如何在Google Map Flutter上显示Widget图标？

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

class CustomMarkerIcon extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 50,
      height: 50,
      decoration: BoxDecoration(
        color: Colors.blue,
        shape: BoxShape.circle,
      ),
      child: Icon(
        Icons.location_on,
        color: Colors.white,
        size: 30,
      ),
    );
  }
}

class MapScreen extends StatefulWidget {
  @override
  _MapScreenState createState() => _MapScreenState();
}

class _MapScreenState extends State<MapScreen> {
  GoogleMapController _mapController;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Google Map Flutter'),
      ),
      body: GoogleMap(
        initialCameraPosition: CameraPosition(
          target: LatLng(37.4219999, -122.0840575),
          zoom: 15,
        ),
        onMapCreated: (controller) {
          setState(() {
            _mapController = controller;
          });
        },
        markers: {
          Marker(
            markerId: MarkerId('marker_1'),
            position: LatLng(37.4219999, -122.0840575),
            icon: BitmapDescriptor.fromBytes(
              _createMarkerIcon(),
            ),
          ),
        },
      ),
    );
  }

  Uint8List _createMarkerIcon() {
    final customIconWidget = CustomMarkerIcon();
    final pixelRatio = ui.window.devicePixelRatio;
    final widgetWidth = customIconWidget.width;
    final widgetHeight = customIconWidget.height;
    final width = (widgetWidth * pixelRatio).toInt();
    final height = (widgetHeight * pixelRatio).toInt();
    final renderWidget = RenderRepaintBoundary(
      child: SizedBox(
        width: widgetWidth,
        height: widgetHeight,
        child: customIconWidget,
      ),
    );
    final renderObject = renderWidget.createRenderObject(context);
    final pixelBounds = ui.Rect.fromLTWH(0, 0, width.toDouble(), height.toDouble());
    final image = ui.SceneBuilder()
      ..pushClipRect(pixelBounds)
      ..addRepaintBoundary(renderObject)
      ..pop();
    final imageBytes = image.toImage(width, height).getBytes();
    return imageBytes.buffer.asUint8List();
  }
}