GtkWindowfullscreen

Asks to place window in the fullscreen state.

Note that you shouldn’t assume the window is definitely fullscreen afterward, because other entities (e.g. the user or window manager) unfullscreen it again, and not all window managers honor requests to fullscreen windows.

You can track the result of this operation via the GdkToplevel:state property, or by listening to notifications of the GtkWindow:fullscreened property.