gboolean gtk_window_is_active ( GtkWindow* window )
Returns whether the window is part of the current active toplevel.
(That is, the toplevel window receiving keystrokes.)
The return value is
TRUE if the window is active toplevel
itself, but also if it is, say, a
GtkPlug embedded in the active toplevel.
You might use this function if you wanted to draw a widget
differently in an active window from a widget in an inactive window.