dev/manual_tests/lib/material_arc.dart - mirrors/flutter - Git at Google

 // Copyright 2016 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:async';
 import 'dart:io';

 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';

 enum _DragTarget {
   start,
   end
 }

 // How close a drag's start position must be to the target point. This is
 // a distance squared.
 const double _kTargetSlop = 2500.0;

 // Used by the Painter classes.
 const double _kPointRadius = 6.0;

 class _DragHandler extends Drag {
   _DragHandler(this.onUpdate, this.onCancel, this.onEnd);

   final GestureDragUpdateCallback onUpdate;
   final GestureDragCancelCallback onCancel;
   final GestureDragEndCallback onEnd;

   @override
   void update(DragUpdateDetails details) {
     onUpdate(details);
   }

   @override
   void cancel() {
     onCancel();
   }

   @override
   void end(DragEndDetails details) {
     onEnd(details);
   }
 }

 class _IgnoreDrag extends Drag {
 }

 class _PointDemoPainter extends CustomPainter {
   _PointDemoPainter({
     Animation<double> repaint,
     this.arc,
   }) : _repaint = repaint, super(repaint: repaint);

   final MaterialPointArcTween arc;
   final Animation<double> _repaint;

   void drawPoint(Canvas canvas, Offset point, Color color) {
     final Paint paint = Paint()
       ..color = color.withOpacity(0.25)
       ..style = PaintingStyle.fill;
     canvas.drawCircle(point, _kPointRadius, paint);
     paint
       ..color = color
       ..style = PaintingStyle.stroke
       ..strokeWidth = 2.0;
     canvas.drawCircle(point, _kPointRadius + 1.0, paint);
   }

   @override
   void paint(Canvas canvas, Size size) {
     final Paint paint = Paint();

     if (arc.center != null)
       drawPoint(canvas, arc.center, Colors.grey.shade400);

     paint
       ..isAntiAlias = false // Work-around for github.com/flutter/flutter/issues/5720
       ..color = Colors.green.withOpacity(0.25)
       ..strokeWidth = 4.0
       ..style = PaintingStyle.stroke;
     if (arc.center != null && arc.radius != null)
       canvas.drawCircle(arc.center, arc.radius, paint);
     else
       canvas.drawLine(arc.begin, arc.end, paint);

     drawPoint(canvas, arc.begin, Colors.green);
     drawPoint(canvas, arc.end, Colors.red);

     paint
       ..color = Colors.green
       ..style = PaintingStyle.fill;
     canvas.drawCircle(arc.lerp(_repaint.value), _kPointRadius, paint);
   }

   @override
   bool hitTest(Offset position) {
     return (arc.begin - position).distanceSquared < _kTargetSlop
         || (arc.end - position).distanceSquared < _kTargetSlop;
   }

   @override
   bool shouldRepaint(_PointDemoPainter oldPainter) => arc != oldPainter.arc;
 }

 class _PointDemo extends StatefulWidget {
   const _PointDemo({ Key key, this.controller }) : super(key: key);

   final AnimationController controller;

   @override
   _PointDemoState createState() => _PointDemoState();
 }

 class _PointDemoState extends State<_PointDemo> {
   final GlobalKey _painterKey = GlobalKey();

   CurvedAnimation _animation;
   _DragTarget _dragTarget;
   Size _screenSize;
   Offset _begin;
   Offset _end;

   @override
   void initState() {
     super.initState();
     _animation = CurvedAnimation(parent: widget.controller, curve: Curves.fastOutSlowIn);
   }

   @override
   void dispose() {
     widget.controller.value = 0.0;
     super.dispose();
   }

