custom painter to draw an image

main.dart

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

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const ImageOnCanvas(),
    );
  }
}

class ImageOnCanvas extends StatefulWidget {
  const ImageOnCanvas({Key? key}) : super(key: key);

  @override
  _ImageOnCanvasState createState() => _ImageOnCanvasState();
}

class _ImageOnCanvasState extends State<ImageOnCanvas> {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<ui.Image>(
      future: _loadImage("assets/images/uno-reverse.png"), // a Future<String> or null
      builder: (BuildContext context, AsyncSnapshot<ui.Image> snapshot) {
        switch (snapshot.connectionState) {
          case ConnectionState.waiting:
            return const Text('Image loading...');
          default:
            if (snapshot.hasError) {
              return Text('Error: ${snapshot.error}');
            } else {
              return CustomPaint(
                  child: const SizedBox(
                    width: 200,
                    height: 200,
                  ),
                  painter: ImagePainter(snapshot.data!));
            }
        }
      },
    );
  }
}

Future<ui.Image> _loadImage(String imageAssetPath) async {
  final ByteData data = await rootBundle.load(imageAssetPath);
  if (data == null) {
    throw 'Unable to read data';
  }
  var codec = await ui.instantiateImageCodec(data.buffer.asUint8List());
  // add additional checking for number of frames etc here
  var frame = await codec.getNextFrame();
  return frame.image;
}

class ImagePainter extends CustomPainter {
  final ui.Image image;

  ImagePainter(this.image);

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawImage(image, const Offset(50, 50), Paint());
  }

  @override
  bool shouldRepaint(ImagePainter oldDelegate) {
    return false;
  }
}