CustomClipper.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Custom Clipper',
      theme: ThemeData(),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ClipPath(
        clipper: MyClipper(),
        child: Container(
          padding: EdgeInsets.symmetric(horizontal: 10),
          height: MediaQuery.of(context).size.height / 2,
          width: double.infinity,
          decoration: BoxDecoration(
            gradient: LinearGradient(
              begin: Alignment.topRight,
              end: Alignment.bottomLeft,
              colors: [
                Color(0xFF3383CD),
                Color(0xFF11249F),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

class MyClipper extends CustomClipper<Path> {
  @override
  Path getClip(Size size) {
    var path = Path();
    path.lineTo(0, size.height);
    path.quadraticBezierTo(
        size.width / 3, size.height / 3, size.width, size.height / 5);
    path.lineTo(size.width, 0);
    path.close();
    return path;
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) {
    return false;
  }
}