   Drag _handleOnStart(Offset position) {
     // TODO(hansmuller): allow the user to drag both points at the same time.
     if (_dragTarget != null)
       return _IgnoreDrag();

     final RenderBox box = _painterKey.currentContext.findRenderObject();
     final double startOffset = (box.localToGlobal(_begin) - position).distanceSquared;
     final double endOffset = (box.localToGlobal(_end) - position).distanceSquared;
     setState(() {
       if (startOffset < endOffset && startOffset < _kTargetSlop)
         _dragTarget = _DragTarget.start;
       else if (endOffset < _kTargetSlop)
         _dragTarget = _DragTarget.end;
       else
         _dragTarget = null;
     });

     return _DragHandler(_handleDragUpdate, _handleDragCancel, _handleDragEnd);
   }

   void _handleDragUpdate(DragUpdateDetails details) {
     switch (_dragTarget) {
       case _DragTarget.start:
         setState(() {
           _begin = _begin + details.delta;
         });
         break;
       case _DragTarget.end:
         setState(() {
           _end = _end + details.delta;
         });
         break;
     }
   }

   void _handleDragCancel() {
     _dragTarget = null;
     widget.controller.value = 0.0;
   }

   void _handleDragEnd(DragEndDetails details) {
     _dragTarget = null;
   }

   @override
   Widget build(BuildContext context) {
     final Size screenSize = MediaQuery.of(context).size;
     if (_screenSize == null || _screenSize != screenSize) {
       _screenSize = screenSize;
       _begin = Offset(screenSize.width * 0.5, screenSize.height * 0.2);
       _end = Offset(screenSize.width * 0.1, screenSize.height * 0.4);
     }

     final MaterialPointArcTween arc = MaterialPointArcTween(begin: _begin, end: _end);
     return RawGestureDetector(
       behavior: _dragTarget == null ? HitTestBehavior.deferToChild : HitTestBehavior.opaque,
       gestures: <Type, GestureRecognizerFactory>{
         ImmediateMultiDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<ImmediateMultiDragGestureRecognizer>(
           () => ImmediateMultiDragGestureRecognizer(),
           (ImmediateMultiDragGestureRecognizer instance) {
             instance
               ..onStart = _handleOnStart;
           },
         ),
       },
       child: ClipRect(
         child: CustomPaint(
           key: _painterKey,
           foregroundPainter: _PointDemoPainter(
             repaint: _animation,
             arc: arc,
           ),
           // Watch out: if this IgnorePointer is left out, then gestures that
           // fail _PointDemoPainter.hitTest() will still be recognized because
           // they do overlap this child, which is as big as the CustomPaint.
           child: IgnorePointer(
             child: Padding(
               padding: const EdgeInsets.all(16.0),
               child: Text(
                 'Tap the refresh button to run the animation. Drag the green '
                 "and red points to change the animation's path.",
                 style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0),
               ),
             ),
           ),
         ),
       ),
     );
   }
 }

 class _RectangleDemoPainter extends CustomPainter {
   _RectangleDemoPainter({
     Animation<double> repaint,
     this.arc,
   }) : _repaint = repaint, super(repaint: repaint);

   final MaterialRectArcTween arc;
   final Animation<double> _repaint;

   void drawPoint(Canvas canvas, Offset p, Color color) {
     final Paint paint = Paint()
       ..color = color.withOpacity(0.25)
       ..style = PaintingStyle.fill;
     canvas.drawCircle(p, _kPointRadius, paint);
     paint
       ..color = color
       ..style = PaintingStyle.stroke
       ..strokeWidth = 2.0;
     canvas.drawCircle(p, _kPointRadius + 1.0, paint);
   }

   void drawRect(Canvas canvas, Rect rect, Color color) {
     final Paint paint = Paint()
       ..color = color.withOpacity(0.25)
       ..strokeWidth = 4.0
       ..style = PaintingStyle.stroke;
     canvas.drawRect(rect, paint);
     drawPoint(canvas, rect.center, color);
   }

   @override
   void paint(Canvas canvas, Size size) {
     drawRect(canvas, arc.begin, Colors.green);
     drawRect(canvas, arc.end, Colors.red);
     drawRect(canvas, arc.lerp(_repaint.value), Colors.blue);
   }

   @override
   bool hitTest(Offset position) {
     return (arc.begin.center - position).distanceSquared < _kTargetSlop
         || (arc.end.center - position).distanceSquared < _kTargetSlop;
   }

   @override
   bool shouldRepaint(_RectangleDemoPainter oldPainter) => arc != oldPainter.arc;
 }

 class _RectangleDemo extends StatefulWidget {
   const _RectangleDemo({ Key key, this.controller }) : super(key: key);

   final AnimationController controller;

