public/lib/ui/flutter/child_view.dart - topaz - Git at Google

 // Copyright 2016 The Fuchsia 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:async';
 import 'dart:ui' as ui;

 import 'package:fidl/fidl.dart';
 import 'package:fidl_fuchsia_sys/fidl.dart';
 import 'package:fidl_fuchsia_math/fidl_async.dart';
 import 'package:fidl_fuchsia_ui_app/fidl.dart' as app;
 import 'package:fidl_fuchsia_ui_viewsv1/fidl_async.dart';
 import 'package:fidl_fuchsia_ui_viewsv1token/fidl.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:fuchsia_scenic_flutter/view_container.dart'
     show
         nextGlobalViewKey,
         globalViewContainer,
         ViewContainerListenerDelegate,
         ViewContainerListenerImpl;
 import 'package:lib.app.dart/app.dart';
 import 'package:meta/meta.dart';
 import 'package:zircon/zircon.dart';

 import 'mozart.dart';

 typedef ChildViewConnectionCallback = void Function(
     ChildViewConnection connection);
 void _emptyConnectionCallback(ChildViewConnection c) {}

 /// A connection with a child view.
 ///
 /// Used with the [ChildView] widget to display a child view.
 class ChildViewConnection implements ViewContainerListenerDelegate {
   ChildViewConnection(InterfaceHandle<ViewOwner> viewOwner,
       {ChildViewConnectionCallback onAvailable,
       ChildViewConnectionCallback onUnavailable})
       : this.fromViewHolderToken(
             EventPair(viewOwner?.passChannel()?.passHandle()),
             onAvailable: onAvailable,
             onUnavailable: onUnavailable);

   ChildViewConnection.fromViewHolderToken(EventPair viewHolderToken,
       {ChildViewConnectionCallback onAvailable,
       ChildViewConnectionCallback onUnavailable})
       : _onAvailableCallback = onAvailable ?? _emptyConnectionCallback,
         _onUnavailableCallback = onUnavailable ?? _emptyConnectionCallback,
         _viewHolderToken = viewHolderToken {
     assert(_viewHolderToken != null);
   }

   factory ChildViewConnection.launch(String url, Launcher launcher,
       {InterfaceRequest<ComponentController> controller,
       InterfaceRequest<ServiceProvider> childServices,
       ChildViewConnectionCallback onAvailable,
       ChildViewConnectionCallback onUnavailable}) {
     final Services services = Services();
     final LaunchInfo launchInfo =
         LaunchInfo(url: url, directoryRequest: services.request());
     try {
       launcher.createComponent(launchInfo, controller);
       return ChildViewConnection.connect(services,
           childServices: childServices,
           onAvailable: onAvailable,
           onUnavailable: onUnavailable);
     } finally {
       services.close();
     }
   }

   factory ChildViewConnection.connect(Services services,
       {InterfaceRequest<ServiceProvider> childServices,
       ChildViewConnectionCallback onAvailable,
       ChildViewConnectionCallback onUnavailable}) {
     final app.ViewProviderProxy viewProvider = app.ViewProviderProxy();
     services.connectToService(viewProvider.ctrl);
     try {
       EventPairPair viewTokens = EventPairPair();
       assert(viewTokens.status == ZX.OK);

       viewProvider.createView(viewTokens.second, childServices, null);
       return ChildViewConnection.fromViewHolderToken(viewTokens.first,
           onAvailable: onAvailable, onUnavailable: onUnavailable);
     } finally {
       viewProvider.ctrl.close();
     }
   }

   final ChildViewConnectionCallback _onAvailableCallback;
   final ChildViewConnectionCallback _onUnavailableCallback;
   EventPair _viewHolderToken;

   int _viewKey;
   ViewProperties _currentViewProperties;
   bool _available = false;

   VoidCallback _onViewInfoAvailable;
   ui.SceneHost _sceneHost;

   @override
   void onAvailable() {
     _available = true;
     if (_onViewInfoAvailable != null) {
       _onViewInfoAvailable();
     }
     _onAvailableCallback(this);
   }

