examples/flutter_gallery/lib/gallery/backdrop.dart - mirrors/flutter - Git at Google

 // Copyright 2018 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:math' as math;

 import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';

 const double _kFrontHeadingHeight = 32.0; // front layer beveled rectangle
 const double _kFrontClosedHeight = 92.0; // front layer height when closed
 const double _kBackAppBarHeight = 56.0; // back layer (options) appbar height

 // The size of the front layer heading's left and right beveled corners.
 final Animatable<BorderRadius> _kFrontHeadingBevelRadius = BorderRadiusTween(
   begin: const BorderRadius.only(
     topLeft: Radius.circular(12.0),
     topRight: Radius.circular(12.0),
   ),
   end: const BorderRadius.only(
     topLeft: Radius.circular(_kFrontHeadingHeight),
     topRight: Radius.circular(_kFrontHeadingHeight),
   ),
 );

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

   final AnimationController controller;
   final AnimationStatus status;
   final Widget child;

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

 class _TappableWhileStatusIsState extends State<_TappableWhileStatusIs> {
   bool _active;

   @override
   void initState() {
     super.initState();
     widget.controller.addStatusListener(_handleStatusChange);
     _active = widget.controller.status == widget.status;
   }

   @override
   void dispose() {
     widget.controller.removeStatusListener(_handleStatusChange);
     super.dispose();
   }

   void _handleStatusChange(AnimationStatus status) {
     final bool value = widget.controller.status == widget.status;
     if (_active != value) {
       setState(() {
         _active = value;
       });
     }
   }

   @override
   Widget build(BuildContext context) {
     return AbsorbPointer(
       absorbing: !_active,
       child: widget.child,
     );
   }
 }

 class _CrossFadeTransition extends AnimatedWidget {
   const _CrossFadeTransition({
     Key key,
     this.alignment = Alignment.center,
     Animation<double> progress,
     this.child0,
     this.child1,
   }) : super(key: key, listenable: progress);

   final AlignmentGeometry alignment;
   final Widget child0;
   final Widget child1;

   @override
   Widget build(BuildContext context) {
     final Animation<double> progress = listenable;

     final double opacity1 = CurvedAnimation(
       parent: ReverseAnimation(progress),
       curve: const Interval(0.5, 1.0),
     ).value;

     final double opacity2 = CurvedAnimation(
       parent: progress,
       curve: const Interval(0.5, 1.0),
     ).value;

     return Stack(
       alignment: alignment,
       children: <Widget>[
         Opacity(
           opacity: opacity1,
           child: Semantics(
             scopesRoute: true,
             explicitChildNodes: true,
             child: child1,
           ),
         ),
         Opacity(
           opacity: opacity2,
           child: Semantics(
             scopesRoute: true,
             explicitChildNodes: true,
             child: child0,
           ),
         ),
       ],
     );
   }
 }

 class _BackAppBar extends StatelessWidget {
   const _BackAppBar({
     Key key,
     this.leading = const SizedBox(width: 56.0),
     @required this.title,
     this.trailing,
   }) : assert(leading != null), assert(title != null), super(key: key);

   final Widget leading;
   final Widget title;
   final Widget trailing;

   @override
   Widget build(BuildContext context) {
     final List<Widget> children = <Widget>[
       Container(
         alignment: Alignment.center,
         width: 56.0,
         child: leading,
       ),
       Expanded(
         child: title,
       ),
     ];

     if (trailing != null) {
       children.add(
         Container(
           alignment: Alignment.center,
           width: 56.0,
           child: trailing,
         ),
       );
     }

     final ThemeData theme = Theme.of(context);

     return IconTheme.merge(
       data: theme.primaryIconTheme,
       child: DefaultTextStyle(
         style: theme.primaryTextTheme.title,
         child: SizedBox(
           height: _kBackAppBarHeight,
           child: Row(children: children),
         ),
       ),
     );
   }
 }

 class Backdrop extends StatefulWidget {
   const Backdrop({
     this.frontAction,
     this.frontTitle,
     this.frontHeading,
     this.frontLayer,
     this.backTitle,
     this.backLayer,
   });

   final Widget frontAction;
   final Widget frontTitle;
   final Widget frontLayer;
   final Widget frontHeading;
   final Widget backTitle;
   final Widget backLayer;

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

 class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin {
   final GlobalKey _backdropKey = GlobalKey(debugLabel: 'Backdrop');
   AnimationController _controller;
   Animation<double> _frontOpacity;

   static final Animatable<double> _frontOpacityTween = Tween<double>(begin: 0.2, end: 1.0)
     .chain(CurveTween(curve: const Interval(0.0, 0.4, curve: Curves.easeInOut)));

