在 Flutter 中建構新一代 UI

1. 事前準備

Flutter 可讓開發人員結合熱重載和宣告式 UI，以疊代方式快速建立新的使用者介面。不過，有時您會需要為介面加入額外的互動功能。這類觸控功能可以簡單的做法，像是在遊標懸停時建立動畫效果，或是做為著色器的擬真著色器，利用 GPU 的強大功能來填充使用者介面。

在本程式碼研究室中，您將建構一個 Flutter 應用程式，該應用程式會運用動畫、著色器和粒子欄位的強大功能來建構使用者介面，在未編寫程式碼的情況下，叫出大眾喜愛的科幻電影和電視節目。

建構項目

您將為末日後科幻主題遊戲建立初始選單頁面。例如使用片段著色器將文字取樣，然後以視覺化方式呈現文字；難度選單可藉由加入動畫來改變網頁的顏色主題，以及使用第二個片段著色器繪製的動畫 OB。假如這樣仍不足夠，只要在程式碼研究室結束時，您就會加入細微的粒子效果，讓頁面呈現動態效果和興趣。

以下螢幕截圖顯示您將透過三種支援的電腦作業系統 (Windows、Linux 和 macOS) 建構的應用程式。為求完整起見，我們提供了網路瀏覽器版本 (也有支援)。動畫和片段著色器到處都是！

在 Windows 上執行的完成應用程式

在 Chrome 瀏覽器中執行完成的應用程式

在 Linux 上執行的完成應用程式

在 macOS 上執行的完成應用程式

必要條件

課程內容

軟硬體需求

2. 開始操作

下載範例程式碼

  1. 前往這個 GitHub 存放區。
  2. 按一下「程式碼」>下載 ZIP 檔案即可下載這個程式碼研究室的所有程式碼。
  3. 將下載的 ZIP 檔案解壓縮，將 codelabs-main 根資料夾解壓縮。您只需要 next-gen-ui/ 子目錄，其中包含 step_01 至 step_06 資料夾，其中包含您在本程式碼研究室中每個步驟建構的原始碼。

下載專案依附元件

  1. 在 VS Code 中，按一下「File」(檔案) > 開啟資料夾 >Codes-main >Next-gen-uis >Step_01 開啟範例專案。
  2. 如果看到 VS Code 對話方塊，提示您下載範例應用程式所需的套件，請按一下「Get package」(取得套件)。

VS Code 對話方塊，提示您下載範例應用程式所需的套件。

  1. 如果您沒有看到 VS Code 對話方塊，提示您下載範例應用程式所需的套件，請開啟終端機，然後前往 step_01 資料夾並執行 flutter pub get 指令。

執行範例應用程式

  1. 在 VS Code 中，請選取您執行的電腦作業系統；如要在網路瀏覽器中測試應用程式，請選取 Chrome。

舉例來說，使用 macOS 做為部署目標時，您會看到以下內容：

顯示 Flutter 目標的 VSCode 狀態列裝飾為 macOS (darwin)

使用 Chrome 做為部署目標時，您會看到以下內容：

顯示 Flutter 目標的 VSCode 狀態列裝飾為 Chrome (網頁 JavaScript)

  1. 開啟 lib/main.dart 檔案，然後按一下 VSCode 中的「播放」按鈕「Start debugging」。應用程式會在電腦作業系統或 Chrome 瀏覽器中啟動。

探索範例應用程式

在範例應用程式中，請注意下列事項：

  • 您隨時可以建構 UI。
  • assets 目錄包含圖片素材資源和您要使用的兩個片段著色器。
  • pubspec.yaml 檔案已列出素材資源，以及您將使用的 pub 套件。
  • lib 目錄包含必要 main.dart 檔案、列出藝術資產和片段著色器路徑的 assets.dart 檔案，以及列出您要使用的 TextStyles 和 Color 的 styles.dart 檔案。
  • lib 目錄也包含 common 目錄，其中包含您將在這個程式碼研究室中使用的一些實用公用程式，以及 orb_shader 目錄，其中包含用於透過頂點著色器顯示 Orb 的 Widget。

啟動應用程式後，畫面會如下所示。

以「Insert Next-Generation UI Here...」的程式碼研究室應用程式執行程式碼

3. 繪製場景

在這個步驟中，您將所有背景藝術素材資源一層疊放在螢幕上。預期一開始看起來有奇怪的單色，但是在這個步驟最後，您為場景新增了幾個顏色。

在場景中新增素材資源

  1. 在 lib 目錄中建立 title_screen 目錄，然後新增 title_screen.dart 檔案。在檔案中新增下列內容：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';

import '../assets.dart';

class TitleScreen extends StatelessWidget {
  const TitleScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: [
            /// Bg-Base
            Image.asset(AssetPaths.titleBgBase),

            /// Bg-Receive
            Image.asset(AssetPaths.titleBgReceive),

            /// Mg-Base
            Image.asset(AssetPaths.titleMgBase),

            /// Mg-Receive
            Image.asset(AssetPaths.titleMgReceive),

            /// Mg-Emit
            Image.asset(AssetPaths.titleMgEmit),

            /// Fg-Rocks
            Image.asset(AssetPaths.titleFgBase),

            /// Fg-Receive
            Image.asset(AssetPaths.titleFgReceive),

            /// Fg-Emit
            Image.asset(AssetPaths.titleFgEmit),
          ],
        ),
      ),
    );
  }
}

這個小工具包含資產堆疊在圖層中的場景。背景、中景和前景圖層分別由兩或三張圖片組成。這些影像會以不同顏色照亮，捕捉光線在場景中移動的情形。

  1. 在 main.dart 檔案中，新增以下內容：

lib/main.dart

import 'dart:io' show Platform;

import 'package:flutter/foundation.dart' show kIsWeb;
import 'package:flutter/material.dart';
import 'package:window_size/window_size.dart';
                                                          // Remove 'styles.dart' import
import 'title_screen/title_screen.dart';                  // Add this import


void main() {
  if (!kIsWeb && (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
    WidgetsFlutterBinding.ensureInitialized();
    setWindowMinSize(const Size(800, 500));
  }
  runApp(const NextGenApp());
}

class NextGenApp extends StatelessWidget {
  const NextGenApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      themeMode: ThemeMode.dark,
      darkTheme: ThemeData(brightness: Brightness.dark),
      home: const TitleScreen(),                          // Replace with this widget
    );
  }
}

這會將應用程式的 UI 替換成藝術素材資源所建立的單色場景。接下來，請為各個圖層上色。

程式碼研究室應用程式僅以背景、中場和前景圖片資產執行，以單色顯示。

新增圖片著色公用程式

將以下內容新增至 title_screen.dart 檔案，即可新增圖片顏色公用程式：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';

import '../assets.dart';

class TitleScreen extends StatelessWidget {
  const TitleScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: [
            /// Bg-Base
            Image.asset(AssetPaths.titleBgBase),

            /// Bg-Receive
            Image.asset(AssetPaths.titleBgReceive),

            /// Mg-Base
            Image.asset(AssetPaths.titleMgBase),

            /// Mg-Receive
            Image.asset(AssetPaths.titleMgReceive),

            /// Mg-Emit
            Image.asset(AssetPaths.titleMgEmit),

            /// Fg-Rocks
            Image.asset(AssetPaths.titleFgBase),

            /// Fg-Receive
            Image.asset(AssetPaths.titleFgReceive),

            /// Fg-Emit
            Image.asset(AssetPaths.titleFgEmit),
          ],
        ),
      ),
    );
  }
}

class _LitImage extends StatelessWidget {                 // Add from here...
  const _LitImage({
    required this.color,
    required this.imgSrc,
    required this.lightAmt,
  });
  final Color color;
  final String imgSrc;
  final double lightAmt;

  @override
  Widget build(BuildContext context) {
    final hsl = HSLColor.fromColor(color);
    return Image.asset(
      imgSrc,
      color: hsl.withLightness(hsl.lightness * lightAmt).toColor(),
      colorBlendMode: BlendMode.modulate,
    );
  }
}                                                         // to here.

