ZTM CustomPainter lesson, with fixed mouth

main.dart

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

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Art Class',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: const MyHomePage(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text('Art Class'),
      ),
      body: CustomPaint(
        size: MediaQuery.of(context).size,
        painter: MyPainter(),
      ),
    );
  }
}

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final linePaint = Paint()..strokeWidth = 10;
    canvas.drawLine(const Offset(50, 150), const Offset(150, 220), linePaint);
    canvas.drawLine(
      Offset(size.width - 50, 150),
      Offset(size.width - 150, 220),
      linePaint,
    );

    final circlePaint = Paint();
    canvas.drawCircle(const Offset(100, 250), 20, circlePaint);
    canvas.drawCircle(Offset(size.width - 100, 250), 20, circlePaint);

    final arcPaint = Paint()
      ..strokeWidth = 10
      ..style = PaintingStyle.stroke;
    final rect = Rect.fromLTWH((size.width / 2) - 110, 350, 220, 300);
    canvas.drawArc(rect, math.pi, math.pi, true, arcPaint);
  }

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