Remove NOTIFICATION_MOVED_IN_PARENT

* This notification makes node children management very inefficient.
* Replaced by a NOTIFICATION_CHILDREN_CHANGED (and children_changed signal).
* Changed Canvas code (and similar) to use the above signal, to perform more efficiently.

This PR breaks compatibility (although this notification was very rarely used, even within the engine), but provides an alternate way to do the same.
It is required for the changes in godotengine#75627 to be entirely effective.

doc/classes/Node.xml

@@ -830,6 +830,11 @@
 				When this signal is received, the child [param node] is still in the tree and valid. This signal is emitted [i]after[/i] the child node's own [signal tree_exiting] and [constant NOTIFICATION_EXIT_TREE].
 			</description>
 		</signal>
+		<signal name="child_order_changed">
+			<description>
+				Emitted when the list of children is changed. This happens when child nodes are added, moved or removed.
+			</description>
+		</signal>
 		<signal name="ready">
 			<description>
 				Emitted when the node is ready. Comes after [method _ready] callback and follows the same rules.
@@ -867,8 +872,8 @@
 			Notification received when the node is about to exit a [SceneTree].
 			This notification is emitted [i]after[/i] the related [signal tree_exiting].
 		</constant>
-		<constant name="NOTIFICATION_MOVED_IN_PARENT" value="12">
-			Notification received when the node is moved in the parent.
+		<constant name="NOTIFICATION_MOVED_IN_PARENT" value="12" is_deprecated="true">
+			This notification is deprecated and is no longer emitted. Use [constant NOTIFICATION_CHILD_ORDER_CHANGED] instead.
 		</constant>
 		<constant name="NOTIFICATION_READY" value="13">
 			Notification received when the node is ready. See [method _ready].
@@ -907,6 +912,9 @@
 		<constant name="NOTIFICATION_PATH_RENAMED" value="23">
 			Notification received when the node's name or one of its parents' name is changed. This notification is [i]not[/i] received when the node is removed from the scene tree to be added to another parent later on.
 		</constant>
+		<constant name="NOTIFICATION_CHILD_ORDER_CHANGED" value="24">
+			Notification received when the list of children is changed. This happens when child nodes are added, moved or removed.
+		</constant>
 		<constant name="NOTIFICATION_INTERNAL_PROCESS" value="25">
 			Notification received every frame when the internal process flag is set (see [method set_process_internal]).
 		</constant>

scene/2d/node_2d.cpp

@@ -385,9 +385,14 @@ Point2 Node2D::to_global(Point2 p_local) const {
 
 void Node2D::_notification(int p_notification) {
 	switch (p_notification) {
-		case NOTIFICATION_MOVED_IN_PARENT: {
+		case NOTIFICATION_ENTER_TREE: {
 			if (get_viewport()) {
-				get_viewport()->gui_set_root_order_dirty();
+				get_parent()->connect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::gui_set_root_order_dirty), CONNECT_REFERENCE_COUNTED);
+			}
+		} break;
+		case NOTIFICATION_EXIT_TREE: {
+			if (get_viewport()) {
+				get_parent()->disconnect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::gui_set_root_order_dirty));
 			}
 		} break;
 	}

scene/2d/skeleton_2d.cpp

@@ -115,6 +115,7 @@ void Bone2D::_notification(int p_what) {
 				bone.bone = this;
 				skeleton->bones.push_back(bone);
 				skeleton->_make_bone_setup_dirty();
+				get_parent()->connect(SNAME("child_order_changed"), callable_mp(skeleton, &Skeleton2D::_make_bone_setup_dirty), CONNECT_REFERENCE_COUNTED);
 			}
 
 			cache_transform = get_transform();
@@ -154,15 +155,6 @@ void Bone2D::_notification(int p_what) {
 #endif // TOOLS_ENABLED
 		} break;
 
-		case NOTIFICATION_MOVED_IN_PARENT: {
-			if (skeleton) {
-				skeleton->_make_bone_setup_dirty();
-			}
-			if (copy_transform_to_cache) {
-				cache_transform = get_transform();
-			}
-		} break;
-
 		case NOTIFICATION_EXIT_TREE: {
 			if (skeleton) {
 				for (int i = 0; i < skeleton->bones.size(); i++) {
@@ -172,7 +164,7 @@ void Bone2D::_notification(int p_what) {
 					}
 				}
 				skeleton->_make_bone_setup_dirty();
-				skeleton = nullptr;
+				get_parent()->disconnect(SNAME("child_order_changed"), callable_mp(skeleton, &Skeleton2D::_make_bone_setup_dirty));
 			}
 			parent_bone = nullptr;
 			set_transform(cache_transform);

