anchor.diff:        final double yAlignEnd = (statusBarHeight + kToolBarHeight / 2.0) / toolBarHeight;
         final double scaleAndAlignEnd = (appBarHeight - toolBarHeight) / appBarHeight;
         final CurvedAnimation scaleAndAlignCurve = new CurvedAnimation(
  -        parent: animation,
  +        parent: _scaffoldAnimation,
           curve: new Interval(0.0, scaleAndAlignEnd)
         );
         children.add(new Padding(
  
positive.code: }
  
  class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
    @override
    Widget build(BuildContext context) {
      assert(debugCheckHasScaffold(context));
      final double statusBarHeight = MediaQuery.of(context).padding.top;
      final Animation<double> animation = Scaffold.of(context).appBarAnimation;
      final double appBarHeight = Scaffold.of(context).appBarHeight + statusBarHeight;
      final double toolBarHeight = kToolBarHeight + statusBarHeight;
      final List<Widget> children = <Widget>[];
  
  
negative.code:       final double fadeStart = (appBarHeight - toolBarHeight * 2.0) / appBarHeight;
        final double fadeEnd = (appBarHeight - toolBarHeight) / appBarHeight;
        final CurvedAnimation opacityCurve = new CurvedAnimation(
          parent: _scaffoldAnimation,
          curve: new Interval(math.max(0.0, fadeStart), math.min(fadeEnd, 1.0))
        );
        final double parallax = new Tween<double>(begin: 0.0, end: appBarHeight / 4.0).evaluate(_scaffoldAnimation);
        children.add(new Positioned(
          top: -parallax,
          left: 0.0,
  