這個 _LitImage 公用程式小工具可根據其發出的光或接收情形，為每個藝術資產重新上色。由於您尚未使用這個新的小工具，因此可能會觸發 Linter 警告。

塗料 (顏色)

修改 title_screen.dart 檔案以上色，如下所示：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';

import '../assets.dart';
import '../styles.dart';                                  // Add this import

class TitleScreen extends StatelessWidget {
  const TitleScreen({super.key});

  final _finalReceiveLightAmt = 0.7;                      // Add this attribute
  final _finalEmitLightAmt = 0.5;                         // And this attribute

  @override
  Widget build(BuildContext context) {
    final orbColor = AppColors.orbColors[0];              // Add this final variable
    final emitColor = AppColors.emitColors[0];            // And this one

    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: [
            /// Bg-Base
            Image.asset(AssetPaths.titleBgBase),

            /// Bg-Receive
            _LitImage(                                    // Modify from here...
              color: orbColor,
              imgSrc: AssetPaths.titleBgReceive,
              lightAmt: _finalReceiveLightAmt,
            ),                                            // to here.

            /// Mg-Base
            _LitImage(                                    // Modify from here...
              imgSrc: AssetPaths.titleMgBase,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),                                            // to here.

            /// Mg-Receive
            _LitImage(                                    // Modify from here...
              imgSrc: AssetPaths.titleMgReceive,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),                                            // to here.

            /// Mg-Emit
            _LitImage(                                    // Modify from here...
              imgSrc: AssetPaths.titleMgEmit,
              color: emitColor,
              lightAmt: _finalEmitLightAmt,
            ),                                            // to here.

            /// Fg-Rocks
            Image.asset(AssetPaths.titleFgBase),

            /// Fg-Receive
            _LitImage(                                    // Modify from here...
              imgSrc: AssetPaths.titleFgReceive,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),                                            // to here.

            /// Fg-Emit
            _LitImage(                                    // Modify from here...
              imgSrc: AssetPaths.titleFgEmit,
              color: emitColor,
              lightAmt: _finalEmitLightAmt,
            ),                                            // to here.
          ],
        ),
      ),
    );
  }
}

class _LitImage extends StatelessWidget {
  const _LitImage({
    required this.color,
    required this.imgSrc,
    required this.lightAmt,
  });
  final Color color;
  final String imgSrc;
  final double lightAmt;

  @override
  Widget build(BuildContext context) {
    final hsl = HSLColor.fromColor(color);
    return Image.asset(
      imgSrc,
      color: hsl.withLightness(hsl.lightness * lightAmt).toColor(),
      colorBlendMode: BlendMode.modulate,
    );
  }
}

我再次回到應用程式的例子，圖片素材資源呈綠色。

搭配藝術資產執行的程式碼研究室應用程式，已色調為綠色。

4. 新增 UI

在這個步驟中，您將使用者介面放置於上一步建立的場景。包括標題、難度選取工具按鈕，以及重要的「開始」按鈕。

新增標題

  1. 在 lib/title_screen 目錄中建立 title_screen_ui.dart 檔案，然後在檔案中加入下列內容：

lib/title_screen/title_screen_ui.dart

import 'package:extra_alignments/extra_alignments.dart';
import 'package:flutter/material.dart';
import 'package:gap/gap.dart';

import '../assets.dart';
import '../common/ui_scaler.dart';
import '../styles.dart';

class TitleScreenUi extends StatelessWidget {
  const TitleScreenUi({
    super.key,
  });
  @override
  Widget build(BuildContext context) {
    return const Padding(
      padding: EdgeInsets.symmetric(vertical: 40, horizontal: 50),
      child: Stack(
        children: [
          /// Title Text
          TopLeft(
            child: UiScaler(
              alignment: Alignment.topLeft,
              child: _TitleText(),
            ),
          ),
        ],
      ),
    );
  }
}

class _TitleText extends StatelessWidget {
  const _TitleText();

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        const Gap(20),
        Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            Transform.translate(
              offset: Offset(-(TextStyles.h1.letterSpacing! * .5), 0),
              child: Text('OUTPOST', style: TextStyles.h1),
            ),
            Image.asset(AssetPaths.titleSelectedLeft, height: 65),
            Text('57', style: TextStyles.h2),
            Image.asset(AssetPaths.titleSelectedRight, height: 65),
          ],
        ),
        Text('INTO THE UNKNOWN', style: TextStyles.h3),
      ],
    );
  }
}

這個小工具包含標題，以及構成此應用程式使用者介面的所有按鈕。

  1. 依照下列方式更新 lib/title_screen/title_screen.dart 檔案：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';

import '../assets.dart';
import '../styles.dart';
import 'title_screen_ui.dart';                            // Add this import

class TitleScreen extends StatelessWidget {
  const TitleScreen({super.key});

  final _finalReceiveLightAmt = 0.7;
  final _finalEmitLightAmt = 0.5;

  @override
  Widget build(BuildContext context) {
    final orbColor = AppColors.orbColors[0];
    final emitColor = AppColors.emitColors[0];

    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: [
            /// Bg-Base
            Image.asset(AssetPaths.titleBgBase),

            /// Bg-Receive
            _LitImage(
              color: orbColor,
              imgSrc: AssetPaths.titleBgReceive,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Base
            _LitImage(
              imgSrc: AssetPaths.titleMgBase,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Receive
            _LitImage(
              imgSrc: AssetPaths.titleMgReceive,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Emit
            _LitImage(
              imgSrc: AssetPaths.titleMgEmit,
              color: emitColor,
              lightAmt: _finalEmitLightAmt,
            ),

            /// Fg-Rocks
            Image.asset(AssetPaths.titleFgBase),

            /// Fg-Receive
            _LitImage(
              imgSrc: AssetPaths.titleFgReceive,
              color: orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Fg-Emit
            _LitImage(
              imgSrc: AssetPaths.titleFgEmit,
              color: emitColor,
              lightAmt: _finalEmitLightAmt,
            ),

            /// UI
            const Positioned.fill(                        // Add from here...
              child: TitleScreenUi(),
            ),                                            // to here.
          ],
        ),
      ),
    );
  }
}

class _LitImage extends StatelessWidget {
  const _LitImage({
    required this.color,
    required this.imgSrc,
    required this.lightAmt,
  });
  final Color color;
  final String imgSrc;
  final double lightAmt;

  @override
  Widget build(BuildContext context) {
    final hsl = HSLColor.fromColor(color);
    return Image.asset(
      imgSrc,
      color: hsl.withLightness(hsl.lightness * lightAmt).toColor(),
      colorBlendMode: BlendMode.modulate,
    );
  }
}

