From edacf2a362fad0bbfb08980ea14202fd25f427e6 Mon Sep 17 00:00:00 2001
From: Hixie <github.com@spam.hixie.ch>
Date: Wed, 20 May 2015 10:52:36 -0700
Subject: [PATCH] Layout API prototype, for discussion

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1093633002
---
 sdk/lib/framework/layout.dart  |   4 +-
 sdk/lib/framework/layout2.dart | 757 +++++++++++++++++++++++++++++++++
 sdk/lib/framework/node.dart    |  12 +-
 3 files changed, 766 insertions(+), 7 deletions(-)
 create mode 100644 sdk/lib/framework/layout2.dart

diff --git a/sdk/lib/framework/layout.dart b/sdk/lib/framework/layout.dart
index 34566802c69..3771a2e8ff4 100644
--- a/sdk/lib/framework/layout.dart
+++ b/sdk/lib/framework/layout.dart
@@ -1,5 +1,7 @@
 library layout;
 
+// This version of layout.dart is a shim version of layout2.dart that is backed using CSS and <div>s.
+
 import 'node.dart';
 import 'dart:sky' as sky;
 import 'dart:collection';
@@ -64,7 +66,7 @@ class ParentData {
   }
 }
 
-abstract class RenderNode extends Node {
+abstract class RenderNode extends AbstractNode {
 
   // LAYOUT
 
diff --git a/sdk/lib/framework/layout2.dart b/sdk/lib/framework/layout2.dart
new file mode 100644
index 00000000000..e3773e2bcc6
--- /dev/null
+++ b/sdk/lib/framework/layout2.dart
@@ -0,0 +1,757 @@
+library layout;
+
+// This version of layout.dart is an update to the other one, this one using new APIs.
+// It will not work in a stock Sky setup currently.
+
+import 'node.dart';
+
+import 'dart:sky' as sky;
+
+// ABSTRACT LAYOUT
+
+class ParentData {
+  void detach() {
+    detachSiblings();
+  }
+  void detachSiblings() { } // workaround for lack of inter-class mixins in Dart
+  void merge(ParentData other) {
+    // override this in subclasses to merge in data from other into this
+    assert(other.runtimeType == this.runtimeType);
+  }
+}
+
+const kLayoutDirections = 4;
+
+double clamp({double min: 0.0, double value: 0.0, double max: double.INFINITY}) {
+  if (value > max)
+    value = max;
+  if (value < min)
+    value = min;
+  return value;
+}
+
+class RenderNodeDisplayList extends sky.PictureRecorder {
+  RenderNodeDisplayList(double width, double height) : super(width, height);
+  void paintChild(RenderNode child, double x, double y) {
+    save();
+    translate(x, y);
+    child.paint(this);
+    restore();
+  }
+}
+
+abstract class RenderNode extends AbstractNode {
+
+  // LAYOUT
+
+  // parentData is only for use by the RenderNode that actually lays this
+  // node out, and any other nodes who happen to know exactly what
+  // kind of node that is.
+  ParentData parentData;
+  void setupPos(RenderNode child) {
+    // override this to setup .parentData correctly for your class
+    if (child.parentData is! ParentData)
+      child.parentData = new ParentData();
+  }
+
+  void adoptChild(RenderNode child) { // only for use by subclasses
+    // call this whenever you decide a node is a child
+    assert(child != null);
+    setupPos(child);
+    super.adoptChild(child);
+  }
+  void dropChild(RenderNode child) { // only for use by subclasses
+    assert(child != null);
+    assert(child.parentData != null);
+    child.parentData.detach();
+    super.dropChild(child);
+  }
+
+  static List<RenderNode> _nodesNeedingLayout = new List<RenderNode>();
+  static bool _debugDoingLayout = false;
+  bool _needsLayout = true;
+  bool get needsLayout => _needsLayout;
+  RenderNode _relayoutSubtreeRoot;
+  void saveRelayoutSubtreeRoot(RenderNode relayoutSubtreeRoot) {
+    _relayoutSubtreeRoot = relayoutSubtreeRoot;
+    assert(_relayoutSubtreeRoot == null || _relayoutSubtreeRoot._relayoutSubtreeRoot == null);
+    assert(_relayoutSubtreeRoot == null || _relayoutSubtreeRoot == parent || _relayoutSubtreeRoot == parent._relayoutSubtreeRoot);
+  }
+  bool debugAncestorsAlreadyMarkedNeedsLayout() {
+    if (_relayoutSubtreeRoot == null)
+      return true;
+    RenderNode node = this;
+    while (node != _relayoutSubtreeRoot) {
+      assert(node._relayoutSubtreeRoot == _relayoutSubtreeRoot);
+      assert(node.parent != null);
+      node = node.parent as RenderNode;
+      if (!node._needsLayout)
+        return false;
+    }
