Flutter實現(xiàn)文字鏤空效果的詳細步驟

更新時間：2025年05月03日 08:19:51 作者：淡寫成灰

這篇文章主要介紹了如何使用Flutter實現(xiàn)文字鏤空效果,包括創(chuàng)建基礎(chǔ)應(yīng)用結(jié)構(gòu)、實現(xiàn)自定義繪制器、構(gòu)建UI界面以及實現(xiàn)顏色選擇按鈕等步驟,并詳細解析了混合模式、Canvas圖層和文字居中處理等關(guān)鍵技術(shù)點,需要的朋友可以參考下

引言

哈哈，2019年初我剛?cè)肼殨r，遇到了一個特別的需求：學(xué)校的卡片上要有個分類標簽，文字部分還得鏤空。當時我剛開始接觸Flutter，對很多功能都不熟悉，這個需求就一直沒能實現(xiàn)，成了我的一個小執(zhí)念?，F(xiàn)在我早已不在那兒工作了，可這兩天閑來無事，突然想起了這個事。趁著五一假期，我開始琢磨畫筆功能，終于把當年實現(xiàn)不了的功能給實現(xiàn)了。

Tip: 這時候可能會有人說：啊，這道題我會，用ShaderMask配置blendMode: BlendMode.srcOut就能實現(xiàn)，但實際上這個組件不能設(shè)置圓角，內(nèi)邊距等相關(guān)內(nèi)容，如果這時候添加一個Container那么鏤空效果也只能看到Container的顏色，而不能看到最底部的圖片

實現(xiàn)原理

文字鏤空效果的核心是使用Canvas和自定義繪制（CustomPainter）來創(chuàng)建一個矩形，然后從中"切出"文字形狀。我們將使用Flutter的BlendMode.dstOut混合模式來實現(xiàn)這一效果。

開始實現(xiàn)

步驟1：創(chuàng)建基礎(chǔ)應(yīng)用結(jié)構(gòu)

首先，我們需要設(shè)置基本的應(yīng)用結(jié)構(gòu)：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Rectangle Text Cutout',
      theme: ThemeData(
        primarySwatch: Colors.teal,
        useMaterial3: true,
      ),
      home: const RectangleDrawingScreen(),
    );
  }
}

這里我們創(chuàng)建了一個基本的MaterialApp，并設(shè)置了主題顏色為teal（青色），啟用了Material 3設(shè)計。

步驟2：創(chuàng)建主屏幕

接下來，我們創(chuàng)建主屏幕，這是一個StatefulWidget，因為我們需要管理多個可變狀態(tài)：

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

  @override
  State<RectangleDrawingScreen> createState() => _RectangleDrawingScreenState();
}

class _RectangleDrawingScreenState extends State<RectangleDrawingScreen> {
  // 定義狀態(tài)變量
  double _cornerRadius = 20.0;
  String _text = "FLUTTER";
  double _fontSize = 60.0;
  Color _rectangleColor = Colors.teal;
  Color _backgroundColor = Colors.white;
  
  // 構(gòu)建UI...
}

我們定義了幾個關(guān)鍵狀態(tài)變量：

_cornerRadius：矩形的圓角半徑
_text：要鏤空的文字
_fontSize：文字大小
_rectangleColor：矩形的顏色
_backgroundColor：背景顏色

步驟3：實現(xiàn)自定義繪制器

這是實現(xiàn)鏤空效果的核心部分 - 自定義繪制器：

class RectangleTextCutoutPainter extends CustomPainter {
  final double cornerRadius;
  final String text;
  final double fontSize;
  final Color rectangleColor;

  RectangleTextCutoutPainter({
    required this.cornerRadius,
    required this.text,
    required this.fontSize,
    required this.rectangleColor,
  });

  @override
  void paint(Canvas canvas, Size size) {
    // 創(chuàng)建矩形區(qū)域
    final Rect rect = Rect.fromLTWH(
      20,
      20,
      size.width - 40,
      size.height - 40,
    );

    // 創(chuàng)建圓角矩形
    final RRect roundedRect = RRect.fromRectAndRadius(
      rect,
      Radius.circular(cornerRadius),
    );