執行這個程式碼就會看到標題，也就是使用者介面的開頭。

程式碼研究室應用程式執行，標題顯示「Outpost [57] Into the unknown」

新增難度按鈕

  1. 為 focusable_control_builder 套件新增匯入項目，藉此更新 title_screen_ui.dart：

lib/title_screen/title_screen_ui.dart

import 'package:extra_alignments/extra_alignments.dart';
import 'package:flutter/material.dart';
import 'package:focusable_control_builder/focusable_control_builder.dart'; // Add import
import 'package:gap/gap.dart';

import '../assets.dart';
import '../common/ui_scaler.dart';
import '../styles.dart';
  1. 請將以下內容新增至 TitleScreenUi 小工具：

lib/title_screen/title_screen_ui.dart

class TitleScreenUi extends StatelessWidget {
  const TitleScreenUi({
    super.key,
    required this.difficulty,                            // Edit from here...
    required this.onDifficultyPressed,
    required this.onDifficultyFocused,
  });

  final int difficulty;
  final void Function(int difficulty) onDifficultyPressed;
  final void Function(int? difficulty) onDifficultyFocused; // to here.

  @override
  Widget build(BuildContext context) {
    return Padding(                                      // Move this const...
      padding: const EdgeInsets.symmetric(vertical: 40, horizontal: 50), // to here.
      child: Stack(
        children: [
          /// Title Text
          const TopLeft(                                 // Add a const here, as well
            child: UiScaler(
              alignment: Alignment.topLeft,
              child: _TitleText(),
            ),
          ),

          /// Difficulty Btns
          BottomLeft(                                    // Add from here...
            child: UiScaler(
              alignment: Alignment.bottomLeft,
              child: _DifficultyBtns(
                difficulty: difficulty,
                onDifficultyPressed: onDifficultyPressed,
                onDifficultyFocused: onDifficultyFocused,
              ),
            ),
          ),                                             // to here.
        ],
      ),
    );
  }
}
  1. 新增以下兩個小工具，以實作難度按鈕：

lib/title_screen/title_screen_ui.dart

class _DifficultyBtns extends StatelessWidget {
  const _DifficultyBtns({
    required this.difficulty,
    required this.onDifficultyPressed,
    required this.onDifficultyFocused,
  });

  final int difficulty;
  final void Function(int difficulty) onDifficultyPressed;
  final void Function(int? difficulty) onDifficultyFocused;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        _DifficultyBtn(
          label: 'Casual',
          selected: difficulty == 0,
          onPressed: () => onDifficultyPressed(0),
          onHover: (over) => onDifficultyFocused(over ? 0 : null),
        ),
        _DifficultyBtn(
          label: 'Normal',
          selected: difficulty == 1,
          onPressed: () => onDifficultyPressed(1),
          onHover: (over) => onDifficultyFocused(over ? 1 : null),
        ),
        _DifficultyBtn(
          label: 'Hardcore',
          selected: difficulty == 2,
          onPressed: () => onDifficultyPressed(2),
          onHover: (over) => onDifficultyFocused(over ? 2 : null),
        ),
        const Gap(20),
      ],
    );
  }
}

class _DifficultyBtn extends StatelessWidget {
  const _DifficultyBtn({
    required this.selected,
    required this.onPressed,
    required this.onHover,
    required this.label,
  });
  final String label;
  final bool selected;
  final VoidCallback onPressed;
  final void Function(bool hasFocus) onHover;

  @override
  Widget build(BuildContext context) {
    return FocusableControlBuilder(
      onPressed: onPressed,
      onHoverChanged: (_, state) => onHover.call(state.isHovered),
      builder: (_, state) {
        return Padding(
          padding: const EdgeInsets.all(8.0),
          child: SizedBox(
            width: 250,
            height: 60,
            child: Stack(
              children: [
                /// Bg with fill and outline
                Container(
                  decoration: BoxDecoration(
                    color: const Color(0xFF00D1FF).withOpacity(.1),
                    border: Border.all(color: Colors.white, width: 5),
                  ),
                ),

                if (state.isHovered || state.isFocused) ...[
                  Container(
                    decoration: BoxDecoration(
                      color: const Color(0xFF00D1FF).withOpacity(.1),
                    ),
                  ),
                ],

                /// cross-hairs (selected state)
                if (selected) ...[
                  CenterLeft(
                    child: Image.asset(AssetPaths.titleSelectedLeft),
                  ),
                  CenterRight(
                    child: Image.asset(AssetPaths.titleSelectedRight),
                  ),
                ],

                /// Label
                Center(
                  child: Text(label.toUpperCase(), style: TextStyles.btn),
                ),
              ],
            ),
          ),
        );
      },
    );
  }
}
  1. 將 TitleScreen 小工具從無狀態轉換為有狀態，然後新增狀態，以便根據難度變更色彩配置：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';

import '../assets.dart';
import '../styles.dart';
import 'title_screen_ui.dart';

class TitleScreen extends StatefulWidget {
  const TitleScreen({super.key});

  @override
  State<TitleScreen> createState() => _TitleScreenState();
}

class _TitleScreenState extends State<TitleScreen> {
  Color get _emitColor =>
      AppColors.emitColors[_difficultyOverride ?? _difficulty];
  Color get _orbColor =>
      AppColors.orbColors[_difficultyOverride ?? _difficulty];

  /// Currently selected difficulty
  int _difficulty = 0;

  /// Currently focused difficulty (if any)
  int? _difficultyOverride;

  void _handleDifficultyPressed(int value) {
    setState(() => _difficulty = value);
  }

  void _handleDifficultyFocused(int? value) {
    setState(() => _difficultyOverride = value);
  }

  final _finalReceiveLightAmt = 0.7;
  final _finalEmitLightAmt = 0.5;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: [
            /// Bg-Base
            Image.asset(AssetPaths.titleBgBase),

            /// Bg-Receive
            _LitImage(
              color: _orbColor,
              imgSrc: AssetPaths.titleBgReceive,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Base
            _LitImage(
              imgSrc: AssetPaths.titleMgBase,
              color: _orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Receive
            _LitImage(
              imgSrc: AssetPaths.titleMgReceive,
              color: _orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Mg-Emit
            _LitImage(
              imgSrc: AssetPaths.titleMgEmit,
              color: _emitColor,
              lightAmt: _finalEmitLightAmt,
            ),

            /// Fg-Rocks
            Image.asset(AssetPaths.titleFgBase),

            /// Fg-Receive
            _LitImage(
              imgSrc: AssetPaths.titleFgReceive,
              color: _orbColor,
              lightAmt: _finalReceiveLightAmt,
            ),

            /// Fg-Emit
            _LitImage(
              imgSrc: AssetPaths.titleFgEmit,
              color: _emitColor,
              lightAmt: _finalEmitLightAmt,
            ),

            /// UI
            Positioned.fill(
              child: TitleScreenUi(
                difficulty: _difficulty,
                onDifficultyFocused: _handleDifficultyFocused,
                onDifficultyPressed: _handleDifficultyPressed,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class _LitImage extends StatelessWidget {
  const _LitImage({
    required this.color,
    required this.imgSrc,
    required this.lightAmt,
  });
  final Color color;
  final String imgSrc;
  final double lightAmt;

