iOS MapView 影像處理

import MapKit

import Foundation

extension UIImage {

    func grayScaleImage() -> UIImage {

        let imageRect = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)

        let colorSpace = CGColorSpaceCreateDeviceGray();

        

        let width = UInt(self.size.width)

        let height = UInt(self.size.height)

        let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: .allZeros);

        context?.draw(self.cgImage!, in: imageRect)

        

        let imageRef = context!.makeImage();

        let newImage = UIImage(cgImage: imageRef!)

        return newImage

    }

}

class OSMTileOverlay: MKTileOverlay {

    let cache = NSCache<NSURL, NSData>()

    let operationQueue = OperationQueue()

    

    override func url(forTilePath path: MKTileOverlayPath) -> URL {

        return URL(string: String(format: "http://tile.openstreetmap.org/%d/%d/%d.png", path.z, path.x, path.y))!

    }

    

    override func loadTile(at path: MKTileOverlayPath, result: @escaping (Data?, Error?) -> Void)  {

        let url = self.url(forTilePath: path)

        if let cachedData = cache.object(forKey: url as NSURL) as? Data {

            result(cachedData, nil)

        } else {

            let request = URLRequest(url: url)

            URLSession.shared.dataTask(with: request, completionHandler: {

                [weak self]

                data, response, error in

                if let data = data {

                    var image = UIImage(data: data)

                    image = image?.grayScaleImage()

                    let newData = UIImagePNGRepresentation(image!)

                    self?.cache.setObject((newData as? NSData)!, forKey: url as NSURL)

                    result(newData, error)

                    return

                }

                result(data, error)

            }).resume()

        }

    }

}