Refactor fn2.dart, since it breached our 1000-line threshold.

sky/sdk/lib/framework/components2/popup_menu.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 'dart:math' as math;
-import 'dart:sky' as sky;
-
-import '../animation/animated_value.dart';
-import '../fn2.dart';
-import '../painting/box_painter.dart';
-import '../theme2/colors.dart';
-import '../theme2/shadows.dart';
-import 'animated_component.dart';
-import 'material.dart';
-import 'popup_menu_item.dart';
-
-const double _kMenuOpenDuration = 300.0;
-const double _kMenuCloseDuration = 200.0;
-const double _kMenuCloseDelay = 100.0;
-
-enum MenuState { hidden, opening, open, closing }
-
-class PopupMenuController {
-  AnimatedValue position = new AnimatedValue(0.0);
-  MenuState _state = MenuState.hidden;
-  MenuState get state => _state;
-
-  bool get canReact => (_state == MenuState.opening) || (_state == MenuState.open);
-
-  open() async {
-    if (_state != MenuState.hidden)
-      return;
-    _state = MenuState.opening;
-    if (await position.animateTo(1.0, _kMenuOpenDuration) == 1.0)
-      _state = MenuState.open;
-  }
-
-  Future _closeState;
-  close() async {
-    var result = new Completer();
-    _closeState = result.future;
-    if ((_state == MenuState.opening) || (_state == MenuState.open)) {
-      _state = MenuState.closing;
-      await position.animateTo(0.0, _kMenuCloseDuration, initialDelay: _kMenuCloseDelay);
-      _state = MenuState.hidden;
-      _closeState = null;
-      result.complete();
-      return result.future;
-    }
-    assert(_closeState != null);
-    return _closeState;
-  }
-}
-
-class PopupMenu extends AnimatedComponent {
-
-  PopupMenu({ Object key, this.controller, this.items, this.level })
-      : super(key: key) {
-    _painter = new BoxPainter(new BoxDecoration(
-      backgroundColor: Grey[50],
-      borderRadius: 2.0,
-      boxShadow: Shadow[level]));
-
-    animate(controller.position, (double value) {
-      _position = value;
-    });
-  }
-
-  PopupMenuController controller;
-  List<List<UINode>> items;
-  int level;
-
-  void syncFields(PopupMenu source) {
-    controller = source.controller;
-    items = source.items;
-    level = source.level;
-    _painter = source._painter;
-    super.syncFields(source);
-  }
-
-  double _position;
-  BoxPainter _painter;
-
-  double _opacityFor(int i) {
-    if (_position == null || _position == 1.0)
-      return 1.0;
-    double unit = 1.0 / items.length;
-    double duration = 1.5 * unit;
-    double start = i * unit;
-    return math.max(0.0, math.min(1.0, (_position - start) / duration));
-  }
-
-  UINode build() {
-    int i = 0;
-    List<UINode> children = new List.from(items.map((List<UINode> item) {
-      double opacity = _opacityFor(i);
-      return new PopupMenuItem(key: i++, children: item, opacity: opacity);
-    }));
-
-    return new Opacity(
-      opacity: math.min(1.0, _position * 3.0),
-      child: new ShrinkWrapWidth(
-        child: new CustomPaint(
-          callback: (sky.Canvas canvas, Size size) {
-            double width = math.min(size.width, size.width * (0.5 + _position * 2.0));
-            double height = math.min(size.height, size.height * _position * 1.5);
-            _painter.paint(canvas, new Rect.fromLTRB(size.width - width, 0.0, width, height));
-          },
-          child: new Container(
-            padding: const EdgeDims.all(8.0),
-            child: new Block(children)
-          )
-        )
-      )
-    );
-  }
-
-}