XPLMGetWindowGeometry
XPLM_API void XPLMGetWindowGeometry(
XPLMWindowID inWindowID,
int * outLeft, /* Can be NULL */
int * outTop, /* Can be NULL */
int * outRight, /* Can be NULL */
int * outBottom); /* Can be NULL */
This routine returns the position and size of a window. The units and coordinate system vary depending on the type of window you have.
If this is a legacy window (one compiled against a pre-XPLM300 version of the SDK, or an XPLM300 window that was not created using XPLMCreateWindowEx()), the units are pixels relative to the main X-Plane display.
If, on the other hand, this is a new X-Plane 11-style window (compiled against the XPLM300 SDK and created using XPLMCreateWindowEx()), the units are global desktop boxels.
Pass NULL to not receive any paramter.