GetCapture (Compact 2013)
This function retrieves the handle to the window, if any, that has captured the mouse or stylus input. Only one window at a time can capture the mouse or stylus input.
The handle of the capture window associated with the current thread indicates success. NULL indicates that no window in the current thread has captured the mouse.
A NULL return value does not indicate that another thread or process in the system has not captured the mouse or stylus; NULL just indicates that the current thread has not captured the mouse or stylus.