main.dart

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

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

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

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

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

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

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

extension OrbitsExtension on List<Orbit> {
  void updateElectronsPosition() {
    this.forEach((orbit) {
      orbit.electrons.forEach((electron) {
        electron.move();
      });
    });
  }
}

class Electron {
  double speed;

  double currentSize;
  double targetSize;

  Color currentColor;
  Color targetColor;

  double _positionPercent = 0;

  double get positionPercent {
    return _positionPercent;
  }

  Electron({
    @required this.currentSize,
    @required this.targetSize,
    @required this.currentColor,
    @required this.targetColor,
    @required this.speed,
  });

  void move() {
    if (_positionPercent >= 1.0) {
      _positionPercent = 0;
    }
    _positionPercent += speed;
  }

  static Electron random() {
    const colors = [
      Colors.greenAccent,
      Colors.redAccent,
      Colors.cyanAccent,
      Colors.purpleAccent,
      Colors.yellowAccent,
    ];
    final size = randD(5, 7);
    final initialSize = size * 8;
    final color = colors[math.Random().nextInt(colors.length)];
    return Electron(
      currentSize: initialSize,
      targetSize: size,
      currentColor: color.withOpacity(0.1),
      targetColor: color,
      speed: randD(0.008, 0.012),
    );
  }
}

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.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: 0.0),
    Orbit(electrons: [], angle: 60.0),
    Orbit(electrons: [], angle: 120.0),
  ];

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'Flutter4Fun.com',
          style: TextStyle(
            color: Colors.white,
          ),
        ),
        backgroundColor: Colors.transparent,
        elevation: 0,
      ),
      backgroundColor: Color(0xFF191636),
      body: Center(
        child: AtomWidget(
          orbits: _orbits,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            _orbits[math.Random().nextInt(_orbits.length)].electrons.add(Electron.random());
          });
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

class AtomWidget extends StatefulWidget {
  final List<Orbit> orbits;

  const AtomWidget({Key key, @required this.orbits}) : super(key: key);

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

class _AtomWidgetState extends State<AtomWidget> with SingleTickerProviderStateMixin {
  Timer t;

  @override
  void initState() {
    super.initState();
    t = Timer.periodic(Duration(milliseconds: 16), (timer) {
      setState(() {
        widget.orbits.updateElectronsPosition();
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    final atomSize = (MediaQuery.of(context).size.shortestSide / 3) * 2;
    return Stack(
      children: [
        ...widget.orbits
            .map(
              (orbit) => Center(
                child: Transform.rotate(
                  angle: degreesToRads(orbit.angle),
                  child: CustomPaint(
                    painter: _OrbitPainter(orbit),
                    size: Size(atomSize, atomSize),
                  ),
                ),
              ),
            )
            .toList(),
        Center(
          child: Container(
            width: atomSize / 10,
            height: atomSize / 10,
            decoration: BoxDecoration(
                shape: BoxShape.circle,
                gradient: LinearGradient(
                  colors: [
                    Color(0xffffc560),
                    Color(0xffff593b),
                  ],
                  begin: Alignment.bottomLeft,
                  end: Alignment.topRight,
                )),
          ),
        )
      ],
    );
  }

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

class _OrbitPainter extends CustomPainter {
  final Orbit orbit;

  _OrbitPainter(this.orbit);

  @override
  void paint(Canvas canvas, Size size) {
    final center = Offset(size.width / 2, size.height / 2);
    Path orbitPath = new Path();

    final width = size.shortestSide;
    final height = width * 0.24;

    orbitPath.addOval(Rect.fromCenter(center: center, width: width, height: height));

    canvas.drawPath(
      orbitPath,
      Paint()
        ..color = Color(0xFF26224f)
        ..style = PaintingStyle.stroke
        ..strokeWidth = 1,
    );

    orbit.electrons.forEach((electron) {
      electron.currentSize = lerpDouble(electron.currentSize, electron.targetSize, 0.08);
      electron.currentColor = Color.lerp(electron.currentColor, electron.targetColor, 0.08);
      final degree = math.pi * 2 * electron.positionPercent;
      canvas.drawCircle(
        center + Offset(math.cos(degree) * (width / 2), math.sin(degree) * (height / 2)),
        electron.currentSize / 2,
        Paint()
          ..color = electron.currentColor
          ..style = PaintingStyle.fill
          ..strokeCap = StrokeCap.round
          ..strokeWidth = electron.currentSize,
      );
    });
  }

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