Split Size into Size and Offset.

sky/engine/core/painting/Rect.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 part of dart.sky;
 
 /// Holds 4 floating-point coordinates for a rectangle.
 class Rect {
   Rect();
 
   Rect.fromLTRB(double left, double top, double right, double bottom) {
     _value
       ..[0] = left
       ..[1] = top
       ..[2] = right
       ..[3] = bottom;
   }
 
   Rect.fromPointAndSize(Point point, Size size) {
     _value
       ..[0] = point.x
       ..[1] = point.y
       ..[2] = point.x + size.width
       ..[3] = point.y + size.height;
   }
 
+  // assumes top-left corner is at the origin (0,0)
   Rect.fromSize(Size size) {
     _value
       ..[2] = size.width
       ..[3] = size.height;
   }
 
   final Float32List _value = new Float32List(4);
   double get left => _value[0];
   double get top => _value[1];
   double get right => _value[2];
   double get bottom => _value[3];
 
-  Point get upperLeft => new Point(left, top);
-  Point get lowerRight => new Point(right, bottom);
   Point get center => new Point(left + right / 2.0, top + bottom / 2.0);
+  Point get topLeft => new Point(left, top);
+  Point get topRight => new Point(right, top);
+  Point get bottomLeft => new Point(left, bottom);
+  Point get bottomRight => new Point(right, bottom);
 
   Size get size => new Size(right - left, bottom - top);
 
   // Rects are inclusive of the top and left edges but exclusive of the bottom
   // right edges.
   bool contains(Point point) {
     return point.x >= left && point.x < right && point.y >= top && point.y < bottom;
   }
 
   bool operator ==(other) {
     if (other is! Rect)
       return false;
     for (var i = 0; i < 4; ++i) {
       if (_value[i] != other._value[i])
         return false;
     }
     return true;
   }
-
   int get hashCode =>_value.fold(373, (value, item) => (37 * value + item.hashCode));
   String toString() => "Rect.fromLTRB($left, $top, $right, $bottom)";
 }