Merge pull request #684 from abarth/explode_box

Split box.dart into many files

examples/rendering/align_items.dart

@@ -9,6 +9,8 @@ import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 import 'solid_color_box.dart';

examples/rendering/baseline.dart

@@ -9,6 +9,8 @@ import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 RenderBox getBox(double lh) {

examples/rendering/borders.dart

@@ -6,6 +6,8 @@ import 'dart:sky' as sky;
 
 import 'package:sky/rendering/block.dart';
 import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 void main() {

examples/rendering/flex.dart

@@ -6,6 +6,8 @@ import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 class RenderSolidColor extends RenderDecoratedBox {

examples/rendering/interactive_flex.dart

@@ -8,10 +8,12 @@ import 'dart:math' as math;
 import 'package:sky/mojo/activity.dart' as activity;
 import 'package:sky/mojo/net/image_cache.dart' as image_cache;
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/image.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 import 'solid_color_box.dart';

examples/rendering/justify_content.dart

@@ -5,10 +5,11 @@
 import 'dart:sky';
 
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 import 'solid_color_box.dart';

examples/rendering/render_paragraph.dart

@@ -5,11 +5,11 @@
 import 'dart:sky';
 
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
 import 'package:sky/rendering/sky_binding.dart';
+import 'package:sky/rendering/proxy_box.dart';
 
 import 'solid_color_box.dart';
 

examples/rendering/sector_layout.dart

@@ -7,6 +7,7 @@ import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/proxy_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 const double kTwoPi = 2 * math.PI;

examples/rendering/shadowed_box.dart

@@ -4,7 +4,8 @@
 
 import 'dart:sky';
 
-import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/theme/colors.dart';
 import 'package:sky/theme/shadows.dart';

examples/rendering/simple_autolayout.dart

@@ -3,11 +3,12 @@
 // found in the LICENSE file.
 
 import 'dart:sky';
-import 'package:sky/rendering/box.dart';
+
+import 'package:cassowary/cassowary.dart' as al;
+import 'package:sky/rendering/auto_layout.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/proxy_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
-import 'package:sky/rendering/auto_layout.dart';
-import 'package:cassowary/cassowary.dart' as al;
 
 void main() {
   RenderDecoratedBox c1 = new RenderDecoratedBox(

examples/rendering/solid_color_box.dart

@@ -3,8 +3,10 @@
 // found in the LICENSE file.
 
 import 'dart:sky' as sky;
-import 'package:sky/rendering/object.dart';
+
 import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/proxy_box.dart';
 
 class RenderSolidColorBox extends RenderDecoratedBox {
   final Size desiredSize;

examples/rendering/spinning_flex.dart

@@ -5,8 +5,9 @@
 import 'dart:sky' as sky;
 
 import 'package:sky/base/scheduler.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:vector_math/vector_math.dart';
 

examples/rendering/transform.dart

@@ -6,6 +6,7 @@ import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/proxy_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:vector_math/vector_math.dart';
 

examples/stocks/lib/main.dart

@@ -9,7 +9,6 @@ import 'dart:sky' as sky;
 
 import 'package:sky/editing/input.dart';
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/theme/typography.dart' as typography;
 import 'package:sky/widgets.dart';

examples/widgets/container.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/widgets/raised_button.dart';
 import 'package:sky/widgets/basic.dart';

examples/widgets/ensure_visible.dart

@@ -8,7 +8,6 @@ import 'package:sky/animation/curves.dart';
 import 'package:sky/base/lerp.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/box.dart';
 import 'package:sky/theme/colors.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/block_viewport.dart';

examples/widgets/piano.dart

@@ -5,7 +5,6 @@
 import 'package:mojo/mojo/url_response.mojom.dart';
 import 'package:sky/mojo/net/fetch.dart';
 import 'package:sky/mojo/shell.dart' as shell;
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/widgets/basic.dart';

examples/widgets/spinning_mixed.dart

@@ -5,12 +5,13 @@
 import 'dart:sky' as sky;
 
 import 'package:sky/base/scheduler.dart' as scheduler;
-import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/widgets/basic.dart';
-import 'package:sky/widgets/raised_button.dart';
 import 'package:sky/widgets/framework.dart';
+import 'package:sky/widgets/raised_button.dart';
 import 'package:vector_math/vector_math.dart';
 
 import '../rendering/solid_color_box.dart';

packages/flutter/lib/rendering/box.dart

@@ -8,11 +8,9 @@ import 'dart:sky' as sky;
 import 'package:sky/base/debug.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/painting/text_style.dart';
-import 'package:sky/rendering/layer.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:vector_math/vector_math.dart';
 
-export 'package:sky/painting/box_painter.dart';
 export 'package:sky/painting/text_style.dart' show TextBaseline;
 
 // GENERIC BOX RENDERING
@@ -478,1265 +476,6 @@ abstract class RenderBox extends RenderObject {
   String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}size: ${size}\n';
 }
 
