How to Draw Shapes using Bezier Curves in a Flutter CustomPainter

Question

I am trying to draw the picture below using the flutter customPainter library. How can I draw this shape?

My codes and the result

import 'package:flutter/material.dart';

class CurvePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = new Paint();
    paint.color = Colors.green[800];
    paint.style = PaintingStyle.fill;

    var path = new Path();
    path.lineTo(0, size.height * 0.3);

    path.quadraticBezierTo(size.width * 0.35, size.height * 0.4, size.width * 0.7, size.height * 0.21);
    path.quadraticBezierTo(size.width * 0.6, size.height * 0.19, size.width * 0.9, size.height * 0.15);
    path.quadraticBezierTo(size.width , size.height * 0.05, size.width * 0.6, 0);

    canvas.drawPath(path, paint);
  }

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

Answer 1

The Bézier curves you chose are not the correct ones.

---

Here I illustrate where I applied which curves. The yellow dots are start & end points and the black dots represent control points.
In the code, I went from left to right (top to bottom) and used arcToPoint instead of conicTo as it works better. Note that arcToPoint draws conic curves as well.

It is just a rough sketch, i.e. the proportions are completely off, but at least I can share the proper Bézier curves you should use in order to achieve your desired output.

@override
void paint(Canvas canvas, Size size) {
  final paint = Paint()
    ..color = Colors.red[800]
    ..style = PaintingStyle.fill;

  final path = new Path()
    ..moveTo(size.width * .6, 0)
    ..quadraticBezierTo(
    size.width * .7,
    size.height * .08,
    size.width * .9,
    size.height * .05,
  )
    ..arcToPoint(
    Offset(
      size.width * .93,
      size.height * .15,
    ),
    radius: Radius.circular(size.height * .05),
    largeArc: true,
  )
    ..cubicTo(
    size.width * .6,
    size.height * .15,
    size.width * .5,
    size.height * .46,
    0,
    size.height * .3,
  )
    ..lineTo(0, 0)
    ..close();

  canvas.drawPath(path, paint);
}

Note that I updated the syntax to use .. cascade notation and the final keyword for the variables.