如何将CustomPaint画布直接覆盖在视频播放器小部件上？

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

class VideoPlayerScreen extends StatefulWidget {
  @override
  _VideoPlayerScreenState createState() => _VideoPlayerScreenState();
}

class _VideoPlayerScreenState extends State<VideoPlayerScreen> {
  VideoPlayerController _controller;

  @override
  void initState() {
    super.initState();
    _controller = VideoPlayerController.network('视频链接');
    _controller.initialize().then((_) {
      setState(() {});
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          _buildVideoPlayer(),
          _buildCustomPaint(),
        ],
      ),
    );
  }

  Widget _buildVideoPlayer() {
    if (_controller.value.isInitialized) {
      return AspectRatio(
        aspectRatio: _controller.value.aspectRatio,
        child: VideoPlayer(_controller),
      );
    } else {
      return Container();
    }
  }

  Widget _buildCustomPaint() {
    return CustomPaint(
      // 在这里绘制你的画布内容
      painter: MyCustomPainter(),
    );
  }
}

class MyCustomPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // 在这里绘制你的画布内容
  }

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: VideoPlayerScreen(),
    );
  }
}