-class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
-
-  // ProxyBox assumes the child will be at 0,0 and will have the same size
-
-  RenderProxyBox([RenderBox child = null]) {
-    this.child = child;
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicWidth(constraints);
-    return super.getMinIntrinsicWidth(constraints);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicWidth(constraints);
-    return super.getMaxIntrinsicWidth(constraints);
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicHeight(constraints);
-    return super.getMinIntrinsicHeight(constraints);
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicHeight(constraints);
-    return super.getMaxIntrinsicHeight(constraints);
-  }
-
-  double computeDistanceToActualBaseline(TextBaseline baseline) {
-    if (child != null)
-      return child.getDistanceToActualBaseline(baseline);
-    return super.computeDistanceToActualBaseline(baseline);
-  }
-
-  void performLayout() {
-    if (child != null) {
-      child.layout(constraints, parentUsesSize: true);
-      size = child.size;
-    } else {
-      performResize();
-    }
-  }
-
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null)
-      child.hitTest(result, position: position);
-    else
-      super.hitTestChildren(result, position: position);
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null)
-      context.paintChild(child, offset.toPoint());
-  }
-}
-
-class RenderConstrainedBox extends RenderProxyBox {
-  RenderConstrainedBox({
-    RenderBox child,
-    BoxConstraints additionalConstraints
-  }) : super(child), _additionalConstraints = additionalConstraints {
-    assert(additionalConstraints != null);
-  }
-
-  BoxConstraints _additionalConstraints;
-  BoxConstraints get additionalConstraints => _additionalConstraints;
-  void set additionalConstraints (BoxConstraints value) {
-    assert(value != null);
-    if (_additionalConstraints == value)
-      return;
-    _additionalConstraints = value;
-    markNeedsLayout();
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicWidth(_additionalConstraints.apply(constraints));
-    return _additionalConstraints.apply(constraints).constrainWidth(0.0);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicWidth(_additionalConstraints.apply(constraints));
-    return _additionalConstraints.apply(constraints).constrainWidth(0.0);
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicHeight(_additionalConstraints.apply(constraints));
-    return _additionalConstraints.apply(constraints).constrainHeight(0.0);
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicHeight(_additionalConstraints.apply(constraints));
-    return _additionalConstraints.apply(constraints).constrainHeight(0.0);
-  }
-
-  void performLayout() {
-    if (child != null) {
-      child.layout(_additionalConstraints.apply(constraints), parentUsesSize: true);
-      size = child.size;
-    } else {
-      size = _additionalConstraints.apply(constraints).constrain(Size.zero);
-    }
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}additionalConstraints: ${additionalConstraints}\n';
-}
-
-class RenderAspectRatio extends RenderProxyBox {
-  RenderAspectRatio({
-    RenderBox child,
-    double aspectRatio
-  }) : super(child), _aspectRatio = aspectRatio {
-    assert(_aspectRatio != null);
-  }
-
-  double _aspectRatio;
-  double get aspectRatio => _aspectRatio;
-  void set aspectRatio (double value) {
-    assert(value != null);
-    if (_aspectRatio == value)
-      return;
-    _aspectRatio = value;
-    markNeedsLayout();
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    return _applyAspectRatio(constraints).height;
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    return _applyAspectRatio(constraints).height;
-  }
-
-  Size _applyAspectRatio(BoxConstraints constraints) {
-    double width = constraints.constrainWidth();
-    double height = constraints.constrainHeight(width / _aspectRatio);
-    return new Size(width, height);
-  }
-
-  bool get sizedByParent => true;
-
-  void performResize() {
-    size = _applyAspectRatio(constraints);
-  }
-
-  void performLayout() {
-    if (child != null)
-      child.layout(new BoxConstraints.tight(size));
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}aspectRatio: ${aspectRatio}\n';
-}
-
-class RenderShrinkWrapWidth extends RenderProxyBox {
-
-  // This class will attempt to size its child to the child's maximum
-  // intrinsic width, snapped to a multiple of the stepWidth, if one
-  // is provided, and given the provided constraints; and will then
-  // adopt the child's resulting dimensions.
-
-  // Note: laying out this class is relatively expensive. Avoid using
-  // it where possible.
-
-  RenderShrinkWrapWidth({
-    double stepWidth,
-    double stepHeight,
-    RenderBox child
-  }) : _stepWidth = stepWidth, _stepHeight = stepHeight, super(child);
-
-  double _stepWidth;
-  double get stepWidth => _stepWidth;
-  void set stepWidth(double value) {
-    if (value == _stepWidth)
-      return;
-    _stepWidth = value;
-    markNeedsLayout();
-  }
-
-  double _stepHeight;
-  double get stepHeight => _stepHeight;
-  void set stepHeight(double value) {
-    if (value == _stepHeight)
-      return;
-    _stepHeight = value;
-    markNeedsLayout();
-  }
-
-  static double applyStep(double input, double step) {
-    if (step == null)
-      return input;
-    return (input / step).ceil() * step;
-  }
-
-  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
-    if (constraints.hasTightWidth)
-      return constraints;
-    double width = child.getMaxIntrinsicWidth(constraints);
-    assert(width == constraints.constrainWidth(width));
-    return constraints.applyWidth(applyStep(width, _stepWidth));
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    return getMaxIntrinsicWidth(constraints);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    if (child == null)
-      return constraints.constrainWidth(0.0);
-    double childResult = child.getMaxIntrinsicWidth(constraints);
-    return constraints.constrainWidth(applyStep(childResult, _stepWidth));
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (child == null)
-      return constraints.constrainWidth(0.0);
-    double childResult = child.getMinIntrinsicHeight(_getInnerConstraints(constraints));
-    return constraints.constrainHeight(applyStep(childResult, _stepHeight));
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    if (child == null)
-      return constraints.constrainWidth(0.0);
-    double childResult = child.getMaxIntrinsicHeight(_getInnerConstraints(constraints));
-    return constraints.constrainHeight(applyStep(childResult, _stepHeight));
-  }
-
-  void performLayout() {
-    if (child != null) {
-      BoxConstraints childConstraints = _getInnerConstraints(constraints);
-      if (_stepHeight != null)
-        childConstraints.applyHeight(getMaxIntrinsicHeight(childConstraints));
-      child.layout(childConstraints, parentUsesSize: true);
-      size = child.size;
-    } else {
-      performResize();
-    }
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}stepWidth: ${stepWidth}\n${prefix}stepHeight: ${stepHeight}\n';
-
-}
-
-class RenderOpacity extends RenderProxyBox {
-  RenderOpacity({ RenderBox child, double opacity })
-    : this._opacity = opacity, super(child) {
-    assert(opacity >= 0.0 && opacity <= 1.0);
-  }
-
-  double _opacity;
-  double get opacity => _opacity;
-  void set opacity (double value) {
-    assert(value != null);
-    assert(value >= 0.0 && value <= 1.0);
-    if (_opacity == value)
-      return;
-    _opacity = value;
-    _cachedPaint = null;
-    markNeedsPaint();
-  }
-
-  int get _alpha => (_opacity * 255).round();
-
-  Paint _cachedPaint;
-  Paint get _paint {
-    if (_cachedPaint == null) {
-      _cachedPaint = new Paint()
-        ..color = new Color.fromARGB(_alpha, 0, 0, 0)
-        ..setTransferMode(sky.TransferMode.srcOver)
-        ..isAntiAlias = false;
-    }
-    return _cachedPaint;
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null) {
-      int a = _alpha;
-
-      if (a == 0)
-        return;
-
-      if (a == 255) {
-        context.paintChild(child, offset.toPoint());
-        return;
-      }
-
-      context.canvas.saveLayer(null, _paint); // TODO(abarth): layerize
-      context.paintChild(child, offset.toPoint());
-      context.canvas.restore();
-    }
-  }
-}
-
-class RenderColorFilter extends RenderProxyBox {
-  RenderColorFilter({ RenderBox child, Color color, sky.TransferMode transferMode })
-    : _color = color, _transferMode = transferMode, super(child) {
-  }
-
-  Color _color;
-  Color get color => _color;
-  void set color (Color value) {
-    assert(value != null);
-    if (_color == value)
-      return;
-    _color = value;
-    _cachedPaint = null;
-    markNeedsPaint();
-  }
-
-  sky.TransferMode _transferMode;
-  sky.TransferMode get transferMode => _transferMode;
-  void set transferMode (sky.TransferMode value) {
-    assert(value != null);
-    if (_transferMode == value)
-      return;
-    _transferMode = value;
-    _cachedPaint = null;
-    markNeedsPaint();
-  }
-
-  Paint _cachedPaint;
-  Paint get _paint {
-    if (_cachedPaint == null) {
-      _cachedPaint = new Paint()
-        ..setColorFilter(new sky.ColorFilter.mode(_color, _transferMode))
-        ..isAntiAlias = false;
-    }
-    return _cachedPaint;
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null) {
-      context.canvas.saveLayer(offset & size, _paint); // TODO(abarth): layerize
-      context.paintChild(child, offset.toPoint());
-      context.canvas.restore();
-    }
-  }
-}
-
-class RenderClipRect extends RenderProxyBox {
-  RenderClipRect({ RenderBox child }) : super(child);
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null)
-      context.paintChildWithClip(child, offset.toPoint(), Offset.zero & size);
-  }
-}
-
-class RenderClipRRect extends RenderProxyBox {
-  RenderClipRRect({ RenderBox child, double xRadius, double yRadius })
-    : _xRadius = xRadius, _yRadius = yRadius, super(child) {
-    assert(_xRadius != null);
-    assert(_yRadius != null);
-  }
-
-  double _xRadius;
-  double get xRadius => _xRadius;
-  void set xRadius (double value) {
-    assert(value != null);
-    if (_xRadius == value)
-      return;
-    _xRadius = value;
-    markNeedsPaint();
-  }
-
-  double _yRadius;
-  double get yRadius => _yRadius;
-  void set yRadius (double value) {
-    assert(value != null);
-    if (_yRadius == value)
-      return;
-    _yRadius = value;
-    markNeedsPaint();
-  }
-
-  final Paint _paint = new Paint()..isAntiAlias = false;
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null) {
-      Rect rect = offset & size;
-      context.canvas.saveLayer(rect, _paint); // TODO(abarth): layerize
-      sky.RRect rrect = new sky.RRect()..setRectXY(rect, xRadius, yRadius);
-      context.canvas.clipRRect(rrect);
-      context.paintChild(child, offset.toPoint());
-      context.canvas.restore();
-    }
-  }
-}
-
-class RenderClipOval extends RenderProxyBox {
-  RenderClipOval({ RenderBox child }) : super(child);
-
-  final Paint _paint = new Paint()..isAntiAlias = false;
-
-  Rect _cachedRect;
-  Path _cachedPath;
-
-  Path _getPath(Rect rect) {
-    if (rect != _cachedRect) {
-      _cachedRect = rect;
-      _cachedPath = new Path()..addOval(_cachedRect);
-    }
-    return _cachedPath;
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null) {
-      Rect rect = offset & size;
-      context.canvas.saveLayer(rect, _paint); // TODO(abarth): layerize
-      context.canvas.clipPath(_getPath(rect));
-      context.paintChild(child, offset.toPoint());
-      context.canvas.restore();
-    }
-  }
-}
-
-abstract class RenderShiftedBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
-
-  // Abstract class for one-child-layout render boxes
-
-  RenderShiftedBox(RenderBox child) {
-    this.child = child;
