fn3: Add a binding for fn3 and sky.

- I extracted the BuildScheduler into a separate binding.dart file.
- Various changes to expose private members that are needed by
  binding.dart.
- Registering the render objects for event dispatch.
- Convert the tests to use the new binding mechanism.

This doesn't yet have a RenderView or event handling.

packages/flutter/lib/src/fn3.dart

@@ -6,3 +6,4 @@ library fn3;
 
 export 'fn3/basic.dart';
 export 'fn3/framework.dart';
+export 'fn3/binding.dart';

packages/flutter/lib/src/fn3/binding.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/animation.dart';
+import 'package:sky/rendering.dart';
+import 'package:sky/src/fn3/framework.dart';
+
+class WidgetSkyBinding extends SkyBinding {
+
+  WidgetSkyBinding({ RenderView renderViewOverride: null })
+    : super(renderViewOverride: renderViewOverride) {
+    BuildableElement.scheduleBuildFor = this.scheduleBuildFor;
+  }
+
+  /// Ensures that there is a SkyBinding object instantiated.
+  static void initWidgetSkyBinding({ RenderView renderViewOverride: null }) {
+    if (SkyBinding.instance == null)
+      new WidgetSkyBinding(renderViewOverride: renderViewOverride);
+    assert(SkyBinding.instance is WidgetSkyBinding);
+  }
+
+  static WidgetSkyBinding get instance => SkyBinding.instance;
+
+  void handleEvent(sky.Event event, BindingHitTestEntry entry) {
+    for (HitTestEntry entry in entry.result.path) {
+      if (entry.target is! RenderObject)
+        continue;
+      for (Widget target in RenderObjectElement.getElementsForRenderObject(entry.target)) {
+        // TODO(ianh): implement event handling
+        // if (target is ListenerElement)
+        //  target.handleEvent(event);
+      }
+    }
+    super.handleEvent(event, entry);
+  }
+
+  void beginFrame(double timeStamp) {
+    buildDirtyElements();
+    super.beginFrame(timeStamp);
+  }
+
+  final List<BuildableElement> _dirtyElements = new List<BuildableElement>();
+
+  int _debugBuildingAtDepth;
+
+  /// Adds an element to the dirty elements list so that it will be rebuilt
+  /// when buildDirtyElements is called.
+  void scheduleBuildFor(BuildableElement element) {
+    assert(_debugBuildingAtDepth == null || element.depth > _debugBuildingAtDepth);
+    assert(!_dirtyElements.contains(element));
+    assert(element.dirty);
+    if (_dirtyElements.isEmpty)
+      scheduler.ensureVisualUpdate();
+    _dirtyElements.add(element);
+  }
+
+  void _absorbDirtyElements(List<BuildableElement> list) {
+    assert(_debugBuildingAtDepth != null);
+    assert(!_dirtyElements.any((element) => element.depth <= _debugBuildingAtDepth));
+    _dirtyElements.sort((BuildableElement a, BuildableElement b) => a.depth - b.depth);
+    list.addAll(_dirtyElements);
+    _dirtyElements.clear();
+  }
+
+  /// Builds all the elements that were marked as dirty using schedule(), in depth order.
+  /// If elements are marked as dirty while this runs, they must be deeper than the algorithm
+  /// has yet reached.
+  /// This is called by beginFrame().
+  void buildDirtyElements() {
+    assert(_debugBuildingAtDepth == null);
+    if (_dirtyElements.isEmpty)
+      return;
+    assert(() { _debugBuildingAtDepth = 0; return true; });
+    List<BuildableElement> sortedDirtyElements = new List<BuildableElement>();
+    int index = 0;
+    do {
+      _absorbDirtyElements(sortedDirtyElements);
+      for (; index < sortedDirtyElements.length; index += 1) {
+        BuildableElement element = sortedDirtyElements[index];
+        assert(() {
+          if (element.depth > _debugBuildingAtDepth)
+            _debugBuildingAtDepth = element.depth;
+          return element.depth == _debugBuildingAtDepth;
+        });
+        element.rebuild();
+      }
+    } while (_dirtyElements.isNotEmpty);
+    assert(() { _debugBuildingAtDepth = null; return true; });
+  }
+}

packages/flutter/lib/src/fn3/framework.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/animation.dart';
 import 'package:sky/rendering.dart';
 
 abstract class Key {
@@ -144,7 +143,7 @@ abstract class ComponentState<T extends StatefulComponent> {
   /// rendering will not be updated.
   void setState(void fn()) {
     fn();
-    _element.scheduleBuild();
+    _element.markNeedsBuild();
   }
 
