Adds support for zOrder and references to parent nodes in sprites

sky/examples/game/lib/transform_node.dart

Index: sky/examples/game/lib/transform_node.dart
diff --git a/sky/examples/game/lib/transform_node.dart b/sky/examples/game/lib/transform_node.dart
index 199ca55f80719ce0d06f337c159b0415f1416fb5..07c08b6233dad84ed27b9996cfd719f4421f10a5 100644
--- a/sky/examples/game/lib/transform_node.dart
+++ b/sky/examples/game/lib/transform_node.dart
@@ -5,6 +5,12 @@ double degrees2radians(double degrees) => degrees * Math.PI/180.8;
 double radians2degrees(double radians) => radians * 180.0/Math.PI;
 
 class TransformNode {
+
+  // Member variables
+
+  SpriteBox _spriteBox;
+  TransformNode _parent;
+
   Vector2 _position;
   double _rotation;
   
@@ -14,11 +20,22 @@ class TransformNode {
   
   double _width;
   double _height;
+
+  double _scaleX;
+  double _scaleY;
   
   Vector2 _pivot;
-  
-  List<TransformNode>children;
-  
+
+  bool visible;
+
+  double _zPosition;
+  int _addedOrder;
+  int _childrenLastAddedOrder;
+  bool _childrenNeedSorting;
+
+  List<TransformNode>_children;
+
+  // Constructors
   
   TransformNode() {
     _width = 0.0;
@@ -26,11 +43,21 @@ class TransformNode {
     _rotation = 0.0;
     _pivot = new Vector2(0.0, 0.0);
     _position = new Vector2(0.0, 0.0);
+    _scaleX = _scaleY = 1.0;
     _isMatrixDirty = false;
     _transform = new Matrix3.identity();
     _pivotTransform = new Matrix3.identity();
-    children = [];
+    _children = [];
+    _childrenNeedSorting = false;
+    _childrenLastAddedOrder = 0;
+    visible = true;
   }
+
+  // Property setters and getters
+
+  SpriteBox get spriteBox => _spriteBox;
+
+  TransformNode get parent => _parent;
   
   double get rotation => _rotation;
   
@@ -38,8 +65,7 @@ class TransformNode {
     _rotation = rotation;
     _isMatrixDirty = true;
   }
-  
-  
+
   Vector2 get position => _position;
   
   void set position(Vector2 position) {
@@ -54,7 +80,6 @@ class TransformNode {
     _isMatrixDirty = true;
   }
   
-  
   double get height => _height;
     
   void set height(double height) {
@@ -68,7 +93,63 @@ class TransformNode {
     _pivot = pivot;
     _isMatrixDirty = true;
   }
-  
+
+  double get zPosition => _zPosition;
+
+  void set zPosition(double zPosition) {
+    _zPosition = zPosition;
+    if (_parent != null) {
+      _parent._childrenNeedSorting = true;
+    }
+  }
+
+  double get scale {
+    assert(_scaleX == _scaleY);
+    return _scaleX;
+  }
+
+  void set scale(double scale) {
+    _scaleX = _scaleY = scale;
+    _isMatrixDirty = true;
+  }
+
+  List<TransformNode> get children => _children;
+
+  // Adding and removing children
+
+  void addChild(TransformNode child) {
+    assert(child._parent == null);
+
+    _childrenNeedSorting = true;
+    _children.add(child);
+    child._parent = this;
+    child._spriteBox = this._spriteBox;
+    _childrenLastAddedOrder += 1;
+    child._addedOrder = _childrenLastAddedOrder;
+  }
+
+  void removeChild(TransformNode child) {
+    if (_children.remove(child)) {
+      child._parent = null;
+      child._spriteBox = null;
+    }
+  }
+
+  void removeFromParent() {
+    assert(_parent != null);
+    _parent.removeFromParent();
+  }
+
+  void removeAllChildren() {
+    for (TransformNode child in _children) {
+      child._parent = null;
+      child._spriteBox = null;
+    }
+    _children = [];
+    _childrenNeedSorting = false;
+  }
+
+  // Calculating the transformation matrix
   
   Matrix3 get transformMatrix {
     if (!_isMatrixDirty) {
@@ -111,8 +192,12 @@ class TransformNode {
     
     return _transform;
   }
+
+  // Rendering
   
   void visit(PictureRecorder canvas) {
+    if (!visible) return;
+
     prePaint(canvas);
     paint(canvas);
     visitChildren(canvas);
@@ -124,6 +209,7 @@ class TransformNode {
     
     canvas.translate(_position[0], _position[1]);
     canvas.rotate(degrees2radians(_rotation));
+    canvas.scale(_scaleX, _scaleY);
     canvas.translate(-_width*_pivot[0], -_height*_pivot[1]);
     
     // TODO: Use transformation matrix instead of individual calls
@@ -137,14 +223,33 @@ class TransformNode {
   }
  
   void visitChildren(PictureRecorder canvas) {
-    children.forEach((child) => child.visit(canvas));
+    // Sort children primarily by zPosition, secondarily by added order
+    if (_childrenNeedSorting) {
+      _children.sort((TransformNode a, TransformNode b) {
+        if (a._zPosition == b._zPosition) {
+          return b._addedOrder - a._addedOrder;
+        }
+        else if (a._zPosition > b._zPosition) {
+          return 1;
+        }
+        else {
+          return -1;
+        }
+      });
+      _childrenNeedSorting = false;
+    }
+
+    // Visit each child
+    _children.forEach((child) => child.visit(canvas));
   }
   
   void postPaint(PictureRecorder canvas) {
     canvas.restore();
   }
 
+  // Receiving update calls
+
   void update(double dt) {
 
   }
-}
+}