RainMaker.dart

/// Credits without which this wouldn't have been possible : Coding With Indy - https://www.youtube.com/watch?v=1VyDHNXFFyg


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

import 'package:flutter/material.dart';

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

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

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

  final String title;

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

class Particle {
  Offset position;
  Offset original;
  double length;
  double speed;
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  double dx = 200;
  Random rgn = Random();
  Timer timer;

  var rains = List<Particle>();

  @override
  void dispose() {
    timer?.cancel(); // disposes the timer made for animation
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    MediaQueryData mediaQuery = MediaQuery.of(context);
    return Scaffold(
      backgroundColor: Colors.grey[800],
      appBar: AppBar(
        title: Text(
          widget.title,
          style: TextStyle(color: Colors.grey[50]),
        ),
      ),
      body: Stack(
        children: [
          CustomPaint(
            painter: RainPainter(
              rains: rains,
            ),
            child: Container(),
          ),
          Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text(
                  'You have pushed the button this many times:',
                  style: TextStyle(color: Colors.grey[50]),
                ),
                Text(
                  '$_counter',
                  style: Theme.of(context).textTheme.headline4.copyWith(
                        color: Colors.grey[50],
                      ),
                ),
              ],
            ),
          ),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          paintMoreLines(mediaQuery.size.width);
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }

  void paintMoreLines(double width) {
    setState(() {
      _counter++;
      print('counter fnc: $_counter');

      // animation timer
      final fps = 50.0;
      var frameDuration = (4000 ~/ fps);
      timer = Timer.periodic(Duration(milliseconds: frameDuration), (timer) {
        setState(() {
          rains.forEach((p) {
            p.position += Offset(0, p.speed + 20);
            // print('dy: ${p.position.dy}');
            if (p.position.dy > 600) {
              p.position = p.original;
            }
          });
        });
      });

      var xx = 0.0;
      // create particles
      for (var i = 0; i < _counter; i++) {
        xx += rgn.nextDouble() * 50.0 + 12.0;
        var dx = xx;
        var dy = -rgn.nextDouble() * 80.0;
        // generate the length and speed
        var len = rgn.nextDouble() * 30.0 + 30.0;
        var speed = rgn.nextDouble() * 3.0 + 1.0;
        rains.add(Particle()
          ..position = Offset(dx, dy)
          ..original = Offset(dx, dy)
          ..speed = speed
          ..length = len);
      }
    });
  }
}

class RainPainter extends CustomPainter {
  List<Particle> rains;

  RainPainter({@required this.rains});
  @override
  void paint(Canvas canvas, Size size) {
    var center = Offset(10, size.height / 8);

    drawRain(canvas, center);
  }

  var W = 600.0;
  void drawRain(Canvas canvas, Offset center) { // custom painter method
    var rain = Paint()
      ..color = Color(0xffdee2ff) //Colors.black
      ..strokeWidth = 10.0
      ..style = PaintingStyle.stroke;

    rains.forEach((p) {
      var p2 = p.position + Offset(0, p.length);
      canvas.drawLine(p.position + center, p2 + center, rain);
    });
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return true;
  }
}

context -
#FlutterCounterChallenge2020