   @override
   _RectangleDemoState createState() => _RectangleDemoState();
 }

 class _RectangleDemoState extends State<_RectangleDemo> {
   final GlobalKey _painterKey = GlobalKey();

   CurvedAnimation _animation;
   _DragTarget _dragTarget;
   Size _screenSize;
   Rect _begin;
   Rect _end;

   @override
   void initState() {
     super.initState();
     _animation = CurvedAnimation(parent: widget.controller, curve: Curves.fastOutSlowIn);
   }

   @override
   void dispose() {
     widget.controller.value = 0.0;
     super.dispose();
   }

   Drag _handleOnStart(Offset position) {
     // TODO(hansmuller): allow the user to drag both points at the same time.
     if (_dragTarget != null)
       return _IgnoreDrag();

     final RenderBox box = _painterKey.currentContext.findRenderObject();
     final double startOffset = (box.localToGlobal(_begin.center) - position).distanceSquared;
     final double endOffset = (box.localToGlobal(_end.center) - position).distanceSquared;
     setState(() {
       if (startOffset < endOffset && startOffset < _kTargetSlop)
         _dragTarget = _DragTarget.start;
       else if (endOffset < _kTargetSlop)
         _dragTarget = _DragTarget.end;
       else
         _dragTarget = null;
     });
     return _DragHandler(_handleDragUpdate, _handleDragCancel, _handleDragEnd);
   }

   void _handleDragUpdate(DragUpdateDetails details) {
     switch (_dragTarget) {
       case _DragTarget.start:
         setState(() {
           _begin = _begin.shift(details.delta);
         });
         break;
       case _DragTarget.end:
         setState(() {
           _end = _end.shift(details.delta);
         });
         break;
     }
   }

   void _handleDragCancel() {
     _dragTarget = null;
     widget.controller.value = 0.0;
   }

   void _handleDragEnd(DragEndDetails details) {
     _dragTarget = null;
   }

   @override
   Widget build(BuildContext context) {
     final Size screenSize = MediaQuery.of(context).size;
     if (_screenSize == null || _screenSize != screenSize) {
       _screenSize = screenSize;
       _begin = Rect.fromLTWH(
         screenSize.width * 0.5, screenSize.height * 0.2,
         screenSize.width * 0.4, screenSize.height * 0.2,
       );
       _end = Rect.fromLTWH(
         screenSize.width * 0.1, screenSize.height * 0.4,
         screenSize.width * 0.3, screenSize.height * 0.3,
       );
     }

     final MaterialRectArcTween arc = MaterialRectArcTween(begin: _begin, end: _end);
     return RawGestureDetector(
       behavior: _dragTarget == null ? HitTestBehavior.deferToChild : HitTestBehavior.opaque,
       gestures: <Type, GestureRecognizerFactory>{
         ImmediateMultiDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<ImmediateMultiDragGestureRecognizer>(
           () => ImmediateMultiDragGestureRecognizer(),
           (ImmediateMultiDragGestureRecognizer instance) {
             instance
               ..onStart = _handleOnStart;
           },
         ),
       },
       child: ClipRect(
         child: CustomPaint(
           key: _painterKey,
           foregroundPainter: _RectangleDemoPainter(
             repaint: _animation,
             arc: arc,
           ),
           // Watch out: if this IgnorePointer is left out, then gestures that
           // fail _RectDemoPainter.hitTest() will still be recognized because
           // they do overlap this child, which is as big as the CustomPaint.
           child: IgnorePointer(
             child: Padding(
               padding: const EdgeInsets.all(16.0),
               child: Text(
                 'Tap the refresh button to run the animation. Drag the rectangles '
                 "to change the animation's path.",
                 style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0),
               ),
             ),
           ),
         ),
       ),
     );
   }
 }

 typedef _DemoBuilder = Widget Function(_ArcDemo demo);

 class _ArcDemo {
   _ArcDemo(this.title, this.builder, TickerProvider vsync)
     : controller = AnimationController(duration: const Duration(milliseconds: 500), vsync: vsync),
       key = GlobalKey(debugLabel: title);

   final String title;
   final _DemoBuilder builder;
   final AnimationController controller;
   final GlobalKey key;
 }

 class AnimationDemo extends StatefulWidget {
   const AnimationDemo({ Key key }) : super(key: key);