   @override
   void initState() {
     super.initState();
     _controller = AnimationController(
       duration: const Duration(milliseconds: 300),
       value: 1.0,
       vsync: this,
     );
     _frontOpacity = _controller.drive(_frontOpacityTween);
   }

   @override
   void dispose() {
     _controller.dispose();
     super.dispose();
   }

   double get _backdropHeight {
     // Warning: this can be safely called from the event handlers but it may
     // not be called at build time.
     final RenderBox renderBox = _backdropKey.currentContext.findRenderObject();
     return math.max(0.0, renderBox.size.height - _kBackAppBarHeight - _kFrontClosedHeight);
   }

   void _handleDragUpdate(DragUpdateDetails details) {
     _controller.value -= details.primaryDelta / (_backdropHeight ?? details.primaryDelta);
   }

   void _handleDragEnd(DragEndDetails details) {
     if (_controller.isAnimating || _controller.status == AnimationStatus.completed)
       return;

     final double flingVelocity = details.velocity.pixelsPerSecond.dy / _backdropHeight;
     if (flingVelocity < 0.0)
       _controller.fling(velocity: math.max(2.0, -flingVelocity));
     else if (flingVelocity > 0.0)
       _controller.fling(velocity: math.min(-2.0, -flingVelocity));
     else
       _controller.fling(velocity: _controller.value < 0.5 ? -2.0 : 2.0);
   }

   void _toggleFrontLayer() {
     final AnimationStatus status = _controller.status;
     final bool isOpen = status == AnimationStatus.completed || status == AnimationStatus.forward;
     _controller.fling(velocity: isOpen ? -2.0 : 2.0);
   }

   Widget _buildStack(BuildContext context, BoxConstraints constraints) {
     final Animation<RelativeRect> frontRelativeRect = _controller.drive(RelativeRectTween(
       begin: RelativeRect.fromLTRB(0.0, constraints.biggest.height - _kFrontClosedHeight, 0.0, 0.0),
       end: const RelativeRect.fromLTRB(0.0, _kBackAppBarHeight, 0.0, 0.0),
     ));

     final List<Widget> layers = <Widget>[
       // Back layer
       Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,
         children: <Widget>[
           _BackAppBar(
             leading: widget.frontAction,
             title: _CrossFadeTransition(
               progress: _controller,
               alignment: AlignmentDirectional.centerStart,
               child0: Semantics(namesRoute: true, child: widget.frontTitle),
               child1: Semantics(namesRoute: true, child: widget.backTitle),
             ),
             trailing: IconButton(
               onPressed: _toggleFrontLayer,
               tooltip: 'Toggle options page',
               icon: AnimatedIcon(
                 icon: AnimatedIcons.close_menu,
                 progress: _controller,
               ),
             ),
           ),
           Expanded(
             child: Visibility(
               child: widget.backLayer,
               visible: _controller.status != AnimationStatus.completed,
               maintainState: true,
             ),
           ),
         ],
       ),
       // Front layer
       PositionedTransition(
         rect: frontRelativeRect,
         child: AnimatedBuilder(
           animation: _controller,
           builder: (BuildContext context, Widget child) {
             return PhysicalShape(
               elevation: 12.0,
               color: Theme.of(context).canvasColor,
               clipper: ShapeBorderClipper(
                 shape: BeveledRectangleBorder(
                   borderRadius: _kFrontHeadingBevelRadius.transform(_controller.value),
                 ),
               ),
               clipBehavior: Clip.antiAlias,
               child: child,
             );
           },
           child: _TappableWhileStatusIs(
             AnimationStatus.completed,
             controller: _controller,
             child: FadeTransition(
               opacity: _frontOpacity,
               child: widget.frontLayer,
             ),
           ),
         ),
       ),
     ];

     // The front "heading" is a (typically transparent) widget that's stacked on
     // top of, and at the top of, the front layer. It adds support for dragging
     // the front layer up and down and for opening and closing the front layer
     // with a tap. It may obscure part of the front layer's topmost child.
     if (widget.frontHeading != null) {
       layers.add(
         PositionedTransition(
           rect: frontRelativeRect,
           child: ExcludeSemantics(
             child: Container(
               alignment: Alignment.topLeft,
               child: GestureDetector(
                 behavior: HitTestBehavior.opaque,
                 onTap: _toggleFrontLayer,
                 onVerticalDragUpdate: _handleDragUpdate,
                 onVerticalDragEnd: _handleDragEnd,
                 child: widget.frontHeading,
               ),
             ),
           ),
         ),
       );
     }

     return Stack(
       key: _backdropKey,
       children: layers,
     );
   }

   @override
   Widget build(BuildContext context) {
     return LayoutBuilder(builder: _buildStack);
   }
 }
	// Copyright 2018 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:math' as math;

	import 'package:flutter/rendering.dart';
	import 'package:flutter/material.dart';

	const double _kFrontHeadingHeight = 32.0; // front layer beveled rectangle
	const double _kFrontClosedHeight = 92.0; // front layer height when closed
	const double _kBackAppBarHeight = 56.0; // back layer (options) appbar height