  @override
  Widget build(BuildContext context) {
    final hsl = HSLColor.fromColor(color);
    return Image.asset(
      imgSrc,
      color: hsl.withLightness(hsl.lightness * lightAmt).toColor(),
      colorBlendMode: BlendMode.modulate,
    );
  }
}

這是使用者介面的兩種不同難度設定。您會發現，在灰階圖片上套用難度的遮罩顏色可創造出逼真的反光效果！

選用一般難度的程式碼研究室應用程式，顯示已色調為紫色和青色的圖片素材資源。

已選取硬核難度的程式碼研究室應用程式，顯示已色調橘色的圖片素材資源。

新增「開始」按鈕

  1. 更新 title_screen_ui.dart 檔案。請將以下內容新增至 TitleScreenUi 小工具：

lib/title_screen/title_screen_ui.dart

class TitleScreenUi extends StatelessWidget {
  const TitleScreenUi({
    super.key,
    required this.difficulty,
    required this.onDifficultyPressed,
    required this.onDifficultyFocused,
  });

  final int difficulty;
  final void Function(int difficulty) onDifficultyPressed;
  final void Function(int? difficulty) onDifficultyFocused;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 40, horizontal: 50),
      child: Stack(
        children: [
          /// Title Text
          const TopLeft(
            child: UiScaler(
              alignment: Alignment.topLeft,
              child: _TitleText(),
            ),
          ),

          /// Difficulty Btns
          BottomLeft(
            child: UiScaler(
              alignment: Alignment.bottomLeft,
              child: _DifficultyBtns(
                difficulty: difficulty,
                onDifficultyPressed: onDifficultyPressed,
                onDifficultyFocused: onDifficultyFocused,
              ),
            ),
          ),

          /// StartBtn
          BottomRight(                                    // Add from here...
            child: UiScaler(
              alignment: Alignment.bottomRight,
              child: Padding(
                padding: const EdgeInsets.only(bottom: 20, right: 40),
                child: _StartBtn(onPressed: () {}),
              ),
            ),
          ),                                              // to here.
        ],
      ),
    );
  }
}
  1. 新增下列小工具以實作啟動按鈕：

lib/title_screen/title_screen_ui.dart

class _StartBtn extends StatefulWidget {
  const _StartBtn({required this.onPressed});
  final VoidCallback onPressed;

  @override
  State<_StartBtn> createState() => _StartBtnState();
}

class _StartBtnState extends State<_StartBtn> {
  AnimationController? _btnAnim;
  bool _wasHovered = false;

  @override
  Widget build(BuildContext context) {
    return FocusableControlBuilder(
      cursor: SystemMouseCursors.click,
      onPressed: widget.onPressed,
      builder: (_, state) {
        if ((state.isHovered || state.isFocused) &&
            !_wasHovered &&
            _btnAnim?.status != AnimationStatus.forward) {
          _btnAnim?.forward(from: 0);
        }
        _wasHovered = (state.isHovered || state.isFocused);
        return SizedBox(
          width: 520,
          height: 100,
          child: Stack(
            children: [
              Positioned.fill(child: Image.asset(AssetPaths.titleStartBtn)),
              if (state.isHovered || state.isFocused) ...[
                Positioned.fill(
                    child: Image.asset(AssetPaths.titleStartBtnHover)),
              ],
              Center(
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.end,
                  children: [
                    Text('START MISSION',
                        style: TextStyles.btn
                            .copyWith(fontSize: 24, letterSpacing: 18)),
                  ],
                ),
              ),
            ],
          ),
        );
      },
    );
  }
}

以下是執行中的應用程式，內含一系列按鈕。

程式碼研究室應用程式已選取一般難度，顯示標題、難度按鈕和開始按鈕。

5. 新增動畫

在這個步驟中，您可以動畫呈現圖片素材資源的使用者介面和顏色轉換效果。

在標題中淡入

在這個步驟中，您將使用多種方法為 Flutter 應用程式建立動畫。其中一種方法是使用 flutter_animate。運用這個套件提供的動畫，可在您熱重重新載入應用程式時自動重播，藉此加快開發疊代速度。

  1. 按照下列方式修改 lib/main.dart 中的程式碼：

lib/main.dart

import 'dart:io' show Platform;

import 'package:flutter/foundation.dart' show kIsWeb;
import 'package:flutter/material.dart';
import 'package:flutter_animate/flutter_animate.dart';   // Add this import
import 'package:window_size/window_size.dart';

import 'title_screen/title_screen.dart';

void main() {
  if (!kIsWeb && (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
    WidgetsFlutterBinding.ensureInitialized();
    setWindowMinSize(const Size(800, 500));
  }
  Animate.restartOnHotReload = true;                     // Add this line
  runApp(const NextGenApp());
}

class NextGenApp extends StatelessWidget {
  const NextGenApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      themeMode: ThemeMode.dark,
      darkTheme: ThemeData(brightness: Brightness.dark),
      home: const TitleScreen(),
    );
  }
}
  1. 若要使用 flutter_animate 套件，必須將其匯入。在 lib/title_screen/title_screen_ui.dart 中新增匯入作業，如下所示：

lib/title_screen/title_screen_ui.dart

import 'package:extra_alignments/extra_alignments.dart';
import 'package:flutter/material.dart';
import 'package:flutter_animate/flutter_animate.dart';   // Add this import
import 'package:focusable_control_builder/focusable_control_builder.dart';
import 'package:gap/gap.dart';

import '../assets.dart';
import '../common/ui_scaler.dart';
import '../styles.dart';

class TitleScreenUi extends StatelessWidget {
  1. 編輯 _TitleText 小工具即可在標題中加入動畫，如下所示：

lib/title_screen/title_screen_ui.dart

class _TitleText extends StatelessWidget {
  const _TitleText();

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        const Gap(20),
        Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            Transform.translate(
              offset: Offset(-(TextStyles.h1.letterSpacing! * .5), 0),
              child: Text('OUTPOST', style: TextStyles.h1),
            ),
            Image.asset(AssetPaths.titleSelectedLeft, height: 65),
            Text('57', style: TextStyles.h2),
            Image.asset(AssetPaths.titleSelectedRight, height: 65),
          ],                                             // Edit from here...
        ).animate().fadeIn(delay: .8.seconds, duration: .7.seconds),
        Text('INTO THE UNKNOWN', style: TextStyles.h3)
            .animate()
            .fadeIn(delay: 1.seconds, duration: .7.seconds),
      ],                                                 // to here.
    );
  }
}
  1. 按下「重新載入」，即可看到標題淡入。