   @override
   void onUnavailable() {
     _available = false;
     _onUnavailableCallback(this);
   }

   void _addChildToViewHost() {
     if (globalViewContainer == null) {
       return;
     }
     assert(_attached);
     assert(_viewHolderToken != null);
     assert(_viewKey == null);
     assert(!_available);
     assert(_sceneHost == null);

     final EventPairPair sceneTokens = EventPairPair();
     assert(sceneTokens.status == ZX.OK);

     // Analyzer doesn't know Handle must be dart:zircon's Handle
     _sceneHost = ui.SceneHost(sceneTokens.first.passHandle());
     _viewKey = nextGlobalViewKey();
     globalViewContainer.addChild2(
         _viewKey, _viewHolderToken, sceneTokens.second);
     _viewHolderToken = null;
     assert(
         !ViewContainerListenerImpl.instance.containsConnectionForKey(_viewKey));
     ViewContainerListenerImpl.instance.addConnectionForKey(_viewKey, this);
   }

   void _removeChildFromViewHost() {
     if (globalViewContainer == null) {
       return;
     }
     assert(!_attached);
     assert(_viewHolderToken == null);
     assert(_viewKey != null);
     assert(_sceneHost != null);
     assert(ViewContainerListenerImpl.instance.getConnectionForKey(_viewKey) ==
         this);
     final EventPairPair viewTokens = EventPairPair();
     assert(viewTokens.status == ZX.OK);
     ViewContainerListenerImpl.instance.removeConnectionForKey(_viewKey);
     _viewHolderToken = viewTokens.first;
     globalViewContainer.removeChild2(_viewKey, viewTokens.second);
     _viewKey = null;
     _available = false;
     _currentViewProperties = null;
     _sceneHost.dispose();
     _sceneHost = null;
   }

   /// Only call when the connection is available.
   void requestFocus() {
     if (_viewKey != null) {
       // TODO(SCN-1186): Use new mechanism to implement RequestFocus.
     }
   }

   // The number of render objects attached to this view. In between frames, we
   // might have more than one connected if we get added to a new render object
   // before we get removed from the old render object. By the time we get around
   // to computing our layout, we must be back to just having one render object.
   int _attachments = 0;
   bool get _attached => _attachments > 0;

   void _attach() {
     assert(_attachments >= 0);
     ++_attachments;
     if (_viewKey == null) {
       _addChildToViewHost();
     }
   }

   void _detach() {
     assert(_attached);
     --_attachments;
     scheduleMicrotask(_removeChildFromViewHostIfNeeded);
   }

   void _removeChildFromViewHostIfNeeded() {
     assert(_attachments >= 0);
     if (_attachments == 0 && _viewKey != null) {
       _removeChildFromViewHost();
     }
   }

   void sendSizeChangeHintHack(
       double widthChangeFactor, double heightChangeFactor) {
     assert(_attached);
     assert(_attachments == 1);
     if (_viewKey == null) {
       return;
     }

     if (globalViewContainer == null) {
       return;
     }

     globalViewContainer.sendSizeChangeHintHack(
         _viewKey, widthChangeFactor, heightChangeFactor);
   }

   ViewProperties _createViewProperties(
       double width,
       double height,
       double insetTop,
       double insetRight,
       double insetBottom,
       double insetLeft,
       bool focusable) {
     if (_currentViewProperties != null &&
         _currentViewProperties.viewLayout.size.width == width &&
         _currentViewProperties.viewLayout.size.height == height &&
         _currentViewProperties.viewLayout.inset.top == insetTop &&
         _currentViewProperties.viewLayout.inset.right == insetRight &&
         _currentViewProperties.viewLayout.inset.bottom == insetBottom &&
         _currentViewProperties.viewLayout.inset.left == insetLeft &&
         (_currentViewProperties.customFocusBehavior == null ||
                 _currentViewProperties.customFocusBehavior.allowFocus) ==
             focusable) {
       return null;
     }