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicWidth(constraints);
-    return super.getMinIntrinsicWidth(constraints);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicWidth(constraints);
-    return super.getMaxIntrinsicWidth(constraints);
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicHeight(constraints);
-    return super.getMinIntrinsicHeight(constraints);
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicHeight(constraints);
-    return super.getMaxIntrinsicHeight(constraints);
-  }
-
-  double computeDistanceToActualBaseline(TextBaseline baseline) {
-    double result;
-    if (child != null) {
-      assert(!needsLayout);
-      result = child.getDistanceToActualBaseline(baseline);
-      assert(child.parentData is BoxParentData);
-      if (result != null)
-        result += child.parentData.position.y;
-    } else {
-      result = super.computeDistanceToActualBaseline(baseline);
-    }
-    return result;
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null)
-      context.paintChild(child, child.parentData.position + offset);
-  }
-
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null) {
-      assert(child.parentData is BoxParentData);
-      child.hitTest(result, position: new Point(position.x - child.parentData.position.x,
-                                                position.y - child.parentData.position.y));
-    }
-  }
-
-}
-
-class RenderPadding extends RenderShiftedBox {
-
-  RenderPadding({ EdgeDims padding, RenderBox child }) : super(child) {
-    assert(padding != null);
-    this.padding = padding;
-  }
-
-  EdgeDims _padding;
-  EdgeDims get padding => _padding;
-  void set padding (EdgeDims value) {
-    assert(value != null);
-    if (_padding == value)
-      return;
-    _padding = value;
-    markNeedsLayout();
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    double totalPadding = padding.left + padding.right;
-    if (child != null)
-      return child.getMinIntrinsicWidth(constraints.deflate(padding)) + totalPadding;
-    return constraints.constrainWidth(totalPadding);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    double totalPadding = padding.left + padding.right;
-    if (child != null)
-      return child.getMaxIntrinsicWidth(constraints.deflate(padding)) + totalPadding;
-    return constraints.constrainWidth(totalPadding);
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    double totalPadding = padding.top + padding.bottom;
-    if (child != null)
-      return child.getMinIntrinsicHeight(constraints.deflate(padding)) + totalPadding;
-    return constraints.constrainHeight(totalPadding);
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    double totalPadding = padding.top + padding.bottom;
-    if (child != null)
-      return child.getMaxIntrinsicHeight(constraints.deflate(padding)) + totalPadding;
-    return constraints.constrainHeight(totalPadding);
-  }
-
-  void performLayout() {
-    assert(padding != null);
-    if (child == null) {
-      size = constraints.constrain(new Size(
-        padding.left + padding.right,
-        padding.top + padding.bottom
-      ));
-      return;
-    }
-    BoxConstraints innerConstraints = constraints.deflate(padding);
-    child.layout(innerConstraints, parentUsesSize: true);
-    assert(child.parentData is BoxParentData);
-    child.parentData.position = new Point(padding.left, padding.top);
-    size = constraints.constrain(new Size(
-      padding.left + child.size.width + padding.right,
-      padding.top + child.size.height + padding.bottom
-    ));
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}padding: ${padding}\n';
-}
-
-class RenderPositionedBox extends RenderShiftedBox {
-
-  // This box aligns a child box within itself. It's only useful for
-  // children that don't always size to fit their parent. For example,
-  // to align a box at the bottom right, you would pass this box a
-  // tight constraint that is bigger than the child's natural size,
-  // with horizontal and vertical set to 1.0.
-
-  RenderPositionedBox({
-    RenderBox child,
-    double horizontal: 0.5,
-    double vertical: 0.5
-  }) : _horizontal = horizontal,
-       _vertical = vertical,
-       super(child) {
-    assert(horizontal != null);
-    assert(vertical != null);
-  }
-
-  double _horizontal;
-  double get horizontal => _horizontal;
-  void set horizontal (double value) {
-    assert(value != null);
-    if (_horizontal == value)
-      return;
-    _horizontal = value;
-    markNeedsLayout();
-  }
-
-  double _vertical;
-  double get vertical => _vertical;
-  void set vertical (double value) {
-    assert(value != null);
-    if (_vertical == value)
-      return;
-    _vertical = value;
-    markNeedsLayout();
-  }
-
-  void performLayout() {
-    if (child != null) {
-      child.layout(constraints.loosen(), parentUsesSize: true);
-      size = constraints.constrain(child.size);
-      assert(child.parentData is BoxParentData);
-      Offset delta = size - child.size;
-      child.parentData.position = (delta.scale(horizontal, vertical)).toPoint();
-    } else {
-      performResize();
-    }
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}horizontal: ${horizontal}\n${prefix}vertical: ${vertical}\n';
-}
-
-class RenderBaseline extends RenderShiftedBox {
-
-  RenderBaseline({
-    RenderBox child,
-    double baseline,
-    TextBaseline baselineType
-  }) : _baseline = baseline,
-       _baselineType = baselineType,
-       super(child) {
-    assert(baseline != null);
-    assert(baselineType != null);
-  }
-
-  double _baseline;
-  double get baseline => _baseline;
-  void set baseline (double value) {
-    assert(value != null);
-    if (_baseline == value)
-      return;
-    _baseline = value;
-    markNeedsLayout();
-  }
-
-  TextBaseline _baselineType;
-  TextBaseline get baselineType => _baselineType;
-  void set baselineType (TextBaseline value) {
-    assert(value != null);
-    if (_baselineType == value)
-      return;
-    _baselineType = value;
-    markNeedsLayout();
-  }
-
-  void performLayout() {
-    if (child != null) {
-      child.layout(constraints.loosen(), parentUsesSize: true);
-      size = constraints.constrain(child.size);
-      assert(child.parentData is BoxParentData);
-      double delta = baseline - child.getDistanceToBaseline(baselineType);
-      child.parentData.position = new Point(0.0, delta);
-    } else {
-      performResize();
-    }
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}baseline: ${baseline}\nbaselineType: ${baselineType}';
-}
-
-enum ScrollDirection { horizontal, vertical, both }
-
-class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
-
-  RenderViewport({
-    RenderBox child,
-    Offset scrollOffset,
-    ScrollDirection scrollDirection: ScrollDirection.vertical
-  }) : _scrollOffset = scrollOffset,
-       _scrollDirection = scrollDirection {
-    assert(_offsetIsSane(scrollOffset, scrollDirection));
-    this.child = child;
-  }
-
-  bool _offsetIsSane(Offset offset, ScrollDirection direction) {
-    switch (direction) {
-      case ScrollDirection.both:
-        return true;
-      case ScrollDirection.horizontal:
-        return offset.dy == 0.0;
-      case ScrollDirection.vertical:
-        return offset.dx == 0.0;
-    }
-  }
-
-  Offset _scrollOffset;
-  Offset get scrollOffset => _scrollOffset;
-  void set scrollOffset(Offset value) {
-    if (value == _scrollOffset)
-      return;
-    assert(_offsetIsSane(value, scrollDirection));
-    _scrollOffset = value;
-    markNeedsPaint();
-  }
-
-  ScrollDirection _scrollDirection;
-  ScrollDirection get scrollDirection => _scrollDirection;
-  void set scrollDirection(ScrollDirection value) {
-    if (value == _scrollDirection)
-      return;
-    assert(_offsetIsSane(scrollOffset, value));
-    _scrollDirection = value;
-    markNeedsLayout();
-  }
-
-  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
-    BoxConstraints innerConstraints;
-    switch (scrollDirection) {
-      case ScrollDirection.both:
-        innerConstraints = new BoxConstraints();
-        break;
-      case ScrollDirection.horizontal:
-        innerConstraints = constraints.heightConstraints();
-        break;
-      case ScrollDirection.vertical:
-        innerConstraints = constraints.widthConstraints();
-        break;
-    }
-    return innerConstraints;
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicWidth(_getInnerConstraints(constraints));
-    return super.getMinIntrinsicWidth(constraints);
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicWidth(_getInnerConstraints(constraints));
-    return super.getMaxIntrinsicWidth(constraints);
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMinIntrinsicHeight(_getInnerConstraints(constraints));
-    return super.getMinIntrinsicHeight(constraints);
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    if (child != null)
-      return child.getMaxIntrinsicHeight(_getInnerConstraints(constraints));
-    return super.getMaxIntrinsicHeight(constraints);
-  }
-
-  // We don't override computeDistanceToActualBaseline(), because we
-  // want the default behaviour (returning null). Otherwise, as you
-  // scroll the RenderViewport, it would shift in its parent if the
-  // parent was baseline-aligned, which makes no sense.
-
-  void performLayout() {
-    if (child != null) {
-      child.layout(_getInnerConstraints(constraints), parentUsesSize: true);
-      size = constraints.constrain(child.size);
-      assert(child.parentData is BoxParentData);
-      child.parentData.position = Point.origin;
-    } else {
-      performResize();
-    }
-  }
-
-  Offset get _scrollOffsetRoundedToIntegerDevicePixels {
-    double devicePixelRatio = sky.view.devicePixelRatio;
-    int dxInDevicePixels = (scrollOffset.dx * devicePixelRatio).round();
-    int dyInDevicePixels = (scrollOffset.dy * devicePixelRatio).round();
-    return new Offset(dxInDevicePixels / devicePixelRatio,
-                      dyInDevicePixels / devicePixelRatio);
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null) {
-      Offset roundedScrollOffset = _scrollOffsetRoundedToIntegerDevicePixels;
-      bool _needsClip = offset < Offset.zero ||
-                        !(offset & size).contains(((offset - roundedScrollOffset) & child.size).bottomRight);
-      if (_needsClip) {
-        context.canvas.save();
-        context.canvas.clipRect(offset & size);
-      }
-      context.paintChild(child, (offset - roundedScrollOffset).toPoint());
-      if (_needsClip)
-        context.canvas.restore();
-    }
-  }
-
-  void applyPaintTransform(Matrix4 transform) {
-    super.applyPaintTransform(transform);
-    transform.translate(-scrollOffset.dx, -scrollOffset.dy);
-  }
-
-  void hitTestChildren(HitTestResult result, { Point position }) {
-    if (child != null) {
-      assert(child.parentData is BoxParentData);
-      Point transformed = position + _scrollOffsetRoundedToIntegerDevicePixels;
-      child.hitTest(result, position: transformed);
-    }
-  }
-}
-
-class RenderImage extends RenderBox {
-  RenderImage({
-    sky.Image image,
-    double width,
-    double height,
-    sky.ColorFilter colorFilter,
-    fit: ImageFit.scaleDown,
-    repeat: ImageRepeat.noRepeat
-  }) : _image = image,
-      _width = width,
-      _height = height,
-      _colorFilter = colorFilter,
-      _fit = fit,
-      _repeat = repeat;
-
-  sky.Image _image;
-  sky.Image get image => _image;
-  void set image (sky.Image value) {
-    if (value == _image)
-      return;
-    _image = value;
-    markNeedsPaint();
-    if (_width == null || _height == null)
-      markNeedsLayout();
-  }
-
-  double _width;
-  double get width => _width;
-  void set width (double value) {
-    if (value == _width)
-      return;
-    _width = value;
-    markNeedsLayout();
-  }
-
-  double _height;
-  double get height => _height;
-  void set height (double value) {
-    if (value == _height)
-      return;
-    _height = value;
