return location for the X coordinate of the device location, relative to the surface origin, or %NULL.
return location for the Y coordinate of the device location, relative to the surface origin, or %NULL.
the GdkSurface under the device position, or %NULL
Obtains the surface underneath @device, returning the location of the device in @win_x and @win_y
Returns %NULL if the surface tree under @device is not known to GDK (for example, belongs to another application).