gdk:device-window-at-position-double (device)

device -- a gdk:device pointer device to query info to

window -- a gdk:window object under the device position, or nil
xwin -- a double float for the x coordinate of the device location, relative to the window origin, or nil
ywin -- a double float for the y coordinate of the device location, relative to the window origin, or nil

Obtains the window underneath the device, returning the location of the device in double precision. Returns nil if the window tree under the device is not known to GDK, for example, belongs to another application.

As a slave device coordinates are those of its master pointer. This function may not be called on devices of type :slave, unless there is an ongoing grab on them. See the gdk:device-grab function.