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33e9822625
Turns out this is actually three simulations in a row, so we now have a system that can transition from one to another. R=eseidel@chromium.org Review URL: https://codereview.chromium.org/1100583002
81 lines
2.8 KiB
Dart
81 lines
2.8 KiB
Dart
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'dart:math' as math;
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import 'mechanics.dart';
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import 'generators.dart';
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const double _kScrollFriction = 0.005;
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const double _kOverscrollFriction = 0.075;
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const double _kBounceSlopeAngle = math.PI / 512.0; // radians
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abstract class ScrollBehavior {
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Simulation release(Particle particle) => null;
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// Returns the new scroll offset.
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double applyCurve(double scrollOffset, double scrollDelta);
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}
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class BoundedScrollBehavior extends ScrollBehavior {
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double minOffset;
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double maxOffset;
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BoundedScrollBehavior({this.minOffset: 0.0, this.maxOffset});
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double applyCurve(double scrollOffset, double scrollDelta) {
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double newScrollOffset = scrollOffset + scrollDelta;
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if (minOffset != null)
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newScrollOffset = math.max(minOffset, newScrollOffset);
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if (maxOffset != null)
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newScrollOffset = math.min(maxOffset, newScrollOffset);
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return newScrollOffset;
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}
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}
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class OverscrollBehavior extends ScrollBehavior {
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Simulation release(Particle particle) {
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System system;
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if (particle.position >= 0.0) {
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if (particle.velocity == 0.0)
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return null;
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System slowdownSystem = new ParticleInBoxWithFriction(
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particle: particle,
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friction: _kScrollFriction,
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box: new GeofenceBox(min: 0.0, onEscape: () {
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(system as Multisystem).transitionToSystem(new ParticleInBoxWithFriction(
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particle: particle,
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friction: _kOverscrollFriction,
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box: new ClosedBox(),
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onStop: () => (system as Multisystem).transitionToSystem(getBounceBackSystem(particle))
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));
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}));
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system = new Multisystem(particle: particle, system: slowdownSystem);
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} else {
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system = getBounceBackSystem(particle);
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}
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return new Simulation(system, terminationCondition: () => particle.position == 0.0);
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}
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System getBounceBackSystem(Particle particle) {
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return new ParticleClimbingRamp(
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particle: particle,
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box: new ClosedBox(max: 0.0),
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theta: _kBounceSlopeAngle,
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targetPosition: 0.0);
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}
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double applyCurve(double scrollOffset, double scrollDelta) {
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double newScrollOffset = scrollOffset + scrollDelta;
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if (newScrollOffset < 0.0) {
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// If we're overscrolling, we want move the scroll offset 2x slower than
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// we would otherwise. Therefore, we "rewind" the newScrollOffset by half
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// the amount that we moved it above. Notice that we clap the "old" value
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// to 0.0 so that we only reduce the portion of scrollDelta that's applied
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// beyond 0.0.
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newScrollOffset -= (newScrollOffset - math.min(0.0, scrollOffset)) / 2.0;
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}
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return newScrollOffset;
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}
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}
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