     SizeF size = SizeF(width: width, height: height);
     InsetF inset = InsetF(
         top: insetTop, right: insetRight, bottom: insetBottom, left: insetLeft);
     ViewLayout viewLayout = ViewLayout(size: size, inset: inset);
     final customFocusBehavior = CustomFocusBehavior(allowFocus: focusable);
     return _currentViewProperties = ViewProperties(
       viewLayout: viewLayout,
       customFocusBehavior: customFocusBehavior,
     );
   }

   void _setChildProperties(
     double width,
     double height,
     double insetTop,
     double insetRight,
     double insetBottom,
     double insetLeft,
     bool focusable,
   ) {
     assert(_attached);
     assert(_attachments == 1);
     assert(_viewKey != null);
     if (globalViewContainer == null) {
       return;
     }
     ViewProperties viewProperties = _createViewProperties(
         width, height, insetTop, insetRight, insetBottom, insetLeft, focusable);
     if (viewProperties == null) {
       return;
     }
     globalViewContainer.setChildProperties(_viewKey, viewProperties);
   }
 }

 class _RenderChildView extends RenderBox {
   /// Creates a child view render object.
   _RenderChildView({
     ChildViewConnection connection,
     bool hitTestable = true,
     bool focusable = true,
   })  : _connection = connection,
         _hitTestable = hitTestable,
         _focusable = focusable,
         assert(hitTestable != null);

   /// The child to display.
   ChildViewConnection get connection => _connection;
   ChildViewConnection _connection;
   set connection(ChildViewConnection value) {
     if (value == _connection) {
       return;
     }
     if (attached && _connection != null) {
       _connection._detach();
       assert(_connection._onViewInfoAvailable != null);
       _connection._onViewInfoAvailable = null;
     }
     _connection = value;
     if (attached && _connection != null) {
       _connection._attach();
       assert(_connection._onViewInfoAvailable == null);
       _connection._onViewInfoAvailable = markNeedsPaint;
     }
     if (_connection == null) {
       markNeedsPaint();
     } else {
       markNeedsLayout();
     }
   }

   /// Whether this child should be included during hit testing.
   bool get hitTestable => _hitTestable;
   bool _hitTestable;
   set hitTestable(bool value) {
     assert(value != null);
     if (value == _hitTestable) {
       return;
     }
     _hitTestable = value;
     if (_connection != null) {
       markNeedsPaint();
     }
   }

   /// Whether this child should be able to recieve focus events
   bool get focusable => _focusable;
   bool _focusable;
   set focusable(bool value) {
     assert(value != null);
     if (value == _focusable) {
       return;
     }
     _focusable = value;
     if (_connection != null) {
       markNeedsPaint();
     }
   }

   @override
   void attach(PipelineOwner owner) {
     super.attach(owner);
     if (_connection != null) {
       _connection._attach();
       assert(_connection._onViewInfoAvailable == null);
       _connection._onViewInfoAvailable = markNeedsPaint;
     }
   }

   @override
   void detach() {
     if (_connection != null) {
       _connection._detach();
       assert(_connection._onViewInfoAvailable != null);
       _connection._onViewInfoAvailable = null;
     }
     super.detach();
   }

   @override
   bool get alwaysNeedsCompositing => true;

   TextPainter _debugErrorMessage;

   double _width;
   double _height;

   @override
   void performLayout() {
     size = constraints.biggest;

     // Ignore if we have no child view connection.
     if (_connection == null) {
       return;
     }

     if (_width != null && _height != null) {
       double deltaWidth = (_width - size.width).abs();
       double deltaHeight = (_height - size.height).abs();

       // Ignore insignificant changes in size that are likely rounding errors.
       if (deltaWidth < 0.0001 && deltaHeight < 0.0001) {
         return;
       }
     }

     _width = size.width;
     _height = size.height;
     _connection._setChildProperties(
         _width, _height, 0.0, 0.0, 0.0, 0.0, _focusable);
     assert(() {
       if (globalViewContainer == null) {
         _debugErrorMessage ??= TextPainter(
             text: TextSpan(
                 text:
                     'Child views are supported only when running in Scenic.'));
         _debugErrorMessage.layout(minWidth: size.width, maxWidth: size.width);
       }
       return true;
     }());
   }