   /// The current configuration (an instance of the corresponding
@@ -201,6 +200,7 @@ abstract class Element<T extends Widget> {
 
   /// An integer that is guaranteed to be greater than the parent's, if any.
   /// The element at the root of the tree must have a depth greater than 0.
+  int get depth => _depth;
   int _depth;
 
   /// The configuration for this element.
@@ -270,6 +270,7 @@ abstract class Element<T extends Widget> {
 
   /// Called when an Element is given a new parent shortly after having been
   /// created.
+  // TODO(ianh): rename to didMount
   void mount(Element parent, dynamic slot) {
     assert(_debugLifecycleState == _ElementLifecycle.initial);
     assert(_widget != null);
@@ -347,20 +348,17 @@ abstract class Element<T extends Widget> {
 
   /// Called when an Element is removed from the tree.
   /// Currently, an Element removed from the tree never returns.
+  // TODO(ianh): rename to didUnmount
   void unmount() {
     assert(_debugLifecycleState == _ElementLifecycle.mounted);
     assert(_widget != null);
     assert(_depth != null);
     assert(() { _debugLifecycleState = _ElementLifecycle.defunct; return true; });
   }
-
-  // TODO(ianh): Merge this into the binding, expose for tests
-  static void flushBuild() {
-    _buildScheduler.buildDirtyElements();
-  }
 }
 
 typedef Widget WidgetBuilder();
+typedef void BuildScheduler(BuildableElement element);
 
 /// Base class for the instantiation of StatelessComponent and StatefulComponent
 /// widgets.
@@ -369,18 +367,29 @@ abstract class BuildableElement<T extends Widget> extends Element<T> {
 
   WidgetBuilder _builder;
   Element _child;
+
+  /// Returns true if the element has been marked as needing rebuilding.
+  bool get dirty => _dirty;
   bool _dirty = true;
 
   void mount(Element parent, dynamic slot) {
     super.mount(parent, slot);
     assert(_child == null);
-    _rebuild();
+    rebuild();
     assert(_child != null);
   }
 
-  // This is also called for the first build
-  void _rebuild() {
+  /// Reinvokes the build() method of the StatelessComponent object (for
+  /// stateless components) or the ComponentState object (for stateful
+  /// components) and then updates the widget tree.
+  ///
+  /// Called automatically during didMount() to generate the first build, by the
+  /// binding when scheduleBuild() has been called to mark this element dirty,
+  /// and by update() when the Widget has changed.
+  void rebuild() {
     assert(_debugLifecycleState == _ElementLifecycle.mounted);
+    if (!_dirty)
+      return;
     _dirty = false;
     Widget built;
     try {
@@ -392,11 +401,7 @@ abstract class BuildableElement<T extends Widget> extends Element<T> {
     _child = _updateChild(_child, built, _slot);
   }
 
-  /// Called by the binding when scheduleBuild() has been called to mark this element dirty.
-  void _rebuildIfNeeded() {
-    if (_dirty)
-      _rebuild();
-  }
+  static BuildScheduler scheduleBuildFor;
 
