I need to know active screen DPI on Linux and Mac OS. I think on linux xlib might be useful, but I can't find a way how to get currect DPI. I want this information to get real screen size in inches.
Thanks in advance!
In X on Linux, call XOpenDisplay() to get the Display, then use DisplayWidthMM() and DisplayHeightMM() together with DisplayWidth() and DisplayHeight() to compute the DPI.
On the Mac, there's almost certainly a more native API to use than X. Mac OS X does not run X Window by default, it has a native windowing environment.