    // 設(shè)置文字樣式
    final textStyle = TextStyle(
      fontSize: fontSize,
      fontWeight: FontWeight.bold,
    );

    final textSpan = TextSpan(
      text: text,
      style: textStyle,
    );

    // 創(chuàng)建文字繪制器
    final textPainter = TextPainter(
      text: textSpan,
      textDirection: TextDirection.ltr,
    );

    // 計算文字位置
    textPainter.layout(
      minWidth: 0,
      maxWidth: size.width,
    );
    final double xCenter = (size.width - textPainter.width) / 2;
    final double yCenter = (size.height - textPainter.height) / 2;

    // 使用圖層和混合模式實現(xiàn)鏤空效果
    canvas.saveLayer(rect.inflate(20), Paint());
    final Paint rectanglePaint = Paint()
      ..color = rectangleColor
      ..style = PaintingStyle.fill;

    canvas.drawRRect(roundedRect, rectanglePaint);
    final Paint cutoutPaint = Paint()
      ..color = Colors.white
      ..style = PaintingStyle.fill
      ..blendMode = BlendMode.dstOut;

    canvas.saveLayer(rect.inflate(20), cutoutPaint);
    textPainter.paint(canvas, Offset(xCenter, yCenter));
    canvas.restore();
    canvas.restore();
  }

  @override
  bool shouldRepaint(covariant RectangleTextCutoutPainter oldDelegate) {
    return oldDelegate.cornerRadius != cornerRadius ||
        oldDelegate.text != text ||
        oldDelegate.fontSize != fontSize ||
        oldDelegate.rectangleColor != rectangleColor;
  }
}

這個自定義繪制器的工作原理是：

創(chuàng)建一個圓角矩形
使用saveLayer和BlendMode.dstOut創(chuàng)建一個混合圖層
在矩形上"切出"文字形狀
使用shouldRepaint方法優(yōu)化重繪性能

