custom_square_clipper.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool clipped = false;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          body: GestureDetector(
        onTap: () {
          setState(() {
            clipped = !clipped;
          });
        },
        child: Center(
          child: ClipRect(
            clipper: clipped ? MyClipper() : null,
            child: Image.network(
              'https://aspgems.com/wp-content/uploads/2020/01/flutter-dart.png',
              fit: BoxFit.cover,
            ),
          ),
        ),
      )),
    );
  }
}

class MyClipper extends CustomClipper<Rect> {
  @override
  Rect getClip(Size size) {
    return Rect.fromLTWH(size.height / 2, 0.0, size.height, size.height);
  }

  @override
  bool shouldReclip(CustomClipper<Rect> oldClipper) => true;
}