Instead of applying a transform for every RenderObject, pass down an Offset for where to paint.

sky/engine/core/painting/Offset.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 a 2D floating-point offset.
 /// Think of this as a vector from an unspecified point
 class Offset extends OffsetBase {
   const Offset(dx, dy) : super(dx, dy);
   Offset.copy(Offset source) : super(source.dx, source.dy);
 
   double get dx => _dx;
   double get dy => _dy;
 
   static const Offset zero = const Offset(0.0, 0.0);
   static const Offset infinite = const Offset(double.INFINITY, double.INFINITY);
 
   Offset scale(double scaleX, double scaleY) => new Offset(dx * scaleX, dy * scaleY);
 
   Offset operator -() => new Offset(-dx, -dy);
   Offset operator -(Offset other) => new Offset(dx - other.dx, dy - other.dy);
-  Offset operator +(Offset other) => new Offset(dx + other.dx, dy + other.dy);
+  dynamic operator +(dynamic other) {
+    if (other is Offset)
+      return new Offset(dx + other.dx, dy + other.dy);
+    if (other is Size)
+      return new Rect.fromLTWH(dx, dy, other.width, other.height);

[abarth-chromium, 2015/06/27 00:39:37]

Wow, an offset + a size is a rect?  Crazy.

+    throw new ArgumentError(other);
+  }
 
   // does the equivalent of "return new Point(0,0) + this"
   Point toPoint() => new Point(this.dx, this.dy);
 
   String toString() => "Offset($dx, $dy)";
 }