	// The size of the front layer heading's left and right beveled corners.
	final Animatable<BorderRadius> _kFrontHeadingBevelRadius = BorderRadiusTween(
	begin: const BorderRadius.only(
	topLeft: Radius.circular(12.0),
	topRight: Radius.circular(12.0),
	),
	end: const BorderRadius.only(
	topLeft: Radius.circular(_kFrontHeadingHeight),
	topRight: Radius.circular(_kFrontHeadingHeight),
	),
	);

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

	final AnimationController controller;
	final AnimationStatus status;
	final Widget child;

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

	class _TappableWhileStatusIsState extends State<_TappableWhileStatusIs> {
	bool _active;

	@override
	void initState() {
	super.initState();
	widget.controller.addStatusListener(_handleStatusChange);
	_active = widget.controller.status == widget.status;
	}

	@override
	void dispose() {
	widget.controller.removeStatusListener(_handleStatusChange);
	super.dispose();
	}

	void _handleStatusChange(AnimationStatus status) {
	final bool value = widget.controller.status == widget.status;
	if (_active != value) {
	setState(() {
	_active = value;
	});
	}
	}

	@override
	Widget build(BuildContext context) {
	return AbsorbPointer(
	absorbing: !_active,
	child: widget.child,
	);
	}
	}

	class _CrossFadeTransition extends AnimatedWidget {
	const _CrossFadeTransition({
	Key key,
	this.alignment = Alignment.center,
	Animation<double> progress,
	this.child0,
	this.child1,
	}) : super(key: key, listenable: progress);

	final AlignmentGeometry alignment;
	final Widget child0;
	final Widget child1;

	@override
	Widget build(BuildContext context) {
	final Animation<double> progress = listenable;

	final double opacity1 = CurvedAnimation(
	parent: ReverseAnimation(progress),
	curve: const Interval(0.5, 1.0),
	).value;

	final double opacity2 = CurvedAnimation(
	parent: progress,
	curve: const Interval(0.5, 1.0),
	).value;

	return Stack(
	alignment: alignment,
	children: <Widget>[
	Opacity(
	opacity: opacity1,
	child: Semantics(
	scopesRoute: true,
	explicitChildNodes: true,
	child: child1,
	),
	),
	Opacity(
	opacity: opacity2,
	child: Semantics(
	scopesRoute: true,
	explicitChildNodes: true,
	child: child0,
	),
	),
	],
	);
	}
	}

	class _BackAppBar extends StatelessWidget {
	const _BackAppBar({
	Key key,
	this.leading = const SizedBox(width: 56.0),
	@required this.title,
	this.trailing,
	}) : assert(leading != null), assert(title != null), super(key: key);

	final Widget leading;
	final Widget title;
	final Widget trailing;

	@override
	Widget build(BuildContext context) {
	final List<Widget> children = <Widget>[
	Container(
	alignment: Alignment.center,
	width: 56.0,
	child: leading,
	),
	Expanded(
	child: title,
	),
	];

	if (trailing != null) {
	children.add(
	Container(
	alignment: Alignment.center,
	width: 56.0,
	child: trailing,
	),
	);
	}

	final ThemeData theme = Theme.of(context);

	return IconTheme.merge(
	data: theme.primaryIconTheme,
	child: DefaultTextStyle(
	style: theme.primaryTextTheme.title,
	child: SizedBox(
	height: _kBackAppBarHeight,
	child: Row(children: children),
	),
	),
	);
	}
	}

	class Backdrop extends StatefulWidget {
	const Backdrop({
	this.frontAction,
	this.frontTitle,
	this.frontHeading,
	this.frontLayer,
	this.backTitle,
	this.backLayer,
	});

	final Widget frontAction;
	final Widget frontTitle;
	final Widget frontLayer;
	final Widget frontHeading;
	final Widget backTitle;
	final Widget backLayer;

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

	class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin {
	final GlobalKey _backdropKey = GlobalKey(debugLabel: 'Backdrop');
	AnimationController _controller;
	Animation<double> _frontOpacity;

	static final Animatable<double> _frontOpacityTween = Tween<double>(begin: 0.2, end: 1.0)
	.chain(CurveTween(curve: const Interval(0.0, 0.4, curve: Curves.easeInOut)));

