HDPI support in jar packaged apps


My main usage of flatpak is the use of josm to edit/add stuff on openstreetmap. I have an HDPI screen , and Help/HiDPISupport – JOSM says I should launch the app with en env variable.
What’s the proper way to do that with flatpack ?

You can do:
flatpak run --env=GDK_SCALE=2 org.openstreetmap.josm

Ideally the flatpak should automatically pick the current scale, but this flatpak app is lacking that support, I’ll submit a MR to add support for that (ok done here).

If it used a toolkit that was a bit more modern, they’d be nothing to do. Gtk3 is over a decade old and supports it well automatically. Qt5, almost.

Just to clarify that the problem with HiDPI are not inherent to Flatpak but rather to toolkits.