Converts a point's coordinates, expressed relative to the top left corner of the client area, to coordinates relative to the top left of the element to which a rendering behavior is attached.
HRESULT retVal = object.TransformGlobalToLocal(ptGlobal, pptLocal);
POINT structure that specifies the point to convert to the element's coordinate system.
Pointer to a POINT structure that receives the point's coordinates relative to the element's top left corner.
If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.