   /// Marks the element as dirty and adds it to the global list of widgets to
   /// rebuild in the next frame.
@@ -405,12 +410,13 @@ abstract class BuildableElement<T extends Widget> extends Element<T> {
   /// applications and components should be structured so as to only mark
   /// components dirty during event handlers before the frame begins, not during
   /// the build itself.
-  void scheduleBuild() {
+  void markNeedsBuild() {
     assert(_debugLifecycleState == _ElementLifecycle.mounted);
     if (_dirty)
       return;
     _dirty = true;
-    _buildScheduler.schedule(this);
+    assert(scheduleBuildFor != null);
+    scheduleBuildFor(this);
   }
 
   void visitChildren(ElementVisitor visitor) {
@@ -434,7 +440,8 @@ class StatelessComponentElement extends BuildableElement<StatelessComponent> {
     super.update(newWidget);
     assert(_widget == newWidget);
     _builder = _widget.build;
-    _rebuild();
+    _dirty = true;
+    rebuild();
   }
 }
 
@@ -456,7 +463,8 @@ class StatefulComponentElement extends BuildableElement<StatefulComponent> {
     StatefulComponent oldConfig = _state._config;
     _state._config = _widget;
     _state.didUpdateConfig(oldConfig);
-    _rebuild();
+    _dirty = true;
+    rebuild();
   }
 
   void unmount() {
@@ -482,8 +490,20 @@ abstract class RenderObjectElement<T extends RenderObjectWidget> extends Element
     return ancestor;
   }
 
+  static Map<RenderObject, RenderObjectElement> _registry = new Map<RenderObject, RenderObjectElement>();
+  static Iterable<RenderObjectElement> getElementsForRenderObject(RenderObject renderObject) sync* {
+    Element target = _registry[renderObject];
+    while (target != null) {
+      yield target;
+      target = target._parent;
+      if (target is RenderObjectElement)
+        break;
+    }
+  }
+
   void mount(Element parent, dynamic slot) {
     super.mount(parent, slot);
+    _registry[renderObject] = this;
     assert(_ancestorRenderObjectElement == null);
     _ancestorRenderObjectElement = _findAncestorRenderObjectElement();
     _ancestorRenderObjectElement?.insertChildRenderObject(renderObject, slot);
@@ -508,6 +528,11 @@ abstract class RenderObjectElement<T extends RenderObjectWidget> extends Element
     }
   }
 
+  void unmount() {
+    super.unmount();
+    _registry.remove(renderObject);
+  }
+
   void insertChildRenderObject(RenderObject child, dynamic slot);
 
   void removeChildRenderObject(RenderObject child);
@@ -572,56 +597,6 @@ class MultiChildRenderObjectElement<T extends MultiChildRenderObjectWidget> exte
   // TODO(ianh): implement
 }
 
-class _BuildScheduler {
-  final List<BuildableElement> _dirtyElements = new List<BuildableElement>();
-
-  int _debugBuildingAtDepth;
-
-  void schedule(BuildableElement element) {
-    assert(_debugBuildingAtDepth == null || element._depth > _debugBuildingAtDepth);
-    assert(!_dirtyElements.contains(element));
-    if (_dirtyElements.isEmpty)
-      scheduler.ensureVisualUpdate();
-    _dirtyElements.add(element);
-  }
-
-  void _absorbDirtyElements(List<BuildableElement> list) {
-    assert(_debugBuildingAtDepth != null);
-    assert(!_dirtyElements.any((element) => element._depth <= _debugBuildingAtDepth));
-    _dirtyElements.sort((BuildableElement a, BuildableElement b) => a._depth - b._depth);
-    list.addAll(_dirtyElements);
-    _dirtyElements.clear();
-  }
-
-  /// Builds all the elements that were marked as dirty using schedule(), in depth order.
-  /// If elements are marked as dirty while this runs, they must be deeper than the algorithm
-  /// has yet reached.
-  void buildDirtyElements() {
-    assert(_debugBuildingAtDepth == null);
-    if (_dirtyElements.isEmpty)
-      return;
-    assert(() { _debugBuildingAtDepth = 0; return true; });
-    List<BuildableElement> sortedDirtyElements = new List<BuildableElement>();
-    int index = 0;
-    do {
-      _absorbDirtyElements(sortedDirtyElements);
-      for (; index < sortedDirtyElements.length; index += 1) {
-        BuildableElement element = sortedDirtyElements[index];
-        assert(() {
-          if (element._depth > _debugBuildingAtDepth)
-            _debugBuildingAtDepth = element._depth;
-          return element._depth == _debugBuildingAtDepth;
-        });
-        element._rebuildIfNeeded();
-      }
-    } while (_dirtyElements.isNotEmpty);
-    assert(() { _debugBuildingAtDepth = null; return true; });
-  }
-}
-
-final _BuildScheduler _buildScheduler = new _BuildScheduler();
-
-
 typedef void WidgetsExceptionHandler(String context, dynamic exception, StackTrace stack);
 /// This callback is invoked whenever an exception is caught by the widget
 /// system. The 'context' argument is a description of what was happening when

