如何将不随地图移动的覆盖添加到GMSMapView？

import GoogleMaps

class ViewController: UIViewController, GMSMapViewDelegate {
    var mapView: GMSMapView!
    var marker: GMSMarker!

    override func viewDidLoad() {
        super.viewDidLoad()

        // 创建地图视图
        let camera = GMSCameraPosition.camera(withLatitude: 37.7749, longitude: -122.4194, zoom: 12.0)
        mapView = GMSMapView.map(withFrame: CGRect.zero, camera: camera)
        mapView.delegate = self
        self.view = mapView

        // 创建标记
        marker = GMSMarker()
        marker.position = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)
        marker.title = "San Francisco"
        marker.map = mapView
    }

    // 实现地图移动时的回调方法
    func mapView(_ mapView: GMSMapView, didChange position: GMSCameraPosition) {
        // 判断当前地图范围
        let visibleRegion = mapView.projection.visibleRegion()
        let bounds = GMSCoordinateBounds(region: visibleRegion)
        let markerBounds = GMSCoordinateBounds(coordinate: marker.position, coordinate: marker.position)
        
        // 判断标记是否在地图范围内
        if bounds.contains(markerBounds.northEast) && bounds.contains(markerBounds.southWest) {
            marker.map = mapView
        } else {
            marker.map = nil
        }
    }
}