flutter image drawing in canvas

main.dart

import 'package:flutter/material.dart';
import 'dart:ui' as ui;
import 'package:flutter/services.dart' show rootBundle;
import 'dart:async';
import 'dart:typed_data';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ui.Image image;
  bool isImageloaded = false;
  void initState() {
    super.initState();
    init();
  }

  Future <Null> init() async {
    final ByteData data = await rootBundle.load('images/lake.jpg');
    image = await loadImage(new Uint8List.view(data.buffer));
  }

  Future<ui.Image> loadImage(List<int> img) async {
    final Completer<ui.Image> completer = new Completer();
    ui.decodeImageFromList(img, (ui.Image img) {
      setState(() {
        isImageloaded = true;
      });
      return completer.complete(img);
    });
    return completer.future;
  }

  Widget _buildImage() {
    if (this.isImageloaded) {
      return new CustomPaint(
          painter: new ImageEditor(image: image),
        );
    } else {
      return new Center(child: new Text('loading'));
    }
  }
  @override
  Widget build(BuildContext context) {

    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Container(
        child: _buildImage(),
      )
    );
  }
}

class ImageEditor extends CustomPainter {


  ImageEditor({
    this.image,
  });

  ui.Image image;

  @override
  void paint(Canvas canvas, Size size) {
    ByteData data = image.toByteData();
    canvas.drawImage(image, new Offset(0.0, 0.0), new Paint());
  }

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

}

If the image is not an asset image, but a file stored on the device, and its path is known, you can do like this:

            Future<ui.Image> loadImage(Uint8List bytes) async {
              final Completer<ui.Image> completer = Completer();
              ui.decodeImageFromList(bytes, (ui.Image img) {
                return completer.complete(img);
              });
              return completer.future;
            }

           File file = File(thePath);
           Uint8List bytes = await file.readAsBytes();
           ui.Image backgroundImage = await loadImage(bytes);

and in the Custom Painter:

    canvas.drawImage(backgroundImage, Offset(0.0, 0.0), Paint());

Works with both .png and .jpg files.

Thanks a lot!!

hello

after testing your code it seems that something has changed the image loading does not work anymore

these normal?

cdl remy

How can I add the eraser mode on canvas but the eraser should not erase the picture?