Organize sky/framework/animation

sky/framework/animation/scroll_curve.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:math' as math;
-import 'mechanics.dart';
-import 'simulation.dart';
-
-const double _kSlope = 0.01;
-
-abstract class ScrollCurve {
-  Simulation release(Particle particle) => null;
-
-  // Returns the new scroll offset.
-  double apply(double scrollOffset, double scrollDelta);
-}
-
-class BoundedScrollCurve extends ScrollCurve {
-  double minOffset;
-  double maxOffset;
-
-  BoundedScrollCurve({this.minOffset: 0.0, this.maxOffset});
-
-  double apply(double scrollOffset, double scrollDelta) {
-    double newScrollOffset = scrollOffset + scrollDelta;
-    if (minOffset != null)
-      newScrollOffset = math.max(minOffset, newScrollOffset);
-    if (maxOffset != null)
-      newScrollOffset = math.min(maxOffset, newScrollOffset);
-    return newScrollOffset;
-  }
-}
-
-class OverscrollCurve extends ScrollCurve {
-  Simulation release(Particle particle) {
-    if (particle.position >= 0.0)
-      return null;
-    System system = new ParticleClimbingRamp(
-        particle: particle,
-        box: new Box(max: 0.0),
-        slope: _kSlope,
-        targetPosition: 0.0);
-    return new Simulation(system,
-        terminationCondition: () => particle.position == 0.0);
-  }
-
-  double apply(double scrollOffset, double scrollDelta) {
-    double newScrollOffset = scrollOffset + scrollDelta;
-    if (newScrollOffset < 0.0) {
-      // If we're overscrolling, we want move the scroll offset 2x slower than
-      // we would otherwise. Therefore, we "rewind" the newScrollOffset by half
-      // the amount that we moved it above. Notice that we clap the "old" value
-      // to 0.0 so that we only reduce the portion of scrollDelta that's applied
-      // beyond 0.0.
-      newScrollOffset -= (newScrollOffset - math.min(0.0, scrollOffset)) / 2.0;
-    }
-    return newScrollOffset;
-  }
-}