Drawing on flutter canvas

import 'package:flutter/material.dart';
class CrosswordGame extends StatefulWidget {
  @override
  _CrosswordGameState createState() => _CrosswordGameState();
}
class _CrosswordGameState extends State<CrosswordGame> {
``@override
  Widget build(BuildContext context) {
return Scaffold(
      body: GestureDetector(
        child: CustomPaint(
          child: Container(),
          painter: ShapePainter(),
        ),
      ),
    );
  }
}
class ShapePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // TODO: implement paint
    
  }
  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    // TODO: implement shouldRepaint
    return null;
  }
}

Rectangle

var paint1 = Paint()
      ..color = Color(0xff995588)
      ..style = PaintingStyle.fill;
 canvas.drawRect(Offset(100, 100) & const Size(200, 150), paint1);

Circle

var paint1 = Paint()
      ..color = Color(0xffaa44aa)
      ..style = PaintingStyle.fill;
 canvas.drawCircle(Offset(200, 200), 100, paint1);

Triangle

var path = Path();
 path.lineTo(size.width, 0);
 path.lineTo(size.height, size.width);
 path.close();
 canvas.drawPath(path, paint);