scene/gui/control.cpp

@@ -3021,6 +3021,8 @@ void Control::_notification(int p_notification) {
 				Viewport *viewport = get_viewport();
 				ERR_FAIL_COND(!viewport);
 				data.RI = viewport->_gui_add_root_control(this);
+
+				get_parent()->connect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::gui_set_root_order_dirty), CONNECT_REFERENCE_COUNTED);
 			}
 
 			data.parent_canvas_item = get_parent_item();
@@ -3049,24 +3051,17 @@ void Control::_notification(int p_notification) {
 			if (data.RI) {
 				get_viewport()->_gui_remove_root_control(data.RI);
 				data.RI = nullptr;
+				get_parent()->disconnect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::gui_set_root_order_dirty));
 			}
 
 			data.parent_canvas_item = nullptr;
 			data.is_rtl_dirty = true;
 		} break;
 
-		case NOTIFICATION_MOVED_IN_PARENT: {
+		case NOTIFICATION_CHILD_ORDER_CHANGED: {
 			// Some parents need to know the order of the children to draw (like TabContainer),
 			// so we update them just in case.
-			Control *parent_control = get_parent_control();
-			if (parent_control) {
-				parent_control->queue_redraw();
-			}
 			queue_redraw();
-
-			if (data.RI) {
-				get_viewport()->gui_set_root_order_dirty();
-			}
 		} break;
 
 		case NOTIFICATION_RESIZED: {

scene/main/canvas_item.cpp

@@ -188,10 +188,13 @@ void CanvasItem::_enter_canvas() {
 	// Resolves to nullptr if the node is top_level.
 	CanvasItem *parent_item = get_parent_item();
 
+	if (get_parent()) {
+		get_viewport()->canvas_parent_mark_dirty(get_parent());
+	}
+
 	if (parent_item) {
 		canvas_layer = parent_item->canvas_layer;
 		RenderingServer::get_singleton()->canvas_item_set_parent(canvas_item, parent_item->get_canvas_item());
-		RenderingServer::get_singleton()->canvas_item_set_draw_index(canvas_item, get_index());
 		RenderingServer::get_singleton()->canvas_item_set_visibility_layer(canvas_item, visibility_layer);
 	} else {
 		Node *n = this;
@@ -227,8 +230,6 @@ void CanvasItem::_enter_canvas() {
 		} else {
 			get_viewport()->gui_reset_canvas_sort_index();
 		}
-
-		get_tree()->call_group_flags(SceneTree::GROUP_CALL_UNIQUE | SceneTree::GROUP_CALL_DEFERRED, canvas_group, SNAME("_top_level_raise_self"));
 	}
 
 	pending_update = false;
@@ -302,21 +303,12 @@ void CanvasItem::_notification(int p_what) {
 			if (!block_transform_notify && !xform_change.in_list()) {
 				get_tree()->xform_change_list.add(&xform_change);
 			}
-		} break;
 
-		case NOTIFICATION_MOVED_IN_PARENT: {
-			if (!is_inside_tree()) {
-				break;
+			if (get_viewport()) {
+				get_parent()->connect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::canvas_parent_mark_dirty).bind(get_parent()), CONNECT_REFERENCE_COUNTED);
 			}
 
-			if (canvas_group != StringName()) {
-				get_tree()->call_group_flags(SceneTree::GROUP_CALL_UNIQUE | SceneTree::GROUP_CALL_DEFERRED, canvas_group, "_top_level_raise_self");
-			} else {
-				ERR_FAIL_COND_MSG(!get_parent_item(), "Moved child is in incorrect state (no canvas group, no canvas item parent).");
-				RenderingServer::get_singleton()->canvas_item_set_draw_index(canvas_item, get_index());
-			}
 		} break;
-
 		case NOTIFICATION_EXIT_TREE: {
 			if (xform_change.in_list()) {
 				get_tree()->xform_change_list.remove(&xform_change);
@@ -332,6 +324,10 @@ void CanvasItem::_notification(int p_what) {
 			}
 			global_invalid = true;
 			parent_visible_in_tree = false;
+
+			if (get_viewport()) {
+				get_parent()->disconnect(SNAME("child_order_changed"), callable_mp(get_viewport(), &Viewport::canvas_parent_mark_dirty).bind(get_parent()));
+			}
 		} break;
 
 		case NOTIFICATION_VISIBILITY_CHANGED: {
@@ -340,6 +336,19 @@ void CanvasItem::_notification(int p_what) {
 	}
 }
 