淡入難度按鈕

  1. 編輯 _DifficultyBtns 小工具，即可在難度按鈕的初始外觀中加入動畫，如下所示：

lib/title_screen/title_screen_ui.dart

class _DifficultyBtns extends StatelessWidget {
  const _DifficultyBtns({
    required this.difficulty,
    required this.onDifficultyPressed,
    required this.onDifficultyFocused,
  });

  final int difficulty;
  final void Function(int difficulty) onDifficultyPressed;
  final void Function(int? difficulty) onDifficultyFocused;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        _DifficultyBtn(
          label: 'Casual',
          selected: difficulty == 0,
          onPressed: () => onDifficultyPressed(0),
          onHover: (over) => onDifficultyFocused(over ? 0 : null),
        )                                                // Add from here...
            .animate()
            .fadeIn(delay: 1.3.seconds, duration: .35.seconds)
            .slide(begin: const Offset(0, .2)),          // to here
        _DifficultyBtn(
          label: 'Normal',
          selected: difficulty == 1,
          onPressed: () => onDifficultyPressed(1),
          onHover: (over) => onDifficultyFocused(over ? 1 : null),
        )                                                // Add from here...
            .animate()
            .fadeIn(delay: 1.5.seconds, duration: .35.seconds)
            .slide(begin: const Offset(0, .2)),          // to here
        _DifficultyBtn(
          label: 'Hardcore',
          selected: difficulty == 2,
          onPressed: () => onDifficultyPressed(2),
          onHover: (over) => onDifficultyFocused(over ? 2 : null),
        )                                                // Add from here...
            .animate()
            .fadeIn(delay: 1.7.seconds, duration: .35.seconds)
            .slide(begin: const Offset(0, .2)),          // to here
        const Gap(20),
      ],
    );
  }
}
  1. 按下「重新載入」，查看難度按鈕就會依序出現，還有稍微向上滑動。

在「開始」按鈕淡入

  1. 編輯 _StartBtnState 狀態類別，即可在開始按鈕中加入動畫，如下所示：

lib/title_screen/title_screen_ui.dart

class _StartBtnState extends State<_StartBtn> {
  AnimationController? _btnAnim;
  bool _wasHovered = false;

  @override
  Widget build(BuildContext context) {
    return FocusableControlBuilder(
      cursor: SystemMouseCursors.click,
      onPressed: widget.onPressed,
      builder: (_, state) {
        if ((state.isHovered || state.isFocused) &&
            !_wasHovered &&
            _btnAnim?.status != AnimationStatus.forward) {
          _btnAnim?.forward(from: 0);
        }
        _wasHovered = (state.isHovered || state.isFocused);
        return SizedBox(
          width: 520,
          height: 100,
          child: Stack(
            children: [
              Positioned.fill(child: Image.asset(AssetPaths.titleStartBtn)),
              if (state.isHovered || state.isFocused) ...[
                Positioned.fill(
                    child: Image.asset(AssetPaths.titleStartBtnHover)),
              ],
              Center(
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.end,
                  children: [
                    Text('START MISSION',
                        style: TextStyles.btn
                            .copyWith(fontSize: 24, letterSpacing: 18)),
                  ],
                ),
              ),
            ],
          )                                              // Edit from here...
              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
              .shimmer(duration: .7.seconds, color: Colors.black),
        )
            .animate()
            .fadeIn(delay: 2.3.seconds)
            .slide(begin: const Offset(0, .2));
      },                                                 // to here.
    );
  }
}
  1. 按下「重新載入」，查看難度按鈕就會依序出現，還有稍微向上滑動。

為難度懸停效果建立動畫

在難度按鈕上加入動畫請編輯 _DifficultyBtn 狀態類別，以達到懸停狀態，如下所示：

lib/title_screen/title_screen_ui.dart

class _DifficultyBtn extends StatelessWidget {
  const _DifficultyBtn({
    required this.selected,
    required this.onPressed,
    required this.onHover,
    required this.label,
  });
  final String label;
  final bool selected;
  final VoidCallback onPressed;
  final void Function(bool hasFocus) onHover;

  @override
  Widget build(BuildContext context) {
    return FocusableControlBuilder(
      onPressed: onPressed,
      onHoverChanged: (_, state) => onHover.call(state.isHovered),
      builder: (_, state) {
        return Padding(
          padding: const EdgeInsets.all(8.0),
          child: SizedBox(
            width: 250,
            height: 60,
            child: Stack(
              children: [
                /// Bg with fill and outline
                AnimatedOpacity(                         // Edit from here
                  opacity: (!selected && (state.isHovered || state.isFocused))
                      ? 1
                      : 0,
                  duration: .3.seconds,
                  child: Container(
                    decoration: BoxDecoration(
                      color: const Color(0xFF00D1FF).withOpacity(.1),
                      border: Border.all(color: Colors.white, width: 5),
                    ),
                  ),
                ),                                       // to here.

                if (state.isHovered || state.isFocused) ...[
                  Container(
                    decoration: BoxDecoration(
                      color: const Color(0xFF00D1FF).withOpacity(.1),
                    ),
                  ),
                ],

                /// cross-hairs (selected state)
                if (selected) ...[
                  CenterLeft(
                    child: Image.asset(AssetPaths.titleSelectedLeft),
                  ),
                  CenterRight(
                    child: Image.asset(AssetPaths.titleSelectedRight),
                  ),
                ],

                /// Label
                Center(
                  child: Text(label.toUpperCase(), style: TextStyles.btn),
                ),
              ],
            ),
          ),
        );
      },
    );
  }
}

當滑鼠遊標懸停在尚未選取的按鈕上時，難度按鈕會顯示 BoxDecoration。

為顏色變更加上動畫效果

  1. 背景色彩瞬間變化非常清晰。在不同色彩配置之間為淺色圖片加上動畫效果較佳。將 flutter_animate 新增至 lib/title_screen/title_screen.dart：

lib/title_screen/title_screen.dart

import 'package:flutter/material.dart';
import 'package:flutter_animate/flutter_animate.dart';    // Add this import

import '../assets.dart';
import '../styles.dart';
import 'title_screen_ui.dart';

class TitleScreen extends StatefulWidget {
  1. 在 lib/title_screen/title_screen.dart 中新增 _AnimatedColors 小工具：

lib/title_screen/title_screen.dart

class _AnimatedColors extends StatelessWidget {
  const _AnimatedColors({
    required this.emitColor,
    required this.orbColor,
    required this.builder,
  });

  final Color emitColor;
  final Color orbColor;

  final Widget Function(BuildContext context, Color orbColor, Color emitColor)
      builder;

  @override
  Widget build(BuildContext context) {
    final duration = .5.seconds;
    return TweenAnimationBuilder(
      tween: ColorTween(begin: emitColor, end: emitColor),
      duration: duration,
      builder: (_, emitColor, __) {
        return TweenAnimationBuilder(
          tween: ColorTween(begin: orbColor, end: orbColor),
          duration: duration,
          builder: (context, orbColor, __) {
            return builder(context, orbColor!, emitColor!);
          },
        );
      },
    );
  }
}
  1. 使用您剛建立的小工具，更新 _TitleScreenState 中的 build 方法，為淺色圖片的色彩加上動畫效果，如下所示：

lib/title_screen/title_screen.dart

class _TitleScreenState extends State<TitleScreen> {
  Color get _emitColor =>
      AppColors.emitColors[_difficultyOverride ?? _difficulty];
  Color get _orbColor =>
      AppColors.orbColors[_difficultyOverride ?? _difficulty];

  /// Currently selected difficulty
  int _difficulty = 0;

  /// Currently focused difficulty (if any)
  int? _difficultyOverride;

  void _handleDifficultyPressed(int value) {
    setState(() => _difficulty = value);
  }

  void _handleDifficultyFocused(int? value) {
    setState(() => _difficultyOverride = value);
  }

  final _finalReceiveLightAmt = 0.7;
  final _finalEmitLightAmt = 0.5;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: _AnimatedColors(                           // Edit from here...
          orbColor: _orbColor,
          emitColor: _emitColor,
          builder: (_, orbColor, emitColor) {
            return Stack(
              children: [
                /// Bg-Base
                Image.asset(AssetPaths.titleBgBase),

