Organize sky/framework/animation

sky/framework/animation/simulation.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 'generator.dart';
-import 'mechanics.dart';
-
-class Simulation {
-  Stream<double> get onTick => _stream;
-  final System system;
-
-  FrameGenerator _generator;
-  Stream<double> _stream;
-  double _previousTime = 0.0;
-
-  Simulation(this.system, {Function terminationCondition, Function onDone}) {
-    _generator = new FrameGenerator(onDone: onDone);
-    _stream = _generator.onTick.map(_update);
-
-    if (terminationCondition != null) {
-      bool done = false;
-      _stream = _stream.takeWhile((_) {
-        if (done)
-          return false;
-        done = terminationCondition();
-        return true;
-      });
-    }
-  }
-
-  void cancel() {
-    _generator.cancel();
-  }
-
-  double _update(double timeStamp) {
-    double previousTime = _previousTime;
-    _previousTime = timeStamp;
-    if (previousTime == 0.0)
-      return timeStamp;
-    double deltaT = timeStamp - previousTime;
-    system.update(deltaT);
-    return timeStamp;
-  }
-}