recently got a new screen and now I have 3 monitors with dpi ranging
from 86 to 283. Previously with only a 122/83dpi combination, I could just
live with adjusting things that they would look reasonable on both screens.
Now with an 1:3.2 range, it isn't that easy. Especially as some applications
try to be intelligent and change settings.

I tried to look up what the way to deal with HiDPI but either articles
are from 5-7 years ago or restricted to Gnome only (I don't use any 
desktop environment so that doesn't help me). I tried using xrandr --scale,
but that just makes everything unreadably small or ugly, if I scale the
application settings.

I don't mind if I have to script stuff or patch applications to
improve things.

So, I have a few questions regarding this:

1) What is the recommended way in dealing with mixed DPI settings?

2) How do applications detect DPI? The X11 setting is 96dpi per default,
but when I plug in the 283dpi monitor, the cursor is being scalled on all
monitors and some application (e.g. Krita) scale based on which screen
they are on.

3) Where can I find the documentation regarding this. I tried to look
it up, but I must have used the wrong keywords. I'm looking for both
X11 behaviour/architecture and API documentation.

Thanks in advance

			Atttila Kinali
<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.

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