                /// Bg-Receive
                _LitImage(
                  color: orbColor,
                  imgSrc: AssetPaths.titleBgReceive,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Mg-Base
                _LitImage(
                  imgSrc: AssetPaths.titleMgBase,
                  color: orbColor,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Mg-Receive
                _LitImage(
                  imgSrc: AssetPaths.titleMgReceive,
                  color: orbColor,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Mg-Emit
                _LitImage(
                  imgSrc: AssetPaths.titleMgEmit,
                  color: emitColor,
                  lightAmt: _finalEmitLightAmt,
                ),

                /// Fg-Rocks
                Image.asset(AssetPaths.titleFgBase),

                /// Fg-Receive
                _LitImage(
                  imgSrc: AssetPaths.titleFgReceive,
                  color: orbColor,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Fg-Emit
                _LitImage(
                  imgSrc: AssetPaths.titleFgEmit,
                  color: emitColor,
                  lightAmt: _finalEmitLightAmt,
                ),

                /// UI
                Positioned.fill(
                  child: TitleScreenUi(
                    difficulty: _difficulty,
                    onDifficultyFocused: _handleDifficultyFocused,
                    onDifficultyPressed: _handleDifficultyPressed,
                  ),
                ),
              ],
            ).animate().fadeIn(duration: 1.seconds, delay: .3.seconds);
          },
        ),                                                // to here.
      ),
    );
  }
}

透過最後的編輯，你已經為畫面上每個元素加入動畫，畫面看起來更美觀！

6. 新增片段著色器

在這個步驟中，您將在應用程式中新增片段著色器。首先，使用著色器修改標題，讓標題看起來更加反烏托邦。接下來，請新增第二個著色器，建立做為頁面主要焦點的 Orb。

使用片段著色器扭曲標題

這項變更會導入 provider 套件，藉此將已編譯的著色器向下傳遞至小工具樹狀結構。如要瞭解著色器的載入方式，請參閱 lib/assets.dart 中的實作。

  1. 按照下列方式修改 lib/main.dart 中的程式碼：

lib/main.dart

import 'dart:io' show Platform;

import 'package:flutter/foundation.dart' show kIsWeb;
import 'package:flutter/material.dart';
import 'package:flutter_animate/flutter_animate.dart';
import 'package:provider/provider.dart';                 // Add this import
import 'package:window_size/window_size.dart';

import 'assets.dart';                                    // Add this import
import 'title_screen/title_screen.dart';

void main() {
  if (!kIsWeb && (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
    WidgetsFlutterBinding.ensureInitialized();
    setWindowMinSize(const Size(800, 500));
  }
  Animate.restartOnHotReload = true;
  runApp(                                                // Edit from here...
    FutureProvider<FragmentPrograms?>(
      create: (context) => loadFragmentPrograms(),
      initialData: null,
      child: const NextGenApp(),
    ),
  );                                                     // to here.
}

class NextGenApp extends StatelessWidget {
  const NextGenApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      themeMode: ThemeMode.dark,
      darkTheme: ThemeData(brightness: Brightness.dark),
      home: const TitleScreen(),
    );
  }
}
  1. 如要利用 provider 套件和 step_01 內含的著色器公用程式，請匯入這些項目。在 lib/title_screen/title_screen_ui.dart 中新增匯入項目，如下所示：

lib/title_screen/title_screen_ui.dart

import 'package:extra_alignments/extra_alignments.dart';
import 'package:flutter/material.dart';
import 'package:flutter_animate/flutter_animate.dart';
import 'package:focusable_control_builder/focusable_control_builder.dart';
import 'package:gap/gap.dart';
import 'package:provider/provider.dart';                 // Add this import

import '../assets.dart';
import '../common/shader_effect.dart';                   // And this import
import '../common/ticking_builder.dart';                 // And this import
import '../common/ui_scaler.dart';
import '../styles.dart';

class TitleScreenUi extends StatelessWidget {
  1. 請編輯 _TitleText 小工具，使用著色器扭曲標題，如下所示：

lib/title_screen/title_screen_ui.dart

class _TitleText extends StatelessWidget {
  const _TitleText();

  @override
  Widget build(BuildContext context) {
    Widget content = Column(                             // Modify this line
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        const Gap(20),
        Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            Transform.translate(
              offset: Offset(-(TextStyles.h1.letterSpacing! * .5), 0),
              child: Text('OUTPOST', style: TextStyles.h1),
            ),
            Image.asset(AssetPaths.titleSelectedLeft, height: 65),
            Text('57', style: TextStyles.h2),
            Image.asset(AssetPaths.titleSelectedRight, height: 65),
          ],
        ).animate().fadeIn(delay: .8.seconds, duration: .7.seconds),
        Text('INTO THE UNKNOWN', style: TextStyles.h3)
            .animate()
            .fadeIn(delay: 1.seconds, duration: .7.seconds),
      ],
    );
    return Consumer<FragmentPrograms?>(                  // Add from here...
      builder: (context, fragmentPrograms, _) {
        if (fragmentPrograms == null) return content;
        return TickingBuilder(
          builder: (context, time) {
            return AnimatedSampler(
              (image, size, canvas) {
                const double overdrawPx = 30;
                final shader = fragmentPrograms.ui.fragmentShader();
                shader
                  ..setFloat(0, size.width)
                  ..setFloat(1, size.height)
                  ..setFloat(2, time)
                  ..setImageSampler(0, image);
                Rect rect = Rect.fromLTWH(-overdrawPx, -overdrawPx,
                    size.width + overdrawPx, size.height + overdrawPx);
                canvas.drawRect(rect, Paint()..shader = shader);
              },
              child: content,
            );
          },
        );
      },
    );                                                   // to here.
  }
}

您應該會看到標題變形，就像是反烏托邦的預期一樣。

新增 Orb

接著在視窗中央新增 Orb。您必須在開始按鈕中加入 onPressed 回呼。

  1. 在 lib/title_screen/title_screen_ui.dart 中，按照以下方式修改 TitleScreenUi：

lib/title_screen/title_screen_ui.dart

class TitleScreenUi extends StatelessWidget {
  const TitleScreenUi({
    super.key,
    required this.difficulty,
    required this.onDifficultyPressed,
    required this.onDifficultyFocused,
    required this.onStartPressed,                         // Add this argument
  });

  final int difficulty;
  final void Function(int difficulty) onDifficultyPressed;
  final void Function(int? difficulty) onDifficultyFocused;
  final VoidCallback onStartPressed;                      // Add this attribute

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 40, horizontal: 50),
      child: Stack(
        children: [
          /// Title Text
          const TopLeft(
            child: UiScaler(
              alignment: Alignment.topLeft,
              child: _TitleText(),
            ),
          ),

          /// Difficulty Btns
          BottomLeft(
            child: UiScaler(
              alignment: Alignment.bottomLeft,
              child: _DifficultyBtns(
                difficulty: difficulty,
                onDifficultyPressed: onDifficultyPressed,
                onDifficultyFocused: onDifficultyFocused,
              ),
            ),
          ),

          /// StartBtn
          BottomRight(
            child: UiScaler(
              alignment: Alignment.bottomRight,
              child: Padding(
                padding: const EdgeInsets.only(bottom: 20, right: 40),
                child: _StartBtn(onPressed: onStartPressed),  // Edit this line
              ),
            ),
          ),
        ],
      ),
    );
  }
}