   @override
   _AnimationDemoState createState() => _AnimationDemoState();
 }

 class _AnimationDemoState extends State<AnimationDemo> with TickerProviderStateMixin {
   List<_ArcDemo> _allDemos;

   @override
   void initState() {
     super.initState();
     _allDemos = <_ArcDemo>[
       _ArcDemo('POINT', (_ArcDemo demo) {
         return _PointDemo(
           key: demo.key,
           controller: demo.controller,
         );
       }, this),
       _ArcDemo('RECTANGLE', (_ArcDemo demo) {
         return _RectangleDemo(
           key: demo.key,
           controller: demo.controller,
         );
       }, this),
     ];
   }

   Future<void> _play(_ArcDemo demo) async {
     await demo.controller.forward();
     if (demo.key.currentState != null && demo.key.currentState.mounted)
       demo.controller.reverse();
   }

   @override
   Widget build(BuildContext context) {
     return DefaultTabController(
       length: _allDemos.length,
       child: Scaffold(
         appBar: AppBar(
           title: const Text('Animation'),
           bottom: TabBar(
             tabs: _allDemos.map<Tab>((_ArcDemo demo) => Tab(text: demo.title)).toList(),
           ),
         ),
         floatingActionButton: Builder(
           builder: (BuildContext context) {
             return FloatingActionButton(
               child: const Icon(Icons.refresh),
               onPressed: () {
                 _play(_allDemos[DefaultTabController.of(context).index]);
               },
             );
           },
         ),
         body: TabBarView(
           children: _allDemos.map<Widget>((_ArcDemo demo) => demo.builder(demo)).toList(),
         ),
       ),
     );
   }
 }

 void main() {
   if (Platform.isMacOS) {
     // TODO(gspencergoog): Update this when TargetPlatform includes macOS. https://github.com/flutter/flutter/issues/31366
     // See https://github.com/flutter/flutter/wiki/Desktop-shells#target-platform-override
     debugDefaultTargetPlatformOverride = TargetPlatform.fuchsia;
   }

   runApp(const MaterialApp(
     home: AnimationDemo(),
   ));
 }
	// Copyright 2016 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:async';
	import 'dart:io';

	import 'package:flutter/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/material.dart';

	enum _DragTarget {
	start,
	end
	}

	// How close a drag's start position must be to the target point. This is
	// a distance squared.
	const double _kTargetSlop = 2500.0;

	// Used by the Painter classes.
	const double _kPointRadius = 6.0;

	class _DragHandler extends Drag {
	_DragHandler(this.onUpdate, this.onCancel, this.onEnd);

	final GestureDragUpdateCallback onUpdate;
	final GestureDragCancelCallback onCancel;
	final GestureDragEndCallback onEnd;

	@override
	void update(DragUpdateDetails details) {
	onUpdate(details);
	}

	@override
	void cancel() {
	onCancel();
	}

	@override
	void end(DragEndDetails details) {
	onEnd(details);
	}
	}

	class _IgnoreDrag extends Drag {
	}

	class _PointDemoPainter extends CustomPainter {
	_PointDemoPainter({
	Animation<double> repaint,
	this.arc,
	}) : _repaint = repaint, super(repaint: repaint);

	final MaterialPointArcTween arc;
	final Animation<double> _repaint;

	void drawPoint(Canvas canvas, Offset point, Color color) {
	final Paint paint = Paint()
	..color = color.withOpacity(0.25)
	..style = PaintingStyle.fill;
	canvas.drawCircle(point, _kPointRadius, paint);
	paint
	..color = color
	..style = PaintingStyle.stroke
	..strokeWidth = 2.0;
	canvas.drawCircle(point, _kPointRadius + 1.0, paint);
	}

