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// 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' show Timer;
import 'dart:math' as math;
import 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/physics.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';
import 'basic.dart';
import 'framework.dart';
import 'notification_listener.dart';
import 'scroll_notification.dart';
import 'ticker_provider.dart';
/// A visual indication that a scroll view has overscrolled.
///
/// A [GlowingOverscrollIndicator] listens for [ScrollNotification]s in order
/// to control the overscroll indication. These notifications are typically
/// generated by a [ScrollView], such as a [ListView] or a [GridView].
///
/// [GlowingOverscrollIndicator] generates [OverscrollIndicatorNotification]
/// before showing an overscroll indication. To prevent the indicator from
/// showing the indication, call [OverscrollIndicatorNotification.disallowGlow]
/// on the notification.
///
/// Created automatically by [ScrollBehavior.buildViewportChrome] on platforms
/// (e.g., Android) that commonly use this type of overscroll indication.
///
/// In a [MaterialApp], the edge glow color is the [ThemeData.accentColor].
class GlowingOverscrollIndicator extends StatefulWidget {
/// Creates a visual indication that a scroll view has overscrolled.
///
/// In order for this widget to display an overscroll indication, the [child]
/// widget must contain a widget that generates a [ScrollNotification], such
/// as a [ListView] or a [GridView].
///
/// The [showLeading], [showTrailing], [axisDirection], [color], and
/// [notificationPredicate] arguments must not be null.
const GlowingOverscrollIndicator({
Key key,
this.showLeading = true,
this.showTrailing = true,
@required this.axisDirection,
@required this.color,
this.notificationPredicate = defaultScrollNotificationPredicate,
this.child,
}) : assert(showLeading != null),
assert(showTrailing != null),
assert(axisDirection != null),
assert(color != null),
assert(notificationPredicate != null),
super(key: key);
/// Whether to show the overscroll glow on the side with negative scroll
/// offsets.
///
/// For a vertical downwards viewport, this is the top side.
///
/// Defaults to true.
///
/// See [showTrailing] for the corresponding control on the other side of the
/// viewport.
final bool showLeading;
/// Whether to show the overscroll glow on the side with positive scroll
/// offsets.
///
/// For a vertical downwards viewport, this is the bottom side.
///
/// Defaults to true.
///
/// See [showLeading] for the corresponding control on the other side of the
/// viewport.
final bool showTrailing;
/// The direction of positive scroll offsets in the [Scrollable] whose
/// overscrolls are to be visualized.
final AxisDirection axisDirection;
/// The axis along which scrolling occurs in the [Scrollable] whose
/// overscrolls are to be visualized.
Axis get axis => axisDirectionToAxis(axisDirection);
/// The color of the glow. The alpha channel is ignored.
final Color color;
/// A check that specifies whether a [ScrollNotification] should be
/// handled by this widget.
///
/// By default, checks whether `notification.depth == 0`. Set it to something
/// else for more complicated layouts.
final ScrollNotificationPredicate notificationPredicate;
/// The widget below this widget in the tree.
///
/// The overscroll indicator will paint on top of this child. This child (and its
/// subtree) should include a source of [ScrollNotification] notifications.
///
/// Typically a [GlowingOverscrollIndicator] is created by a
/// [ScrollBehavior.buildViewportChrome] method, in which case
/// the child is usually the one provided as an argument to that method.