步驟4：構(gòu)建UI界面

現(xiàn)在，讓我們實現(xiàn)主界面，包括預(yù)覽區(qū)域和控制面板：

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      title: const Text('Rectangle Text Cutout'),
      backgroundColor: Colors.teal.shade100,
    ),
    body: Column(
      children: [
        // 預(yù)覽區(qū)域
        Expanded(
          child: Container(
            color: Colors.grey[200],
            child: Center(
              child: Stack(
                children: [
                  // 背景圖片
                  Positioned.fill(
                    child: Image.network(
                      "https://p6-xtjj-sign.byteimg.com/tos-cn-i-73owjymdk6/d11fee3a97464bca82c9291435cc2a89~tplv-73owjymdk6-jj-mark-v1:0:0:0:0:5o6Y6YeR5oqA5pyv56S-5Yy6IEAg5reh5YaZ5oiQ54Gw:q75.awebp?rk3s=f64ab15b&x-expires=1746213056&x-signature=ylstmk1m2eVeu8bI%2BhDJkVUHe7U%3D",
                      fit: BoxFit.cover,
                    ),
                  ),
                  // 自定義繪制
                  CustomPaint(
                    size: const Size(double.infinity, double.infinity),
                    painter: RectangleTextCutoutPainter(
                      cornerRadius: _cornerRadius,
                      text: _text,
                      fontSize: _fontSize,
                      rectangleColor: _rectangleColor,
                    ),
                  ),
                  // 額外的ShaderMask效果
                  ShaderMask(
                    blendMode: BlendMode.srcOut,
                    child: Text(
                      _text,
                    ),
                    shaderCallback: (bounds) =>
                        LinearGradient(colors: [Colors.black], stops: [0.0])
                            .createShader(bounds),
                  ),
                ],
              ),
            ),
          ),
        ),
        // 控制面板
        Container(
          padding: const EdgeInsets.all(16),
          color: Colors.grey[200],
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              // 圓角控制
              const Text('Corner Radius:', style: TextStyle(fontWeight: FontWeight.bold)),
              Slider(
                value: _cornerRadius,
                min: 0,
                max: 100,
                divisions: 100,
                label: _cornerRadius.round().toString(),
                activeColor: Colors.teal,
                onChanged: (value) {
                  setState(() {
                    _cornerRadius = value;
                  });
                },
              ),
              // 字體大小控制
              const SizedBox(height: 10),
              const Text('Font Size:', style: TextStyle(fontWeight: FontWeight.bold)),
              Slider(
                value: _fontSize,
                min: 20,
                max: 120,
                divisions: 100,
                label: _fontSize.round().toString(),
                activeColor: Colors.teal,
                onChanged: (value) {
                  setState(() {
                    _fontSize = value;
                  });
                },
              ),
              // 文字輸入
              const SizedBox(height: 10),
              TextField(
                decoration: const InputDecoration(
                  labelText: 'Text to Cut Out',
                  border: OutlineInputBorder(),
                  focusedBorder: OutlineInputBorder(
                    borderSide: BorderSide(color: Colors.teal),
                  ),
                ),
                onChanged: (value) {
                  setState(() {
                    _text = value;
                  });
                },
                controller: TextEditingController(text: _text),
              ),
              // 矩形顏色選擇
              const SizedBox(height: 16),
              Row(
                children: [
                  const Text('Rectangle Color: ', style: TextStyle(fontWeight: FontWeight.bold)),
                  const SizedBox(width: 10),
                  _buildColorButton(Colors.teal),
                  _buildColorButton(Colors.blue),
                  _buildColorButton(Colors.red),
                  _buildColorButton(Colors.purple),
                  _buildColorButton(Colors.orange),
                ],
              ),
              // 背景顏色選擇
              const SizedBox(height: 16),
              Row(
                children: [
                  const Text('Background Color: ', style: TextStyle(fontWeight: FontWeight.bold)),
                  const SizedBox(width: 10),
                  _buildBackgroundColorButton(Colors.white),
                  _buildBackgroundColorButton(Colors.grey.shade300),
                  _buildBackgroundColorButton(Colors.yellow.shade100),
                  _buildBackgroundColorButton(Colors.blue.shade100),
                  _buildBackgroundColorButton(Colors.pink.shade100),
                ],
              ),
            ],
          ),
        ),
      ],
    ),
  );
}

步驟5：實現(xiàn)顏色選擇按鈕

最后，我們實現(xiàn)顏色選擇按鈕的構(gòu)建方法：

Widget _buildColorButton(Color color) {
  return GestureDetector(
    onTap: () {
      setState(() {
        _rectangleColor = color;
      });
    },
    child: Container(
      margin: const EdgeInsets.only(right: 8),
      width: 30,
      height: 30,
      decoration: BoxDecoration(
        color: color,
        shape: BoxShape.circle,
        border: Border.all(
          color: _rectangleColor == color ? Colors.black : Colors.transparent,
          width: 2,
        ),
      ),
    ),
  );
}

Widget _buildBackgroundColorButton(Color color) {
  return GestureDetector(
    onTap: () {
      setState(() {
        _backgroundColor = color;
      });
    },
    child: Container(
      margin: const EdgeInsets.only(right: 8),
      width: 30,
      height: 30,
      decoration: BoxDecoration(
        color: color,
        shape: BoxShape.circle,
        border: Border.all(
          color: _backgroundColor == color ? Colors.black : Colors.transparent,
          width: 2,
        ),
      ),
    ),
  );
}

關(guān)鍵技術(shù)點解析

1. 混合模式（BlendMode）的應(yīng)用

在這個效果中，最關(guān)鍵的技術(shù)是使用BlendMode.dstOut混合模式。這個混合模式會從目標圖像（矩形）中"減去"源圖像（文字），從而創(chuàng)建出文字形狀的"洞"。

final Paint cutoutPaint = Paint()
  ..color = Colors.white
  ..style = PaintingStyle.fill
  ..blendMode = BlendMode.dstOut;

