circle_touches

main.dart

import 'dart:async';
import 'dart:math';

import 'package:flutter/material.dart';

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

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

const color1 = Color(0xfff4f231);
const color2 = Color(0xff04d435);
const color3 = Color(0xff0f5eff);
const color4 = Color(0xff05eeff);
const color5 = Color(0xffee036c);

const neonColors = [
  color1,
  color2,
  color3,
  color4,
  color5,
];

extension <T> on List<T> {
  T random() => this[Random().nextInt(this.length)];
}

class MyHomePage extends StatefulWidget {
  MyHomePage() : super();

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

class _MyHomePageState extends State<MyHomePage> {
  List<Circle> _circles = [];

  @override
  void initState() {
    Timer.periodic(Duration(milliseconds: 16), (timer) {
      updateCircles();
    });
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color(0xFF021a45),
      body: Listener(
        onPointerUp: (pointerUpEvent) {
          print('onTapUp');
          setState(() {
            _circles.add(
              Circle(
                color: neonColors.random(),
                radius: 1,
                position: pointerUpEvent.localPosition,
                speed: Random().nextDouble() * 2.5 + 0.5,
                opacity: 1.0,
              ),
            );
          });
        },
        child: CustomPaint(
          painter: MyCustomPainter(_circles),
          size: Size(
            double.infinity,
            double.infinity,
          ),
        ),
      ),
    );
  }

  void updateCircles() {
    setState(() {
      final deadCircles = <int>[];
      _circles = _circles.asMap().entries.map((entry) {
        final index = entry.key;
        final circle = entry.value;
        var newOpacity = circle.opacity - (circle.speed / 200);
        if (newOpacity <= 0) {
          newOpacity = 0;
          deadCircles.add(index);
        }
        return circle.copyWith(
          radius: circle.radius + circle.speed,
          opacity: newOpacity,
        );
      }).toList();

      deadCircles.forEach((index) { _circles.removeAt(index); });

    });
  }

}

class MyCustomPainter extends CustomPainter {
  final List<Circle> _showingCircles;

  MyCustomPainter(this._showingCircles);

  final circlePaint = Paint()
    ..isAntiAlias = true
    ..style = PaintingStyle.stroke
    ..strokeWidth = 6;

  @override
  void paint(Canvas canvas, Size size) {
    _showingCircles.forEach((circle) {
      circlePaint..color = circle.color.withOpacity(circle.opacity);
      canvas.drawCircle(circle.position, circle.radius, circlePaint);
    });
  }

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

class Circle {
  final Offset position;
  final Color color;
  final double radius;
  final double speed;
  final double opacity;

  Circle({
    required this.position,
    required this.color,
    required this.radius,
    required this.speed,
    required this.opacity,
  });

  Circle copyWith({
    Offset? position,
    Color? color,
    double? radius,
    double? speed,
    double? opacity,
  }) {
    return Circle(
      position: position ?? this.position,
      color: color ?? this.color,
      radius: radius ?? this.radius,
      speed: speed ?? this.speed,
      opacity: opacity ?? this.opacity,
    );
  }
}