final Widget child;
@override
_GlowingOverscrollIndicatorState createState() => _GlowingOverscrollIndicatorState();
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(EnumProperty<AxisDirection>('axisDirection', axisDirection));
String showDescription;
if (showLeading && showTrailing) {
showDescription = 'both sides';
} else if (showLeading) {
showDescription = 'leading side only';
} else if (showTrailing) {
showDescription = 'trailing side only';
} else {
showDescription = 'neither side (!)';
}
properties.add(MessageProperty('show', showDescription));
properties.add(ColorProperty('color', color, showName: false));
}
}
class _GlowingOverscrollIndicatorState extends State<GlowingOverscrollIndicator> with TickerProviderStateMixin {
_GlowController _leadingController;
_GlowController _trailingController;
Listenable _leadingAndTrailingListener;
@override
void initState() {
super.initState();
_leadingController = _GlowController(vsync: this, color: widget.color, axis: widget.axis);
_trailingController = _GlowController(vsync: this, color: widget.color, axis: widget.axis);
_leadingAndTrailingListener = Listenable.merge(<Listenable>[_leadingController, _trailingController]);
}
@override
void didUpdateWidget(GlowingOverscrollIndicator oldWidget) {
super.didUpdateWidget(oldWidget);
if (oldWidget.color != widget.color || oldWidget.axis != widget.axis) {
_leadingController.color = widget.color;
_leadingController.axis = widget.axis;
_trailingController.color = widget.color;
_trailingController.axis = widget.axis;
}
}
Type _lastNotificationType;
final Map<bool, bool> _accepted = <bool, bool>{false: true, true: true};
bool _handleScrollNotification(ScrollNotification notification) {
if (!widget.notificationPredicate(notification))
return false;
if (notification is OverscrollNotification) {
_GlowController controller;
if (notification.overscroll < 0.0) {
controller = _leadingController;
} else if (notification.overscroll > 0.0) {
controller = _trailingController;
} else {
assert(false);
}
final bool isLeading = controller == _leadingController;
if (_lastNotificationType != OverscrollNotification) {
final OverscrollIndicatorNotification confirmationNotification = OverscrollIndicatorNotification(leading: isLeading);
confirmationNotification.dispatch(context);
_accepted[isLeading] = confirmationNotification._accepted;
}
assert(controller != null);
assert(notification.metrics.axis == widget.axis);
if (_accepted[isLeading]) {
if (notification.velocity != 0.0) {
assert(notification.dragDetails == null);
controller.absorbImpact(notification.velocity.abs());
} else {
assert(notification.overscroll != 0.0);
if (notification.dragDetails != null) {
assert(notification.dragDetails.globalPosition != null);
final RenderBox renderer = notification.context.findRenderObject();
assert(renderer != null);
assert(renderer.hasSize);
final Size size = renderer.size;
final Offset position = renderer.globalToLocal(notification.dragDetails.globalPosition);
switch (notification.metrics.axis) {
case Axis.horizontal:
controller.pull(notification.overscroll.abs(), size.width, position.dy.clamp(0.0, size.height), size.height);
break;
case Axis.vertical:
controller.pull(notification.overscroll.abs(), size.height, position.dx.clamp(0.0, size.width), size.width);
break;
}
}
}
}
} else if (notification is ScrollEndNotification || notification is ScrollUpdateNotification) {
if ((notification as dynamic).dragDetails != null) {
_leadingController.scrollEnd();
_trailingController.scrollEnd();
}
}
_lastNotificationType = notification.runtimeType;
return false;
}
@override
void dispose() {
_leadingController.dispose();
_trailingController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return NotificationListener<ScrollNotification>(
onNotification: _handleScrollNotification,
child: RepaintBoundary(
child: CustomPaint(
foregroundPainter: _GlowingOverscrollIndicatorPainter(
leadingController: widget.showLeading ? _leadingController : null,
trailingController: widget.showTrailing ? _trailingController : null,
axisDirection: widget.axisDirection,
repaint: _leadingAndTrailingListener,
),
child: RepaintBoundary(
child: widget.child,
),
),
),
);
}
}
// The Glow logic is a port of the logic in the following file:
// https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/widget/EdgeEffect.java
// as of December 2016.
enum _GlowState { idle, absorb, pull, recede }
class _GlowController extends ChangeNotifier {
_GlowController({
@required TickerProvider vsync,
@required Color color,
@required Axis axis,
}) : assert(vsync != null),
assert(color != null),
assert(axis != null),
_color = color,
_axis = axis {
_glowController = AnimationController(vsync: vsync)
..addStatusListener(_changePhase);
final Animation<double> decelerator = CurvedAnimation(
parent: _glowController,
curve: Curves.decelerate,
)..addListener(notifyListeners);
_glowOpacity = decelerator.drive(_glowOpacityTween);
_glowSize = decelerator.drive(_glowSizeTween);
_displacementTicker = vsync.createTicker(_tickDisplacement);
}
// animation of the main axis direction
_GlowState _state = _GlowState.idle;
AnimationController _glowController;
Timer _pullRecedeTimer;
// animation values
final Tween<double> _glowOpacityTween = Tween<double>(begin: 0.0, end: 0.0);
Animation<double> _glowOpacity;
final Tween<double> _glowSizeTween = Tween<double>(begin: 0.0, end: 0.0);
Animation<double> _glowSize;
// animation of the cross axis position
Ticker _displacementTicker;
Duration _displacementTickerLastElapsed;
double _displacementTarget = 0.5;
double _displacement = 0.5;
// tracking the pull distance
double _pullDistance = 0.0;
Color get color => _color;
Color _color;
set color(Color value) {
assert(color != null);
if (color == value)
return;
_color = value;
notifyListeners();
}
Axis get axis => _axis;
Axis _axis;
set axis(Axis value) {
assert(axis != null);
if (axis == value)
return;
_axis = value;
notifyListeners();
}
static const Duration _recedeTime = Duration(milliseconds: 600);
static const Duration _pullTime = Duration(milliseconds: 167);
static const Duration _pullHoldTime = Duration(milliseconds: 167);
static const Duration _pullDecayTime = Duration(milliseconds: 2000);
static final Duration _crossAxisHalfTime = Duration(microseconds: (Duration.microsecondsPerSecond / 60.0).round());
static const double _maxOpacity = 0.5;
static const double _pullOpacityGlowFactor = 0.8;
static const double _velocityGlowFactor = 0.00006;
static const double _sqrt3 = 1.73205080757; // const math.sqrt(3)
static const double _widthToHeightFactor = (3.0 / 4.0) * (2.0 - _sqrt3);
// absorbed velocities are clamped to the range _minVelocity.._maxVelocity
static const double _minVelocity = 100.0; // logical pixels per second
static const double _maxVelocity = 10000.0; // logical pixels per second
@override
void dispose() {
_glowController.dispose();
_displacementTicker.dispose();
_pullRecedeTimer?.cancel();
super.dispose();
}
/// Handle a scroll slamming into the edge at a particular velocity.
