Obtains the surface underneath this, returning the location of the device in win_x and
win_y.
Returns null if the surface tree under this is not known to GDK (for example, belongs to another application).
| this |
pointer `GdkDevice` to query info to |
| win_x |
return location for the X coordinate of the device location relative to the surface origin |
| win_y |
return location for the Y coordinate of the device location relative to the surface origin |
|
the `GdkSurface` under the device position |