Short-circuit the relayoutSubtreeRoot when the child couldn't change dimensions anyway because the …

sky/examples/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';
 
 const double kTwoPi = 2 * math.PI;
 
-class SectorConstraints {
+class SectorConstraints extends Constraints {
   const SectorConstraints({
     this.minDeltaRadius: 0.0,
     this.maxDeltaRadius: double.INFINITY,
     this.minDeltaTheta: 0.0,
     this.maxDeltaTheta: kTwoPi
   });
 
   const SectorConstraints.tight({ double deltaRadius: 0.0, double deltaTheta: 0.0 })
     : minDeltaRadius = deltaRadius,
       maxDeltaRadius = deltaRadius,
       minDeltaTheta = deltaTheta,
       maxDeltaTheta = deltaTheta;
 
   final double minDeltaRadius;
   final double maxDeltaRadius;
   final double minDeltaTheta;
   final double maxDeltaTheta;
 
   double constrainDeltaRadius(double deltaRadius) {
     return clamp(min: minDeltaRadius, max: maxDeltaRadius, value: deltaRadius);
   }
 
   double constrainDeltaTheta(double deltaTheta) {
     return clamp(min: minDeltaTheta, max: maxDeltaTheta, value: deltaTheta);
   }
+
+  bool get isTight => minDeltaTheta >= maxDeltaTheta && minDeltaTheta >= maxDeltaTheta;
 }
 
 class SectorDimensions {
   const SectorDimensions({ this.deltaRadius: 0.0, this.deltaTheta: 0.0 });
 
   factory SectorDimensions.withConstraints(
     SectorConstraints constraints,
     { double deltaRadius: 0.0, double deltaTheta: 0.0 }
   ) {
     return new SectorDimensions(
@@ skipping 15 matching lines @@
 
   void setParentData(RenderObject child) {
     if (child.parentData is! SectorParentData)
       child.parentData = new SectorParentData();
   }
 
   SectorDimensions getIntrinsicDimensions(SectorConstraints constraints, double radius) {
     return new SectorDimensions.withConstraints(constraints);
   }
 
-  SectorConstraints get constraints { SectorConstraints result = super.constraints; return result; }
+  SectorConstraints get constraints => super.constraints;
   void performResize() {
     // default behaviour for subclasses that have sizedByParent = true
     deltaRadius = constraints.constrainDeltaRadius(0.0);
     deltaTheta = constraints.constrainDeltaTheta(0.0);
   }
   void performLayout() {
     // descendants have to either override performLayout() to set both
     // the dimensions and lay out children, or, set sizedByParent to
     // true so that performResize()'s logic above does its thing.
     assert(sizedByParent);
@@ skipping 432 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());
 }