import 'dart:ui' as ui;

import 'package:flutter/services.dart';
import 'package:flutter/material.dart';

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: FutureBuilder(
          future: () async {
            final imageBytes = await rootBundle.load('lib/assets/img.jpeg');
            final image = await decodeImageFromList(imageBytes.buffer.asUint8List());
            final program = await ui.FragmentProgram.fromAsset('lib/assets/simple.frag');

            return (image, program);
          }(),
          builder: (context, snapshot) {
            if (snapshot.hasData == false) {
              return const Center(child: CircularProgressIndicator());
            }

            final image = snapshot.data!.$1;
            final program = snapshot.data!.$2;
            return Opacity(
              opacity: 0.5,
              child: Center(
                child: FittedBox(
                  child: SizedBox(
                    width: image.width.toDouble(),
                    height: image.height.toDouble(),
                    child: CustomPaint(
                      painter: MyCustomPainter(
                        image: image,
                        program: program,
                      ),
                    ),
                  ),
                ),
              ),
            );
          },
        ),
      ),
    );
  }
}

class MyCustomPainter extends CustomPainter {
  const MyCustomPainter({
    required this.image,
    required this.program,
  });

  final ui.Image image;
  final ui.FragmentProgram program;

  @override
  void paint(Canvas canvas, Size size) {
    final shader = program.fragmentShader();
    shader.setFloat(0, image.width.toDouble());
    shader.setFloat(1, image.height.toDouble());
    shader.setImageSampler(0, image);

    final paint = Paint()..shader = shader;
    canvas.drawRect(Offset.zero & size, paint);
  }

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