	@override
	void paint(Canvas canvas, Size size) {
	final Paint paint = Paint();

	if (arc.center != null)
	drawPoint(canvas, arc.center, Colors.grey.shade400);

	paint
	..isAntiAlias = false // Work-around for github.com/flutter/flutter/issues/5720
	..color = Colors.green.withOpacity(0.25)
	..strokeWidth = 4.0
	..style = PaintingStyle.stroke;
	if (arc.center != null && arc.radius != null)
	canvas.drawCircle(arc.center, arc.radius, paint);
	else
	canvas.drawLine(arc.begin, arc.end, paint);

	drawPoint(canvas, arc.begin, Colors.green);
	drawPoint(canvas, arc.end, Colors.red);

	paint
	..color = Colors.green
	..style = PaintingStyle.fill;
	canvas.drawCircle(arc.lerp(_repaint.value), _kPointRadius, paint);
	}

	@override
	bool hitTest(Offset position) {
	return (arc.begin - position).distanceSquared < _kTargetSlop
	\|\| (arc.end - position).distanceSquared < _kTargetSlop;
	}

	@override
	bool shouldRepaint(_PointDemoPainter oldPainter) => arc != oldPainter.arc;
	}

	class _PointDemo extends StatefulWidget {
	const _PointDemo({ Key key, this.controller }) : super(key: key);

	final AnimationController controller;

	@override
	_PointDemoState createState() => _PointDemoState();
	}

	class _PointDemoState extends State<_PointDemo> {
	final GlobalKey _painterKey = GlobalKey();

	CurvedAnimation _animation;
	_DragTarget _dragTarget;
	Size _screenSize;
	Offset _begin;
	Offset _end;

	@override
	void initState() {
	super.initState();
	_animation = CurvedAnimation(parent: widget.controller, curve: Curves.fastOutSlowIn);
	}

	@override
	void dispose() {
	widget.controller.value = 0.0;
	super.dispose();
	}

	Drag _handleOnStart(Offset position) {
	// TODO(hansmuller): allow the user to drag both points at the same time.
	if (_dragTarget != null)
	return _IgnoreDrag();

	final RenderBox box = _painterKey.currentContext.findRenderObject();
	final double startOffset = (box.localToGlobal(_begin) - position).distanceSquared;
	final double endOffset = (box.localToGlobal(_end) - position).distanceSquared;
	setState(() {
	if (startOffset < endOffset && startOffset < _kTargetSlop)
	_dragTarget = _DragTarget.start;
	else if (endOffset < _kTargetSlop)
	_dragTarget = _DragTarget.end;
	else
	_dragTarget = null;
	});

	return _DragHandler(_handleDragUpdate, _handleDragCancel, _handleDragEnd);
	}

	void _handleDragUpdate(DragUpdateDetails details) {
	switch (_dragTarget) {
	case _DragTarget.start:
	setState(() {
	_begin = _begin + details.delta;
	});
	break;
	case _DragTarget.end:
	setState(() {
	_end = _end + details.delta;
	});
	break;
	}
	}

	void _handleDragCancel() {
	_dragTarget = null;
	widget.controller.value = 0.0;
	}

	void _handleDragEnd(DragEndDetails details) {
	_dragTarget = null;
	}

	@override
	Widget build(BuildContext context) {
	final Size screenSize = MediaQuery.of(context).size;
	if (_screenSize == null \|\| _screenSize != screenSize) {
	_screenSize = screenSize;
	_begin = Offset(screenSize.width * 0.5, screenSize.height * 0.2);
	_end = Offset(screenSize.width * 0.1, screenSize.height * 0.4);
	}

	final MaterialPointArcTween arc = MaterialPointArcTween(begin: _begin, end: _end);
	return RawGestureDetector(
	behavior: _dragTarget == null ? HitTestBehavior.deferToChild : HitTestBehavior.opaque,
	gestures: <Type, GestureRecognizerFactory>{
	ImmediateMultiDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<ImmediateMultiDragGestureRecognizer>(
	() => ImmediateMultiDragGestureRecognizer(),
	(ImmediateMultiDragGestureRecognizer instance) {
	instance
	..onStart = _handleOnStart;
	},
	),
	},
	child: ClipRect(
	child: CustomPaint(
	key: _painterKey,
	foregroundPainter: _PointDemoPainter(
	repaint: _animation,
	arc: arc,
	),
	// Watch out: if this IgnorePointer is left out, then gestures that
	// fail _PointDemoPainter.hitTest() will still be recognized because
	// they do overlap this child, which is as big as the CustomPaint.
	child: IgnorePointer(
	child: Padding(
	padding: const EdgeInsets.all(16.0),
	child: Text(
	'Tap the refresh button to run the animation. Drag the green '
	"and red points to change the animation's path.",
	style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0),
	),
	),
	),
	),
	),
	);
	}
	}

