Adds a child to this node.
The same node cannot be added to multiple nodes.
addChild(new Sprite(myImage));
Source
void addChild(Node child) { assert(child != null); assert(child._parent == null); assert(() { Node node = this; while (node.parent != null) node = node.parent; assert(node != child); // indicates we are about to create a cycle return true; }); _childrenNeedSorting = true; _children.add(child); child._parent = this; child._spriteBox = this._spriteBox; _childrenLastAddedOrder += 1; child._addedOrder = _childrenLastAddedOrder; if (_spriteBox != null) _spriteBox._registerNode(child); }