現在您已使用回呼修改開始按鈕，需要大幅修改 lib/title_screen/title_screen.dart 檔案。

  1. 按照下列方式修改匯入內容：

lib/title_screen/title_screen.dart

import 'dart:math';                                       // Add this import
import 'dart:ui';                                         // And this import

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';                   // Add this import
import 'package:flutter_animate/flutter_animate.dart';

import '../assets.dart';
import '../orb_shader/orb_shader_config.dart';            // And this import
import '../orb_shader/orb_shader_widget.dart';            // And this import too
import '../styles.dart';
import 'title_screen_ui.dart';

class TitleScreen extends StatefulWidget {
  1. 修改 _TitleScreenState 以使其符合以下內容。類別的每個部分幾乎都是受到某種程度的修改。

lib/title_screen/title_screen.dart

class _TitleScreenState extends State<TitleScreen>
    with SingleTickerProviderStateMixin {
  final _orbKey = GlobalKey<OrbShaderWidgetState>();

  /// Editable Settings
  /// 0-1, receive lighting strength
  final _minReceiveLightAmt = .35;
  final _maxReceiveLightAmt = .7;

  /// 0-1, emit lighting strength
  final _minEmitLightAmt = .5;
  final _maxEmitLightAmt = 1;

  /// Internal
  var _mousePos = Offset.zero;

  Color get _emitColor =>
      AppColors.emitColors[_difficultyOverride ?? _difficulty];
  Color get _orbColor =>
      AppColors.orbColors[_difficultyOverride ?? _difficulty];

  /// Currently selected difficulty
  int _difficulty = 0;

  /// Currently focused difficulty (if any)
  int? _difficultyOverride;
  double _orbEnergy = 0;
  double _minOrbEnergy = 0;

  double get _finalReceiveLightAmt {
    final light =
        lerpDouble(_minReceiveLightAmt, _maxReceiveLightAmt, _orbEnergy) ?? 0;
    return light + _pulseEffect.value * .05 * _orbEnergy;
  }

  double get _finalEmitLightAmt {
    return lerpDouble(_minEmitLightAmt, _maxEmitLightAmt, _orbEnergy) ?? 0;
  }

  late final _pulseEffect = AnimationController(
    vsync: this,
    duration: _getRndPulseDuration(),
    lowerBound: -1,
    upperBound: 1,
  );

  Duration _getRndPulseDuration() => 100.ms + 200.ms * Random().nextDouble();

  double _getMinEnergyForDifficulty(int difficulty) => switch (difficulty) {
        1 => 0.3,
        2 => 0.6,
        _ => 0,
      };


  @override
  void initState() {
    super.initState();
    _pulseEffect.forward();
    _pulseEffect.addListener(_handlePulseEffectUpdate);
  }

  void _handlePulseEffectUpdate() {
    if (_pulseEffect.status == AnimationStatus.completed) {
      _pulseEffect.reverse();
      _pulseEffect.duration = _getRndPulseDuration();
    } else if (_pulseEffect.status == AnimationStatus.dismissed) {
      _pulseEffect.duration = _getRndPulseDuration();
      _pulseEffect.forward();
    }
  }

  void _handleDifficultyPressed(int value) {
    setState(() => _difficulty = value);
    _bumpMinEnergy();
  }

  Future<void> _bumpMinEnergy([double amount = 0.1]) async {
    setState(() {
      _minOrbEnergy = _getMinEnergyForDifficulty(_difficulty) + amount;
    });
    await Future<void>.delayed(.2.seconds);
    setState(() {
      _minOrbEnergy = _getMinEnergyForDifficulty(_difficulty);
    });
  }

  void _handleStartPressed() => _bumpMinEnergy(0.3);

  void _handleDifficultyFocused(int? value) {
    setState(() {
      _difficultyOverride = value;
      if (value == null) {
        _minOrbEnergy = _getMinEnergyForDifficulty(_difficulty);
      } else {
        _minOrbEnergy = _getMinEnergyForDifficulty(value);
      }
    });
  }

  /// Update mouse position so the orbWidget can use it, doing it here prevents
  /// btns from blocking the mouse-move events in the widget itself.
  void _handleMouseMove(PointerHoverEvent e) {
    setState(() {
      _mousePos = e.localPosition;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: MouseRegion(
          onHover: _handleMouseMove,
          child: _AnimatedColors(
            orbColor: _orbColor,
            emitColor: _emitColor,
            builder: (_, orbColor, emitColor) {
              return Stack(
                children: [
                  /// Bg-Base
                  Image.asset(AssetPaths.titleBgBase),

                  /// Bg-Receive
                  _LitImage(
                    color: orbColor,
                    imgSrc: AssetPaths.titleBgReceive,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalReceiveLightAmt,
                  ),

                  /// Orb
                  Positioned.fill(
                    child: Stack(
                      children: [
                        // Orb
                        OrbShaderWidget(
                          key: _orbKey,
                          mousePos: _mousePos,
                          minEnergy: _minOrbEnergy,
                          config: OrbShaderConfig(
                            ambientLightColor: orbColor,
                            materialColor: orbColor,
                            lightColor: orbColor,
                          ),
                          onUpdate: (energy) => setState(() {
                            _orbEnergy = energy;
                          }),
                        ),
                      ],
                    ),
                  ),

                  /// Mg-Base
                  _LitImage(
                    imgSrc: AssetPaths.titleMgBase,
                    color: orbColor,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalReceiveLightAmt,
                  ),

                  /// Mg-Receive
                  _LitImage(
                    imgSrc: AssetPaths.titleMgReceive,
                    color: orbColor,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalReceiveLightAmt,
                  ),

                  /// Mg-Emit
                  _LitImage(
                    imgSrc: AssetPaths.titleMgEmit,
                    color: emitColor,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalEmitLightAmt,
                  ),

                  /// Fg-Rocks
                  Image.asset(AssetPaths.titleFgBase),

                  /// Fg-Receive
                  _LitImage(
                    imgSrc: AssetPaths.titleFgReceive,
                    color: orbColor,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalReceiveLightAmt,
                  ),

                  /// Fg-Emit
                  _LitImage(
                    imgSrc: AssetPaths.titleFgEmit,
                    color: emitColor,
                    pulseEffect: _pulseEffect,
                    lightAmt: _finalEmitLightAmt,
                  ),

                  /// UI
                  Positioned.fill(
                    child: TitleScreenUi(
                      difficulty: _difficulty,
                      onDifficultyFocused: _handleDifficultyFocused,
                      onDifficultyPressed: _handleDifficultyPressed,
                      onStartPressed: _handleStartPressed,
                    ),
                  ),
                ],
              ).animate().fadeIn(duration: 1.seconds, delay: .3.seconds);
            },
          ),
        ),
      ),
    );
  }
}
  1. 按照下列方式修改 _LitImage：

lib/title_screen/title_screen.dart

class _LitImage extends StatelessWidget {
  const _LitImage({
    required this.color,
    required this.imgSrc,
    required this.pulseEffect,                            // Add this parameter
    required this.lightAmt,
  });
  final Color color;
  final String imgSrc;
  final AnimationController pulseEffect;                  // Add this attribute
  final double lightAmt;

