virtual void start_grab (GdkEvent *, Gdk::Cursor *);
virtual void motion (GdkEvent *, bool);
virtual void finished (GdkEvent *, bool) = 0;
virtual void start_grab (GdkEvent *, Gdk::Cursor *);
virtual void motion (GdkEvent *, bool);
virtual void finished (GdkEvent *, bool) = 0;