Expose Node child manipulation callbacks

Corrected Control's not calling base child_notify methods

Corrected Window not calling base child_notify methods

doc/classes/Node.xml

@@ -22,6 +22,14 @@
 		<link title="All Demos">https://github.com/godotengine/godot-demo-projects/</link>
 	</tutorials>
 	<methods>
+		<method name="_add_child_notify" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="child" type="Node" />
+			<description>
+				Called after a node is added as a child.
+				[b]Note:[/b] This method is called on application start for every node already in the tree as well.
+			</description>
+		</method>
 		<method name="_enter_tree" qualifiers="virtual">
 			<return type="void" />
 			<description>
@@ -55,6 +63,13 @@
 				[b]Note:[/b] This method is only called if the node is present in the scene tree (i.e. if it's not an orphan).
 			</description>
 		</method>
+		<method name="_move_child_notify" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="child" type="Node" />
+			<description>
+				Called after a child is moved within the node.
+			</description>
+		</method>
 		<method name="_physics_process" qualifiers="virtual">
 			<return type="void" />
 			<param index="0" name="delta" type="float" />
@@ -84,6 +99,13 @@
 				[b]Note:[/b] [method _ready] may be called only once for each node. After removing a node from the scene tree and adding it again, [code]_ready[/code] will not be called a second time. This can be bypassed by requesting another call with [method request_ready], which may be called anywhere before adding the node again.
 			</description>
 		</method>
+		<method name="_remove_child_notify" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="child" type="Node" />
+			<description>
+				Called when a child is removed within the node.
+			</description>
+		</method>
 		<method name="_shortcut_input" qualifiers="virtual">
 			<return type="void" />
 			<param index="0" name="event" type="InputEvent" />

scene/main/node.cpp

@@ -411,15 +411,18 @@ void Node::_propagate_groups_dirty() {
 }
 
 void Node::add_child_notify(Node *p_child) {
-	// to be used when not wanted
+	// Called when a node is added as a child to this one.
+	GDVIRTUAL_CALL(_add_child_notify, p_child);
 }
 
 void Node::remove_child_notify(Node *p_child) {
-	// to be used when not wanted
+	// Called when a child is removed from this node.
+	GDVIRTUAL_CALL(_remove_child_notify, p_child);
 }
 
 void Node::move_child_notify(Node *p_child) {
-	// to be used when not wanted
+	// Called when a child is moved inside this node.
+	GDVIRTUAL_CALL(_move_child_notify, p_child);
 }
 
 void Node::owner_changed_notify() {
@@ -2956,6 +2959,9 @@ void Node::_bind_methods() {
 	GDVIRTUAL_BIND(_shortcut_input, "event");
 	GDVIRTUAL_BIND(_unhandled_input, "event");
 	GDVIRTUAL_BIND(_unhandled_key_input, "event");
+	GDVIRTUAL_BIND(_add_child_notify, "child");
+	GDVIRTUAL_BIND(_remove_child_notify, "child");
+	GDVIRTUAL_BIND(_move_child_notify, "child");
 }
 
 String Node::_get_name_num_separator() {

scene/main/node.h

@@ -246,6 +246,10 @@ protected:
 	GDVIRTUAL1(_unhandled_input, Ref<InputEvent>)
 	GDVIRTUAL1(_unhandled_key_input, Ref<InputEvent>)
 
+	GDVIRTUAL1(_add_child_notify, Node *)
+	GDVIRTUAL1(_remove_child_notify, Node *)
+	GDVIRTUAL1(_move_child_notify, Node *)
+
 public:
 	enum {
 		// you can make your own, but don't use the same numbers as other notifications in other nodes

scene/main/window.cpp

@@ -1284,12 +1284,16 @@ Rect2i Window::get_usable_parent_rect() const {
 }
 
 void Window::add_child_notify(Node *p_child) {
+	Viewport::add_child_notify(p_child);
+
 	if (is_inside_tree() && wrap_controls) {
 		child_controls_changed();
 	}
 }
 
 void Window::remove_child_notify(Node *p_child) {
+	Viewport::remove_child_notify(p_child);
+
 	if (is_inside_tree() && wrap_controls) {
 		child_controls_changed();
 	}