   @override
   bool hitTestSelf(Offset position) => true;

   @override
   void paint(PaintingContext context, Offset offset) {
     assert(needsCompositing);
     if (_connection?._available == true) {
       context.addLayer(ChildSceneLayer(
         offset: offset,
         width: _width,
         height: _height,
         sceneHost: _connection._sceneHost,
         hitTestable: hitTestable,
       ));
     }
     assert(() {
       if (globalViewContainer == null) {
         context.canvas.drawRect(
             offset & size, Paint()..color = Color(0xFF0000FF));
         _debugErrorMessage.paint(context.canvas, offset);
       }
       return true;
     }());
   }

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(
       DiagnosticsProperty<ChildViewConnection>(
         'connection',
         connection,
       ),
     );
   }
 }

 /// A layer that represents content from another process.
 class ChildSceneLayer extends Layer {
   /// Creates a layer that displays content rendered by another process.
   ///
   /// All of the arguments must not be null.
   ChildSceneLayer({
     this.offset = Offset.zero,
     this.width = 0.0,
     this.height = 0.0,
     this.sceneHost,
     this.hitTestable = true,
   });

   /// Offset from parent in the parent's coordinate system.
   Offset offset;

   /// The horizontal extent of the child, in logical pixels.
   double width;

   /// The vertical extent of the child, in logical pixels.
   double height;

   /// The host site for content rendered by the child.
   ui.SceneHost sceneHost;

   /// Whether this child should be included during hit testing.
   ///
   /// Defaults to true.
   bool hitTestable;

   @override
   ui.EngineLayer addToScene(ui.SceneBuilder builder,
       [Offset layerOffset = Offset.zero]) {
     builder.addChildScene(
       offset: offset + layerOffset,
       width: width,
       height: height,
       sceneHost: sceneHost,
       hitTestable: hitTestable,
     );
     return null;
   }

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description
       ..add(DiagnosticsProperty<Offset>('offset', offset))
       ..add(DoubleProperty('width', width))
       ..add(DoubleProperty('height', height))
       ..add(DiagnosticsProperty<ui.SceneHost>('sceneHost', sceneHost))
       ..add(DiagnosticsProperty<bool>('hitTestable', hitTestable));
   }

   @override
   S find<S>(Offset regionOffset) => null;
 }

 /// A widget that is replaced by content from another process.
 ///
 /// Requires a [MediaQuery] ancestor to provide appropriate media information to
 /// the child.
 @immutable
 class ChildView extends LeafRenderObjectWidget {
   /// Creates a widget that is replaced by content from another process.
   ChildView({this.connection, this.hitTestable = true, this.focusable = true})
       : super(key: GlobalObjectKey(connection));

   /// A connection to the child whose content will replace this widget.
   final ChildViewConnection connection;

   /// Whether this child should be included during hit testing.
   ///
   /// Defaults to true.
   final bool hitTestable;

   /// Whether this child and its children should be allowed to receive focus.
   ///
   /// Defaults to true.
   final bool focusable;

   @override
   _RenderChildView createRenderObject(BuildContext context) {
     return _RenderChildView(
       connection: connection,
       hitTestable: hitTestable,
       focusable: focusable,
     );
   }

