virtual bool on_motion_notify_event(GdkEventMotion* event); //for dragging
virtual bool on_scroll_event(GdkEventScroll* event); //for zooming
virtual bool on_button_press_event(GdkEventButton *event); //for clicking
virtual bool on_button_release_event(GdkEventButton *event); //for clicking
virtual bool on_motion_notify_event(GdkEventMotion* event); //for dragging
virtual bool on_scroll_event(GdkEventScroll* event); //for zooming
virtual bool on_button_press_event(GdkEventButton *event); //for clicking
virtual bool on_button_release_event(GdkEventButton *event); //for clicking