gdk:device-position (device)

device -- a gdk:device pointer device to query status about

screen -- a gdk:screen object the device is on, or nil
x -- an integer with the root window x coordinate of device, or nil
y -- an integer with the root window y coordinate of device, or nil

Gets the current location of the device. 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.