XPLM_API void       XPLMGetAllMonitorBoundsGlobal(
                         XPLMReceiveMonitorBoundsGlobal_f inMonitorBoundsCallback,    
                         void *               inRefcon);    

This routine immediately calls you back with the bounds (in boxels) of each full-screen X-Plane window within the X-Plane global desktop space. Note that if a monitor is not covered by an X-Plane window, you cannot get its bounds this way. Likewise, monitors with only an X-Plane window (not in full-screen mode) will not be included.

If X-Plane is running in full-screen and your monitors are of the same size and configured contiguously in the OS, then the combined global bounds of all full-screen monitors will match the total global desktop bounds, as returned by XPLMGetScreenBoundsGlobal(). (Of course, if X-Plane is running in windowed mode, this will not be the case. Likewise, if you have differently sized monitors, the global desktop space will include wasted space.)

Note that this function’s monitor indices match those provided by XPLMGetAllMonitorBoundsOS(), 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 due to 150% or 200% scaling).