-    markNeedsLayout();
-  }
-
-  sky.ColorFilter _colorFilter;
-  sky.ColorFilter get colorFilter => _colorFilter;
-  void set colorFilter (sky.ColorFilter value) {
-    if (value == _colorFilter)
-      return;
-    _colorFilter = value;
-    markNeedsPaint();
-  }
-
-  ImageFit _fit;
-  ImageFit get fit => _fit;
-  void set fit (ImageFit value) {
-    if (value == _fit)
-      return;
-    _fit = value;
-    markNeedsPaint();
-  }
-
-  ImageRepeat _repeat;
-  ImageRepeat get repeat => _repeat;
-  void set repeat (ImageRepeat value) {
-    if (value == _repeat)
-      return;
-    _repeat = value;
-    markNeedsPaint();
-  }
-
-  Size _sizeForConstraints(BoxConstraints constraints) {
-    // Folds the given |width| and |height| into |cosntraints| so they can all
-    // be treated uniformly.
-    constraints = new BoxConstraints.tightFor(
-      width: _width,
-      height: _height
-    ).apply(constraints);
-
-    if (constraints.isTight || _image == null)
-      return constraints.smallest;
-
-    // This algorithm attempts to find a size for the RenderImage that fits in
-    // the given constraints and preserves the image's intrinisc aspect ratio.
-    // Its goals as follow:
-    //
-    //  - The dimensions of the RenderImage fit within the constraints.
-    //  - The aspect ratio of the RenderImage matches the instrinsic aspect
-    //    ratio of the image.
-    //  - The RenderImage's dimension are maximal subject to being smaller than
-    //    the intrinsic size of the image.
-
-    double width = _image.width.toDouble();
-    double height = _image.height.toDouble();
-    assert(width > 0.0);
-    assert(height > 0.0);
-    double aspectRatio = width / height;
-
-    if (width > constraints.maxWidth) {
-      width = constraints.maxWidth;
-      height = width / aspectRatio;
-    }
-
-    if (height > constraints.maxHeight) {
-      height = constraints.maxHeight;
-      width = height * aspectRatio;
-    }
-
-    if (width < constraints.minWidth) {
-      width = constraints.minWidth;
-      height = width / aspectRatio;
-    }
-
-    if (height < constraints.minHeight) {
-      height = constraints.minHeight;
-      width = height * aspectRatio;
-    }
-
-    return constraints.constrain(new Size(width, height));
-  }
-
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    if (_width == null && _height == null)
-      return constraints.constrainWidth(0.0);
-    return _sizeForConstraints(constraints).width;
-  }
-
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    return _sizeForConstraints(constraints).width;
-  }
-
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    if (_width == null && _height == null)
-      return constraints.constrainHeight(0.0);
-    return _sizeForConstraints(constraints).height;
-  }
-
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    return _sizeForConstraints(constraints).height;
-  }
-
-  void performLayout() {
-    size = _sizeForConstraints(constraints);
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (_image == null)
-      return;
-    paintImage(
-      canvas: context.canvas,
-      rect: offset & size,
-      image: _image,
-      colorFilter: _colorFilter,
-      fit: _fit,
-      repeat: _repeat
-    );
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}width: ${width}\n${prefix}height: ${height}\n';
-}
-
-class RenderDecoratedBox extends RenderProxyBox {
-
-  RenderDecoratedBox({
-    BoxDecoration decoration,
-    RenderBox child
-  }) : _painter = new BoxPainter(decoration), super(child);
-
-  final BoxPainter _painter;
-
-  BoxDecoration get decoration => _painter.decoration;
-  void set decoration (BoxDecoration value) {
-    assert(value != null);
-    if (value == _painter.decoration)
-      return;
-    _removeBackgroundImageListenerIfNeeded();
-    _painter.decoration = value;
-    _addBackgroundImageListenerIfNeeded();
-    markNeedsPaint();
-  }
-
-  bool get _needsBackgroundImageListener {
-    return attached &&
-        _painter.decoration != null &&
-        _painter.decoration.backgroundImage != null;
-  }
-
-  void _addBackgroundImageListenerIfNeeded() {
-    if (_needsBackgroundImageListener)
-      _painter.decoration.backgroundImage.addChangeListener(markNeedsPaint);
-  }
-
-  void _removeBackgroundImageListenerIfNeeded() {
-    if (_needsBackgroundImageListener)
-      _painter.decoration.backgroundImage.removeChangeListener(markNeedsPaint);
-  }
-
-  void attach() {
-    super.attach();
-    _addBackgroundImageListenerIfNeeded();
-  }
-
-  void detach() {
-    _removeBackgroundImageListenerIfNeeded();
-    super.detach();
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    assert(size.width != null);
-    assert(size.height != null);
-    _painter.paint(context.canvas, offset & size);
-    super.paint(context, offset);
-  }
-
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}decoration:\n${_painter.decoration.toString(prefix + "  ")}\n';
-}
-
-class RenderTransform extends RenderProxyBox {
-  RenderTransform({
-    Matrix4 transform,
-    RenderBox child
-  }) : super(child) {
-    assert(transform != null);
-    this.transform = transform;
-  }
-
-  Matrix4 _transform;
-
-  void set transform(Matrix4 value) {
-    assert(value != null);
-    if (_transform == value)
-      return;
-    _transform = new Matrix4.copy(value);
-    markNeedsPaint();
-  }
-
-  void setIdentity() {
-    _transform.setIdentity();
-    markNeedsPaint();
-  }
-
-  void rotateX(double radians) {
-    _transform.rotateX(radians);
-    markNeedsPaint();
-  }
-
-  void rotateY(double radians) {
-    _transform.rotateY(radians);
-    markNeedsPaint();
-  }
-
-  void rotateZ(double radians) {
-    _transform.rotateZ(radians);
-    markNeedsPaint();
-  }
-
-  void translate(x, [double y = 0.0, double z = 0.0]) {
-    _transform.translate(x, y, z);
-    markNeedsPaint();
-  }
-
-  void scale(x, [double y, double z]) {
-    _transform.scale(x, y, z);
-    markNeedsPaint();
-  }
-
-  bool hitTest(HitTestResult result, { Point position }) {
-    Matrix4 inverse = new Matrix4.zero();
-    // TODO(abarth): Check the determinant for degeneracy.
-    inverse.copyInverse(_transform);
-
-    Vector3 position3 = new Vector3(position.x, position.y, 0.0);
-    Vector3 transformed3 = inverse.transform3(position3);
-    Point transformed = new Point(transformed3.x, transformed3.y);
-    return super.hitTest(result, position: transformed);
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    context.canvas.save();
-    context.canvas.translate(offset.dx, offset.dy);
-    context.canvas.concat(_transform.storage);
-    super.paint(context, Offset.zero);
-    context.canvas.restore();
-  }
-
-  void applyPaintTransform(Matrix4 transform) {
-    super.applyPaintTransform(transform);
-    transform.multiply(_transform);
-  }
-
-  String debugDescribeSettings(String prefix) {
-    List<String> result = _transform.toString().split('\n').map((s) => '$prefix  $s\n').toList();
-    result.removeLast();
-    return '${super.debugDescribeSettings(prefix)}${prefix}transform matrix:\n${result.join()}';
-  }
-}
-
-typedef void SizeChangedCallback(Size newSize);
-
-class RenderSizeObserver extends RenderProxyBox {
-  RenderSizeObserver({
-    this.callback,
-    RenderBox child
-  }) : super(child) {
-    assert(callback != null);
-  }
-
-  SizeChangedCallback callback;
-
-  void performLayout() {
-    Size oldSize = size;
-
-    super.performLayout();
-
-    if (oldSize != size)
-      callback(size);
-  }
-}
-
-typedef void CustomPaintCallback(PaintingCanvas canvas, Size size);
-
-class RenderCustomPaint extends RenderProxyBox {
-
-  RenderCustomPaint({
-    CustomPaintCallback callback,
-    RenderBox child
-  }) : super(child) {
-    assert(callback != null);
-    _callback = callback;
-  }
-
-  CustomPaintCallback _callback;
-  void set callback (CustomPaintCallback value) {
-    assert(value != null || !attached);
-    if (_callback == value)
-      return;
-    _callback = value;
-    markNeedsPaint();
-  }
-
-  void attach() {
-    assert(_callback != null);
-    super.attach();
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    assert(_callback != null);
-    context.canvas.translate(offset.dx, offset.dy);
-    _callback(context.canvas, size);
-    // TODO(abarth): We should translate back before calling super because in
-    // the future, super.paint might switch our compositing layer.
-    super.paint(context, Offset.zero);
-    context.canvas.translate(-offset.dx, -offset.dy);
-  }
-}
-
-// RENDER VIEW LAYOUT MANAGER
-
-class ViewConstraints {
-  const ViewConstraints({
-    this.size: Size.zero,
-    this.orientation
-  });
-  final Size size;
-  final int orientation;
-}
-
-class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox> {
-  RenderView({
-    RenderBox child,
-    this.timeForRotation: const Duration(microseconds: 83333)
-  }) {
-    this.child = child;
-  }
-
-  Size _size = Size.zero;
-  Size get size => _size;
-
-  int _orientation; // 0..3
-  int get orientation => _orientation;
-  Duration timeForRotation;
-
-  ViewConstraints _rootConstraints;
-  ViewConstraints get rootConstraints => _rootConstraints;
-  void set rootConstraints(ViewConstraints value) {
-    if (_rootConstraints == value)
-      return;
-    _rootConstraints = value;
-    markNeedsLayout();
-  }
-
-  ContainerLayer _rootLayer;
-
-  // We never call layout() on this class, so this should never get
-  // checked. (This class is laid out using scheduleInitialLayout().)
-  bool debugDoesMeetConstraints() { assert(false); return false; }
-
-  void performResize() {
-    assert(false);
-  }
-
-  void performLayout() {
-    if (_rootConstraints.orientation != _orientation) {
-      if (_orientation != null && child != null)
-        child.rotate(oldAngle: _orientation, newAngle: _rootConstraints.orientation, time: timeForRotation);
-      _orientation = _rootConstraints.orientation;
-    }
-    _size = _rootConstraints.size;
-    assert(!_size.isInfinite);
-
-    if (child != null)
-      child.layout(new BoxConstraints.tight(_size));
-  }
-
-  void rotate({ int oldAngle, int newAngle, Duration time }) {
-    assert(false); // nobody tells the screen to rotate, the whole rotate() dance is started from our performResize()
-  }
-
-  bool hitTest(HitTestResult result, { Point position }) {
-    if (child != null) {
-      Rect childBounds = Point.origin & child.size;
-      if (childBounds.contains(position))
-        child.hitTest(result, position: position);
-    }
-    result.add(new HitTestEntry(this));
-    return true;
-  }
-
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null)
-      context.paintChild(child, offset.toPoint());
-  }
-
-  void paintFrame() {
-    sky.tracing.begin('RenderView.paintFrame');
-    try {
-      final double devicePixelRatio = sky.view.devicePixelRatio;
-      Matrix4 transform = new Matrix4.diagonal3Values(devicePixelRatio, devicePixelRatio, 1.0);
-      _rootLayer = new TransformLayer(transform: transform);
-      PaintingContext context = new PaintingContext(Offset.zero, size);
-      _rootLayer.add(context.layer);
-      context.paintChild(child, Point.origin);
-      context.endRecording();
-    } finally {
-      sky.tracing.end('RenderView.paintFrame');
-    }
-  }
-
-  void compositeFrame() {
-    sky.tracing.begin('RenderView.compositeFrame');
-    try {
-      sky.PictureRecorder recorder = new sky.PictureRecorder();
-      sky.Canvas canvas = new sky.Canvas(recorder, Point.origin & (size * sky.view.devicePixelRatio));
-      _rootLayer.paint(canvas);
-      sky.view.picture = recorder.endRecording();
-    } finally {
-      sky.tracing.end('RenderView.compositeFrame');
-    }
-  }
-
-  Rect get paintBounds => Point.origin & size;
-}
-
-class RenderIgnorePointer extends RenderProxyBox {
-  RenderIgnorePointer({ RenderBox child }) : super(child);
-  bool hitTest(HitTestResult result, { Point position }) {
-    return false;
-  }
-}
 
