Flesh out Rect/Point/Size classes in dart:sky

sky/engine/core/painting/Rect.dart

Index: sky/engine/core/painting/Rect.dart
diff --git a/sky/engine/core/painting/Rect.dart b/sky/engine/core/painting/Rect.dart
index cb2afec7d773e004e1ec77a276ea82dce7d6df77..be9cc9906d13175136798098f009cf2073056764 100644
--- a/sky/engine/core/painting/Rect.dart
+++ b/sky/engine/core/painting/Rect.dart
@@ -11,7 +11,38 @@ class Rect {
   double get right => _value[2];
   double get bottom => _value[3];
 
+  Rect() : new Float32List(4);
+
+  Rect.fromPointAndSize(Point point, Size size) {

[Hixie, 2015/05/28 17:20:11]

why isn't this a constructor?

+    _value = new Float32List(4)
+        ..[0] = point.x
+        ..[1] = point.y
+        ..[2] = point.x + size.width
+        ..[3] = point.y + size.height;
+  }
+
+  Rect.fromLTRB(double left, double top, double right, double bottom) {

[Hixie, 2015/05/28 17:20:11]

ditto

+    _value = new Float32List(4)
+        ..[0] = left
+        ..[1] = top
+        ..[2] = right
+        ..[3] = bottom;
+  }
+
+  Point get upperLeft => new Point(left, top);
+  Point get lowerRight => new Point(right, bottom);
+
+  Size get size => new Rect(right - left, bottom - top);

[Matt Perry, 2015/05/28 16:41:21]

new Size

+
+  // Rects are inclusive of the top and left edges but exclusive of the bottom
+  // right edges.
+  bool contains(Point point) => point.x >= left && point.x < right
+                             && point.y >= top && point.y < bottom;
+
   void setLTRB(double left, double top, double right, double bottom) {
-    _value = new Float32List.fromList([left, top, right, bottom]);
+    _value[0] = left
+        ..[1] = top
+        ..[2] = right
+        ..[3] = bottom;
   }
 }