XPLM_API void       XPLMGetMouseLocationGlobal(
                         int *                outX,    /* Can be NULL */
                         int *                outY);    /* Can be NULL */

Returns the current mouse location in global desktop boxels. Unlike XPLMGetMouseLocation(), the bottom left of the main X-Plane window is not guaranteed to be (0, 0)—instead, the origin is the lower left of the entire global desktop space. In addition, this routine gives the real mouse location when the mouse goes to X-Plane windows other than the primary display. Thus, it can be used with both pop-out windows and secondary monitors.

This is the mouse location function to use with modern windows (i.e., those created by XPLMCreateWindowEx()).

Pass NULL to not receive info about either parameter.