Break dependency of AnimationPerformance on AnimatedValue

sky/sdk/lib/animation/timeline.dart

+// Copyright 2015 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 '../base/scheduler.dart' as scheduler;
+import 'curves.dart';
+
+class Ticker {
+  Ticker(Function onTick) : _onTick = onTick;
+
+  final Function _onTick;
+
+  Completer _completer;
+  int _animationId;
+
+  Future start() {
+    assert(!isTicking);
+    _completer = new Completer();
+    _scheduleTick();
+    return _completer.future;
+  }
+
+  void stop() {
+    if (!isTicking)
+      return;
+
+    if (_animationId != null) {
+      scheduler.cancelAnimationFrame(_animationId);
+      _animationId = null;
+    }
+
+    Completer localCompleter = _completer;
+    _completer = null;
+
+    // We take the _completer into a local variable so that !isTicking when we
+    // actually complete the future.
+    assert(!isTicking);
+    localCompleter.complete();
+  }
+
+  bool get isTicking => _completer != null;
+
+  void _tick(double timeStamp) {
+    assert(isTicking);
+    assert(_animationId != null);
+    _animationId = null;
+
+    _onTick(timeStamp);
+
+    if (isTicking)
+      _scheduleTick();
+  }
+
+  void _scheduleTick() {
+    assert(isTicking);
+    assert(_animationId == null);
+    _animationId = scheduler.requestAnimationFrame(_tick);
+  }
+}
+
+class Timeline {
+
+  Timeline(Function onTick, { double initialValue: 0.0 })
+    : _onTick = onTick, _value = initialValue {
+    _ticker = new Ticker(_tick);
+  }
+
+  final Function _onTick;
+  Ticker _ticker;
+
+  double _value;
+  double get value => _value;
+  void set value(double newValue) {
+    assert(newValue != null);
+    assert(!_ticker.isTicking);
+    _value = newValue;
+    _onTick(_value);
+  }
+
+  double _initialDelay;
+  double _duration;
+  double _begin;
+  double _end;
+  Curve _curve;

[Matt Perry, 2015/07/09 17:38:08]

This class seems overly complicated to me. If it's truly just a Timeline, it
should always animate linearly. All we need for AnimationPerformance is a
stopwatch: start from 0, tick for |duration|, end at 1.0. Methods you need:
start, stop, pause, get/set value, onTick, onDone.

If we need something more complicated, we should use an Animated<Double>.

[abarth-chromium, 2015/07/09 17:48:30]

Ok.  I'll remove that functionality.

+
+  double _startTime;
+  double _t;
+
+  Future start({
+    double initialDelay: 0.0,
+    double duration,
+    double begin: 0.0,
+    double end: 1.0,
+    Curve curve: linear
+  }) {
+    assert(initialDelay != null);
+    assert(duration != null && duration > 0.0);
+    assert(begin != null);
+    assert(end != null);
+    assert(curve != null);
+
+    assert(!_ticker.isTicking);
+
+    _initialDelay = initialDelay;
+    _duration = duration;
+    _begin = begin;
+    _end = end;
+    _curve = curve;
+
+    _startTime = null;
+    _t = 0.0;
+    _value = begin;
+
+    return _ticker.start();
+  }
+
+  Future animateTo(double target, {
+    double initialDelay: 0.0,
+    double duration,
+    Curve curve: linear
+  }) {
+    return start(initialDelay: initialDelay,
+                 duration: duration,
+                 begin: _value,
+                 end: target,
+                 curve: curve);
+  }
+
+  void stop() {
+    _initialDelay = null;
+    _duration = null;
+    _begin = null;
+    _end = null;
+    _curve = null;
+
+    _startTime = null;
+    _t = null;
+
+    _ticker.stop();
+  }
+
+  bool get isAnimating => _t != null;
+
+  void _tick(double timeStamp) {
+    if (_startTime == null)
+      _startTime = timeStamp;
+
+    _t = ((timeStamp - (_startTime + _initialDelay)) / _duration).clamp(0.0, 1.0);
+
+    final bool isLastTick = _t >= 1.0;
+
+    _value = isLastTick ? _end : _begin + (_end - _begin) * _curve.transform(_t);
+    _onTick(_value);
+
+    if (isLastTick)
+      stop();
+  }
+}