Flutter画布编辑插件fabricjs的使用

发布于 1周前 作者 nodeper 来自 Flutter

Flutter画布编辑插件fabricjs的使用

fabricjs 是一个用于在Dart环境中使用的fabric.js库的API。它允许你在Web应用中创建和操作复杂的图形。

示例

要运行此示例，请在项目根目录下执行 webdev serve example:8081 命令。

示例代码

import 'dart:html' as html;
import 'dart:math' as math;

import 'package:fabricjs/fabricjs.dart';
import 'package:js/js_util.dart';

final rnd = math.Random();

void main() {
  // 获取HTML元素
  final canvasEle = html.querySelector('#canvas') as html.CanvasElement;
  final btnDrawToggle = html.querySelector('#btnDrawToggle');
  final wrapper = html.querySelector('.wrapper');

  // 初始化Canvas对象
  final canvas = Canvas(
      canvasEle,
      jsify({
        'hoverCursor': 'pointer',
        'selection': true,
        'selectionBorderColor': 'blue',
        'isDrawingMode': false
      }));

  // 添加10个随机矩形和圆形
  for (final i in List.generate(10, (i) => i)) {
    var x = rnd.nextDouble() * (canvasEle.width! - 120);
    var y = rnd.nextDouble() * (canvasEle.height! - 120);
    if (i % 2 == 0) {
      canvas.add(Rect(jsify({
        'left': x,
        'top': y,
        'width': rnd.nextInt(120),
        'height': rnd.nextInt(120),
        'fill': genColor()
      })));
    } else {
      canvas.add(Circle(jsify({
        'left': x,
        'top': y,
        'radius': rnd.nextInt(90),
        'fill': genColor(),
      })));
    }
  }

  // 监听对象移动事件
  canvas.on('object:moving', allowInterop((ObjectMovingEvent e) {
    final target = e.target as FabricObject;
    html.querySelector('#spanX')?.text = target.left.toStringAsFixed(2);
    html.querySelector('#spanY')?.text = target.top.toStringAsFixed(2);
  }));

  // 切换绘制模式
  btnDrawToggle?.onClick.listen((e) {
    canvas.isDrawingMode = !canvas.isDrawingMode;
    btnDrawToggle.text = canvas.isDrawingMode ? 'Draw Mode' : 'Selection Mode';
  });

  // 监听键盘按键事件
  wrapper?.onKeyDown.listen((event) {
    if (event.keyCode == html.KeyCode.DELETE) {
      final targets = canvas.getActiveObjects();
      if (targets.isNotEmpty) {
        canvas.remove(targets);
        for (var element in targets) {
          canvas.remove(element);
        }
      }
      canvas.discardActiveObject().renderAll();
    }
  });
}

// 生成随机颜色
String genColor() {
  int r = rnd.nextInt(256);
  int g = rnd.nextInt(256);
  int b = rnd.nextInt(256);
  String hexColor = '#${r.toRadixString(16).padLeft(2, '0')}'
      '${g.toRadixString(16).padLeft(2, '0')}'
      '${b.toRadixString(16).padLeft(2, '0')}';
  return hexColor;
}

HTML文件

<!doctype html>
<html>

<head>
  <title>Fabric.js 和 Dart 互操作示例</title>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/5.3.1/fabric.min.js"></script>
  <script defer type="application/javascript" src="example.dart.js"></script>
  <style type="text/css">
    html,
    body {
      margin: 0;
      background-color: rgb(211, 211, 211);
      height: 100%;
      font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    }

    .main {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100%;
    }

    .wrapper {
      background-color: rgb(255, 255, 255);
      outline: none;
    }

    .tools {
      color: white;
      background-color: rgb(130, 129, 129);
    }
  </style>
</head>

<body>
  <div class="main">
    <div class="container">
      <div class="wrapper" tabindex="1000">
        <canvas id="canvas" height="450" width="600"></canvas>
      </div>
      <div class="tools">
        <button id="btnDrawToggle" type="button">Selection Mode</button>
        <span>X:<span id="spanX"></span></span>
        <span>Y:<span id="spanY"></span></span>
        示例来自<a href="http://fabricjs.com/">Fabric.js</a>的Dart API
      </div>
    </div>
  </div>
</body>