2. Canvas圖層（Layer）的使用

我們使用canvas.saveLayer()和canvas.restore()來創(chuàng)建和管理圖層，這是實現(xiàn)復(fù)雜繪制效果的關(guān)鍵：

canvas.saveLayer(rect.inflate(20), Paint());
// 繪制矩形
canvas.saveLayer(rect.inflate(20), cutoutPaint);
// 繪制文字
canvas.restore();
canvas.restore();

3. 文字居中處理

為了讓文字在矩形中居中顯示，我們需要計算正確的位置：

final double xCenter = (size.width - textPainter.width) / 2;
final double yCenter = (size.height - textPainter.height) / 2;

code

為了方便大家查閱，下面貼出完整代碼

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Rectangle Text Cutout',
      theme: ThemeData(
        primarySwatch: Colors.teal,
        useMaterial3: true,
      ),
      home: const RectangleDrawingScreen(),
    );
  }
}

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

  @override
  State<RectangleDrawingScreen> createState() => _RectangleDrawingScreenState();
}

class _RectangleDrawingScreenState extends State<RectangleDrawingScreen> {
  double _cornerRadius = 20.0;
  String _text = "FLUTTER";
  double _fontSize = 60.0;
  Color _rectangleColor = Colors.teal;
  Color _backgroundColor = Colors.white;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Rectangle Text Cutout'),
        backgroundColor: Colors.teal.shade100,
      ),
      body: Column(
        children: [

          Expanded(
            child: Container(
              color: Colors.grey[200],
              child: Center(
                child: Stack(
                  children: [
                    Positioned.fill(
                      child: Image.network(
                        "https://p6-xtjj-sign.byteimg.com/tos-cn-i-73owjymdk6/d11fee3a97464bca82c9291435cc2a89~tplv-73owjymdk6-jj-mark-v1:0:0:0:0:5o6Y6YeR5oqA5pyv56S-5Yy6IEAg5reh5YaZ5oiQ54Gw:q75.awebp?rk3s=f64ab15b&x-expires=1746213056&x-signature=ylstmk1m2eVeu8bI%2BhDJkVUHe7U%3D",
                        fit: BoxFit.cover,
                      ),
                    ),
                    CustomPaint(
                      size: const Size(double.infinity, double.infinity),
                      painter: RectangleTextCutoutPainter(
                        cornerRadius: _cornerRadius,
                        text: _text,
                        fontSize: _fontSize,
                        rectangleColor: _rectangleColor,
                      ),
                    ),
                    ShaderMask(
                      blendMode: BlendMode.srcOut,
                      child: Text(
                        _text,
                      ),
                      shaderCallback: (bounds) =>
                          LinearGradient(colors: [Colors.black], stops: [0.0])
                              .createShader(bounds),
                    ),
                  ],
                ),
              ),
            ),
          ),
          Container(
            padding: const EdgeInsets.all(16),
            color: Colors.grey[200],
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                const Text('Corner Radius:', style: TextStyle(fontWeight: FontWeight.bold)),
                Slider(
                  value: _cornerRadius,
                  min: 0,
                  max: 100,
                  divisions: 100,
                  label: _cornerRadius.round().toString(),
                  activeColor: Colors.teal,
                  onChanged: (value) {
                    setState(() {
                      _cornerRadius = value;
                    });
                  },
                ),
                const SizedBox(height: 10),
                const Text('Font Size:', style: TextStyle(fontWeight: FontWeight.bold)),
                Slider(
                  value: _fontSize,
                  min: 20,
                  max: 120,
                  divisions: 100,
                  label: _fontSize.round().toString(),
                  activeColor: Colors.teal,
                  onChanged: (value) {
                    setState(() {
                      _fontSize = value;
                    });
                  },
                ),
                const SizedBox(height: 10),
                TextField(
                  decoration: const InputDecoration(
                    labelText: 'Text to Cut Out',
                    border: OutlineInputBorder(),
                    focusedBorder: OutlineInputBorder(
                      borderSide: BorderSide(color: Colors.teal),
                    ),
                  ),
                  onChanged: (value) {
                    setState(() {
                      _text = value;
                    });
                  },
                  controller: TextEditingController(text: _text),
                ),
                const SizedBox(height: 16),
                Row(
                  children: [
                    const Text('Rectangle Color: ', style: TextStyle(fontWeight: FontWeight.bold)),
                    const SizedBox(width: 10),
                    _buildColorButton(Colors.teal),
                    _buildColorButton(Colors.blue),
                    _buildColorButton(Colors.red),
                    _buildColorButton(Colors.purple),
                    _buildColorButton(Colors.orange),
                  ],
                ),
                const SizedBox(height: 16),
                Row(
                  children: [
                    const Text('Background Color: ', style: TextStyle(fontWeight: FontWeight.bold)),
                    const SizedBox(width: 10),
                    _buildBackgroundColorButton(Colors.white),
                    _buildBackgroundColorButton(Colors.grey.shade300),
                    _buildBackgroundColorButton(Colors.yellow.shade100),
                    _buildBackgroundColorButton(Colors.blue.shade100),
                    _buildBackgroundColorButton(Colors.pink.shade100),
                  ],
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildColorButton(Color color) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _rectangleColor = color;
        });
      },
      child: Container(
        margin: const EdgeInsets.only(right: 8),
        width: 30,
        height: 30,
        decoration: BoxDecoration(
          color: color,
          shape: BoxShape.circle,
          border: Border.all(
            color: _rectangleColor == color ? Colors.black : Colors.transparent,
            width: 2,
          ),
        ),
      ),
    );
  }

