main.dart

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

import 'package:flutter/material.dart';
import 'dart:math' as math;

class Electron {
  double speed;
  double currentSize;
  double targetSize;
  Color color;
  double currentPositionDegree;

  Electron({
    @required this.speed,
    @required this.currentSize,
    @required this.targetSize,
    @required this.color,
    @required this.currentPositionDegree,
  });
}

class Orbit {
  final List<Electron> electrons;
  final angle;

  Orbit({
    @required this.electrons,
    @required this.angle,
  });
}

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter4Fun.com',
      theme: ThemeData(
        primarySwatch: Colors.yellow,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: HomePage(),
    );
  }
}

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

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

class _HomePageState extends State<HomePage> {
  List<Orbit> orbits = [
    Orbit(electrons: [], angle: 0),
    Orbit(electrons: [], angle: 60),
    Orbit(electrons: [], angle: 120),
  ];

  Timer timer;

  @override
  void initState() {
    super.initState();
    timer = new Timer.periodic(
      Duration(milliseconds: 16),
      (t) {
        setState(() {
          orbits.forEach((orbit) {
            orbit.electrons.forEach((electron) {
              electron.currentPositionDegree += electron.speed;
              electron.currentSize = lerpDouble(electron.currentSize, electron.targetSize, 0.07);
            });
          });
        });
      },
    );
  }

  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color(0xFF191636),
      body: Center(
        child: Stack(
          children: orbits
              .map(
                (orbit) => Transform.rotate(
                  angle: degreesToRads(orbit.angle),
                  child: CustomPaint(painter: _OrbitPainter(orbit.electrons), size: Size(300, 100)),
                ),
              )
              .toList(),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          final randomOrbit = orbits[math.Random().nextInt(orbits.length)];
          final size = randomDoubleBetween(4, 8);
          randomOrbit.electrons.add(
            Electron(
              speed: randomDoubleBetween(1, 3),
              currentSize: size * 10,
              targetSize: size,
              color: randomColor([
                Colors.purpleAccent,
                Colors.yellowAccent,
                Colors.cyanAccent,
              ]),
              currentPositionDegree: 0,
            ),
          );
        },
        child: Icon(Icons.add),
      ),
    );
  }

  @override
  void dispose() {
    timer.cancel();
    super.dispose();
  }
}

class _OrbitPainter extends CustomPainter {
  final List<Electron> electrons;

  _OrbitPainter(this.electrons);

  @override
  void paint(Canvas canvas, Size size) {
    final center = Offset(size.width / 2, size.height / 2);
    final rect = Rect.fromCenter(center: center, width: size.width, height: size.height);
    canvas.drawOval(
      rect,
      Paint()
        ..color = Colors.white
        ..style = PaintingStyle.stroke
        ..strokeWidth = 1,
    );

    electrons.forEach((electron) {
      final degree = degreesToRads(electron.currentPositionDegree);
      final electronPos = center +
          Offset(
            math.cos(degree) * (size.width / 2),
            math.sin(degree) * (size.height / 2),
          );
      canvas.drawCircle(electronPos, electron.currentSize, Paint()..color = electron.color);
    });
  }

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

num degreesToRads(num deg) {
  return (deg * math.pi) / 180.0;
}

double randomDoubleBetween(double min, double max) => Random().nextDouble() * (max - min) + min;

Color randomColor(List<Color> colors) {
  return colors[Random().nextInt(colors.length)];
}