+void CanvasItem::update_draw_order() {
+	if (!is_inside_tree()) {
+		return;
+	}
+
+	if (canvas_group != StringName()) {
+		get_tree()->call_group_flags(SceneTree::GROUP_CALL_UNIQUE | SceneTree::GROUP_CALL_DEFERRED, canvas_group, "_top_level_raise_self");
+	} else {
+		ERR_FAIL_COND_MSG(!get_parent_item(), "Moved child is in incorrect state (no canvas group, no canvas item parent).");
+		RenderingServer::get_singleton()->canvas_item_set_draw_index(canvas_item, get_index());
+	}
+}
+
 void CanvasItem::_window_visibility_changed() {
 	if (visible) {
 		_propagate_visibility_changed(window->is_visible());

scene/main/canvas_item.h

@@ -212,6 +212,8 @@ class CanvasItem : public Node {
 	virtual Transform2D _edit_get_transform() const;
 #endif
 
+	void update_draw_order();
+
 	/* VISIBILITY */
 
 	void set_visible(bool p_visible);

scene/main/canvas_layer.cpp

@@ -180,25 +180,30 @@ void CanvasLayer::_notification(int p_what) {
 			viewport = vp->get_viewport_rid();
 
 			RenderingServer::get_singleton()->viewport_attach_canvas(viewport, canvas);
-			RenderingServer::get_singleton()->viewport_set_canvas_stacking(viewport, canvas, layer, get_index());
 			RenderingServer::get_singleton()->viewport_set_canvas_transform(viewport, canvas, transform);
 			_update_follow_viewport();
+
+			if (vp) {
+				get_parent()->connect(SNAME("child_order_changed"), callable_mp(vp, &Viewport::canvas_parent_mark_dirty).bind(get_parent()), CONNECT_REFERENCE_COUNTED);
+				vp->canvas_parent_mark_dirty(get_parent());
+			}
 		} break;
 
 		case NOTIFICATION_EXIT_TREE: {
 			ERR_FAIL_NULL_MSG(vp, "Viewport is not initialized.");
+			get_parent()->disconnect(SNAME("child_order_changed"), callable_mp(vp, &Viewport::canvas_parent_mark_dirty).bind(get_parent()));
 
 			vp->_canvas_layer_remove(this);
 			RenderingServer::get_singleton()->viewport_remove_canvas(viewport, canvas);
 			viewport = RID();
 			_update_follow_viewport(false);
 		} break;
+	}
+}
 
-		case NOTIFICATION_MOVED_IN_PARENT: {
-			if (is_inside_tree()) {
-				RenderingServer::get_singleton()->viewport_set_canvas_stacking(viewport, canvas, layer, get_index());
-			}
-		} break;
+void CanvasLayer::update_draw_order() {
+	if (is_inside_tree()) {
+		RenderingServer::get_singleton()->viewport_set_canvas_stacking(viewport, canvas, layer, get_index());
 	}
 }
 

scene/main/canvas_layer.h

@@ -67,6 +67,8 @@ class CanvasLayer : public Node {
 	void _validate_property(PropertyInfo &p_property) const;
 
 public:
+	void update_draw_order();
+
 	void set_layer(int p_xform);
 	int get_layer() const;
 

scene/main/node.cpp

@@ -393,9 +393,9 @@ void Node::_move_child(Node *p_child, int p_index, bool p_ignore_end) {
 	}
 	// notification second
 	move_child_notify(p_child);
-	for (int i = motion_from; i <= motion_to; i++) {
-		data.children[i]->notification(NOTIFICATION_MOVED_IN_PARENT);
-	}
+	notification(NOTIFICATION_CHILD_ORDER_CHANGED);
+	emit_signal(SNAME("child_order_changed"));
+
 	p_child->_propagate_groups_dirty();
 
 	data.blocked--;
@@ -1124,6 +1124,8 @@ void Node::_add_child_nocheck(Node *p_child, const StringName &p_name) {
 	//recognize children created in this node constructor
 	p_child->data.parent_owned = data.in_constructor;
 	add_child_notify(p_child);
+	notification(NOTIFICATION_CHILD_ORDER_CHANGED);
+	emit_signal(SNAME("child_order_changed"));
 }
 
 void Node::add_child(Node *p_child, bool p_force_readable_name, InternalMode p_internal) {
@@ -1213,10 +1215,8 @@ void Node::remove_child(Node *p_child) {
 	child_count = data.children.size();
 	children = data.children.ptrw();
 