+    assert(node._relayoutSubtreeRoot == null);
+    return true;
+  }
+  void markNeedsLayout() {
+    assert(!_debugDoingLayout);
+    assert(!_debugDoingPaint);
+    if (_needsLayout) {
+      assert(debugAncestorsAlreadyMarkedNeedsLayout());
+      return;
+    }
+    _needsLayout = true;
+    if (_relayoutSubtreeRoot != null)
+      parent.markNeedsLayout();
+    else
+      _nodesNeedingLayout.add(this);
+  }
+  static void flushLayout() {
+    _debugDoingLayout = true;
+    List<RenderNode> dirtyNodes = _nodesNeedingLayout;
+    _nodesNeedingLayout = new List<RenderNode>();
+    dirtyNodes..sort((a, b) => a.depth - b.depth)..forEach((node) {
+      if (node._needsLayout && node.attached)
+        node._doLayout();
+    });
+    _debugDoingLayout = false;
+  }
+  void _doLayout() {
+    try {
+      assert(_relayoutSubtreeRoot == null);
+      relayout();
+    } catch (e, stack) {
+      print('Exception raised during layout of ${this}: ${e}');
+      print(stack);
+      return;
+    }
+    assert(!_needsLayout); // check that the relayout() method marked us "not dirty"
+  }
+  /* // this method's signature is subclass-specific, but will exist in
+     // some form in all subclasses:
+     void layout({arguments..., RenderNode relayoutSubtreeRoot}) {
+       bool childArgumentsChanged = ...; // true if arguments we're going to pass to the children are different than last time, false otherwise
+       if (this node has an opinion about its size, e.g. because it autosizes based on kids, or has an intrinsic dimension) {
+         if (relayoutSubtreeRoot != null) {
+           saveRelayoutSubtreeRoot(relayoutSubtreeRoot);
+           // for each child, if we are going to size ourselves around them:
+           if (child.needsLayout || childArgumentsChanged)
+             child.layout(... relayoutSubtreeRoot: relayoutSubtreeRoot);
+           width = ...;
+           height = ...;
+         } else {
+           saveRelayoutSubtreeRoot(null); // you can skip this if there's no way you would ever have called saveRelayoutSubtreeRoot() before
+           // we're the root of the relayout subtree
+           // for each child, if we are going to size ourselves around them:
+           if (child.needsLayout || childArgumentsChanged)
+             child.layout(... relayoutSubtreeRoot: this);
+           width = ...;
+           height = ...;
+         }
+       } else {
+         // we're sizing ourselves exclusively on input from the parent (arguments to this function)
+         // ignore relayoutSubtreeRoot
+         saveRelayoutSubtreeRoot(null); // you can skip this if there's no way you would ever have called saveRelayoutSubtreeRoot() before
+         width = ...; // based on input from arguments only
+         height = ...; // based on input from arguments only
+       }
+       // for each child whose size we'll ignore when deciding ours:
+       if (child.needsLayout || childArgumentsChanged)
+         child.layout(... relayoutSubtreeRoot: null); // or just omit relayoutSubtreeRoot
+       layoutDone();
+       return;
+     }
+  */
+  void relayout() {
+    // Override this to perform relayout without your parent's
+    // involvement.
+    //
+    // This is what is called after the first layout(), if you mark
+    // yourself dirty and don't have a _relayoutSubtreeRoot set; in
+    // other words, either if your parent doesn't care what size you
+    // are (and thus didn't pass a relayoutSubtreeRoot to your
+    // layout() method) or if you sized yourself entirely based on
+    // what your parents told you, and not based on your children (and
+    // thus you never called saveRelayoutSubtreeRoot()).
+    //
+    // In the former case, you can resize yourself here at will. In
+    // the latter case, just leave your dimensions unchanged.
+    //
+    // If _relayoutSubtreeRoot is set (i.e. you called saveRelayout-
+    // SubtreeRoot() in your layout(), with a relayoutSubtreeRoot
+    // argument that was non-null), then if you mark yourself as dirty
+    // then we'll tell that subtree root instead, and the layout will
+    // occur via the layout() tree rather than starting from this
+    // relayout() method.
