XPLM_API void       XPLMGetAllMonitorBoundsOS(
                         XPLMReceiveMonitorBoundsOS_f inMonitorBoundsCallback,    
                         void *               inRefcon);    

This routine immediately calls you back with the bounds (in pixels) of each monitor within the operating system’s global desktop space. Note that unlike XPLMGetAllMonitorBoundsGlobal(), this may include monitors that have no X-Plane window on them.

Note that this function’s monitor indices match those provided by XPLMGetAllMonitorBoundsGlobal(), but the coordinates are different (since the X-Plane global desktop may not match the operating system’s global desktop, and one X-Plane boxel may be larger than one pixel).