Screen objects are the GDK representation of the screen on which windows can be displayed and on which the pointer
moves.
X originally identified screens with physical screens, but nowadays it is more common to have a single Screen which
combines several physical monitors (see get_n_monitors).
GdkScreen is used throughout GDK and GTK+ to specify which screen the top level windows are to be displayed on. it is also used to query the
screen specification and default settings such as the default visual (
get_system_visual), the dimensions of the physical monitors (
get_monitor_geometry), etc.