+    //
+    // when calling children's layout() methods, skip any children
+    // that have needsLayout == false unless the arguments you are
+    // passing in have changed since the last time
+    assert(_relayoutSubtreeRoot == null);
+    layoutDone();
+  }
+  void layoutDone({bool needsPaint: true}) {
+    // make sure to call this at the end of your layout() or relayout()
+    _needsLayout = false;
+    if (needsPaint)
+      markNeedsPaint();
+  }
+
+  // when the parent has rotated (e.g. when the screen has been turned
+  // 90 degrees), immediately prior to layout() being called for the
+  // new dimensions, rotate() is called with the old and new angles.
+  // The next time paint() is called, the coordinate space will have
+  // been rotated N quarter-turns clockwise, where:
+  //    N = newAngle-oldAngle
+  // ...but the rendering is expected to remain the same, pixel for
+  // pixel, on the output device. Then, the layout() method or
+  // equivalent will be invoked.
+
+  void rotate({
+    int oldAngle, // 0..3
+    int newAngle, // 0..3
+    Duration time
+  }) { }
+
+
+  // HIT TESTING  
+
+  void handlePointer(sky.PointerEvent event) {
+    // override this if you have children, to hand it to the appropriate child
+    // override this if you want to do anything with the pointer event
+  }
+
+
+  // PAINTING
+
+  static bool _debugDoingPaint = false;
+  void markNeedsPaint() {
+    assert(!_debugDoingPaint);
+    var ancestor = this;
+    while (ancestor.parent != null)
+      ancestor = ancestor.parent;
+    assert(ancestor is Screen);
+    ancestor.paintFrame();
+  }
+  void paint(RenderNodeDisplayList canvas) { }
+
+}
+
+
+// GENERIC MIXIN FOR RENDER NODES THAT TAKE A LIST OF CHILDREN
+
+abstract class ContainerParentDataMixin<ChildType extends RenderNode> {
+  ChildType previousSibling;
+  ChildType nextSibling;
+  void detachSiblings() {
+    if (previousSibling != null) {
+      assert(previousSibling.parentData is ContainerParentDataMixin<ChildType>);
+      assert(previousSibling != this);
+      assert(previousSibling.parentData.nextSibling == this);
+      previousSibling.parentData.nextSibling = nextSibling;
+    }
+    if (nextSibling != null) {
+      assert(nextSibling.parentData is ContainerParentDataMixin<ChildType>);
+      assert(nextSibling != this);
+      assert(nextSibling.parentData.previousSibling == this);
+      nextSibling.parentData.previousSibling = previousSibling;
+    }
+    previousSibling = null;
+    nextSibling = null;
+  }
+}
+
+abstract class ContainerRenderNodeMixin<ChildType extends RenderNode, ParentDataType extends ContainerParentDataMixin<ChildType>> implements RenderNode {
+  // abstract class that has only InlineNode children
+
+  bool _debugUltimatePreviousSiblingOf(ChildType child, { ChildType equals }) {
+    assert(child.parentData is ParentDataType);
+    while (child.parentData.previousSibling != null) {
+      assert(child.parentData.previousSibling != child);
+      child = child.parentData.previousSibling;
+      assert(child.parentData is ParentDataType);
+    }
+    return child == equals;
+  }
+  bool _debugUltimateNextSiblingOf(ChildType child, { ChildType equals }) {
+    assert(child.parentData is ParentDataType);
+    while (child.parentData.nextSibling != null) {
+      assert(child.parentData.nextSibling != child);
+      child = child.parentData.nextSibling;
+      assert(child.parentData is ParentDataType);
+    }
+    return child == equals;
+  }
+
+  ChildType _firstChild;
+  ChildType _lastChild;
+  void add(ChildType child, { ChildType before }) {
+    assert(child != this);
+    assert(before != this);
+    assert(child != before);
+    assert(child != _firstChild);
+    assert(child != _lastChild);
+    adoptChild(child);
+    assert(child.parentData is ParentDataType);
+    assert(child.parentData.nextSibling == null);
+    assert(child.parentData.previousSibling == null);
+    if (before == null) {
+      // append at the end (_lastChild)
+      child.parentData.previousSibling = _lastChild;
+      if (_lastChild != null) {
