isFullscreen

Retrieves the current fullscreen state of @window.

Note that since fullscreening is ultimately handled by the window manager and happens asynchronously to an application request, you shouldn’t assume the return value of this function changing immediately (or at all), as an effect of calling method@Gtk.Window.fullscreen or method@Gtk.Window.unfullscreen.

If the window isn't yet mapped, the value returned will whether the initial requested state is fullscreen.