   @override
   void updateRenderObject(BuildContext context, _RenderChildView renderObject) {
     renderObject
       ..connection = connection
       ..hitTestable = hitTestable
       ..focusable = focusable;
   }
 }

 class View {
   /// Provide services to Scenic throught |provider|.
   ///
   /// |services| should contain the list of service names offered by the
   /// |provider|.
   static void offerServiceProvider(
       InterfaceHandle<ServiceProvider> provider, List<String> services) {
     // Analyzer doesn't know Handle must be dart:zircon's Handle
     Scenic.offerServiceProvider(provider.passChannel().handle, services);
   }
 }
	// Copyright 2016 The Fuchsia 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:async';
	import 'dart:ui' as ui;

	import 'package:fidl/fidl.dart';
	import 'package:fidl_fuchsia_sys/fidl.dart';
	import 'package:fidl_fuchsia_math/fidl_async.dart';
	import 'package:fidl_fuchsia_ui_app/fidl.dart' as app;
	import 'package:fidl_fuchsia_ui_viewsv1/fidl_async.dart';
	import 'package:fidl_fuchsia_ui_viewsv1token/fidl.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/widgets.dart';
	import 'package:fuchsia_scenic_flutter/view_container.dart'
	show
	nextGlobalViewKey,
	globalViewContainer,
	ViewContainerListenerDelegate,
	ViewContainerListenerImpl;
	import 'package:lib.app.dart/app.dart';
	import 'package:meta/meta.dart';
	import 'package:zircon/zircon.dart';

	import 'mozart.dart';

	typedef ChildViewConnectionCallback = void Function(
	ChildViewConnection connection);
	void _emptyConnectionCallback(ChildViewConnection c) {}

	/// A connection with a child view.
	///
	/// Used with the [ChildView] widget to display a child view.
	class ChildViewConnection implements ViewContainerListenerDelegate {
	ChildViewConnection(InterfaceHandle<ViewOwner> viewOwner,
	{ChildViewConnectionCallback onAvailable,
	ChildViewConnectionCallback onUnavailable})
	: this.fromViewHolderToken(
	EventPair(viewOwner?.passChannel()?.passHandle()),
	onAvailable: onAvailable,
	onUnavailable: onUnavailable);

	ChildViewConnection.fromViewHolderToken(EventPair viewHolderToken,
	{ChildViewConnectionCallback onAvailable,
	ChildViewConnectionCallback onUnavailable})
	: _onAvailableCallback = onAvailable ?? _emptyConnectionCallback,
	_onUnavailableCallback = onUnavailable ?? _emptyConnectionCallback,
	_viewHolderToken = viewHolderToken {
	assert(_viewHolderToken != null);
	}

	factory ChildViewConnection.launch(String url, Launcher launcher,
	{InterfaceRequest<ComponentController> controller,
	InterfaceRequest<ServiceProvider> childServices,
	ChildViewConnectionCallback onAvailable,
	ChildViewConnectionCallback onUnavailable}) {
	final Services services = Services();
	final LaunchInfo launchInfo =
	LaunchInfo(url: url, directoryRequest: services.request());
	try {
	launcher.createComponent(launchInfo, controller);
	return ChildViewConnection.connect(services,
	childServices: childServices,
	onAvailable: onAvailable,
	onUnavailable: onUnavailable);
	} finally {
	services.close();
	}
	}

	factory ChildViewConnection.connect(Services services,
	{InterfaceRequest<ServiceProvider> childServices,
	ChildViewConnectionCallback onAvailable,
	ChildViewConnectionCallback onUnavailable}) {
	final app.ViewProviderProxy viewProvider = app.ViewProviderProxy();
	services.connectToService(viewProvider.ctrl);
	try {
	EventPairPair viewTokens = EventPairPair();
	assert(viewTokens.status == ZX.OK);

	viewProvider.createView(viewTokens.second, childServices, null);
	return ChildViewConnection.fromViewHolderToken(viewTokens.first,
	onAvailable: onAvailable, onUnavailable: onUnavailable);
	} finally {
	viewProvider.ctrl.close();
	}
	}

	final ChildViewConnectionCallback _onAvailableCallback;
	final ChildViewConnectionCallback _onUnavailableCallback;
	EventPair _viewHolderToken;

	int _viewKey;
	ViewProperties _currentViewProperties;
	bool _available = false;

	VoidCallback _onViewInfoAvailable;
	ui.SceneHost _sceneHost;

	@override
	void onAvailable() {
	_available = true;
	if (_onViewInfoAvailable != null) {
	_onViewInfoAvailable();
	}
	_onAvailableCallback(this);
	}

