+ const DisplayFuncType get_display_callback() const;
+ const KeyboardFuncType get_keyboard_callback() const;
+ const MouseButtonFuncType get_mouse_button_callback() const;
+ const MouseMotionFuncType get_mouse_motion_callback() const;
+
+ // win hierarchy
+ void add_child(Window *win);
+ void remove_child(Window *win);
+
+ Window **get_children();
+ int get_children_count() const;
+
+ const Window *get_parent() const;
+ Window *get_parent();
+