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

sky/sdk/lib/example/rendering/sector_layout.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.
 
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/sky_binding.dart';
@@ skipping 108 matching lines @@
 
   BoxDecoration _decoration;
   BoxDecoration get decoration => _decoration;
   void set decoration (BoxDecoration value) {
     if (value == _decoration)
       return;
     _decoration = value;
     markNeedsPaint();
   }
 
-  // origin must be set to the center of the circle
-  void paint(RenderCanvas canvas) {
+  // offset must point to the center of the circle
+  void paint(RenderCanvas canvas, Offset offset) {
     assert(deltaRadius != null);
     assert(deltaTheta != null);
     assert(parentData is SectorParentData);
 
     if (_decoration == null)
       return;
 
     if (_decoration.backgroundColor != null) {
       Paint paint = new Paint()..color = _decoration.backgroundColor;
       Path path = new Path();
       double outerRadius = (parentData.radius + deltaRadius);
-      Rect outerBounds = new Rect.fromLTRB(-outerRadius, -outerRadius, outerRadius, outerRadius);
+      Rect outerBounds = new Rect.fromLTRB(offset.dx-outerRadius, offset.dy-outerRadius, offset.dx+outerRadius, offset.dy+outerRadius);
       path.arcTo(outerBounds, parentData.theta, deltaTheta, true);
       double innerRadius = parentData.radius;
-      Rect innerBounds = new Rect.fromLTRB(-innerRadius, -innerRadius, innerRadius, innerRadius);
+      Rect innerBounds = new Rect.fromLTRB(offset.dx-innerRadius, offset.dy-innerRadius, offset.dx+innerRadius, offset.dy+innerRadius);
       path.arcTo(innerBounds, parentData.theta + deltaTheta, -deltaTheta, false);
       path.close();
       canvas.drawPath(path, paint);
     }
   }
 
 }
 
 class SectorChildListParentData extends SectorParentData with ContainerParentDataMixin<RenderSector> { }
 
@@ skipping 99 matching lines @@
       assert(child.parentData is SectorChildListParentData);
       child = child.parentData.nextSibling;
       if (child != null) {
         innerTheta += paddingTheta;
         remainingDeltaTheta -= paddingTheta;
       }
     }
     deltaTheta = innerTheta;
   }
 
-  // paint origin is 0,0 of our circle
+  // offset must point to the center of our circle
   // each sector then knows how to paint itself at its location
-  void paint(RenderCanvas canvas) {
+  void paint(RenderCanvas canvas, Offset offset) {
     // TODO(ianh): avoid code duplication
-    super.paint(canvas);
+    super.paint(canvas, offset);
     RenderSector child = firstChild;
     while (child != null) {
       assert(child.parentData is SectorChildListParentData);
-      canvas.paintChild(child, Point.origin);
+      canvas.paintChild(child, offset.toPoint());
       child = child.parentData.nextSibling;
     }
   }
 
 }
 
 class RenderSectorSlice extends RenderSectorWithChildren {
   // lays out RenderSector children in a stack
 
   RenderSectorSlice({
@@ skipping 76 matching lines @@
       childRadius += child.deltaRadius;
       remainingDeltaRadius -= child.deltaRadius;
       assert(child.parentData is SectorChildListParentData);
       child = child.parentData.nextSibling;
       childRadius += padding;
       remainingDeltaRadius -= padding;
     }
     deltaRadius = childRadius - this.parentData.radius;
   }
 
-  // paint origin is 0,0 of our circle
+  // offset must point to the center of our circle
   // each sector then knows how to paint itself at its location
-  void paint(RenderCanvas canvas) {
+  void paint(RenderCanvas canvas, Offset offset) {
     // TODO(ianh): avoid code duplication
-    super.paint(canvas);
+    super.paint(canvas, offset);
     RenderSector child = firstChild;
     while (child != null) {
       assert(child.parentData is SectorChildListParentData);
-      canvas.paintChild(child, Point.origin);
+      canvas.paintChild(child, offset.toPoint());
       child = child.parentData.nextSibling;
     }
   }
 
 }
 
 class RenderBoxToRenderSectorAdapter extends RenderBox {
 
   RenderBoxToRenderSectorAdapter({ double innerRadius: 0.0, RenderSector child }) :
     _innerRadius = innerRadius {
@@ skipping 66 matching lines @@
       double maxChildDeltaRadius = math.min(constraints.maxWidth, constraints.maxHeight) / 2.0 - innerRadius;
       assert(child.parentData is SectorParentData);
       child.parentData.radius = innerRadius;
       child.parentData.theta = 0.0;
       child.layout(new SectorConstraints(maxDeltaRadius: maxChildDeltaRadius), parentUsesSize: true);
       double dimension = (innerRadius + child.deltaRadius) * 2.0;
       size = constraints.constrain(new Size(dimension, dimension));
     }
   }
 
-  // paint origin is 0,0 of our circle
-  void paint(RenderCanvas canvas) {
-    super.paint(canvas);
+  void paint(RenderCanvas canvas, Offset offset) {
+    super.paint(canvas, offset);
     if (child != null) {
-      Rect bounds = new Rect.fromSize(size);
+      Rect bounds = offset + size;
+      // we move the offset to the center of the circle for the RenderSectors
       canvas.paintChild(child, bounds.center);
     }
   }
 
   bool hitTest(HitTestResult result, { Point position }) {
     double x = position.x;
     double y = position.y;
     if (child == null)
       return false;
     // translate to our origin
@@ skipping 51 matching lines @@
   stack.add(new RenderSolidColor(const Color(0xFFFFFF00), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFFFF9000), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFF00FF00)));
   rootCircle.add(stack);
   return new RenderBoxToRenderSectorAdapter(innerRadius: 50.0, child: rootCircle);
 }
 
 void main() {
   new SkyBinding(root: buildSectorExample());
 }