如何在Flutter中从画布中获取PNG图像数据？

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

GlobalKey globalKey = GlobalKey();

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: RepaintBoundary(
            key: globalKey,
            child: CustomPaint(
              painter: MyPainter(),
              size: Size(200, 200),
            ),
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            capturePng();
          },
          child: Icon(Icons.camera),
        ),
      ),
    );
  }
}

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // 绘制你的图形
    // ...
  }

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

void capturePng() async {
  RenderRepaintBoundary boundary = globalKey.currentContext.findRenderObject();
  ui.Image image = await boundary.toImage();
  ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
  Uint8List pngBytes = byteData.buffer.asUint8List();

  // 处理图像数据
  // ...
}