Ported: Physics Interpolation 2D - reset on NOTIFICATION_ENTER_TREE

As a convenience, physics interpolation is reset automatically on entering the tree. This will be desired in most situations, and saves the user having to write code for this explicitly.
- lawnjelly
bcfca5ec86

scene/2d/canvas_item.cpp

@@ -592,6 +592,19 @@ void CanvasItem::_notification(int p_what) {
 				get_tree()->xform_change_list.add(&xform_change);
 			}
 
+			// If using physics interpolation, reset for this node only,
+			// as a helper, as in most cases, users will want items reset when
+			// adding to the tree.
+			// In cases where they move immediately after adding,
+			// there will be little cost in having two resets as these are cheap,
+			// and it is worth it for convenience.
+			// Do not propagate to children, as each child of an added branch
+			// receives its own NOTIFICATION_ENTER_TREE, and this would
+			// cause unnecessary duplicate resets.
+			if (is_physics_interpolated_and_enabled()) {
+				notification(NOTIFICATION_RESET_PHYSICS_INTERPOLATION);
+			}
+
 			if (get_viewport()) {
 				get_parent()->connect(SceneStringNames::get_singleton()->child_order_changed, get_viewport(), SceneStringNames::get_singleton()->canvas_parent_mark_dirty, varray(get_parent()), CONNECT_REFERENCE_COUNTED);
 			}