Split box.dart into many files

Sadly, box.dart has grown much longer than 1000 lines. This patch splits it up
into several files based on the class hierarchy. Fortunately, many of these
classes are loosely coupled to each other.

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/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/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';