  @override
  Widget build(BuildContext context) {
    final hsl = HSLColor.fromColor(color);
    return ListenableBuilder(                             // Edit from here...
      listenable: pulseEffect,
      builder: (context, child) {
        return Image.asset(
          imgSrc,
          color: hsl.withLightness(hsl.lightness * lightAmt).toColor(),
          colorBlendMode: BlendMode.modulate,
        );
      },
    );                                                    // to here.
  }
}

這就是新增的成因。

7. 新增粒子動畫

在這個步驟中，您將新增粒子動畫，在應用程式中產生細微的閃爍動作。

隨處加入粒子

  1. 建立新的 lib/title_screen/particle_overlay.dart 檔案，然後加入下列程式碼：

lib/title_screen/particle_overlay.dart

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:particle_field/particle_field.dart';
import 'package:rnd/rnd.dart';

class ParticleOverlay extends StatelessWidget {
  const ParticleOverlay({super.key, required this.color, required this.energy});

  final Color color;
  final double energy;

  @override
  Widget build(BuildContext context) {
    return ParticleField(
      spriteSheet: SpriteSheet(
        image: const AssetImage('assets/images/particle-wave.png'),
      ),
      // blend the image's alpha with the specified color:
      blendMode: BlendMode.dstIn,

      // this runs every tick:
      onTick: (controller, _, size) {
        List<Particle> particles = controller.particles;

        // add a new particle with random angle, distance & velocity:
        double a = rnd(pi * 2);
        double dist = rnd(1, 4) * 35 + 150 * energy;
        double vel = rnd(1, 2) * (1 + energy * 1.8);
        particles.add(Particle(
          // how many ticks this particle will live:
          lifespan: rnd(1, 2) * 20 + energy * 15,
          // starting distance from center:
          x: cos(a) * dist,
          y: sin(a) * dist,
          // starting velocity:
          vx: cos(a) * vel,
          vy: sin(a) * vel,
          // other starting values:
          rotation: a,
          scale: rnd(1, 2) * 0.6 + energy * 0.5,
        ));

        // update all of the particles:
        for (int i = particles.length - 1; i >= 0; i--) {
          Particle p = particles[i];
          if (p.lifespan <= 0) {
            // particle is expired, remove it:
            particles.removeAt(i);
            continue;
          }
          p.update(
            scale: p.scale * 1.025,
            vx: p.vx * 1.025,
            vy: p.vy * 1.025,
            color: color.withOpacity(p.lifespan * 0.001 + 0.01),
            lifespan: p.lifespan - 1,
          );
        }
      },
    );
  }
}
  1. 修改 lib/title_screen/title_screen.dart 的匯入內容，如下所示：

lib/title_screen/title_screen.dart

import 'dart:math';
import 'dart:ui';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_animate/flutter_animate.dart';

import '../assets.dart';
import '../orb_shader/orb_shader_config.dart';
import '../orb_shader/orb_shader_widget.dart';
import '../styles.dart';
import 'particle_overlay.dart';                          // Add this import
import 'title_screen_ui.dart';

class TitleScreen extends StatefulWidget {
  1. 修改 _TitleScreenState 的 build 方法，將 ParticleOverlay 新增至 UI，如下所示：

lib/title_screen/title_screen.dart

@override
Widget build(BuildContext context) {
  return Scaffold(
    backgroundColor: Colors.black,
    body: Center(
      child: MouseRegion(
        onHover: _handleMouseMove,
        child: _AnimatedColors(
          orbColor: _orbColor,
          emitColor: _emitColor,
          builder: (_, orbColor, emitColor) {
            return Stack(
              children: [
                /// Bg-Base
                Image.asset(AssetPaths.titleBgBase),

                /// Bg-Receive
                _LitImage(
                  color: orbColor,
                  imgSrc: AssetPaths.titleBgReceive,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Orb
                Positioned.fill(
                  child: Stack(
                    children: [
                      // Orb
                      OrbShaderWidget(
                        key: _orbKey,
                        mousePos: _mousePos,
                        minEnergy: _minOrbEnergy,
                        config: OrbShaderConfig(
                          ambientLightColor: orbColor,
                          materialColor: orbColor,
                          lightColor: orbColor,
                        ),
                        onUpdate: (energy) => setState(() {
                          _orbEnergy = energy;
                        }),
                      ),
                    ],
                  ),
                ),

                /// Mg-Base
                _LitImage(
                  imgSrc: AssetPaths.titleMgBase,
                  color: orbColor,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Mg-Receive
                _LitImage(
                  imgSrc: AssetPaths.titleMgReceive,
                  color: orbColor,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Mg-Emit
                _LitImage(
                  imgSrc: AssetPaths.titleMgEmit,
                  color: emitColor,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalEmitLightAmt,
                ),

                /// Particle Field
                Positioned.fill(                          // Add from here...
                  child: IgnorePointer(
                    child: ParticleOverlay(
                      color: orbColor,
                      energy: _orbEnergy,
                    ),
                  ),
                ),                                        // to here.

                /// Fg-Rocks
                Image.asset(AssetPaths.titleFgBase),

                /// Fg-Receive
                _LitImage(
                  imgSrc: AssetPaths.titleFgReceive,
                  color: orbColor,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalReceiveLightAmt,
                ),

                /// Fg-Emit
                _LitImage(
                  imgSrc: AssetPaths.titleFgEmit,
                  color: emitColor,
                  pulseEffect: _pulseEffect,
                  lightAmt: _finalEmitLightAmt,
                ),

                /// UI
                Positioned.fill(
                  child: TitleScreenUi(
                    difficulty: _difficulty,
                    onDifficultyFocused: _handleDifficultyFocused,
                    onDifficultyPressed: _handleDifficultyPressed,
                    onStartPressed: _handleStartPressed,
                  ),
                ),
              ],
            ).animate().fadeIn(duration: 1.seconds, delay: .3.seconds);
          },
        ),
      ),
    ),
  );
}

最終結果包含在多個平台上呈現的動畫、片段著色器和粒子效果！

隨處可見粒子，即使是網路也無妨

程式碼存在一個輕微問題。在網頁上執行 Flutter 時，可使用兩種替代的轉譯引擎：CanvasKit 引擎 (電腦類別瀏覽器預設使用) 與 HTML DOM 轉譯器 (行動裝置預設使用)。問題在於 HTML DOM 轉譯器不支援片段著色器。

解決方法是只使用 CanvasKit 轉譯器建構網頁版。方法是在建構指令中新增標記，如下所示：

$ flutter build web --web-renderer canvaskit
Font asset "MaterialIcons-Regular.otf" was tree-shaken, reducing it from 1645184 to 7692 bytes (99.5% reduction). Tree-shaking can be disabled by providing the --no-tree-shake-icons flag
when building your app.
Font asset "CupertinoIcons.ttf" was tree-shaken, reducing it from 257628 to 1172 bytes (99.5% reduction). Tree-shaking can be disabled by providing the --no-tree-shake-icons flag when
building your app.
Compiling lib/main.dart for the Web...                             15.6s
✓ Built build/web

以下是您的一切努力，現在會顯示在 Chrome 瀏覽器中。

8. 恭喜

您建立了功能完整的遊戲簡介畫面，內含動畫、片段著色器和粒子動畫！您現在可以在 Flutter 支援的所有平台上使用這些技術。

瞭解詳情