packages/unit/test/fn3/render_object_widget_test.dart

@@ -8,6 +8,12 @@ final BoxDecoration kBoxDecorationA = new BoxDecoration();
 final BoxDecoration kBoxDecorationB = new BoxDecoration();
 final BoxDecoration kBoxDecorationC = new BoxDecoration();
 
+class TestComponent extends StatelessComponent {
+  const TestComponent({ this.child });
+  final Widget child;
+  Widget build() => child;
+}
+
 void main() {
   test('RenderObjectWidget smoke test', () {
     WidgetTester tester = new WidgetTester();

packages/unit/test/fn3/stateful_component_test.dart

@@ -78,7 +78,8 @@ void main() {
     checkTree(kBoxDecorationB);
 
     flipStatefulComponent(tester);
-    Element.flushBuild();
+
+    tester.pumpFrameWithoutChange();
 
     checkTree(kBoxDecorationA);
 
@@ -105,7 +106,8 @@ void main() {
     expect(TestBuildCounter.buildCount, equals(1));
 
     flipStatefulComponent(tester);
-    Element.flushBuild();
+
+    tester.pumpFrameWithoutChange();
 
     expect(TestBuildCounter.buildCount, equals(1));
   });

packages/unit/test/fn3/widget_tester.dart

-import 'package:sky/src/fn3/framework.dart';
+import 'package:sky/src/fn3.dart';
 
-class TestComponent extends StatelessComponent {
-  TestComponent({ this.child });
-  final Widget child;
+class RootComponent extends StatefulComponent {
+  RootComponentState createState() => new RootComponentState(this);
+}
+
+class RootComponentState extends ComponentState<RootComponent> {
+  RootComponentState(RootComponent widget) : super(widget);
+  Widget _child = new DecoratedBox(decoration: new BoxDecoration());
+  Widget get child => _child;
+  void set child(Widget value) {
+    if (value != _child) {
+      setState(() {
+        _child = value;
+      });
+    }
+  }
   Widget build() => child;
 }
 
-final Object _rootSlot = new Object();
+const Object _rootSlot = const Object();
 
 class WidgetTester {
-  StatelessComponentElement _rootElement;
+
+  WidgetTester() {
+    WidgetSkyBinding.initWidgetSkyBinding();
+    _rootElement = new StatefulComponentElement(new RootComponent());
+    _rootElement.mount(null, _rootSlot);
+  }
+
+  StatefulComponentElement _rootElement;
 
   void walkElements(ElementVisitor visitor) {
     void walk(Element element) {
@@ -35,12 +54,12 @@ class WidgetTester {
   }
 
   void pumpFrame(Widget widget) {
-    if (_rootElement == null) {
-      _rootElement = new StatelessComponentElement(new TestComponent(child: widget));
-      _rootElement.mount(null, _rootSlot);
-    } else {
-      _rootElement.update(new TestComponent(child: widget));
-    }
+    (_rootElement.state as RootComponentState).child = widget;
+    WidgetSkyBinding.instance.beginFrame(0.0); // TODO(ianh): https://github.com/flutter/engine/issues/1084
+  }
+
+  void pumpFrameWithoutChange() {
+    WidgetSkyBinding.instance.beginFrame(0.0); // TODO(ianh): https://github.com/flutter/engine/issues/1084
   }
 
 }