Implementing HiDpi scaling

[fedang]

Hello all,

I am writing a small X11 app using cairo as the drawing backend. I was 
wondering if and how to implement
fractional scaling to accommodate high dpi screens. After searching 
online I found almost nothing, so here I am.

Can someone give me some pointers on what to do? I can get a scale 
factor for the screens (depending on the size)
but I have no idea how to actually use it in the draw code.


Regards