Flutter 自定义绘图 CustomPainter 雪花效果

import 'dart:math';

import 'package:flutter/material.dart';

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

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  late AnimationController _controller;
  final List<SnowSlake> _snowflakes =
      List.generate(1000, (index) => SnowSlake());
  @override
  void initState() {
    _controller =
        AnimationController(vsync: this, duration: const Duration(seconds: 1))
          ..repeat();
    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: double.infinity,
      decoration: const BoxDecoration(
        color: Colors.blue,
        gradient: LinearGradient(
            begin: Alignment.topCenter,
            end: Alignment.bottomCenter,
            colors: [Colors.blue, Colors.lightBlue, Colors.white],
            stops: [0, 0.7, 1]),
      ),
      child: AnimatedBuilder(
        animation: _controller,
        builder: (_, __) {
          _snowflakes.forEach((snow) => snow.fall());
          return CustomPaint(
            painter: MyPainter(_snowflakes),
            child: const Text('demo'),
          );
        },
      ),
    );
  }
}

class MyPainter extends CustomPainter {
  final List<SnowSlake> snowfakes;

  MyPainter(this.snowfakes);
  @override
  void paint(Canvas canvas, Size size) {
    final whitePaint = Paint()..color = Colors.white;
    canvas.drawCircle(size.center(const Offset(0, 130)), 50, whitePaint);
    canvas.drawOval(
        Rect.fromCenter(
            center: size.center(const Offset(0, 280)), width: 200, height: 250),
        whitePaint);
    for (var snowSlake in snowfakes) {
      canvas.drawCircle(
          Offset(snowSlake.x, snowSlake.y), snowSlake.radius, whitePaint);
    }
  }

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

class SnowSlake {
  double x = Random().nextDouble() * 400;
  double y = Random().nextDouble() * 800;
  double radius = Random().nextDouble() * 2 + 2;
  double velocity = Random().nextDouble() * 4 + 2;
  fall() {
    y += velocity;
    if (y > 800) {
      y = 0;
      x = Random().nextDouble() * 400;
      radius = Random().nextDouble() * 2 + 2;
      velocity = Random().nextDouble() * 4 + 2;
    }
  }
}

视频网址：Flutter 动画教程 3-3 直接操作底层的CustomPainter_哔哩哔哩_bilibili