	@override
	void onUnavailable() {
	_available = false;
	_onUnavailableCallback(this);
	}

	void _addChildToViewHost() {
	if (globalViewContainer == null) {
	return;
	}
	assert(_attached);
	assert(_viewHolderToken != null);
	assert(_viewKey == null);
	assert(!_available);
	assert(_sceneHost == null);

	final EventPairPair sceneTokens = EventPairPair();
	assert(sceneTokens.status == ZX.OK);

	// Analyzer doesn't know Handle must be dart:zircon's Handle
	_sceneHost = ui.SceneHost(sceneTokens.first.passHandle());
	_viewKey = nextGlobalViewKey();
	globalViewContainer.addChild2(
	_viewKey, _viewHolderToken, sceneTokens.second);
	_viewHolderToken = null;
	assert(
	!ViewContainerListenerImpl.instance.containsConnectionForKey(_viewKey));
	ViewContainerListenerImpl.instance.addConnectionForKey(_viewKey, this);
	}

	void _removeChildFromViewHost() {
	if (globalViewContainer == null) {
	return;
	}
	assert(!_attached);
	assert(_viewHolderToken == null);
	assert(_viewKey != null);
	assert(_sceneHost != null);
	assert(ViewContainerListenerImpl.instance.getConnectionForKey(_viewKey) ==
	this);
	final EventPairPair viewTokens = EventPairPair();
	assert(viewTokens.status == ZX.OK);
	ViewContainerListenerImpl.instance.removeConnectionForKey(_viewKey);
	_viewHolderToken = viewTokens.first;
	globalViewContainer.removeChild2(_viewKey, viewTokens.second);
	_viewKey = null;
	_available = false;
	_currentViewProperties = null;
	_sceneHost.dispose();
	_sceneHost = null;
	}

	/// Only call when the connection is available.
	void requestFocus() {
	if (_viewKey != null) {
	// TODO(SCN-1186): Use new mechanism to implement RequestFocus.
	}
	}

	// The number of render objects attached to this view. In between frames, we
	// might have more than one connected if we get added to a new render object
	// before we get removed from the old render object. By the time we get around
	// to computing our layout, we must be back to just having one render object.
	int _attachments = 0;
	bool get _attached => _attachments > 0;

	void _attach() {
	assert(_attachments >= 0);
	++_attachments;
	if (_viewKey == null) {
	_addChildToViewHost();
	}
	}

	void _detach() {
	assert(_attached);
	--_attachments;
	scheduleMicrotask(_removeChildFromViewHostIfNeeded);
	}

	void _removeChildFromViewHostIfNeeded() {
	assert(_attachments >= 0);
	if (_attachments == 0 && _viewKey != null) {
	_removeChildFromViewHost();
	}
	}

	void sendSizeChangeHintHack(
	double widthChangeFactor, double heightChangeFactor) {
	assert(_attached);
	assert(_attachments == 1);
	if (_viewKey == null) {
	return;
	}

	if (globalViewContainer == null) {
	return;
	}

	globalViewContainer.sendSizeChangeHintHack(
	_viewKey, widthChangeFactor, heightChangeFactor);
	}

	ViewProperties _createViewProperties(
	double width,
	double height,
	double insetTop,
	double insetRight,
	double insetBottom,
	double insetLeft,
	bool focusable) {
	if (_currentViewProperties != null &&
	_currentViewProperties.viewLayout.size.width == width &&
	_currentViewProperties.viewLayout.size.height == height &&
	_currentViewProperties.viewLayout.inset.top == insetTop &&
	_currentViewProperties.viewLayout.inset.right == insetRight &&
	_currentViewProperties.viewLayout.inset.bottom == insetBottom &&
	_currentViewProperties.viewLayout.inset.left == insetLeft &&
	(_currentViewProperties.customFocusBehavior == null \|\|
	_currentViewProperties.customFocusBehavior.allowFocus) ==
	focusable) {
	return null;
	}