-	for (int i = idx; i < child_count; i++) {
-		children[i]->data.index = i;
-		children[i]->notification(NOTIFICATION_MOVED_IN_PARENT);
-	}
+	notification(NOTIFICATION_CHILD_ORDER_CHANGED);
+	emit_signal(SNAME("child_order_changed"));
 
 	p_child->data.parent = nullptr;
 	p_child->data.index = -1;
@@ -2974,6 +2974,7 @@ void Node::_bind_methods() {
 	BIND_CONSTANT(NOTIFICATION_DRAG_BEGIN);
 	BIND_CONSTANT(NOTIFICATION_DRAG_END);
 	BIND_CONSTANT(NOTIFICATION_PATH_RENAMED);
+	BIND_CONSTANT(NOTIFICATION_CHILD_ORDER_CHANGED);
 	BIND_CONSTANT(NOTIFICATION_INTERNAL_PROCESS);
 	BIND_CONSTANT(NOTIFICATION_INTERNAL_PHYSICS_PROCESS);
 	BIND_CONSTANT(NOTIFICATION_POST_ENTER_TREE);
@@ -3027,6 +3028,7 @@ void Node::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("tree_exited"));
 	ADD_SIGNAL(MethodInfo("child_entered_tree", PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT, "Node")));
 	ADD_SIGNAL(MethodInfo("child_exiting_tree", PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT, "Node")));
+	ADD_SIGNAL(MethodInfo("child_order_changed"));
 
 	ADD_PROPERTY(PropertyInfo(Variant::STRING_NAME, "name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NONE), "set_name", "get_name");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "unique_name_in_owner", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR), "set_unique_name_in_owner", "is_unique_name_in_owner");

scene/main/node.h

@@ -264,7 +264,7 @@ class Node : public Object {
 		NOTIFICATION_DRAG_BEGIN = 21,
 		NOTIFICATION_DRAG_END = 22,
 		NOTIFICATION_PATH_RENAMED = 23,
-		//NOTIFICATION_TRANSLATION_CHANGED = 24, moved below
+		NOTIFICATION_CHILD_ORDER_CHANGED = 24,
 		NOTIFICATION_INTERNAL_PROCESS = 25,
 		NOTIFICATION_INTERNAL_PHYSICS_PROCESS = 26,
 		NOTIFICATION_POST_ENTER_TREE = 27,

scene/main/viewport.cpp

@@ -165,6 +165,31 @@ ViewportTexture::~ViewportTexture() {
 	}
 }
 
+void Viewport::_process_dirty_canvas_parent_orders() {
+	for (const ObjectID &id : gui.canvas_parents_with_dirty_order) {
+		Object *obj = ObjectDB::get_instance(id);
+		if (!obj) {
+			continue; // May have been deleted.
+		}
+
+		Node *n = static_cast<Node *>(obj);
+		for (int i = 0; i < n->get_child_count(); i++) {
+			Node *c = n->get_child(i);
+			CanvasItem *ci = Object::cast_to<CanvasItem>(c);
+			if (ci) {
+				ci->update_draw_order();
+				continue;
+			}
+			CanvasLayer *cl = Object::cast_to<CanvasLayer>(c);
+			if (cl) {
+				cl->update_draw_order();
+			}
+		}
+	}
+
+	gui.canvas_parents_with_dirty_order.clear();
+}
+
 void Viewport::_sub_window_update_order() {
 	if (gui.sub_windows.size() < 2) {
 		return;
@@ -929,6 +954,14 @@ Rect2 Viewport::get_visible_rect() const {
 	return r;
 }
 
+void Viewport::canvas_parent_mark_dirty(Node *p_node) {
+	bool request_update = gui.canvas_parents_with_dirty_order.is_empty();
+	gui.canvas_parents_with_dirty_order.insert(p_node->get_instance_id());
+	if (request_update) {
+		MessageQueue::get_singleton()->push_callable(callable_mp(this, &Viewport::_process_dirty_canvas_parent_orders));
+	}
+}
+
 void Viewport::_update_audio_listener_2d() {
 	if (AudioServer::get_singleton()) {
 		AudioServer::get_singleton()->notify_listener_changed();

scene/main/viewport.h

@@ -376,6 +376,7 @@ class Viewport : public Node {
 		double tooltip_delay = 0.0;
 		bool roots_order_dirty = false;
 		List<Control *> roots;
+		HashSet<ObjectID> canvas_parents_with_dirty_order;
 		int canvas_sort_index = 0; //for sorting items with canvas as root
 		bool dragging = false;
 		bool drag_successful = false;
@@ -468,6 +469,8 @@ class Viewport : public Node {
 	virtual bool _can_consume_input_events() const { return true; }
 	uint64_t event_count = 0;
 
+	void _process_dirty_canvas_parent_orders();
+
 protected:
 	void _set_size(const Size2i &p_size, const Size2i &p_size_2d_override, bool p_allocated);
 
@@ -480,6 +483,8 @@ class Viewport : public Node {
 	static void _bind_methods();
 
 public:
+	void canvas_parent_mark_dirty(Node *p_node);
+
 	uint64_t get_processed_events_count() const { return event_count; }
 
 	AudioListener2D *get_audio_listener_2d() const;