	@override
	void initState() {
	super.initState();
	_controller = AnimationController(
	duration: const Duration(milliseconds: 300),
	value: 1.0,
	vsync: this,
	);
	_frontOpacity = _controller.drive(_frontOpacityTween);
	}

	@override
	void dispose() {
	_controller.dispose();
	super.dispose();
	}

	double get _backdropHeight {
	// Warning: this can be safely called from the event handlers but it may
	// not be called at build time.
	final RenderBox renderBox = _backdropKey.currentContext.findRenderObject();
	return math.max(0.0, renderBox.size.height - _kBackAppBarHeight - _kFrontClosedHeight);
	}

	void _handleDragUpdate(DragUpdateDetails details) {
	_controller.value -= details.primaryDelta / (_backdropHeight ?? details.primaryDelta);
	}

	void _handleDragEnd(DragEndDetails details) {
	if (_controller.isAnimating \|\| _controller.status == AnimationStatus.completed)
	return;

	final double flingVelocity = details.velocity.pixelsPerSecond.dy / _backdropHeight;
	if (flingVelocity < 0.0)
	_controller.fling(velocity: math.max(2.0, -flingVelocity));
	else if (flingVelocity > 0.0)
	_controller.fling(velocity: math.min(-2.0, -flingVelocity));
	else
	_controller.fling(velocity: _controller.value < 0.5 ? -2.0 : 2.0);
	}

	void _toggleFrontLayer() {
	final AnimationStatus status = _controller.status;
	final bool isOpen = status == AnimationStatus.completed \|\| status == AnimationStatus.forward;
	_controller.fling(velocity: isOpen ? -2.0 : 2.0);
	}

	Widget _buildStack(BuildContext context, BoxConstraints constraints) {
	final Animation<RelativeRect> frontRelativeRect = _controller.drive(RelativeRectTween(
	begin: RelativeRect.fromLTRB(0.0, constraints.biggest.height - _kFrontClosedHeight, 0.0, 0.0),
	end: const RelativeRect.fromLTRB(0.0, _kBackAppBarHeight, 0.0, 0.0),
	));

	final List<Widget> layers = <Widget>[
	// Back layer
	Column(
	crossAxisAlignment: CrossAxisAlignment.stretch,
	children: <Widget>[
	_BackAppBar(
	leading: widget.frontAction,
	title: _CrossFadeTransition(
	progress: _controller,
	alignment: AlignmentDirectional.centerStart,
	child0: Semantics(namesRoute: true, child: widget.frontTitle),
	child1: Semantics(namesRoute: true, child: widget.backTitle),
	),
	trailing: IconButton(
	onPressed: _toggleFrontLayer,
	tooltip: 'Toggle options page',
	icon: AnimatedIcon(
	icon: AnimatedIcons.close_menu,
	progress: _controller,
	),
	),
	),
	Expanded(
	child: Visibility(
	child: widget.backLayer,
	visible: _controller.status != AnimationStatus.completed,
	maintainState: true,
	),
	),
	],
	),
	// Front layer
	PositionedTransition(
	rect: frontRelativeRect,
	child: AnimatedBuilder(
	animation: _controller,
	builder: (BuildContext context, Widget child) {
	return PhysicalShape(
	elevation: 12.0,
	color: Theme.of(context).canvasColor,
	clipper: ShapeBorderClipper(
	shape: BeveledRectangleBorder(
	borderRadius: _kFrontHeadingBevelRadius.transform(_controller.value),
	),
	),
	clipBehavior: Clip.antiAlias,
	child: child,
	);
	},
	child: _TappableWhileStatusIs(
	AnimationStatus.completed,
	controller: _controller,
	child: FadeTransition(
	opacity: _frontOpacity,
	child: widget.frontLayer,
	),
	),
	),
	),
	];

	// The front "heading" is a (typically transparent) widget that's stacked on
	// top of, and at the top of, the front layer. It adds support for dragging
	// the front layer up and down and for opening and closing the front layer
	// with a tap. It may obscure part of the front layer's topmost child.
	if (widget.frontHeading != null) {
	layers.add(
	PositionedTransition(
	rect: frontRelativeRect,
	child: ExcludeSemantics(
	child: Container(
	alignment: Alignment.topLeft,
	child: GestureDetector(
	behavior: HitTestBehavior.opaque,
	onTap: _toggleFrontLayer,
	onVerticalDragUpdate: _handleDragUpdate,
	onVerticalDragEnd: _handleDragEnd,
	child: widget.frontHeading,
	),
	),
	),
	),
	);
	}

	return Stack(
	key: _backdropKey,
	children: layers,
	);
	}

	@override
	Widget build(BuildContext context) {
	return LayoutBuilder(builder: _buildStack);
	}
	}