 // HELPER METHODS FOR RENDERBOX CONTAINERS
 abstract class RenderBoxContainerDefaultsMixin<ChildType extends RenderBox, ParentDataType extends ContainerParentDataMixin<ChildType>> implements ContainerRenderObjectMixin<ChildType, ParentDataType> {

packages/flutter/lib/rendering/image.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:sky' as sky;
+
+import 'package:sky/painting/box_painter.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/box.dart';
+
+class RenderImage extends RenderBox {
+  RenderImage({
+    sky.Image image,
+    double width,
+    double height,
+    sky.ColorFilter colorFilter,
+    fit: ImageFit.scaleDown,
+    repeat: ImageRepeat.noRepeat
+  }) : _image = image,
+      _width = width,
+      _height = height,
+      _colorFilter = colorFilter,
+      _fit = fit,
+      _repeat = repeat;
+
+  sky.Image _image;
+  sky.Image get image => _image;
+  void set image (sky.Image value) {
+    if (value == _image)
+      return;
+    _image = value;
+    markNeedsPaint();
+    if (_width == null || _height == null)
+      markNeedsLayout();
+  }
+
+  double _width;
+  double get width => _width;
+  void set width (double value) {
+    if (value == _width)
+      return;
+    _width = value;
+    markNeedsLayout();
+  }
+
+  double _height;
+  double get height => _height;
+  void set height (double value) {
+    if (value == _height)
+      return;
+    _height = value;
+    markNeedsLayout();
+  }
+
+  sky.ColorFilter _colorFilter;
+  sky.ColorFilter get colorFilter => _colorFilter;
+  void set colorFilter (sky.ColorFilter value) {
+    if (value == _colorFilter)
+      return;
+    _colorFilter = value;
+    markNeedsPaint();
+  }
+
+  ImageFit _fit;
+  ImageFit get fit => _fit;
+  void set fit (ImageFit value) {
+    if (value == _fit)
+      return;
+    _fit = value;
+    markNeedsPaint();
+  }
+
+  ImageRepeat _repeat;
+  ImageRepeat get repeat => _repeat;
+  void set repeat (ImageRepeat value) {
+    if (value == _repeat)
+      return;
+    _repeat = value;
+    markNeedsPaint();
+  }
+
+  Size _sizeForConstraints(BoxConstraints constraints) {
+    // Folds the given |width| and |height| into |cosntraints| so they can all
+    // be treated uniformly.
+    constraints = new BoxConstraints.tightFor(
+      width: _width,
+      height: _height
+    ).apply(constraints);
+
+    if (constraints.isTight || _image == null)
+      return constraints.smallest;
+
+    // This algorithm attempts to find a size for the RenderImage that fits in
+    // the given constraints and preserves the image's intrinisc aspect ratio.
+    // Its goals as follow:
+    //
+    //  - The dimensions of the RenderImage fit within the constraints.
+    //  - The aspect ratio of the RenderImage matches the instrinsic aspect
+    //    ratio of the image.
+    //  - The RenderImage's dimension are maximal subject to being smaller than
+    //    the intrinsic size of the image.
+
+    double width = _image.width.toDouble();
+    double height = _image.height.toDouble();
+    assert(width > 0.0);
+    assert(height > 0.0);
+    double aspectRatio = width / height;
+
+    if (width > constraints.maxWidth) {
+      width = constraints.maxWidth;
+      height = width / aspectRatio;
+    }
+
+    if (height > constraints.maxHeight) {
+      height = constraints.maxHeight;
+      width = height * aspectRatio;
+    }
+
+    if (width < constraints.minWidth) {
+      width = constraints.minWidth;
+      height = width / aspectRatio;
+    }
+
+    if (height < constraints.minHeight) {
+      height = constraints.minHeight;
+      width = height * aspectRatio;
+    }
+
+    return constraints.constrain(new Size(width, height));
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    if (_width == null && _height == null)
+      return constraints.constrainWidth(0.0);
+    return _sizeForConstraints(constraints).width;
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    return _sizeForConstraints(constraints).width;
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (_width == null && _height == null)
+      return constraints.constrainHeight(0.0);
+    return _sizeForConstraints(constraints).height;
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    return _sizeForConstraints(constraints).height;
+  }
+
+  void performLayout() {
+    size = _sizeForConstraints(constraints);
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (_image == null)
+      return;
+    paintImage(
+      canvas: context.canvas,
+      rect: offset & size,
+      image: _image,
+      colorFilter: _colorFilter,
+      fit: _fit,
+      repeat: _repeat
+    );
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}width: ${width}\n${prefix}height: ${height}\n';
+}