	SizeF size = SizeF(width: width, height: height);
	InsetF inset = InsetF(
	top: insetTop, right: insetRight, bottom: insetBottom, left: insetLeft);
	ViewLayout viewLayout = ViewLayout(size: size, inset: inset);
	final customFocusBehavior = CustomFocusBehavior(allowFocus: focusable);
	return _currentViewProperties = ViewProperties(
	viewLayout: viewLayout,
	customFocusBehavior: customFocusBehavior,
	);
	}

	void _setChildProperties(
	double width,
	double height,
	double insetTop,
	double insetRight,
	double insetBottom,
	double insetLeft,
	bool focusable,
	) {
	assert(_attached);
	assert(_attachments == 1);
	assert(_viewKey != null);
	if (globalViewContainer == null) {
	return;
	}
	ViewProperties viewProperties = _createViewProperties(
	width, height, insetTop, insetRight, insetBottom, insetLeft, focusable);
	if (viewProperties == null) {
	return;
	}
	globalViewContainer.setChildProperties(_viewKey, viewProperties);
	}
	}

	class _RenderChildView extends RenderBox {
	/// Creates a child view render object.
	_RenderChildView({
	ChildViewConnection connection,
	bool hitTestable = true,
	bool focusable = true,
	}) : _connection = connection,
	_hitTestable = hitTestable,
	_focusable = focusable,
	assert(hitTestable != null);

	/// The child to display.
	ChildViewConnection get connection => _connection;
	ChildViewConnection _connection;
	set connection(ChildViewConnection value) {
	if (value == _connection) {
	return;
	}
	if (attached && _connection != null) {
	_connection._detach();
	assert(_connection._onViewInfoAvailable != null);
	_connection._onViewInfoAvailable = null;
	}
	_connection = value;
	if (attached && _connection != null) {
	_connection._attach();
	assert(_connection._onViewInfoAvailable == null);
	_connection._onViewInfoAvailable = markNeedsPaint;
	}
	if (_connection == null) {
	markNeedsPaint();
	} else {
	markNeedsLayout();
	}
	}

	/// Whether this child should be included during hit testing.
	bool get hitTestable => _hitTestable;
	bool _hitTestable;
	set hitTestable(bool value) {
	assert(value != null);
	if (value == _hitTestable) {
	return;
	}
	_hitTestable = value;
	if (_connection != null) {
	markNeedsPaint();
	}
	}

	/// Whether this child should be able to recieve focus events
	bool get focusable => _focusable;
	bool _focusable;
	set focusable(bool value) {
	assert(value != null);
	if (value == _focusable) {
	return;
	}
	_focusable = value;
	if (_connection != null) {
	markNeedsPaint();
	}
	}

	@override
	void attach(PipelineOwner owner) {
	super.attach(owner);
	if (_connection != null) {
	_connection._attach();
	assert(_connection._onViewInfoAvailable == null);
	_connection._onViewInfoAvailable = markNeedsPaint;
	}
	}

	@override
	void detach() {
	if (_connection != null) {
	_connection._detach();
	assert(_connection._onViewInfoAvailable != null);
	_connection._onViewInfoAvailable = null;
	}
	super.detach();
	}

	@override
	bool get alwaysNeedsCompositing => true;

	TextPainter _debugErrorMessage;

	double _width;
	double _height;

	@override
	void performLayout() {
	size = constraints.biggest;

	// Ignore if we have no child view connection.
	if (_connection == null) {
	return;
	}

	if (_width != null && _height != null) {
	double deltaWidth = (_width - size.width).abs();
	double deltaHeight = (_height - size.height).abs();

	// Ignore insignificant changes in size that are likely rounding errors.
	if (deltaWidth < 0.0001 && deltaHeight < 0.0001) {
	return;
	}
	}

	_width = size.width;
	_height = size.height;
	_connection._setChildProperties(
	_width, _height, 0.0, 0.0, 0.0, 0.0, _focusable);
	assert(() {
	if (globalViewContainer == null) {
	_debugErrorMessage ??= TextPainter(
	text: TextSpan(
	text:
	'Child views are supported only when running in Scenic.'));
	_debugErrorMessage.layout(minWidth: size.width, maxWidth: size.width);
	}
	return true;
	}());
	}

