Function XPUDragWidget 

pub unsafe extern "C" fn XPUDragWidget(
    inMessage: XPWidgetMessage,
    inWidget: XPWidgetID,
    inParam1: isize,
    inParam2: isize,
    inLeft: c_int,
    inTop: c_int,
    inRight: c_int,
    inBottom: c_int,
) -> c_int

XPUDragWidget

XPUDragWidget drags the widget in response to mouse clicks. Pass in not only the event, but the global coordinates of the drag region, which might be a sub-region of your widget (for example, a title bar).