+        assert(_lastChild.parentData is ParentDataType);
+        _lastChild.parentData.nextSibling = child;
+      }
+      _lastChild = child;
+      if (_firstChild == null)
+        _firstChild = child;
+    } else {
+      assert(_firstChild != null);
+      assert(_lastChild != null);
+      assert(_debugUltimatePreviousSiblingOf(before, equals: _firstChild));
+      assert(_debugUltimateNextSiblingOf(before, equals: _lastChild));
+      assert(before.parentData is ParentDataType);
+      if (before.parentData.previousSibling == null) {
+        // insert at the start (_firstChild); we'll end up with two or more children
+        assert(before == _firstChild);
+        child.parentData.nextSibling = before;
+        before.parentData.previousSibling = child;
+        _firstChild = child;
+      } else {
+        // insert in the middle; we'll end up with three or more children
+        // set up links from child to siblings
+        child.parentData.previousSibling = before.parentData.previousSibling;
+        child.parentData.nextSibling = before;
+        // set up links from siblings to child
+        assert(child.parentData.previousSibling.parentData is ParentDataType);
+        assert(child.parentData.nextSibling.parentData is ParentDataType);
+        child.parentData.previousSibling.parentData.nextSibling = child;
+        child.parentData.nextSibling.parentData.previousSibling = child;
+        assert(before.parentData.previousSibling == child);
+      }
+    }
+    markNeedsLayout();
+  }
+  void remove(ChildType child) {
+    assert(child.parentData is ParentDataType);
+    assert(_debugUltimatePreviousSiblingOf(child, equals: _firstChild));
+    assert(_debugUltimateNextSiblingOf(child, equals: _lastChild));
+    if (child.parentData.previousSibling == null) {
+      assert(_firstChild == child);
+      _firstChild = child.parentData.nextSibling;
+    } else {
+      assert(child.parentData.previousSibling.parentData is ParentDataType);
+      child.parentData.previousSibling.parentData.nextSibling = child.parentData.nextSibling;
+    }
+    if (child.parentData.nextSibling == null) {
+      assert(_lastChild == child);
+      _lastChild = child.parentData.previousSibling;
+    } else {
+      assert(child.parentData.nextSibling.parentData is ParentDataType);
+      child.parentData.nextSibling.parentData.previousSibling = child.parentData.previousSibling;
+    }
+    child.parentData.previousSibling = null;
+    child.parentData.nextSibling = null;
+    dropChild(child);
+    markNeedsLayout();
+  }
+  void redepthChildren() {
+    ChildType child = _firstChild;
+    while (child != null) {
+      redepthChild(child);
+      assert(child.parentData is ParentDataType);
+      child = child.parentData.nextSibling;
+    }
+  }
+  void attachChildren() {
+    ChildType child = _firstChild;
+    while (child != null) {
+      child.attach();
+      assert(child.parentData is ParentDataType);
+      child = child.parentData.nextSibling;
+    }
+  }
+  void detachChildren() {
+    ChildType child = _firstChild;
+    while (child != null) {
+      child.detach();
+      assert(child.parentData is ParentDataType);
+      child = child.parentData.nextSibling;
+    }
+  }
+
+  ChildType get firstChild => _firstChild;
+  ChildType get lastChild => _lastChild;
+  ChildType childAfter(ChildType child) {
+    assert(child.parentData is ParentDataType);
+    return child.parentData.nextSibling;
+  }
+
+}
+
+
+// GENERIC BOX RENDERING
+// Anything that has a concept of x, y, width, height is going to derive from this
+
+class BoxDimensions {
+  const BoxDimensions({this.width, this.height});
+  final double width;
+  final double height;
+}
+
+class BoxParentData extends ParentData {
+  double x = 0.0;
+  double y = 0.0;
+}
+
+abstract class RenderBox extends RenderNode {
+
+  void setupPos(RenderNode child) {
+    if (child.parentData is! BoxParentData)
+      child.parentData = new BoxParentData();
+  }
+
+  // override this to report what dimensions you would have if you
+  // were laid out with the given constraints this can walk the tree
