Determine high-dpi setting

[Kasper Peeters <kasper peeters phi-sci com>]

Hi,

This question is only partially related to gtkmm, so apologies for the
bandwidth. I am looking for the current recommended way to determine
the font-scaling factor (for high-dpi displays) on a system, so I can
scale images with the same factor. 

I can do things like

  auto settings = Gio::Settings::create("org.cinnamon.desktop.interface"); 
  float scale = settings->get_double("text-scaling-factor");

but that works only for the cinnamon desktop. Is there anything that
works in general (or at least most of the available desktops)?

Thanks,
Kasper