Split Size into Size and Offset.

sky/examples/game/lib/sprite_box.dart

 part of sprites;
 
 /// Options for setting up a [SpriteBox].
 ///
 ///  * [nativePoints], use the same points as the parent [Widget].
 ///  * [letterbox], use the size of the root node for the coordinate system, constrain the aspect ratio and trim off
 ///  areas that end up outside the screen.
 ///  * [stretch], use the size of the root node for the coordinate system, scale it to fit the size of the box.
 ///  * [scaleToFit], similar to the letterbox option, but instead of trimming areas the sprite system will be scaled
 ///  down to fit the box.
@@ skipping 66 matching lines @@
   }
 
   // Properties
 
   /// The root node of the node tree that is rendered by this box.
   ///
   ///     var rootNode = mySpriteBox.rootNode;
   NodeWithSize get rootNode => _rootNode;
 
   void performLayout() {
-    size = constraints.constrain(Size.infinite);
+    size = constraints.biggest;
     _invalidateTransformMatrix();
     _callSpriteBoxPerformedLayout(_rootNode);
   }
 
   // Event handling
 
   void _addEventTargets(Node node, List<Node> eventTargets) {
     List children = node.children;
     int i = 0;
 
@@ skipping 273 matching lines @@
   ///
   ///     if (event.pointer == firstPointerId) {
   ///       // Do something
   ///     }
   final int pointer;
 
   /// Creates a new SpriteBoxEvent, typically this is done internally inside the SpriteBox.
   ///
   ///     var event = new SpriteBoxEvent(new Point(50.0, 50.0), 'pointerdown', 0);
   SpriteBoxEvent(this.boxPosition, this.type, this.pointer);
-}
+}