Flutter几何计算插件convex_hull的使用

Info

convex_hull 插件用于计算给定点集的凸包。该插件实现了 Andrew’s monotone chain algorithm，这是一种高效的 O(n log n) 算法。

(Maonus, CC BY-SA 4.0, via Wikimedia Commons)

Usage

函数介绍

库中包含一个 convexHull 函数，它接受一个泛型对象列表和访问 x 和 y 坐标的函数，并返回形成凸包的对象列表。

示例代码

以下是一个完整的示例，演示如何使用 convex_hull 插件来计算给定点集的凸包：

import 'package:convex_hull/convex_hull.dart';
import 'package:flutter/material.dart';

class Example {
  final double xCoordinate;
  final double yCoordinate;
  final String info;

  const Example(this.xCoordinate, this.yCoordinate, this.info);

  @override
  String toString() => 'Example($xCoordinate, $yCoordinate, "$info")';
}

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

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

class ConvexHullExample extends StatefulWidget {
  @override
  _ConvexHullExampleState createState() => _ConvexHullExampleState();
}

class _ConvexHullExampleState extends State<ConvexHullExample> {
  List<Example> points = [
    Example(0.0, 0.0, "1"),
    Example(2.0, 0.0, "2"),
    Example(2.0, 2.0, "3"),
    Example(0.0, 2.0, "6"),
    Example(1.0, 1.0, "f1"), // lies within convex hull
  ];

  List<Example> hullPoints;

  @override
  void initState() {
    super.initState();
    hullPoints = convexHull<Example>(points, x: (e) => e.xCoordinate, y: (e) => e.yCoordinate);
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Expanded(
          child: CustomPaint(
            painter: PointsPainter(points, hullPoints),
            size: Size.infinite,
          ),
        ),
        Text('Convex Hull Points:'),
        ListView.builder(
          shrinkWrap: true,
          itemCount: hullPoints.length,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text(hullPoints[index].toString()),
            );
          },
        ),
      ],
    );
  }
}

class PointsPainter extends CustomPainter {
  final List<Example> points;
  final List<Example> hullPoints;

  PointsPainter(this.points, this.hullPoints);

  @override
  void paint(Canvas canvas, Size size) {
    final Paint pointPaint = Paint()
      ..color = Colors.blue
      ..strokeWidth = 2.0;

    final Paint hullPaint = Paint()
      ..color = Colors.red
      ..strokeWidth = 2.0
      ..style = PaintingStyle.stroke;

    final Offset center = Offset(size.width / 2, size.height / 2);
    final double scale = 100;

    for (var point in points) {
      canvas.drawCircle(
        Offset(center.dx + point.xCoordinate * scale, center.dy - point.yCoordinate * scale),
        5.0,
        pointPaint,
      );
    }

    if (hullPoints.isNotEmpty) {
      Path path = Path();
      for (int i = 0; i < hullPoints.length; i++) {
        Offset offset = Offset(center.dx + hullPoints[i].xCoordinate * scale, center.dy - hullPoints[i].yCoordinate * scale);
        if (i == 0) {
          path.moveTo(offset.dx, offset.dy);
        } else {
          path.lineTo(offset.dx, offset.dy);
        }
      }
      path.close();
      canvas.drawPath(path, hullPaint);
    }
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}

说明

• Example 类：定义了一个包含 x 和 y 坐标以及额外信息的类。
• main 函数：启动应用并设置主页为 MyApp。
• MyApp 类：创建了一个简单的 Flutter 应用程序，包含一个标题栏和 ConvexHullExample 组件。
• ConvexHullExample 类：负责计算凸包并在屏幕上显示点和凸包。
• PointsPainter 类：自定义绘制器，用于在屏幕上绘制点和凸包路径。

通过这个示例，你可以看到如何使用 convex_hull 插件来计算凸包，并将其可视化。希望这对您有所帮助！