	class _RectangleDemoPainter extends CustomPainter {
	_RectangleDemoPainter({
	Animation<double> repaint,
	this.arc,
	}) : _repaint = repaint, super(repaint: repaint);

	final MaterialRectArcTween arc;
	final Animation<double> _repaint;

	void drawPoint(Canvas canvas, Offset p, Color color) {
	final Paint paint = Paint()
	..color = color.withOpacity(0.25)
	..style = PaintingStyle.fill;
	canvas.drawCircle(p, _kPointRadius, paint);
	paint
	..color = color
	..style = PaintingStyle.stroke
	..strokeWidth = 2.0;
	canvas.drawCircle(p, _kPointRadius + 1.0, paint);
	}

	void drawRect(Canvas canvas, Rect rect, Color color) {
	final Paint paint = Paint()
	..color = color.withOpacity(0.25)
	..strokeWidth = 4.0
	..style = PaintingStyle.stroke;
	canvas.drawRect(rect, paint);
	drawPoint(canvas, rect.center, color);
	}

	@override
	void paint(Canvas canvas, Size size) {
	drawRect(canvas, arc.begin, Colors.green);
	drawRect(canvas, arc.end, Colors.red);
	drawRect(canvas, arc.lerp(_repaint.value), Colors.blue);
	}

	@override
	bool hitTest(Offset position) {
	return (arc.begin.center - position).distanceSquared < _kTargetSlop
	\|\| (arc.end.center - position).distanceSquared < _kTargetSlop;
	}

	@override
	bool shouldRepaint(_RectangleDemoPainter oldPainter) => arc != oldPainter.arc;
	}

	class _RectangleDemo extends StatefulWidget {
	const _RectangleDemo({ Key key, this.controller }) : super(key: key);

	final AnimationController controller;

	@override
	_RectangleDemoState createState() => _RectangleDemoState();
	}

	class _RectangleDemoState extends State<_RectangleDemo> {
	final GlobalKey _painterKey = GlobalKey();

	CurvedAnimation _animation;
	_DragTarget _dragTarget;
	Size _screenSize;
	Rect _begin;
	Rect _end;

	@override
	void initState() {
	super.initState();
	_animation = CurvedAnimation(parent: widget.controller, curve: Curves.fastOutSlowIn);
	}

	@override
	void dispose() {
	widget.controller.value = 0.0;
	super.dispose();
	}

	Drag _handleOnStart(Offset position) {
	// TODO(hansmuller): allow the user to drag both points at the same time.
	if (_dragTarget != null)
	return _IgnoreDrag();

	final RenderBox box = _painterKey.currentContext.findRenderObject();
	final double startOffset = (box.localToGlobal(_begin.center) - position).distanceSquared;
	final double endOffset = (box.localToGlobal(_end.center) - position).distanceSquared;
	setState(() {
	if (startOffset < endOffset && startOffset < _kTargetSlop)
	_dragTarget = _DragTarget.start;
	else if (endOffset < _kTargetSlop)
	_dragTarget = _DragTarget.end;
	else
	_dragTarget = null;
	});
	return _DragHandler(_handleDragUpdate, _handleDragCancel, _handleDragEnd);
	}

	void _handleDragUpdate(DragUpdateDetails details) {
	switch (_dragTarget) {
	case _DragTarget.start:
	setState(() {
	_begin = _begin.shift(details.delta);
	});
	break;
	case _DragTarget.end:
	setState(() {
	_end = _end.shift(details.delta);
	});
	break;
	}
	}

	void _handleDragCancel() {
	_dragTarget = null;
	widget.controller.value = 0.0;
	}

	void _handleDragEnd(DragEndDetails details) {
	_dragTarget = null;
	}

	@override
	Widget build(BuildContext context) {
	final Size screenSize = MediaQuery.of(context).size;
	if (_screenSize == null \|\| _screenSize != screenSize) {
	_screenSize = screenSize;
	_begin = Rect.fromLTWH(
	screenSize.width * 0.5, screenSize.height * 0.2,
	screenSize.width * 0.4, screenSize.height * 0.2,
	);
	_end = Rect.fromLTWH(
	screenSize.width * 0.1, screenSize.height * 0.4,
	screenSize.width * 0.3, screenSize.height * 0.3,
	);
	}

