Fixes matrix transformations in sprites

sky/examples/game/lib/node_with_size.dart

+part of sprites;
+
+abstract class NodeWithSize extends Node {
+  Size size;
+  Point pivot;
+
+  NodeWithSize() {
+    size = new Size(0.0, 0.0);
+    pivot = new Point(0.0, 0.0);

[abarth-chromium, 2015/06/11 00:20:20]

Size.zero
Point.origin

+  }
+
+  NodeWithSize.withSize(Size size, [Point pivot]);
+
+  void applyTransformForPivot(PictureRecorder canvas) {
+    if (pivot.x != 0 || pivot.y != 0) {
+      double pivotInPointsX = size.width * pivot.x;
+      double pivotInPointsY = size.height * pivot.y;
+      canvas.translate(-pivotInPointsX, -pivotInPointsY);
+    }
+  }
+
+  bool hitTest (Point nodePoint) {
+
+    double minX = -size.width * pivot.x;
+    double minY = -size.height * pivot.y;
+    double maxX = minX + size.width;
+    double maxY = minY + size.height;
+    return (nodePoint.x >= minX && nodePoint.x < maxX &&
+            nodePoint.y >= minY && nodePoint.y < maxY);
+  }
+}