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

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.fromLTWH(double left, double top, double width, double height) {
+    _value
+      ..[0] = left
+      ..[1] = top
+      ..[2] = left + width
+      ..[3] = top + height;
+  }
+
   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) {
@@ skipping 27 matching lines @@
       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)";
 }