Remove animation from Gallery header (#4322)

Although beautiful, having a continuous animation on the front page of the
gallery gives the impression that Flutter burns battery and makes phones hot.
This patch replaces the animation with solid purple. However, we might
eventually want to use a static image.

examples/flutter_gallery/lib/gallery/header.dart

-// Copyright 2016 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 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
-import 'package:flutter_sprites/flutter_sprites.dart';
-
-class GalleryHeader extends StatefulWidget {
-  @override
-  _GalleryHeaderState createState() => new _GalleryHeaderState();
-}
-
-class _GalleryHeaderState extends State<GalleryHeader> {
-  _FlutterHeaderNode _headerNode;
-  ImageMap _images;
-
-  Future<Null> _loadAssets() async {
-    final AssetBundle bundle = DefaultAssetBundle.of(context);
-    _images = new ImageMap(bundle);
-    await _images.load(<String>[
-      'packages/flutter_gallery_assets/grain.png',
-      'packages/flutter_gallery_assets/shadow.png',
-    ]);
-  }
-
-  @override
-  void initState() {
-    super.initState();
-    _loadAssets().then((_) {
-      setState(() {
-        _headerNode = new _FlutterHeaderNode(_images);
-      });
-    });
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return _headerNode == null ? new Container() : new SpriteWidget(_headerNode);
-  }
-}
-
-const Size _kCanvasSize = const Size(1024.0, 1024.0);
-const Point _kCenterPoint = const Point(512.0, 512.0);
-
-class _FlutterHeaderNode extends NodeWithSize {
-  _FlutterHeaderNode(this._images) : super(_kCanvasSize) {
-    clippingLayer.opacity = 0.0;
-    clippingLayer.actions.run(new ActionTween((double a) => clippingLayer.opacity = a, 0.0, 1.0, 0.5));
-    addChild(clippingLayer);
-
-    clippingLayer.addChild(new _BackgroundBox());
-
-    paperAnimation = new _PaperAnimation(_images);
-    paperAnimation.position = _kCenterPoint;
-    clippingLayer.addChild(paperAnimation);
-
-    final Sprite grain = new Sprite.fromImage(_images['packages/flutter_gallery_assets/grain.png'])
-      ..position = _kCenterPoint;
-    clippingLayer.addChild(grain);
-
-    userInteractionEnabled = true;
-  }
-
-  final ImageMap _images;
-  final Layer clippingLayer = new Layer();
-  _PaperAnimation paperAnimation;
-
-  @override
-  void spriteBoxPerformedLayout() {
-    clippingLayer.layerRect = spriteBox.visibleArea;
-  }
-}
-
-final List<_PaperConfig> _kPaperConfigs = <_PaperConfig>[
-  new _PaperConfig(
-    color: Colors.deepPurple[500],
-    startPosition: const Point(-300.0, -300.0),
-    startRotation: -10.0,
-    rotationSpeed: -1.0,
-    parallaxDepth: 0.0,
-    rect: new Rect.fromLTRB(-1024.0, -280.0, 1024.0, 280.0)
-  ),
-  new _PaperConfig(
-    color: Colors.purple[400],
-    startPosition: const Point(550.0, 0.0),
-    startRotation: 45.0,
-    rotationSpeed: 0.7,
-    parallaxDepth: 1.0,
-    rect: new Rect.fromLTRB(-512.0, -512.0, 512.0, 512.0)
-  ),
-  new _PaperConfig(
-    color: Colors.purple[600],
-    startPosition: const Point(550.0, 0.0),
-    startRotation: 55.0,
-    rotationSpeed: 0.9,
-    parallaxDepth: 2.0,
-    rect: new Rect.fromLTRB(-512.0, -512.0, 512.0, 512.0)
-  ),
-  new _PaperConfig(
-    color: Colors.purple[700],
-    startPosition: const Point(550.0, 0.0),
-    startRotation: 65.0,
-    rotationSpeed: 1.1,
-    parallaxDepth: 3.0,
-    rect: new Rect.fromLTRB(-512.0, -512.0, 512.0, 512.0)
-  )
-];
-
-class _PaperAnimation extends Node {
-  _PaperAnimation(ImageMap images) {
-    for (_PaperConfig config in _kPaperConfigs) {
-
-      final _PaperSheet sheet = new _PaperSheet(config);
-      final _PaperSheetShadow shadow = new _PaperSheetShadow(config, images);
-
-      addChild(shadow);
-      addChild(sheet);
-      _sheets.add(sheet);
-
-      shadow.constraints = <Constraint>[
-        new ConstraintRotationToNodeRotation(sheet),
-        new ConstraintPositionToNode(sheet, offset: const Offset(0.0, 8.0))
-      ];
-    }
-  }
-
-  final List<_PaperSheet> _sheets = <_PaperSheet>[];
-}
-
-class _PaperConfig {
-  _PaperConfig({
-    this.color,
-    this.startPosition,
-    this.startRotation,
-    this.rotationSpeed,
-    this.parallaxDepth,
-    this.rect
-  });
-
-  final Color color;
-  final Point startPosition;
-  final double startRotation;
-  final double rotationSpeed;
-  final double parallaxDepth;
-  final Rect rect;
-}
-
-class _PaperSheet extends Node {
-  _PaperSheet(this._config) {
-    _paperPaint.color = _config.color;
-
-    position = _config.startPosition;
-    rotation = _config.startRotation;
-  }
-
-  final _PaperConfig _config;
-  final Paint _paperPaint = new Paint();
-
-  @override
-  void paint(Canvas canvas) {
-    canvas.drawRect(_config.rect, _paperPaint);
-  }
-
-  @override
-  void update(double dt) {
-    rotation += _config.rotationSpeed * dt;
-  }
-}
-
-class _PaperSheetShadow extends Node {
-  _PaperSheetShadow(this._config, ImageMap images) {
-    NineSliceSprite shadow = new NineSliceSprite.fromImage(
-      images['packages/flutter_gallery_assets/shadow.png'],
-      new Size(
-        _config.rect.size.width + 32.0,
-        _config.rect.size.height + 32.0
-      ),
-      const EdgeInsets.all(0.375)
-    );
-    shadow.drawCenterPart = false;
-    shadow.opacity = 0.5;
-    addChild(shadow);
-  }
-
-  final _PaperConfig _config;
-}
-
-class _BackgroundBox extends Node {
-  final Paint _boxPaint = new Paint()..color = Colors.purple[500];
-
-  @override
-  void paint(Canvas canvas) {
-    canvas.drawRect(new Rect.fromLTWH(0.0, 0.0, _kCanvasSize.width, _kCanvasSize.height), _boxPaint);
-  }
-}

examples/flutter_gallery/lib/gallery/home.dart

@@ -7,7 +7,6 @@ import 'package:flutter/widgets.dart';
 
 import '../demo/all.dart';
 import 'drawer.dart';
-import 'header.dart';
 import 'item.dart';
 
 const double _kFlexibleSpaceMaxHeight = 256.0;
@@ -60,8 +59,7 @@ class GalleryHomeState extends State<GalleryHome> {
       appBar: new AppBar(
         expandedHeight: _kFlexibleSpaceMaxHeight,
         flexibleSpace: new FlexibleSpaceBar(
-          title: new Text('Flutter gallery'),
-          background: new GalleryHeader()
+          title: new Text('Flutter gallery')
         )
       ),
       appBarBehavior: AppBarBehavior.under,