Optimizes sprite performance by minimizing the number of calls to action controllers

packages/flutter/example/game/lib/node.dart

@@ -65,6 +65,7 @@ class Node {
   ActionController get actions {
     if (_actions == null) {
       _actions = new ActionController();
+      if (_spriteBox != null) _spriteBox._actionControllers = null;
     }
     return _actions;
   }
@@ -201,7 +202,7 @@ class Node {
     child._spriteBox = this._spriteBox;
     _childrenLastAddedOrder += 1;
     child._addedOrder = _childrenLastAddedOrder;
-    if (_spriteBox != null) _spriteBox._eventTargets = null;
+    if (_spriteBox != null) _spriteBox._registerNode(child);
   }
 
   /// Removes a child from this node.
@@ -212,7 +213,7 @@ class Node {
     if (_children.remove(child)) {
       child._parent = null;
       child._spriteBox = null;
-      if (_spriteBox != null) _spriteBox._eventTargets = null;
+      if (_spriteBox != null) _spriteBox._deregisterNode(child);
     }
   }
 
@@ -234,7 +235,7 @@ class Node {
     }
     _children = [];
     _childrenNeedSorting = false;
-    if (_spriteBox != null) _spriteBox._eventTargets = null;
+    if (_spriteBox != null) _spriteBox._deregisterNode(null);
   }
 
   void _sortChildren() {

packages/flutter/example/game/lib/sprite_box.dart

@@ -71,6 +71,8 @@ class SpriteBox extends RenderBox {
 
   List<Node> _eventTargets;
 
+  List<ActionController> _actionControllers;
+
   Rect _visibleArea;
 
   Rect get visibleArea {
@@ -131,6 +133,18 @@ class SpriteBox extends RenderBox {
     _callSpriteBoxPerformedLayout(_rootNode);
   }
 
+  // Adding and removing nodes
+
+  _registerNode(Node node) {
+    _actionControllers = null;
+    _eventTargets = null;
+  }
+
+  _deregisterNode(Node node) {
+    _actionControllers = null;
+    _eventTargets = null;
+  }
+
   // Event handling
 
   void _addEventTargets(Node node, List<Node> eventTargets) {
@@ -342,19 +356,32 @@ class SpriteBox extends RenderBox {
     // if (_numFrames % 60 == 0)
     //   print("delta: $delta fps: $_frameRate");
 
-    _runActions(_rootNode, delta);
+    _runActions(delta);
     _callUpdate(_rootNode, delta);
+
+    // Schedule next update
     _scheduleTick();
+
+    // Make sure the node graph is redrawn
     markNeedsPaint();
   }
 
-  void _runActions(Node node, double dt) {
-    if (node._actions != null) {
-      node._actions.step(dt);
+  void _runActions(double dt) {
+    if (_actionControllers == null) {
+      _actionControllers = [];
+      _addActionControllers(_rootNode, _actionControllers);
+    }
+    for (ActionController actions in _actionControllers) {
+      actions.step(dt);
     }
+  }
+
+  void _addActionControllers(Node node, List<ActionController> controllers) {
+    if (node._actions != null) controllers.add(node._actions);
+
     for (int i = node.children.length - 1; i >= 0; i--) {
       Node child = node.children[i];
-      _runActions(child, dt);
+      _addActionControllers(child, controllers);
     }
   }