+  // if it must, but it should be as cheap as possible; just get the
+  // dimensions and nothing else (e.g. don't calculate hypothetical
+  // child positions if they're not needed to determine dimensions)
+  BoxDimensions getIntrinsicDimensions({
+    double minWidth: 0.0,
+    double maxWidth: double.INFINITY,
+    double minHeight: 0.0,
+    double maxHeight: double.INFINITY
+  }) {
+    return new BoxDimensions(
+      width: clamp(min: minWidth, max: maxWidth),
+      height: clamp(min: minHeight, max: maxHeight)
+    );
+  }
+
+  void layout({
+    double minWidth: 0.0,
+    double maxWidth: double.INFINITY,
+    double minHeight: 0.0,
+    double maxHeight: double.INFINITY,
+    RenderNode relayoutSubtreeRoot
+  }) {
+    width = clamp(min: minWidth, max: maxWidth);
+    height = clamp(min: minHeight, max: maxHeight);
+    layoutDone();
+  }
+
+  double width;
+  double height;
+
+  void rotate({
+    int oldAngle, // 0..3
+    int newAngle, // 0..3
+    Duration time
+  }) { }
+
+}
+
+
+// SCREEN LAYOUT MANAGER
+
+class Screen extends RenderNode {
+
+  Screen({
+    RenderBox root,
+    this.timeForRotation: const Duration(microseconds: 83333)
+  }) {
+    assert(root != null);
+    this.root = root;
+  }
+
+  double _width;
+  double get width => _width;
+  double _height;
+  double get height => _height;
+
+  int _orientation; // 0..3
+  int get orientation => _orientation;
+  Duration timeForRotation;
+
+  RenderBox _root;
+  RenderBox get root => _root;
+  void set root (RenderBox value) {
+    assert(root != null);
+    _root = value;
+    adoptChild(_root);
+    markNeedsLayout();
+  }
+
+  void layout({
+    double newWidth,
+    double newHeight,
+    int newOrientation
+  }) {
+    assert(root != null);
+    if (newOrientation != orientation) {
+      if (orientation != null)
+        root.rotate(oldAngle: orientation, newAngle: newOrientation, time: timeForRotation);
+      _orientation = newOrientation;
+    }
+    if ((newWidth != width) || (newHeight != height)) {
+      _width = newWidth;
+      _height = newHeight;
+      relayout();
+    }
+  }
+
+  void relayout() {
+    assert(root != null);
+    root.layout(
+      minWidth: width,
+      maxWidth: width,
+      minHeight: height,
+      maxHeight: height
+    );
+    assert(root.width == width);
+    assert(root.height == height);
+  }
+
+  void rotate({ int oldAngle, int newAngle, Duration time }) {
+    assert(false); // nobody tells the screen to rotate, the whole rotate() dance is started from our layout()
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    canvas.paintChild(root, 0.0, 0.0);
+  }
+
+  void paintFrame() {
+    RenderNode._debugDoingPaint = true;
+    var canvas = new RenderNodeDisplayList(sky.view.width, sky.view.height);
+    paint(canvas);
+    sky.view.picture = canvas.endRecording();
+    sky.view.schedulePaint();
+    RenderNode._debugDoingPaint = false;
+  }
+
+}
+
+
+// BLOCK LAYOUT MANAGER
+
+class EdgeDims {
+  // used for e.g. padding
+  const EdgeDims(this.top, this.right, this.bottom, this.left);
+  final double top;
+  final double right;
+  final double bottom;
+  final double left;
+  operator ==(EdgeDims other) => (top == other.top) ||
+                                 (right == other.right) ||
+                                 (bottom == other.bottom) ||
+                                 (left == other.left);
+}
+
+class BlockParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> { }
+
+class BlockBox extends RenderBox with ContainerRenderNodeMixin<RenderBox, BlockParentData> {
+  // lays out RenderBox children in a vertical stack
+  // uses the maximum width provided by the parent
+  // sizes itself to the height of its child stack
+
+  BlockBox({
+    EdgeDims padding: const EdgeDims(0.0, 0.0, 0.0, 0.0)
+  }) {
+    _padding = padding;
+  }
+
+  EdgeDims _padding;
+  EdgeDims get padding => _padding;
+  void set padding(EdgeDims value) {
+    assert(value != null);
+    if (_padding != value) {
+      _padding = value;
+      markNeedsLayout();
+    }
+  }
+
+  void setupPos(RenderBox child) {
+    if (child.parentData is! BlockParentData)
