XPLM_API void XPLMGetScreenBoundsGlobal( int * outLeft, /* Can be NULL */ int * outTop, /* Can be NULL */ int * outRight, /* Can be NULL */ int * outBottom); /* Can be NULL */
This routine returns the bounds of the "global" X-Plane desktop, in boxels. Unlike the non-global version XPLMGetScreenSize(), this is multi-monitor aware. There are three primary consequences of multimonitor awareness.
First, if the user is running X-Plane in full-screen on two or more monitors (typically configured using one full-screen window per monitor), the global desktop will be sized to include all X-Plane windows.
Second, the origin of the screen coordinates is not guaranteed to be (0, 0). Suppose the user has two displays side-by-side, both running at 1080p. Suppose further that they've configured their OS to make the left display their "primary" monitor, and that X-Plane is running in full-screen on their right monitor only. In this case, the global desktop bounds would be the rectangle from (1920, 0) to (3840, 1080). If the user later asked X-Plane to draw on their primary monitor as well, the bounds would change to (0, 0) to (3840, 1080).
Finally, if the usable area of the virtual desktop is not a perfect rectangle (for instance, because the monitors have different resolutions or because one monitor is configured in the operating system to be above and to the right of the other), the global desktop will include any wasted space. Thus, if you have two 1080p monitors, and monitor 2 is configured to have its bottom left touch monitor 1's upper right, your global desktop area would be the rectangle from (0, 0) to (3840, 2160).
Note that popped-out windows (windows drawn in their own operating system windows, rather than "floating" within X-Plane) are not included in these bounds.