| // Copyright 2014 The Flutter 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/foundation.dart'; |
| import 'package:flutter/physics.dart'; |
| |
| /// An implementation of scroll physics that matches iOS. |
| /// |
| /// See also: |
| /// |
| /// * [ClampingScrollSimulation], which implements Android scroll physics. |
| class BouncingScrollSimulation extends Simulation { |
| /// Creates a simulation group for scrolling on iOS, with the given |
| /// parameters. |
| /// |
| /// The position and velocity arguments must use the same units as will be |
| /// expected from the [x] and [dx] methods respectively (typically logical |
| /// pixels and logical pixels per second respectively). |
| /// |
| /// The leading and trailing extents must use the unit of length, the same |
| /// unit as used for the position argument and as expected from the [x] |
| /// method (typically logical pixels). |
| /// |
| /// The units used with the provided [SpringDescription] must similarly be |
| /// consistent with the other arguments. A default set of constants is used |
| /// for the `spring` description if it is omitted; these defaults assume |
| /// that the unit of length is the logical pixel. |
| BouncingScrollSimulation({ |
| required double position, |
| required double velocity, |
| required this.leadingExtent, |
| required this.trailingExtent, |
| required this.spring, |
| double constantDeceleration = 0, |
| super.tolerance, |
| }) : assert(position != null), |
| assert(velocity != null), |
| assert(leadingExtent != null), |
| assert(trailingExtent != null), |
| assert(leadingExtent <= trailingExtent), |
| assert(spring != null) { |
| if (position < leadingExtent) { |
| _springSimulation = _underscrollSimulation(position, velocity); |
| _springTime = double.negativeInfinity; |
| } else if (position > trailingExtent) { |
| _springSimulation = _overscrollSimulation(position, velocity); |
| _springTime = double.negativeInfinity; |
| } else { |
| // Taken from UIScrollView.decelerationRate (.normal = 0.998) |
| // 0.998^1000 = ~0.135 |
| _frictionSimulation = FrictionSimulation(0.135, position, velocity, constantDeceleration: constantDeceleration); |
| final double finalX = _frictionSimulation.finalX; |
| if (velocity > 0.0 && finalX > trailingExtent) { |
| _springTime = _frictionSimulation.timeAtX(trailingExtent); |
| _springSimulation = _overscrollSimulation( |
| trailingExtent, |
| math.min(_frictionSimulation.dx(_springTime), maxSpringTransferVelocity), |
| ); |
| assert(_springTime.isFinite); |
| } else if (velocity < 0.0 && finalX < leadingExtent) { |
| _springTime = _frictionSimulation.timeAtX(leadingExtent); |
| _springSimulation = _underscrollSimulation( |
| leadingExtent, |
| math.min(_frictionSimulation.dx(_springTime), maxSpringTransferVelocity), |
| ); |
| assert(_springTime.isFinite); |
| } else { |
| _springTime = double.infinity; |
| } |
| } |
| assert(_springTime != null); |
| } |
| |
| /// The maximum velocity that can be transferred from the inertia of a ballistic |
| /// scroll into overscroll. |
| static const double maxSpringTransferVelocity = 5000.0; |
| |
| /// When [x] falls below this value the simulation switches from an internal friction |
| /// model to a spring model which causes [x] to "spring" back to [leadingExtent]. |
| final double leadingExtent; |
| |
| /// When [x] exceeds this value the simulation switches from an internal friction |
| /// model to a spring model which causes [x] to "spring" back to [trailingExtent]. |
| final double trailingExtent; |
| |
| /// The spring used to return [x] to either [leadingExtent] or [trailingExtent]. |
| final SpringDescription spring; |
| |
| late FrictionSimulation _frictionSimulation; |
| late Simulation _springSimulation; |
| late double _springTime; |
| double _timeOffset = 0.0; |
| |
| Simulation _underscrollSimulation(double x, double dx) { |
| return ScrollSpringSimulation(spring, x, leadingExtent, dx); |
| } |
| |
| Simulation _overscrollSimulation(double x, double dx) { |
| return ScrollSpringSimulation(spring, x, trailingExtent, dx); |
| } |
| |
| Simulation _simulation(double time) { |
| final Simulation simulation; |
| if (time > _springTime) { |
| _timeOffset = _springTime.isFinite ? _springTime : 0.0; |
| simulation = _springSimulation; |
