move widgets on draw if region size is same

src/layout/module.rs

@@ -10,6 +10,7 @@ pub trait UiModule: Any {
     fn on_draw(&mut self, inst: &WidgetInstance) {}
     fn on_undraw(&mut self, inst: &WidgetInstance) {}
     fn on_remove(&mut self, id: &Id) {}
+    fn on_move(&mut self, inst: &WidgetInstance) {}
 }
 
 #[derive(Default)]