</html>

更多关于Flutter画布编辑插件fabricjs的使用的实战系列教程也可以访问 https://www.itying.com/category-92-b0.html

1 回复

更多关于Flutter画布编辑插件fabricjs的使用的实战系列教程也可以访问 https://www.itying.com/category-92-b0.html


在Flutter中直接使用Fabric.js是不可能的，因为Fabric.js是一个专门为Canvas设计的JavaScript库，而Flutter主要使用Dart语言进行开发，并且有自己的渲染机制。不过，如果你想在Flutter应用中实现类似Fabric.js的功能（如画布编辑、图形绘制、图形管理等），你可以使用一些Flutter特有的包或者自己实现这些功能。

下面是一个简单的Flutter代码示例，展示如何使用canvas绘制一些基本的图形，并模拟一些简单的编辑功能（比如拖动）。这个示例不会完全复制Fabric.js的所有功能，但可以给出一个基本的起点。

首先，确保你的pubspec.yaml文件中包含了必要的依赖项（本例中不需要额外的依赖项，因为Flutter自带的CustomPaint和GestureDetector已经足够）：

dependencies:
  flutter:
    sdk: flutter

然后，你可以创建一个Flutter应用，并在其中实现基本的画布编辑功能：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Canvas Example'),
        ),
        body: CanvasEditor(),
      ),
    );
  }
}

class Shape {
  Offset position;
  double width;
  double height;
  Color color;

  Shape({required this.position, required this.width, required this.height, required this.color});
}

class CanvasEditor extends StatefulWidget {
  @override
  _CanvasEditorState createState() => _CanvasEditorState();
}

class _CanvasEditorState extends State<CanvasEditor> {
  List<Shape> shapes = [];
  Offset? _dragStartPosition;
  Shape? _draggedShape;

  void _handleDragStart(Shape shape, Offset position) {
    _dragStartPosition = position;
    _draggedShape = shape;
  }

  void _handleDragUpdate(DragUpdateDetails details) {
    if (_draggedShape != null && _dragStartPosition != null) {
      final Offset delta = details.delta;
      setState(() {
        _draggedShape!.position += delta;
      });
    }
  }

  void _handleDragEnd(DragEndDetails details) {
    _dragStartPosition = null;
    _draggedShape = null;
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onPanDown: (details) {
        final Offset tapPosition = details.globalPosition;
        final RenderBox box = context.findRenderObject() as RenderBox;
        final Offset localPosition = box.globalToLocal(tapPosition);
        
        // Here you would typically add a new shape at the tapped position
        // For simplicity, we'll just log the position
        print('Tap position: $localPosition');
        // Example: Add a new rectangle
        setState(() {
          shapes.add(Shape(position: localPosition, width: 100, height: 100, color: Colors.blue));
        });
      },
      onPanUpdate: (details) => _handleDragUpdate(details),
      onPanEnd: (details) => _handleDragEnd(details),
      child: CustomPaint(
        size: Size.infinite,
        painter: _CanvasPainter(shapes),
      ),
    );
  }
}

class _CanvasPainter extends CustomPainter {
  final List<Shape> shapes;

  _CanvasPainter(this.shapes);

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..style = PaintingStyle.fill;

    for (final Shape shape in shapes) {
      paint.color = shape.color;
      canvas.drawRect(
        Rect.fromLTWH(shape.position.dx, shape.position.dy, shape.width, shape.height),
        paint,
      );
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return oldDelegate != this;
  }
}

这个示例中，我们定义了一个Shape类来表示画布上的图形，并使用CustomPaint和CustomPainter来绘制这些图形。我们通过GestureDetector来监听用户的触摸事件，实现拖动功能。当用户触摸屏幕时，我们可以在触摸位置添加一个新的图形；当用户拖动时，我们可以更新被拖动图形的位置。

请注意，这个示例只是一个非常基本的实现，没有包括Fabric.js提供的所有功能（如旋转、缩放、多选、撤销/重做等）。如果你需要这些高级功能，你可能需要自己实现它们，或者寻找一个更全面的Flutter画布编辑库（如果有的话）。

回到顶部