packages/flutter/lib/rendering/proxy_box.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:sky' as sky;
+
+import 'package:sky/painting/box_painter.dart';
+import 'package:sky/painting/text_style.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/box.dart';
+import 'package:vector_math/vector_math.dart';
+
+export 'package:sky/painting/box_painter.dart';
+
+class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
+
+  // ProxyBox assumes the child will be at 0,0 and will have the same size
+
+  RenderProxyBox([RenderBox child = null]) {
+    this.child = child;
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicWidth(constraints);
+    return super.getMinIntrinsicWidth(constraints);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicWidth(constraints);
+    return super.getMaxIntrinsicWidth(constraints);
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicHeight(constraints);
+    return super.getMinIntrinsicHeight(constraints);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicHeight(constraints);
+    return super.getMaxIntrinsicHeight(constraints);
+  }
+
+  double computeDistanceToActualBaseline(TextBaseline baseline) {
+    if (child != null)
+      return child.getDistanceToActualBaseline(baseline);
+    return super.computeDistanceToActualBaseline(baseline);
+  }
+
+  void performLayout() {
+    if (child != null) {
+      child.layout(constraints, parentUsesSize: true);
+      size = child.size;
+    } else {
+      performResize();
+    }
+  }
+
+  void hitTestChildren(HitTestResult result, { Point position }) {
+    if (child != null)
+      child.hitTest(result, position: position);
+    else
+      super.hitTestChildren(result, position: position);
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null)
+      context.paintChild(child, offset.toPoint());
+  }
+}
+
+class RenderConstrainedBox extends RenderProxyBox {
+  RenderConstrainedBox({
+    RenderBox child,
+    BoxConstraints additionalConstraints
+  }) : super(child), _additionalConstraints = additionalConstraints {
+    assert(additionalConstraints != null);
+  }
+
+  BoxConstraints _additionalConstraints;
+  BoxConstraints get additionalConstraints => _additionalConstraints;
+  void set additionalConstraints (BoxConstraints value) {
+    assert(value != null);
+    if (_additionalConstraints == value)
+      return;
+    _additionalConstraints = value;
+    markNeedsLayout();
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicWidth(_additionalConstraints.apply(constraints));
+    return _additionalConstraints.apply(constraints).constrainWidth(0.0);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicWidth(_additionalConstraints.apply(constraints));
+    return _additionalConstraints.apply(constraints).constrainWidth(0.0);
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicHeight(_additionalConstraints.apply(constraints));
+    return _additionalConstraints.apply(constraints).constrainHeight(0.0);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicHeight(_additionalConstraints.apply(constraints));
+    return _additionalConstraints.apply(constraints).constrainHeight(0.0);
+  }
+
+  void performLayout() {
+    if (child != null) {
+      child.layout(_additionalConstraints.apply(constraints), parentUsesSize: true);
+      size = child.size;
+    } else {
+      size = _additionalConstraints.apply(constraints).constrain(Size.zero);
+    }
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}additionalConstraints: ${additionalConstraints}\n';
+}
+
+class RenderAspectRatio extends RenderProxyBox {
+  RenderAspectRatio({
+    RenderBox child,
+    double aspectRatio
+  }) : super(child), _aspectRatio = aspectRatio {
+    assert(_aspectRatio != null);
+  }
+
+  double _aspectRatio;
+  double get aspectRatio => _aspectRatio;
+  void set aspectRatio (double value) {
+    assert(value != null);
+    if (_aspectRatio == value)
+      return;
+    _aspectRatio = value;
+    markNeedsLayout();
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    return _applyAspectRatio(constraints).height;
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    return _applyAspectRatio(constraints).height;
+  }
+
+  Size _applyAspectRatio(BoxConstraints constraints) {
+    double width = constraints.constrainWidth();
+    double height = constraints.constrainHeight(width / _aspectRatio);
+    return new Size(width, height);
+  }
+
+  bool get sizedByParent => true;
+
+  void performResize() {
+    size = _applyAspectRatio(constraints);
+  }
+
+  void performLayout() {
+    if (child != null)
+      child.layout(new BoxConstraints.tight(size));
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}aspectRatio: ${aspectRatio}\n';
+}
+
+class RenderShrinkWrapWidth extends RenderProxyBox {
+
+  // This class will attempt to size its child to the child's maximum
+  // intrinsic width, snapped to a multiple of the stepWidth, if one
+  // is provided, and given the provided constraints; and will then
+  // adopt the child's resulting dimensions.
+
+  // Note: laying out this class is relatively expensive. Avoid using
+  // it where possible.
+
+  RenderShrinkWrapWidth({
+    double stepWidth,
+    double stepHeight,
+    RenderBox child
+  }) : _stepWidth = stepWidth, _stepHeight = stepHeight, super(child);
+
+  double _stepWidth;
+  double get stepWidth => _stepWidth;
+  void set stepWidth(double value) {
+    if (value == _stepWidth)
+      return;
+    _stepWidth = value;
+    markNeedsLayout();
+  }
+
+  double _stepHeight;
+  double get stepHeight => _stepHeight;
+  void set stepHeight(double value) {
+    if (value == _stepHeight)
+      return;
+    _stepHeight = value;
+    markNeedsLayout();
+  }
+
+  static double applyStep(double input, double step) {
+    if (step == null)
+      return input;
+    return (input / step).ceil() * step;
+  }
+
+  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
+    if (constraints.hasTightWidth)
+      return constraints;
+    double width = child.getMaxIntrinsicWidth(constraints);
+    assert(width == constraints.constrainWidth(width));
+    return constraints.applyWidth(applyStep(width, _stepWidth));
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    return getMaxIntrinsicWidth(constraints);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    if (child == null)
+      return constraints.constrainWidth(0.0);
+    double childResult = child.getMaxIntrinsicWidth(constraints);
+    return constraints.constrainWidth(applyStep(childResult, _stepWidth));
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (child == null)
+      return constraints.constrainWidth(0.0);
+    double childResult = child.getMinIntrinsicHeight(_getInnerConstraints(constraints));
+    return constraints.constrainHeight(applyStep(childResult, _stepHeight));
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    if (child == null)
+      return constraints.constrainWidth(0.0);
+    double childResult = child.getMaxIntrinsicHeight(_getInnerConstraints(constraints));
+    return constraints.constrainHeight(applyStep(childResult, _stepHeight));
+  }
+
+  void performLayout() {
+    if (child != null) {
+      BoxConstraints childConstraints = _getInnerConstraints(constraints);
+      if (_stepHeight != null)
+        childConstraints.applyHeight(getMaxIntrinsicHeight(childConstraints));
+      child.layout(childConstraints, parentUsesSize: true);
+      size = child.size;
+    } else {
+      performResize();
+    }
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}stepWidth: ${stepWidth}\n${prefix}stepHeight: ${stepHeight}\n';
+
+}
+
+class RenderOpacity extends RenderProxyBox {
+  RenderOpacity({ RenderBox child, double opacity })
+    : this._opacity = opacity, super(child) {
+    assert(opacity >= 0.0 && opacity <= 1.0);
+  }
+
+  double _opacity;
+  double get opacity => _opacity;
+  void set opacity (double value) {
+    assert(value != null);
+    assert(value >= 0.0 && value <= 1.0);
+    if (_opacity == value)
+      return;
+    _opacity = value;
+    _cachedPaint = null;
+    markNeedsPaint();
+  }
+
+  int get _alpha => (_opacity * 255).round();
+
+  Paint _cachedPaint;
+  Paint get _paint {
+    if (_cachedPaint == null) {
+      _cachedPaint = new Paint()
+        ..color = new Color.fromARGB(_alpha, 0, 0, 0)
+        ..setTransferMode(sky.TransferMode.srcOver)
+        ..isAntiAlias = false;
+    }
+    return _cachedPaint;
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      int a = _alpha;
+
+      if (a == 0)
+        return;
+
+      if (a == 255) {
+        context.paintChild(child, offset.toPoint());
+        return;
+      }
+
+      context.canvas.saveLayer(null, _paint); // TODO(abarth): layerize
+      context.paintChild(child, offset.toPoint());
+      context.canvas.restore();
+    }
+  }
+}
+
+class RenderColorFilter extends RenderProxyBox {
+  RenderColorFilter({ RenderBox child, Color color, sky.TransferMode transferMode })
+    : _color = color, _transferMode = transferMode, super(child) {
+  }
+
+  Color _color;
+  Color get color => _color;
+  void set color (Color value) {
+    assert(value != null);
+    if (_color == value)
+      return;
+    _color = value;
+    _cachedPaint = null;
+    markNeedsPaint();
+  }
+
+  sky.TransferMode _transferMode;
+  sky.TransferMode get transferMode => _transferMode;
+  void set transferMode (sky.TransferMode value) {
+    assert(value != null);
+    if (_transferMode == value)
+      return;
+    _transferMode = value;
+    _cachedPaint = null;
+    markNeedsPaint();
+  }
+
+  Paint _cachedPaint;
+  Paint get _paint {
+    if (_cachedPaint == null) {
+      _cachedPaint = new Paint()
+        ..setColorFilter(new sky.ColorFilter.mode(_color, _transferMode))
+        ..isAntiAlias = false;
+    }
+    return _cachedPaint;
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      context.canvas.saveLayer(offset & size, _paint); // TODO(abarth): layerize
+      context.paintChild(child, offset.toPoint());
+      context.canvas.restore();
+    }
+  }
+}
+
+class RenderClipRect extends RenderProxyBox {
+  RenderClipRect({ RenderBox child }) : super(child);
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null)
+      context.paintChildWithClip(child, offset.toPoint(), Offset.zero & size);
+  }
+}
+
+class RenderClipRRect extends RenderProxyBox {
+  RenderClipRRect({ RenderBox child, double xRadius, double yRadius })
+    : _xRadius = xRadius, _yRadius = yRadius, super(child) {
+    assert(_xRadius != null);
+    assert(_yRadius != null);
+  }
+
+  double _xRadius;
+  double get xRadius => _xRadius;
+  void set xRadius (double value) {
+    assert(value != null);
+    if (_xRadius == value)
+      return;
+    _xRadius = value;
+    markNeedsPaint();
+  }
+
+  double _yRadius;
+  double get yRadius => _yRadius;
+  void set yRadius (double value) {
+    assert(value != null);
+    if (_yRadius == value)
+      return;
+    _yRadius = value;
+    markNeedsPaint();
+  }
+
+  final Paint _paint = new Paint()..isAntiAlias = false;
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      Rect rect = offset & size;
+      context.canvas.saveLayer(rect, _paint); // TODO(abarth): layerize
+      sky.RRect rrect = new sky.RRect()..setRectXY(rect, xRadius, yRadius);
+      context.canvas.clipRRect(rrect);
+      context.paintChild(child, offset.toPoint());
+      context.canvas.restore();
+    }
+  }
+}
+
+class RenderClipOval extends RenderProxyBox {
+  RenderClipOval({ RenderBox child }) : super(child);
+
+  final Paint _paint = new Paint()..isAntiAlias = false;
+
+  Rect _cachedRect;
+  Path _cachedPath;
+
+  Path _getPath(Rect rect) {
+    if (rect != _cachedRect) {
+      _cachedRect = rect;
+      _cachedPath = new Path()..addOval(_cachedRect);
+    }
+    return _cachedPath;
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      Rect rect = offset & size;
+      context.canvas.saveLayer(rect, _paint); // TODO(abarth): layerize
+      context.canvas.clipPath(_getPath(rect));
+      context.paintChild(child, offset.toPoint());
+      context.canvas.restore();
+    }
+  }
+}
+
+class RenderDecoratedBox extends RenderProxyBox {
+
+  RenderDecoratedBox({
+    BoxDecoration decoration,
+    RenderBox child
+  }) : _painter = new BoxPainter(decoration), super(child);
+
+  final BoxPainter _painter;
+
+  BoxDecoration get decoration => _painter.decoration;
+  void set decoration (BoxDecoration value) {
+    assert(value != null);
+    if (value == _painter.decoration)
+      return;
+    _removeBackgroundImageListenerIfNeeded();
+    _painter.decoration = value;
+    _addBackgroundImageListenerIfNeeded();
+    markNeedsPaint();
+  }
+
+  bool get _needsBackgroundImageListener {
+    return attached &&
+        _painter.decoration != null &&
+        _painter.decoration.backgroundImage != null;
+  }
+
+  void _addBackgroundImageListenerIfNeeded() {
+    if (_needsBackgroundImageListener)
+      _painter.decoration.backgroundImage.addChangeListener(markNeedsPaint);
+  }
+
+  void _removeBackgroundImageListenerIfNeeded() {
+    if (_needsBackgroundImageListener)
+      _painter.decoration.backgroundImage.removeChangeListener(markNeedsPaint);
+  }
+
+  void attach() {
+    super.attach();
+    _addBackgroundImageListenerIfNeeded();
+  }
+
+  void detach() {
+    _removeBackgroundImageListenerIfNeeded();
+    super.detach();
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    assert(size.width != null);
+    assert(size.height != null);
+    _painter.paint(context.canvas, offset & size);
+    super.paint(context, offset);
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}decoration:\n${_painter.decoration.toString(prefix + "  ")}\n';
+}
+
+class RenderTransform extends RenderProxyBox {
+  RenderTransform({
+    Matrix4 transform,
+    RenderBox child
+  }) : super(child) {
+    assert(transform != null);
+    this.transform = transform;
+  }
+
+  Matrix4 _transform;
+
+  void set transform(Matrix4 value) {
+    assert(value != null);
+    if (_transform == value)
+      return;
+    _transform = new Matrix4.copy(value);
+    markNeedsPaint();
+  }
+
+  void setIdentity() {
+    _transform.setIdentity();
+    markNeedsPaint();
+  }
+
+  void rotateX(double radians) {
+    _transform.rotateX(radians);
+    markNeedsPaint();
+  }
+
+  void rotateY(double radians) {
+    _transform.rotateY(radians);
+    markNeedsPaint();
+  }
+
+  void rotateZ(double radians) {
+    _transform.rotateZ(radians);
+    markNeedsPaint();
+  }
+
+  void translate(x, [double y = 0.0, double z = 0.0]) {
+    _transform.translate(x, y, z);
+    markNeedsPaint();
+  }
+
+  void scale(x, [double y, double z]) {
+    _transform.scale(x, y, z);
+    markNeedsPaint();
+  }
+
+  bool hitTest(HitTestResult result, { Point position }) {
+    Matrix4 inverse = new Matrix4.zero();
+    // TODO(abarth): Check the determinant for degeneracy.
+    inverse.copyInverse(_transform);
+
+    Vector3 position3 = new Vector3(position.x, position.y, 0.0);
+    Vector3 transformed3 = inverse.transform3(position3);
+    Point transformed = new Point(transformed3.x, transformed3.y);
+    return super.hitTest(result, position: transformed);
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    context.canvas.save();
+    context.canvas.translate(offset.dx, offset.dy);
+    context.canvas.concat(_transform.storage);
+    super.paint(context, Offset.zero);
+    context.canvas.restore();
+  }
+
+  void applyPaintTransform(Matrix4 transform) {
+    super.applyPaintTransform(transform);
+    transform.multiply(_transform);
+  }
+
+  String debugDescribeSettings(String prefix) {
+    List<String> result = _transform.toString().split('\n').map((s) => '$prefix  $s\n').toList();
+    result.removeLast();
+    return '${super.debugDescribeSettings(prefix)}${prefix}transform matrix:\n${result.join()}';
+  }
+}
+
+typedef void SizeChangedCallback(Size newSize);
+
+class RenderSizeObserver extends RenderProxyBox {
+  RenderSizeObserver({
+    this.callback,
+    RenderBox child
+  }) : super(child) {
+    assert(callback != null);
+  }
+
+  SizeChangedCallback callback;
+
+  void performLayout() {
+    Size oldSize = size;
+
+    super.performLayout();
+
+    if (oldSize != size)
+      callback(size);
+  }
+}
+
+typedef void CustomPaintCallback(PaintingCanvas canvas, Size size);
+
+class RenderCustomPaint extends RenderProxyBox {
+
+  RenderCustomPaint({
+    CustomPaintCallback callback,
+    RenderBox child
+  }) : super(child) {
+    assert(callback != null);
+    _callback = callback;
+  }
+
+  CustomPaintCallback _callback;
+  void set callback (CustomPaintCallback value) {
+    assert(value != null || !attached);
+    if (_callback == value)
+      return;
+    _callback = value;
+    markNeedsPaint();
+  }
+
+  void attach() {
+    assert(_callback != null);
+    super.attach();
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    assert(_callback != null);
+    context.canvas.translate(offset.dx, offset.dy);
+    _callback(context.canvas, size);
+    // TODO(abarth): We should translate back before calling super because in
+    // the future, super.paint might switch our compositing layer.
+    super.paint(context, Offset.zero);
+    context.canvas.translate(-offset.dx, -offset.dy);
+  }
+}
+
+class RenderIgnorePointer extends RenderProxyBox {
+  RenderIgnorePointer({ RenderBox child }) : super(child);
+  bool hitTest(HitTestResult result, { Point position }) {
+    return false;
+  }
+}

