Linux/HiDPI scaling when gnome set to autodetect

[benwaffle]

When org.gnome.desktop.interface scaling-factor is 0, GNOME automatically detects that I have a hidpi screen but atom does not. It's a minor issue since i can easily change scaling-factor to 2

[mtwebster]

Applications really should not rely on this setting for detecting the current scale factor. This is a user preference setting for gnome-shell. Other desktops can and will use a different schema altogether to store this preference. The correct place to query the current scale factor is from the X server itself, via some toolkit's api, or using the X11 api directly to read the server xsettings. This will also prevent you from ending up in normal-dpi mode when 'autodetect' is enabled for that gsettings key (0).

[kpeeters]

Slightly off-topic but I can't find the info anywhere else: can anyone comment on how to "query the current scale factor from the X server itself, via some toolkit's api, or using the X11 api directly to read the server xsettings", as mentioned by mtwebster, preferably using gtk?

[mtwebster]

This probably works in most cases: https://developer.gnome.org/gdk3/stable/GdkScreen.html#gdk-screen-get-monitor-scale-factor

In python you could do something like:

from gi.repository import Gdk
factor = Gdk.Screen.get_default().get_monitor_scale_factor(0)

Note the deprecation warning - in Gtk 3.22 it's highly recommended to go through the GdkMonitor api instead... old monitor reporting from GdkScreen/GdkDisplay is unreliable (and more or less unmaintained - this is what deprecated means to them.)

Something else to note, the 0 isn't technically appropriate - you should be sure you're using a valid monitor index, but under X server, all monitors will have the same scale factor, and I'm pretty certain there's always a monitor 0.

[kpeeters]

That works, but it turns out I actually wanted not just the scale factor, but also the (independent) text scale factor. Any idea how to get the equivalent of org.gnome.desktop.interface.text-scaling-factor ?