KDE dynamic high-dpi text scaling

Question

I am looking for an equivalent of the following gnome setup, in KDE:

Under gnome+X11, I can get instant scaling of gnome apps, KDE apps and chrome/chromium (>v49) when plugging my high-dpi monitor (27" 4K) by running:

gsettings set org.gnome.desktop.interface text-scaling-factor 1.4

Note that (in a neophyte's words) this is not doing framebuffer-level scaling (that would be gnome's scaling-factor), it' only telling the toolkits to use bigger fonts (images are not affected).

This gets picked-up instantly by gnome, qt, chrome. Other aps, like Intellij IDEs or Firefox need a restart (for Firefox I could script in a change of layout.css.devPixelsPerPx).

On the other hand, in KDE, both Plasma "Displays - Scale Display" and "Fonts - Force fonts DPI" settings require a restart of all apps including the same KDE apps which autodetected the gnome scaling change!!

This may be due to the KDE-GTK theme picking up the gnome setting, but still, it means Qt can redraw the interface in response to the change.

Am I overlooking something? Can I modify the same low-level setting underlying the gnome one, from KDE? Is there something that can be improved in KDE code to improve the situation?

I ran through Arch and Debian doc without success.

Answer 1

Running kwin --replace & in a terminal seems to help at least with newly started applications.

In addition one can throw in a:

kquitapp5 plasmashell
kstart5 plasmashell

Ideas from: https://askubuntu.com/questions/481329/can-i-restart-the-kde-plasma-desktop-without-logging-out

See also: https://askubuntu.com/questions/878023/how-do-i-change-display-scaling-dynamically