CPD/Pong/lib/main.dart

import 'package:flutter/material.dart';

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

class PongGame extends StatelessWidget {
  const PongGame({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Pong Game',
      theme:
          ThemeData(scaffoldBackgroundColor: Color.fromARGB(255, 41, 38, 38)),
      home: const StartScreen(),
    );
  }
}

class StartScreen extends StatelessWidget {
  const StartScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GestureDetector(
        onTap: () {
          Navigator.of(context).push(MaterialPageRoute(
            builder: (context) {
              return const GameScreen();
            },
          ));
        },
        child: const Center(
          child: Text(
            'Berühren um zu beginnen!',
            key: Key("tapToStart"),
            style: TextStyle(
              fontSize: 30,
              fontWeight: FontWeight.bold,
              color: Colors.white,
            ),
          ),
        ),
      ),
    );
  }
}

class GameScreen extends StatefulWidget {
  const GameScreen({super.key});

  @override
  State<GameScreen> createState() => _GameScreenState();
}

class _GameScreenState extends State<GameScreen> {
  final racketWidth = 120.0;
  final racketHeight = 25.0;
  final racketBottomOffset = 100.0;

  double ballX = 0;
  double ballY = 0;
  double racketX = 20;
  double racketY = 0;

  moveRacket(double x) {
    setState(() {
      racketX = x - racketWidth / 2;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GestureDetector(
        onHorizontalDragUpdate: (details) {
          moveRacket(details.globalPosition.dx);
        },
        child: CustomPaint(
          key: const Key("customPaint"),
          painter: PongGamePainter(
              racketHeight: 30,
              racketWidth: 100,
              racketX: racketX,
              racketBottomOffset: racketBottomOffset,
              ballSize: 20,
              ballX: 10,
              ballY: 10),
          size: Size.infinite,
        ),
      ),
    );
  }
}

class PongGamePainter extends CustomPainter {
  final double ballSize;
  final double ballX;
  final double ballY;

  final double racketX;
  final double racketWidth;
  final double racketHeight;
  final double racketBottomOffset;

  PongGamePainter({
    required this.ballSize,
    required this.ballX,
    required this.ballY,
    required this.racketX,
    required this.racketWidth,
    required this.racketHeight,
    required this.racketBottomOffset,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final racketPaint = Paint()..color = Colors.white;
    final ballPaint = Paint()..color = Colors.white;

    canvas.drawOval(
      Rect.fromLTWH(ballX, ballY, ballSize, ballSize),
      ballPaint,
    );

    canvas.drawRect(
      Rect.fromLTWH(
        racketX,
        size.height - racketHeight - racketBottomOffset,
        racketWidth,
        racketHeight,
      ),
      racketPaint,
    );
  }

  @override
  bool shouldRepaint(covariant PongGamePainter oldDelegate) {
    return ballX != oldDelegate.ballX ||
        ballY != oldDelegate.ballY ||
        racketX != oldDelegate.racketX;
  }
}