	@override
	bool hitTestSelf(Offset position) => true;

	@override
	void paint(PaintingContext context, Offset offset) {
	assert(needsCompositing);
	if (_connection?._available == true) {
	context.addLayer(ChildSceneLayer(
	offset: offset,
	width: _width,
	height: _height,
	sceneHost: _connection._sceneHost,
	hitTestable: hitTestable,
	));
	}
	assert(() {
	if (globalViewContainer == null) {
	context.canvas.drawRect(
	offset & size, Paint()..color = Color(0xFF0000FF));
	_debugErrorMessage.paint(context.canvas, offset);
	}
	return true;
	}());
	}

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	description.add(
	DiagnosticsProperty<ChildViewConnection>(
	'connection',
	connection,
	),
	);
	}
	}

	/// A layer that represents content from another process.
	class ChildSceneLayer extends Layer {
	/// Creates a layer that displays content rendered by another process.
	///
	/// All of the arguments must not be null.
	ChildSceneLayer({
	this.offset = Offset.zero,
	this.width = 0.0,
	this.height = 0.0,
	this.sceneHost,
	this.hitTestable = true,
	});

	/// Offset from parent in the parent's coordinate system.
	Offset offset;

	/// The horizontal extent of the child, in logical pixels.
	double width;

	/// The vertical extent of the child, in logical pixels.
	double height;

	/// The host site for content rendered by the child.
	ui.SceneHost sceneHost;

	/// Whether this child should be included during hit testing.
	///
	/// Defaults to true.
	bool hitTestable;

	@override
	ui.EngineLayer addToScene(ui.SceneBuilder builder,
	[Offset layerOffset = Offset.zero]) {
	builder.addChildScene(
	offset: offset + layerOffset,
	width: width,
	height: height,
	sceneHost: sceneHost,
	hitTestable: hitTestable,
	);
	return null;
	}

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	description
	..add(DiagnosticsProperty<Offset>('offset', offset))
	..add(DoubleProperty('width', width))
	..add(DoubleProperty('height', height))
	..add(DiagnosticsProperty<ui.SceneHost>('sceneHost', sceneHost))
	..add(DiagnosticsProperty<bool>('hitTestable', hitTestable));
	}

	@override
	S find<S>(Offset regionOffset) => null;
	}

	/// A widget that is replaced by content from another process.
	///
	/// Requires a [MediaQuery] ancestor to provide appropriate media information to
	/// the child.
	@immutable
	class ChildView extends LeafRenderObjectWidget {
	/// Creates a widget that is replaced by content from another process.
	ChildView({this.connection, this.hitTestable = true, this.focusable = true})
	: super(key: GlobalObjectKey(connection));

	/// A connection to the child whose content will replace this widget.
	final ChildViewConnection connection;

	/// Whether this child should be included during hit testing.
	///
	/// Defaults to true.
	final bool hitTestable;

	/// Whether this child and its children should be allowed to receive focus.
	///
	/// Defaults to true.
	final bool focusable;

	@override
	_RenderChildView createRenderObject(BuildContext context) {
	return _RenderChildView(
	connection: connection,
	hitTestable: hitTestable,
	focusable: focusable,
	);
	}

	@override
	void updateRenderObject(BuildContext context, _RenderChildView renderObject) {
	renderObject
	..connection = connection
	..hitTestable = hitTestable
	..focusable = focusable;
	}
	}

	class View {
	/// Provide services to Scenic throught \|provider\|.
	///
	/// \|services\| should contain the list of service names offered by the
	/// \|provider\|.
	static void offerServiceProvider(
	InterfaceHandle<ServiceProvider> provider, List<String> services) {
	// Analyzer doesn't know Handle must be dart:zircon's Handle
	Scenic.offerServiceProvider(provider.passChannel().handle, services);
	}
	}