[LukeShu]

I did a write-up of the low-levels of how it works on Xorg: https://reddit.com/r/archlinux/comments/c8hgt8/my_laptop_has...

Missing from that:

- Gnome actually does the scaling in the compositor, not in the X server itself.

- Most desktop environments should be doing all that for you. At the time I wrote that (over 2 years ago), in Gnome you had to go in to an advanced settings menu and enable "experimental fractional scaling"; I'm not sure if that's still true today.

- Some things pick up the DPI from the XSETTINGS protocol, not from the XRDB. Specifically, parts of Java's AWT/Swing do this. But other parts use the XRDB. And they conflict with eachother. When I last looked at Swing (April-ish 2020) it was impossible to get it to do the right thing on X11 (I was working on a patch, but then I had some life disruptions and never came back to it).