flutter painter 随机点

random_point_painter.dart

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

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        width: double.infinity,
        height: double.infinity,
        child: CustomPaint(
          painter: MyPainter(),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

class MyPainter extends CustomPainter {
  Paint p = Paint()
    ..color = Colors.green
    ..strokeWidth = 2
    ..isAntiAlias = true;

  @override
  void paint(Canvas canvas, Size size) {
    var points = <Offset>[];
    var startPoint = size.centerLeft(Offset.zero).translate(15, 0);
    points.add(startPoint);
    for (var i = 0, lastPoint = startPoint; i < 200; i++) {
      var y = Random().nextInt(15);
      if (Random().nextBool()) {
        y = -y;
      } else {
        y = y.abs();
      }
      var point = lastPoint.translate(1.5, y.toDouble());
      points.add(point);
      lastPoint = point;
    }
    p.strokeWidth = 1.5;
    canvas.drawPoints(PointMode.points, points, p);
    p.strokeWidth = 2;
    canvas.drawPoints(PointMode.polygon, points, p);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => true;
}