///
/// The velocity must be positive.
void absorbImpact(double velocity) {
assert(velocity >= 0.0);
_pullRecedeTimer?.cancel();
_pullRecedeTimer = null;
velocity = velocity.clamp(_minVelocity, _maxVelocity);
_glowOpacityTween.begin = _state == _GlowState.idle ? 0.3 : _glowOpacity.value;
_glowOpacityTween.end = (velocity * _velocityGlowFactor).clamp(_glowOpacityTween.begin, _maxOpacity);
_glowSizeTween.begin = _glowSize.value;
_glowSizeTween.end = math.min(0.025 + 7.5e-7 * velocity * velocity, 1.0);
_glowController.duration = Duration(milliseconds: (0.15 + velocity * 0.02).round());
_glowController.forward(from: 0.0);
_displacement = 0.5;
_state = _GlowState.absorb;
}
/// Handle a user-driven overscroll.
///
/// The `overscroll` argument should be the scroll distance in logical pixels,
/// the `extent` argument should be the total dimension of the viewport in the
/// main axis in logical pixels, the `crossAxisOffset` argument should be the
/// distance from the leading (left or top) edge of the cross axis of the
/// viewport, and the `crossExtent` should be the size of the cross axis. For
/// example, a pull of 50 pixels up the middle of a 200 pixel high and 100
/// pixel wide vertical viewport should result in a call of `pull(50.0, 200.0,
/// 50.0, 100.0)`. The `overscroll` value should be positive regardless of the
/// direction.
void pull(double overscroll, double extent, double crossAxisOffset, double crossExtent) {
_pullRecedeTimer?.cancel();
_pullDistance += overscroll / 200.0; // This factor is magic. Not clear why we need it to match Android.
_glowOpacityTween.begin = _glowOpacity.value;
_glowOpacityTween.end = math.min(_glowOpacity.value + overscroll / extent * _pullOpacityGlowFactor, _maxOpacity);
final double height = math.min(extent, crossExtent * _widthToHeightFactor);
_glowSizeTween.begin = _glowSize.value;
_glowSizeTween.end = math.max(1.0 - 1.0 / (0.7 * math.sqrt(_pullDistance * height)), _glowSize.value);
_displacementTarget = crossAxisOffset / crossExtent;
if (_displacementTarget != _displacement) {
if (!_displacementTicker.isTicking) {
assert(_displacementTickerLastElapsed == null);
_displacementTicker.start();
}
} else {
_displacementTicker.stop();
_displacementTickerLastElapsed = null;
}
_glowController.duration = _pullTime;
if (_state != _GlowState.pull) {
_glowController.forward(from: 0.0);
_state = _GlowState.pull;
} else {
if (!_glowController.isAnimating) {
assert(_glowController.value == 1.0);
notifyListeners();
}
}
_pullRecedeTimer = Timer(_pullHoldTime, () => _recede(_pullDecayTime));
}
void scrollEnd() {
if (_state == _GlowState.pull)
_recede(_recedeTime);
}
void _changePhase(AnimationStatus status) {
if (status != AnimationStatus.completed)
return;
switch (_state) {
case _GlowState.absorb:
_recede(_recedeTime);
break;
case _GlowState.recede:
_state = _GlowState.idle;
_pullDistance = 0.0;
break;
case _GlowState.pull:
case _GlowState.idle:
break;
}
}
void _recede(Duration duration) {
if (_state == _GlowState.recede || _state == _GlowState.idle)
return;
_pullRecedeTimer?.cancel();
_pullRecedeTimer = null;
_glowOpacityTween.begin = _glowOpacity.value;
_glowOpacityTween.end = 0.0;
_glowSizeTween.begin = _glowSize.value;
_glowSizeTween.end = 0.0;
_glowController.duration = duration;
_glowController.forward(from: 0.0);
_state = _GlowState.recede;
}
void _tickDisplacement(Duration elapsed) {
if (_displacementTickerLastElapsed != null) {
final double t = (elapsed.inMicroseconds - _displacementTickerLastElapsed.inMicroseconds).toDouble();
_displacement = _displacementTarget - (_displacementTarget - _displacement) * math.pow(2.0, -t / _crossAxisHalfTime.inMicroseconds);
notifyListeners();
}
if (nearEqual(_displacementTarget, _displacement, Tolerance.defaultTolerance.distance)) {
_displacementTicker.stop();
_displacementTickerLastElapsed = null;