| } else { |
| _timeOffset = 0.0; |
| simulation = _frictionSimulation; |
| } |
| return simulation..tolerance = tolerance; |
| } |
| |
| @override |
| double x(double time) => _simulation(time).x(time - _timeOffset); |
| |
| @override |
| double dx(double time) => _simulation(time).dx(time - _timeOffset); |
| |
| @override |
| bool isDone(double time) => _simulation(time).isDone(time - _timeOffset); |
| |
| @override |
| String toString() { |
| return '${objectRuntimeType(this, 'BouncingScrollSimulation')}(leadingExtent: $leadingExtent, trailingExtent: $trailingExtent)'; |
| } |
| } |
| |
| /// An implementation of scroll physics that matches Android. |
| /// |
| /// See also: |
| /// |
| /// * [BouncingScrollSimulation], which implements iOS scroll physics. |
| // |
| // This class is based on Scroller.java from Android: |
| // https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/widget |
| // |
| // The "See..." comments below refer to Scroller methods and values. Some |
| // simplifications have been made. |
| class ClampingScrollSimulation extends Simulation { |
| /// Creates a scroll physics simulation that matches Android scrolling. |
| ClampingScrollSimulation({ |
| required this.position, |
| required this.velocity, |
| this.friction = 0.015, |
| super.tolerance, |
| }) : assert(_flingVelocityPenetration(0.0) == _initialVelocityPenetration) { |
| _duration = _flingDuration(velocity); |
| _distance = (velocity * _duration / _initialVelocityPenetration).abs(); |
| } |
| |
| /// The position of the particle at the beginning of the simulation. |
| final double position; |
| |
| /// The velocity at which the particle is traveling at the beginning of the |
| /// simulation. |
| final double velocity; |
| |
| /// The amount of friction the particle experiences as it travels. |
| /// |
| /// The more friction the particle experiences, the sooner it stops. |
| final double friction; |
| |
| late double _duration; |
| late double _distance; |
| |
| // See DECELERATION_RATE. |
| static final double _kDecelerationRate = math.log(0.78) / math.log(0.9); |
| |
| // See computeDeceleration(). |
| static double _decelerationForFriction(double friction) { |
| return friction * 61774.04968; |
| } |
| |
| // See getSplineFlingDuration(). Returns a value in seconds. |
| double _flingDuration(double velocity) { |
| // See mPhysicalCoeff |
| final double scaledFriction = friction * _decelerationForFriction(0.84); |
| |
| // See getSplineDeceleration(). |
| final double deceleration = math.log(0.35 * velocity.abs() / scaledFriction); |
| |
| return math.exp(deceleration / (_kDecelerationRate - 1.0)); |
| } |
| |
| // Based on a cubic curve fit to the Scroller.computeScrollOffset() values |
| // produced for an initial velocity of 4000. The value of Scroller.getDuration() |
| // and Scroller.getFinalY() were 686ms and 961 pixels respectively. |
| // |
| // Algebra courtesy of Wolfram Alpha. |
| // |
| // f(x) = scrollOffset, x is time in milliseconds |
| // f(x) = 3.60882×10^-6 x^3 - 0.00668009 x^2 + 4.29427 x - 3.15307 |
| // f(x) = 3.60882×10^-6 x^3 - 0.00668009 x^2 + 4.29427 x, so f(0) is 0 |
| // f(686ms) = 961 pixels |
| // Scale to f(0 <= t <= 1.0), x = t * 686 |
| // f(t) = 1165.03 t^3 - 3143.62 t^2 + 2945.87 t |
| // Scale f(t) so that 0.0 <= f(t) <= 1.0 |
| // f(t) = (1165.03 t^3 - 3143.62 t^2 + 2945.87 t) / 961.0 |
| // = 1.2 t^3 - 3.27 t^2 + 3.065 t |
| static const double _initialVelocityPenetration = 3.065; |
| static double _flingDistancePenetration(double t) { |
| return (1.2 * t * t * t) - (3.27 * t * t) + (_initialVelocityPenetration * t); |
| } |
| |
| // The derivative of the _flingDistancePenetration() function. |
| static double _flingVelocityPenetration(double t) { |
| return (3.6 * t * t) - (6.54 * t) + _initialVelocityPenetration; |
| } |
| |
| @override |
| double x(double time) { |
| final double t = clampDouble(time / _duration, 0.0, 1.0); |
| return position + _distance * _flingDistancePenetration(t) * velocity.sign; |
| } |
| |
| @override |
| double dx(double time) { |
| final double t = clampDouble(time / _duration, 0.0, 1.0); |
| return _distance * _flingVelocityPenetration(t) * velocity.sign / _duration; |
| } |
| |
| @override |
| bool isDone(double time) { |
| return time >= _duration; |
| } |
| } |