MKMapView renderInContext - iPhone 4（视网膜）问题

并添加案例代码：

swift
import UIKit
import MapKit
class MapViewController: UIViewController {
    
    @IBOutlet weak var mapView: MKMapView!
    func captureMapView() -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(mapView.bounds.size, true, UIScreen.main.scale)
        
        guard let context = UIGraphicsGetCurrentContext() else {
            return nil
        }
        
        mapView.layer.render(in: context)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        
        UIGraphicsEndImageContext()
        
        return image
    }
    
    func saveMapViewImage() {
        if let image = captureMapView() {
            UIImageWriteToSavedPhotosAlbum(image, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
        }
    }
    
    @objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) {
        if let error = error {
            print("保存图片时发生错误：\(error.localizedDescription)")
        } else {
            print("图片保存成功！")
        }
    }
}