} else {
_displacementTickerLastElapsed = elapsed;
}
}
void paint(Canvas canvas, Size size) {
if (_glowOpacity.value == 0.0)
return;
final double baseGlowScale = size.width > size.height ? size.height / size.width : 1.0;
final double radius = size.width * 3.0 / 2.0;
final double height = math.min(size.height, size.width * _widthToHeightFactor);
final double scaleY = _glowSize.value * baseGlowScale;
final Rect rect = Rect.fromLTWH(0.0, 0.0, size.width, height);
final Offset center = Offset((size.width / 2.0) * (0.5 + _displacement), height - radius);
final Paint paint = Paint()..color = color.withOpacity(_glowOpacity.value);
canvas.save();
canvas.scale(1.0, scaleY);
canvas.clipRect(rect);
canvas.drawCircle(center, radius, paint);
canvas.restore();
}
}
class _GlowingOverscrollIndicatorPainter extends CustomPainter {
_GlowingOverscrollIndicatorPainter({
this.leadingController,
this.trailingController,
this.axisDirection,
Listenable repaint,
}) : super(
repaint: repaint,
);
/// The controller for the overscroll glow on the side with negative scroll offsets.
///
/// For a vertical downwards viewport, this is the top side.
final _GlowController leadingController;
/// The controller for the overscroll glow on the side with positive scroll offsets.
///
/// For a vertical downwards viewport, this is the bottom side.
final _GlowController trailingController;
/// The direction of the viewport.
final AxisDirection axisDirection;
static const double piOver2 = math.pi / 2.0;
void _paintSide(Canvas canvas, Size size, _GlowController controller, AxisDirection axisDirection, GrowthDirection growthDirection) {
if (controller == null)
return;
switch (applyGrowthDirectionToAxisDirection(axisDirection, growthDirection)) {
case AxisDirection.up:
controller.paint(canvas, size);
break;
case AxisDirection.down:
canvas.save();
canvas.translate(0.0, size.height);
canvas.scale(1.0, -1.0);
controller.paint(canvas, size);
canvas.restore();
break;
case AxisDirection.left:
canvas.save();
canvas.rotate(piOver2);
canvas.scale(1.0, -1.0);
controller.paint(canvas, Size(size.height, size.width));
canvas.restore();
break;
case AxisDirection.right:
canvas.save();
canvas.translate(size.width, 0.0);
canvas.rotate(piOver2);
controller.paint(canvas, Size(size.height, size.width));
canvas.restore();
break;
}
}
@override
void paint(Canvas canvas, Size size) {
_paintSide(canvas, size, leadingController, axisDirection, GrowthDirection.reverse);
_paintSide(canvas, size, trailingController, axisDirection, GrowthDirection.forward);
}
@override
bool shouldRepaint(_GlowingOverscrollIndicatorPainter oldDelegate) {
return oldDelegate.leadingController != leadingController
|| oldDelegate.trailingController != trailingController;
}
}
/// A notification that an [GlowingOverscrollIndicator] will start showing an
/// overscroll indication.
///
/// To prevent the indicator from showing the indication, call [disallowGlow] on
/// the notification.
///
/// See also:
///
/// * [GlowingOverscrollIndicator], which generates this type of notification.
class OverscrollIndicatorNotification extends Notification with ViewportNotificationMixin {
/// Creates a notification that an [GlowingOverscrollIndicator] will start
/// showing an overscroll indication.
///
/// The [leading] argument must not be null.
OverscrollIndicatorNotification({
@required this.leading,
});
/// Whether the indication will be shown on the leading edge of the scroll
/// view.
final bool leading;
bool _accepted = true;
/// Call this method if the glow should be prevented.
void disallowGlow() {
_accepted = false;
}
@override
void debugFillDescription(List<String> description) {
super.debugFillDescription(description);
description.add('side: ${leading ? "leading edge" : "trailing edge"}');
}
}
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