packages/flutter/lib/rendering/shifted_box.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 'package:sky/painting/box_painter.dart';
+import 'package:sky/painting/text_style.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/box.dart';
+
+abstract class RenderShiftedBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
+
+  // Abstract class for one-child-layout render boxes
+
+  RenderShiftedBox(RenderBox child) {
+    this.child = child;
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicWidth(constraints);
+    return super.getMinIntrinsicWidth(constraints);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicWidth(constraints);
+    return super.getMaxIntrinsicWidth(constraints);
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicHeight(constraints);
+    return super.getMinIntrinsicHeight(constraints);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicHeight(constraints);
+    return super.getMaxIntrinsicHeight(constraints);
+  }
+
+  double computeDistanceToActualBaseline(TextBaseline baseline) {
+    double result;
+    if (child != null) {
+      assert(!needsLayout);
+      result = child.getDistanceToActualBaseline(baseline);
+      assert(child.parentData is BoxParentData);
+      if (result != null)
+        result += child.parentData.position.y;
+    } else {
+      result = super.computeDistanceToActualBaseline(baseline);
+    }
+    return result;
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null)
+      context.paintChild(child, child.parentData.position + offset);
+  }
+
+  void hitTestChildren(HitTestResult result, { Point position }) {
+    if (child != null) {
+      assert(child.parentData is BoxParentData);
+      child.hitTest(result, position: new Point(position.x - child.parentData.position.x,
+                                                position.y - child.parentData.position.y));
+    }
+  }
+
+}
+
+class RenderPadding extends RenderShiftedBox {
+
+  RenderPadding({ EdgeDims padding, RenderBox child }) : super(child) {
+    assert(padding != null);
+    this.padding = padding;
+  }
+
+  EdgeDims _padding;
+  EdgeDims get padding => _padding;
+  void set padding (EdgeDims value) {
+    assert(value != null);
+    if (_padding == value)
+      return;
+    _padding = value;
+    markNeedsLayout();
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    double totalPadding = padding.left + padding.right;
+    if (child != null)
+      return child.getMinIntrinsicWidth(constraints.deflate(padding)) + totalPadding;
+    return constraints.constrainWidth(totalPadding);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    double totalPadding = padding.left + padding.right;
+    if (child != null)
+      return child.getMaxIntrinsicWidth(constraints.deflate(padding)) + totalPadding;
+    return constraints.constrainWidth(totalPadding);
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    double totalPadding = padding.top + padding.bottom;
+    if (child != null)
+      return child.getMinIntrinsicHeight(constraints.deflate(padding)) + totalPadding;
+    return constraints.constrainHeight(totalPadding);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    double totalPadding = padding.top + padding.bottom;
+    if (child != null)
+      return child.getMaxIntrinsicHeight(constraints.deflate(padding)) + totalPadding;
+    return constraints.constrainHeight(totalPadding);
+  }
+
+  void performLayout() {
+    assert(padding != null);
+    if (child == null) {
+      size = constraints.constrain(new Size(
+        padding.left + padding.right,
+        padding.top + padding.bottom
+      ));
+      return;
+    }
+    BoxConstraints innerConstraints = constraints.deflate(padding);
+    child.layout(innerConstraints, parentUsesSize: true);
+    assert(child.parentData is BoxParentData);
+    child.parentData.position = new Point(padding.left, padding.top);
+    size = constraints.constrain(new Size(
+      padding.left + child.size.width + padding.right,
+      padding.top + child.size.height + padding.bottom
+    ));
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}padding: ${padding}\n';
+}
+
+class RenderPositionedBox extends RenderShiftedBox {
+
+  // This box aligns a child box within itself. It's only useful for
+  // children that don't always size to fit their parent. For example,
+  // to align a box at the bottom right, you would pass this box a
+  // tight constraint that is bigger than the child's natural size,
+  // with horizontal and vertical set to 1.0.
+
+  RenderPositionedBox({
+    RenderBox child,
+    double horizontal: 0.5,
+    double vertical: 0.5
+  }) : _horizontal = horizontal,
+       _vertical = vertical,
+       super(child) {
+    assert(horizontal != null);
+    assert(vertical != null);
+  }
+
+  double _horizontal;
+  double get horizontal => _horizontal;
+  void set horizontal (double value) {
+    assert(value != null);
+    if (_horizontal == value)
+      return;
+    _horizontal = value;
+    markNeedsLayout();
+  }
+
+  double _vertical;
+  double get vertical => _vertical;
+  void set vertical (double value) {
+    assert(value != null);
+    if (_vertical == value)
+      return;
+    _vertical = value;
+    markNeedsLayout();
+  }
+
+  void performLayout() {
+    if (child != null) {
+      child.layout(constraints.loosen(), parentUsesSize: true);
+      size = constraints.constrain(child.size);
+      assert(child.parentData is BoxParentData);
+      Offset delta = size - child.size;
+      child.parentData.position = (delta.scale(horizontal, vertical)).toPoint();
+    } else {
+      performResize();
+    }
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}horizontal: ${horizontal}\n${prefix}vertical: ${vertical}\n';
+}
+
+class RenderBaseline extends RenderShiftedBox {
+
+  RenderBaseline({
+    RenderBox child,
+    double baseline,
+    TextBaseline baselineType
+  }) : _baseline = baseline,
+       _baselineType = baselineType,
+       super(child) {
+    assert(baseline != null);
+    assert(baselineType != null);
+  }
+
+  double _baseline;
+  double get baseline => _baseline;
+  void set baseline (double value) {
+    assert(value != null);
+    if (_baseline == value)
+      return;
+    _baseline = value;
+    markNeedsLayout();
+  }
+
+  TextBaseline _baselineType;
+  TextBaseline get baselineType => _baselineType;
+  void set baselineType (TextBaseline value) {
+    assert(value != null);
+    if (_baselineType == value)
+      return;
+    _baselineType = value;
+    markNeedsLayout();
+  }
+
+  void performLayout() {
+    if (child != null) {
+      child.layout(constraints.loosen(), parentUsesSize: true);
+      size = constraints.constrain(child.size);
+      assert(child.parentData is BoxParentData);
+      double delta = baseline - child.getDistanceToBaseline(baselineType);
+      child.parentData.position = new Point(0.0, delta);
+    } else {
+      performResize();
+    }
+  }
+
+  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}baseline: ${baseline}\nbaselineType: ${baselineType}';
+}