  Widget _buildBackgroundColorButton(Color color) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _backgroundColor = color;
        });
      },
      child: Container(
        margin: const EdgeInsets.only(right: 8),
        width: 30,
        height: 30,
        decoration: BoxDecoration(
          color: color,
          shape: BoxShape.circle,
          border: Border.all(
            color: _backgroundColor == color ? Colors.black : Colors.transparent,
            width: 2,
          ),
        ),
      ),
    );
  }
}

class RectangleTextCutoutPainter extends CustomPainter {
  final double cornerRadius;
  final String text;
  final double fontSize;
  final Color rectangleColor;

  RectangleTextCutoutPainter({
    required this.cornerRadius,
    required this.text,
    required this.fontSize,
    required this.rectangleColor,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final Rect rect = Rect.fromLTWH(
      20,
      20,
      size.width - 40,
      size.height - 40,
    );

    final RRect roundedRect = RRect.fromRectAndRadius(
      rect,
      Radius.circular(cornerRadius),
    );

    final textStyle = TextStyle(
      fontSize: fontSize,
      fontWeight: FontWeight.bold,
    );

    final textSpan = TextSpan(
      text: text,
      style: textStyle,
    );

    final textPainter = TextPainter(
      text: textSpan,
      textDirection: TextDirection.ltr,
    );

    textPainter.layout(
      minWidth: 0,
      maxWidth: size.width,
    );
    final double xCenter = (size.width - textPainter.width) / 2;
    final double yCenter = (size.height - textPainter.height) / 2;

    canvas.saveLayer(rect.inflate(20), Paint());
    final Paint rectanglePaint = Paint()
      ..color = rectangleColor
      ..style = PaintingStyle.fill;

    canvas.drawRRect(roundedRect, rectanglePaint);
    final Paint cutoutPaint = Paint()
      ..color = Colors.white
      ..style = PaintingStyle.fill
      ..blendMode = BlendMode.dstOut;

    canvas.saveLayer(rect.inflate(20), cutoutPaint);
    textPainter.paint(canvas, Offset(xCenter, yCenter));
    canvas.restore();
    canvas.restore();
  }

  @override
  bool shouldRepaint(covariant RectangleTextCutoutPainter oldDelegate) {
    return oldDelegate.cornerRadius != cornerRadius ||
        oldDelegate.text != text ||
        oldDelegate.fontSize != fontSize ||
        oldDelegate.rectangleColor != rectangleColor;
  }
}

以上就是Flutter實現(xiàn)文字鏤空效果的詳細步驟的詳細內(nèi)容，更多關(guān)于Flutter文字鏤空效果的資料請關(guān)注腳本之家其它相關(guān)文章！

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