- void (*_resize)(void *obj);
- void (*_add_child)(void *obj);
- int (*_remove_child)(void *obj);
+ // update area's content and update size (width/heith).
+ // return '1' if size changed, '0' otherwise.
+ int (*_resize)(void *obj);
+ // after pos/size changed, the rendering engine will call _on_change_layout(Area*)
+ int on_changed;
+ void (*_on_change_layout)(void *obj);