packages/flutter/lib/rendering/sky_binding.dart

@@ -4,10 +4,11 @@
 
 import 'dart:sky' as sky;
 
-import 'package:sky/base/scheduler.dart' as scheduler;
 import 'package:sky/base/hit_test.dart';
+import 'package:sky/base/scheduler.dart' as scheduler;
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/view.dart';
 
 int _hammingWeight(int value) {
   if (value == 0)

packages/flutter/lib/rendering/toggleable.dart

@@ -9,6 +9,7 @@ import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/animation/curves.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/proxy_box.dart';
 
 typedef void ValueChanged(bool value);
 

packages/flutter/lib/rendering/view.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:sky' as sky;
+
+import 'package:sky/rendering/layer.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/box.dart';
+import 'package:vector_math/vector_math.dart';
+
+class ViewConstraints {
+  const ViewConstraints({
+    this.size: Size.zero,
+    this.orientation
+  });
+  final Size size;
+  final int orientation;
+}
+
+class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox> {
+  RenderView({
+    RenderBox child,
+    this.timeForRotation: const Duration(microseconds: 83333)
+  }) {
+    this.child = child;
+  }
+
+  Size _size = Size.zero;
+  Size get size => _size;
+
+  int _orientation; // 0..3
+  int get orientation => _orientation;
+  Duration timeForRotation;
+
+  ViewConstraints _rootConstraints;
+  ViewConstraints get rootConstraints => _rootConstraints;
+  void set rootConstraints(ViewConstraints value) {
+    if (_rootConstraints == value)
+      return;
+    _rootConstraints = value;
+    markNeedsLayout();
+  }
+
+  ContainerLayer _rootLayer;
+
+  // We never call layout() on this class, so this should never get
+  // checked. (This class is laid out using scheduleInitialLayout().)
+  bool debugDoesMeetConstraints() { assert(false); return false; }
+
+  void performResize() {
+    assert(false);
+  }
+
+  void performLayout() {
+    if (_rootConstraints.orientation != _orientation) {
+      if (_orientation != null && child != null)
+        child.rotate(oldAngle: _orientation, newAngle: _rootConstraints.orientation, time: timeForRotation);
+      _orientation = _rootConstraints.orientation;
+    }
+    _size = _rootConstraints.size;
+    assert(!_size.isInfinite);
+
+    if (child != null)
+      child.layout(new BoxConstraints.tight(_size));
+  }
+
+  void rotate({ int oldAngle, int newAngle, Duration time }) {
+    assert(false); // nobody tells the screen to rotate, the whole rotate() dance is started from our performResize()
+  }
+
+  bool hitTest(HitTestResult result, { Point position }) {
+    if (child != null) {
+      Rect childBounds = Point.origin & child.size;
+      if (childBounds.contains(position))
+        child.hitTest(result, position: position);
+    }
+    result.add(new HitTestEntry(this));
+    return true;
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null)
+      context.paintChild(child, offset.toPoint());
+  }
+
+  void paintFrame() {
+    sky.tracing.begin('RenderView.paintFrame');
+    try {
+      final double devicePixelRatio = sky.view.devicePixelRatio;
+      Matrix4 transform = new Matrix4.diagonal3Values(devicePixelRatio, devicePixelRatio, 1.0);
+      _rootLayer = new TransformLayer(transform: transform);
+      PaintingContext context = new PaintingContext(Offset.zero, size);
+      _rootLayer.add(context.layer);
+      context.paintChild(child, Point.origin);
+      context.endRecording();
+    } finally {
+      sky.tracing.end('RenderView.paintFrame');
+    }
+  }
+
+  void compositeFrame() {
+    sky.tracing.begin('RenderView.compositeFrame');
+    try {
+      sky.PictureRecorder recorder = new sky.PictureRecorder();
+      sky.Canvas canvas = new sky.Canvas(recorder, Point.origin & (size * sky.view.devicePixelRatio));
+      _rootLayer.paint(canvas);
+      sky.view.picture = recorder.endRecording();
+    } finally {
+      sky.tracing.end('RenderView.compositeFrame');
+    }
+  }
+
+  Rect get paintBounds => Point.origin & size;
+}

packages/flutter/lib/rendering/viewport.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:sky' as sky;
+
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/box.dart';
+import 'package:vector_math/vector_math.dart';
+
+enum ScrollDirection { horizontal, vertical, both }
+
+class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
+
+  RenderViewport({
+    RenderBox child,
+    Offset scrollOffset,
+    ScrollDirection scrollDirection: ScrollDirection.vertical
+  }) : _scrollOffset = scrollOffset,
+       _scrollDirection = scrollDirection {
+    assert(_offsetIsSane(scrollOffset, scrollDirection));
+    this.child = child;
+  }
+
+  bool _offsetIsSane(Offset offset, ScrollDirection direction) {
+    switch (direction) {
+      case ScrollDirection.both:
+        return true;
+      case ScrollDirection.horizontal:
+        return offset.dy == 0.0;
+      case ScrollDirection.vertical:
+        return offset.dx == 0.0;
+    }
+  }
+
+  Offset _scrollOffset;
+  Offset get scrollOffset => _scrollOffset;
+  void set scrollOffset(Offset value) {
+    if (value == _scrollOffset)
+      return;
+    assert(_offsetIsSane(value, scrollDirection));
+    _scrollOffset = value;
+    markNeedsPaint();
+  }
+
+  ScrollDirection _scrollDirection;
+  ScrollDirection get scrollDirection => _scrollDirection;
+  void set scrollDirection(ScrollDirection value) {
+    if (value == _scrollDirection)
+      return;
+    assert(_offsetIsSane(scrollOffset, value));
+    _scrollDirection = value;
+    markNeedsLayout();
+  }
+
+  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
+    BoxConstraints innerConstraints;
+    switch (scrollDirection) {
+      case ScrollDirection.both:
+        innerConstraints = new BoxConstraints();
+        break;
+      case ScrollDirection.horizontal:
+        innerConstraints = constraints.heightConstraints();
+        break;
+      case ScrollDirection.vertical:
+        innerConstraints = constraints.widthConstraints();
+        break;
+    }
+    return innerConstraints;
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicWidth(_getInnerConstraints(constraints));
+    return super.getMinIntrinsicWidth(constraints);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicWidth(_getInnerConstraints(constraints));
+    return super.getMaxIntrinsicWidth(constraints);
+  }
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMinIntrinsicHeight(_getInnerConstraints(constraints));
+    return super.getMinIntrinsicHeight(constraints);
+  }
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) {
+    if (child != null)
+      return child.getMaxIntrinsicHeight(_getInnerConstraints(constraints));
+    return super.getMaxIntrinsicHeight(constraints);
+  }
+
+  // We don't override computeDistanceToActualBaseline(), because we
+  // want the default behaviour (returning null). Otherwise, as you
+  // scroll the RenderViewport, it would shift in its parent if the
+  // parent was baseline-aligned, which makes no sense.
+
+  void performLayout() {
+    if (child != null) {
+      child.layout(_getInnerConstraints(constraints), parentUsesSize: true);
+      size = constraints.constrain(child.size);
+      assert(child.parentData is BoxParentData);
+      child.parentData.position = Point.origin;
+    } else {
+      performResize();
+    }
+  }
+
+  Offset get _scrollOffsetRoundedToIntegerDevicePixels {
+    double devicePixelRatio = sky.view.devicePixelRatio;
+    int dxInDevicePixels = (scrollOffset.dx * devicePixelRatio).round();
+    int dyInDevicePixels = (scrollOffset.dy * devicePixelRatio).round();
+    return new Offset(dxInDevicePixels / devicePixelRatio,
+                      dyInDevicePixels / devicePixelRatio);
+  }
+
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      Offset roundedScrollOffset = _scrollOffsetRoundedToIntegerDevicePixels;
+      bool _needsClip = offset < Offset.zero ||
+                        !(offset & size).contains(((offset - roundedScrollOffset) & child.size).bottomRight);
+      if (_needsClip) {
+        context.canvas.save();
+        context.canvas.clipRect(offset & size);
+      }
+      context.paintChild(child, (offset - roundedScrollOffset).toPoint());
+      if (_needsClip)
+        context.canvas.restore();
+    }
+  }
+
+  void applyPaintTransform(Matrix4 transform) {
+    super.applyPaintTransform(transform);
+    transform.translate(-scrollOffset.dx, -scrollOffset.dy);
+  }
+
+  void hitTestChildren(HitTestResult result, { Point position }) {
+    if (child != null) {
+      assert(child.parentData is BoxParentData);
+      Point transformed = position + _scrollOffsetRoundedToIntegerDevicePixels;
+      child.hitTest(result, position: transformed);
+    }
+  }
+}

packages/flutter/lib/widgets/basic.dart

@@ -14,18 +14,24 @@ import 'package:sky/painting/paragraph_painter.dart';
 import 'package:sky/rendering/block.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
+import 'package:sky/rendering/image.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
+import 'package:sky/rendering/proxy_box.dart';
+import 'package:sky/rendering/shifted_box.dart';
 import 'package:sky/rendering/stack.dart';
+import 'package:sky/rendering/viewport.dart';
 import 'package:sky/widgets/default_text_style.dart';
 import 'package:sky/widgets/framework.dart';
 
 export 'package:sky/base/hit_test.dart' show EventDisposition, combineEventDispositions;
 export 'package:sky/rendering/block.dart' show BlockDirection;
-export 'package:sky/rendering/box.dart' show BackgroundImage, BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims, ScrollDirection;
+export 'package:sky/rendering/box.dart' show BoxConstraints;
 export 'package:sky/rendering/flex.dart' show FlexDirection, FlexJustifyContent, FlexAlignItems;
 export 'package:sky/rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
+export 'package:sky/rendering/proxy_box.dart' show BackgroundImage, BoxDecoration, BoxShadow, Border, BorderSide, EdgeDims;
 export 'package:sky/rendering/toggleable.dart' show ValueChanged;
+export 'package:sky/rendering/viewport.dart' show ScrollDirection;
 export 'package:sky/widgets/framework.dart' show Key, GlobalKey, Widget, Component, StatefulComponent, App, runApp, Listener, ParentDataNode;
 
 // PAINTING NODES

packages/flutter/lib/widgets/framework.dart

@@ -12,6 +12,7 @@ import 'package:sky/mojo/activity.dart' as activity;
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/sky_binding.dart';
+import 'package:sky/rendering/view.dart';
 
 export 'package:sky/base/hit_test.dart' show EventDisposition, combineEventDispositions;
 export 'package:sky/rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;

packages/flutter/lib/widgets/icon_button.dart

@@ -4,7 +4,6 @@
 
 import 'dart:sky' as sky;
 
-import 'package:sky/rendering/box.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/icon.dart';
 import 'package:sky/widgets/framework.dart';

packages/flutter/lib/widgets/ink_well.dart

@@ -10,6 +10,7 @@ import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/animation/curves.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/proxy_box.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/framework.dart';
 

packages/flutter/lib/widgets/scrollable.dart

@@ -10,6 +10,7 @@ import 'package:sky/animation/animated_simulation.dart';
 import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/viewport.dart';
 import 'package:sky/theme/view_configuration.dart' as config;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/block_viewport.dart';

packages/flutter/lib/widgets/tabs.dart

@@ -13,6 +13,7 @@ import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/viewport.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/theme/typography.dart' as typography;
 import 'package:sky/widgets/basic.dart';