Modern system often have special handling for high dpi screens. Older applications are usually scaled to match applications that are dpi aware. This however doesn't look nearly as good as if it is done properly.
We should implement proper high dpi support in FLTK so that the client looks nice on these systems.
A first step might be to do a dumb scaling of most things and just render the text at the proper dpi, as that is the primary problem.
*** Bug 5791 has been marked as a duplicate of this bug. ***
Note bug 7047.
Implementing proper high dpi support in FLTK is not trivial work. A different approach could be to abandon FLTK in favor of for example Qt (see bug 4031) which already has support for this.
Some work has been done on the upcoming FLTK 1.4 branch:
This might be an interesting algorithm if we want some fancier scaling:
Another interesting scaling algorithm is AMD's FidelityFX Super Resolution. It is apparently freely available.
It's designed to run as a shader, though, which could complicate things.