+      child.parentData = new BlockParentData();
+  }
+
+  // override this to report what dimensions you would have if you
+  // were laid out with the given constraints this can walk the tree
+  // if it must, but it should be as cheap as possible; just get the
+  // dimensions and nothing else (e.g. don't calculate hypothetical
+  // child positions if they're not needed to determine dimensions)
+  BoxDimensions getIntrinsicDimensions({
+    double minWidth: 0.0,
+    double maxWidth: double.INFINITY,
+    double minHeight: 0.0,
+    double maxHeight: double.INFINITY
+  }) {
+    double outerHeight = _padding.top + _padding.bottom;
+    double outerWidth = clamp(min: minWidth, max: maxWidth);
+    double innerWidth = outerWidth - (_padding.left + _padding.right);
+    RenderBox child = _firstChild;
+    while (child != null) {
+      outerHeight += child.getIntrinsicDimensions(minWidth: innerWidth, maxWidth: innerWidth).height;
+      assert(child.parentData is BlockParentData);
+      child = child.parentData.nextSibling;
+    }
+    return new BoxDimensions(
+      width: outerWidth,
+      height: clamp(min: minHeight, max: maxHeight, value: outerHeight)
+    );
+  }
+
+  double _minHeight; // value cached from parent for relayout call
+  double _maxHeight; // value cached from parent for relayout call
+  void layout({
+    double minWidth: 0.0,
+    double maxWidth: double.INFINITY,
+    double minHeight: 0.0,
+    double maxHeight: double.INFINITY,
+    RenderNode relayoutSubtreeRoot
+  }) {
+    if (relayoutSubtreeRoot != null)
+      saveRelayoutSubtreeRoot(relayoutSubtreeRoot);
+    relayoutSubtreeRoot = relayoutSubtreeRoot == null ? this : relayoutSubtreeRoot;
+    width = clamp(min: minWidth, max: maxWidth);
+    _minHeight = minHeight;
+    _maxHeight = maxHeight;
+    internalLayout(relayoutSubtreeRoot);
+  }
+
+  void relayout() {
+    internalLayout(this);
+  }
+
+  void internalLayout(RenderNode relayoutSubtreeRoot) {
+    assert(_minHeight != null);
+    assert(_maxHeight != null);
+    double y = _padding.top;
+    double innerWidth = width - (_padding.left + _padding.right);
+    RenderBox child = _firstChild;
+    while (child != null) {
+      child.layout(minWidth: innerWidth, maxWidth: innerWidth, relayoutSubtreeRoot: relayoutSubtreeRoot);
+      assert(child.parentData is BlockParentData);
+      child.parentData.x = 0.0;
+      child.parentData.y = y;
+      y += child.height;
+      child = child.parentData.nextSibling;
+    }
+    height = clamp(min: _minHeight, value: y + _padding.bottom, max: _maxHeight);
+    layoutDone();
+  }
+
+  void handlePointer(sky.PointerEvent event, { double x: 0.0, double y: 0.0 }) {
+    // the x, y parameters have the top left of the node's box as the origin
+    RenderBox child = _lastChild;
+    while (child != null) {
+      assert(child.parentData is BlockParentData);
+      if ((x >= child.parentData.x) && (x < child.parentData.x + child.width) &&
+          (y >= child.parentData.y) && (y < child.parentData.y + child.height)) {
+        child.handlePointer(event, x: x-child.parentData.x, y: y-child.parentData.y);
+        break;
+      }
+      child = child.parentData.previousSibling;
+    }
+    super.handlePointer(event);
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    RenderBox child = _firstChild;
+    while (child != null) {
+      assert(child.parentData is BlockParentData);
+      canvas.paintChild(child, child.parentData.x, child.parentData.y);
+      child = child.parentData.nextSibling;
+    }
+  }
+
+}
+
+class FlexBoxParentData extends BoxParentData {
+  int flex;
+  void merge(FlexBoxParentData other) {
+    if (other.flex != null)
+      flex = other.flex;
+    super.merge(other);
+  }
+}
+
+enum FlexDirection { Row, Column }
+
+// TODO(ianh): FlexBox
+
+
+// SCAFFOLD LAYOUT MANAGER
+
+// a sample special-purpose layout manager
+
+class ScaffoldBox extends RenderBox {
+
+  ScaffoldBox(this.toolbar, this.body, this.statusbar, this.drawer) {
+    assert(body != null);
+  }
+
+  final RenderBox toolbar;
+  final RenderBox body;