	final MaterialRectArcTween arc = MaterialRectArcTween(begin: _begin, end: _end);
	return RawGestureDetector(
	behavior: _dragTarget == null ? HitTestBehavior.deferToChild : HitTestBehavior.opaque,
	gestures: <Type, GestureRecognizerFactory>{
	ImmediateMultiDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<ImmediateMultiDragGestureRecognizer>(
	() => ImmediateMultiDragGestureRecognizer(),
	(ImmediateMultiDragGestureRecognizer instance) {
	instance
	..onStart = _handleOnStart;
	},
	),
	},
	child: ClipRect(
	child: CustomPaint(
	key: _painterKey,
	foregroundPainter: _RectangleDemoPainter(
	repaint: _animation,
	arc: arc,
	),
	// Watch out: if this IgnorePointer is left out, then gestures that
	// fail _RectDemoPainter.hitTest() will still be recognized because
	// they do overlap this child, which is as big as the CustomPaint.
	child: IgnorePointer(
	child: Padding(
	padding: const EdgeInsets.all(16.0),
	child: Text(
	'Tap the refresh button to run the animation. Drag the rectangles '
	"to change the animation's path.",
	style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0),
	),
	),
	),
	),
	),
	);
	}
	}

	typedef _DemoBuilder = Widget Function(_ArcDemo demo);

	class _ArcDemo {
	_ArcDemo(this.title, this.builder, TickerProvider vsync)
	: controller = AnimationController(duration: const Duration(milliseconds: 500), vsync: vsync),
	key = GlobalKey(debugLabel: title);

	final String title;
	final _DemoBuilder builder;
	final AnimationController controller;
	final GlobalKey key;
	}

	class AnimationDemo extends StatefulWidget {
	const AnimationDemo({ Key key }) : super(key: key);

	@override
	_AnimationDemoState createState() => _AnimationDemoState();
	}

	class _AnimationDemoState extends State<AnimationDemo> with TickerProviderStateMixin {
	List<_ArcDemo> _allDemos;

	@override
	void initState() {
	super.initState();
	_allDemos = <_ArcDemo>[
	_ArcDemo('POINT', (_ArcDemo demo) {
	return _PointDemo(
	key: demo.key,
	controller: demo.controller,
	);
	}, this),
	_ArcDemo('RECTANGLE', (_ArcDemo demo) {
	return _RectangleDemo(
	key: demo.key,
	controller: demo.controller,
	);
	}, this),
	];
	}

	Future<void> _play(_ArcDemo demo) async {
	await demo.controller.forward();
	if (demo.key.currentState != null && demo.key.currentState.mounted)
	demo.controller.reverse();
	}

	@override
	Widget build(BuildContext context) {
	return DefaultTabController(
	length: _allDemos.length,
	child: Scaffold(
	appBar: AppBar(
	title: const Text('Animation'),
	bottom: TabBar(
	tabs: _allDemos.map<Tab>((_ArcDemo demo) => Tab(text: demo.title)).toList(),
	),
	),
	floatingActionButton: Builder(
	builder: (BuildContext context) {
	return FloatingActionButton(
	child: const Icon(Icons.refresh),
	onPressed: () {
	_play(_allDemos[DefaultTabController.of(context).index]);
	},
	);
	},
	),
	body: TabBarView(
	children: _allDemos.map<Widget>((_ArcDemo demo) => demo.builder(demo)).toList(),
	),
	),
	);
	}
	}

	void main() {
	if (Platform.isMacOS) {
	// TODO(gspencergoog): Update this when TargetPlatform includes macOS. https://github.com/flutter/flutter/issues/31366
	// See https://github.com/flutter/flutter/wiki/Desktop-shells#target-platform-override
	debugDefaultTargetPlatformOverride = TargetPlatform.fuchsia;
	}

	runApp(const MaterialApp(
	home: AnimationDemo(),
	));
	}