+  final RenderBox statusbar;
+  final RenderBox drawer;
+
+  void layout({
+    double minWidth: 0.0,
+    double maxWidth: double.INFINITY,
+    double minHeight: 0.0,
+    double maxHeight: double.INFINITY,
+    RenderNode relayoutSubtreeRoot
+  }) {
+    width = clamp(min: minWidth, max: maxWidth);
+    height = clamp(min: minHeight, max: maxHeight);
+    relayout();
+  }
+
+  static const kToolbarHeight = 100.0;
+  static const kStatusbarHeight = 50.0;
+
+  void relayout() {
+    double bodyHeight = height;
+    if (toolbar != null) {
+      toolbar.layout(minWidth: width, maxWidth: width, minHeight: kToolbarHeight, maxHeight: kToolbarHeight);
+      assert(toolbar.parentData is BoxParentData);
+      toolbar.parentData.x = 0.0;
+      toolbar.parentData.y = 0.0;
+      bodyHeight -= kToolbarHeight;
+    }
+    if (statusbar != null) {
+      statusbar.layout(minWidth: width, maxWidth: width, minHeight: kStatusbarHeight, maxHeight: kStatusbarHeight);
+      assert(statusbar.parentData is BoxParentData);
+      statusbar.parentData.x = 0.0;
+      statusbar.parentData.y = height - kStatusbarHeight;
+      bodyHeight -= kStatusbarHeight;
+    }
+    body.layout(minWidth: width, maxWidth: width, minHeight: bodyHeight, maxHeight: bodyHeight);
+    if (drawer != null)
+      drawer.layout(minWidth: 0.0, maxWidth: width, minHeight: height, maxHeight: height);
+    layoutDone();
+  }
+
+  void handlePointer(sky.PointerEvent event, { double x: 0.0, double y: 0.0 }) {
+    if ((drawer != null) && (x < drawer.width)) {
+      drawer.handlePointer(event, x: x, y: y);
+    } else if ((toolbar != null) && (y < toolbar.height)) {
+      toolbar.handlePointer(event, x: x, y: y);
+    } else if ((statusbar != null) && (y > (statusbar.parentData as BoxParentData).y)) {
+      statusbar.handlePointer(event, x: x, y: y-(statusbar.parentData as BoxParentData).y);
+    } else {
+      body.handlePointer(event, x: x, y: y-(body.parentData as BoxParentData).y);
+    }
+    super.handlePointer(event, x: x, y: y);
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    canvas.paintChild(body, (body.parentData as BoxParentData).x, (body.parentData as BoxParentData).y);
+    if (statusbar != null)
+      canvas.paintChild(statusbar, (statusbar.parentData as BoxParentData).x, (statusbar.parentData as BoxParentData).y);
+    if (toolbar != null)
+      canvas.paintChild(toolbar, (toolbar.parentData as BoxParentData).x, (toolbar.parentData as BoxParentData).y);
+    if (drawer != null)
+      canvas.paintChild(drawer, (drawer.parentData as BoxParentData).x, (drawer.parentData as BoxParentData).y);
+  }
+
+}
diff --git a/sdk/lib/framework/node.dart b/sdk/lib/framework/node.dart
index ea51099c43f..59dbfbdcd99 100644
--- a/sdk/lib/framework/node.dart
+++ b/sdk/lib/framework/node.dart
@@ -1,6 +1,6 @@
 library node;
 
-class Node {
+class AbstractNode {
 
   // Nodes always have a 'depth' greater than their ancestors'.
   // There's no guarantee regarding depth between siblings. The depth
@@ -15,7 +15,7 @@ class Node {
 
   int _depth = 0;
   int get depth => _depth;
-  void redepthChild(Node child) { // internal, do not call
+  void redepthChild(AbstractNode child) { // internal, do not call
     assert(child._attached == _attached);
     if (child._depth <= _depth) {
       child._depth = _depth + 1;
@@ -44,9 +44,9 @@ class Node {
   }
   detachChildren() { } // workaround for lack of inter-class mixins in Dart
 
-  Node _parent;
-  Node get parent => _parent;
-  void adoptChild(Node child) { // only for use by subclasses
+  AbstractNode _parent;
+  AbstractNode get parent => _parent;
+  void adoptChild(AbstractNode child) { // only for use by subclasses
     assert(child != null);
     assert(child._parent == null);
     child._parent = this;
@@ -54,7 +54,7 @@ class Node {
       child.attach();
     redepthChild(child);
   }
-  void dropChild(Node child) { // only for use by subclasses
+  void dropChild(AbstractNode child) { // only for use by subclasses
     assert(child != null);
     assert(child._parent == this);
     assert(child.attached == attached);