sample.swift

import UIKit
import CoreImage
import Metal
import MetalKit

class ViewController: UIViewController {
    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var mtkView: MTKView!
    
    // Metal resources
    var device: MTLDevice!
    var commandQueue: MTLCommandQueue!
    var sourceTexture: MTLTexture!
    
    // Core Image resources
    var context: CIContext!
    let filter = CIFilter(name: "CIGaussianBlur")!
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        

        // UIBlurEffect
        
        let blurEffect = UIBlurEffect(style: .light)
        let blurEffectView = UIVisualEffectView()
        blurEffectView.frame = CGRect(x: 0, y: 0, width: imageView.frame.width, height: 400)
        blurEffectView.center = imageView.center
        self.imageView.addSubview(blurEffectView)
        UIView.animate(withDuration: 5) {
            blurEffectView.effect = blurEffect
        }
        
        // CIFilter
        
        let blurredRect = CGRect(x: 0,
                                 y: imageView.center.y - 200,
                                 width: imageView.frame.width,
                                 height: 400)
        let context = CIContext()
        imageView.image = imageView.image?.blurredImage(with: context,
                                                        radius: 20,
                                                        atRect: blurredRect)
        
        // Metal
        
        
            
    device = MTLCreateSystemDefaultDevice()
    commandQueue = device.makeCommandQueue()
    let textureLoader = MTKTextureLoader(device: device)
    sourceTexture = try! textureLoader.newTexture(cgImage: UIImage(named: "street.png")!.cgImage!)
    let view = self.mtkView!
    view.delegate = self
    view.device = device
    view.framebufferOnly = false

    context = CIContext(mtlDevice: device)
}


}
extension ViewController: MTKViewDelegate {
    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {
        
    }
    
    
    func draw(in view: MTKView) {
        if let currentDrawable = view.currentDrawable,
           let commandBuffer = commandQueue.makeCommandBuffer() {
            
            let inputImage = CIImage(mtlTexture: sourceTexture)!.oriented(.down)
            filter.setValue(inputImage, forKey: kCIInputImageKey)
            filter.setValue(10.0, forKey: kCIInputRadiusKey)
            
            context.render(filter.outputImage!,
                to: currentDrawable.texture,
                commandBuffer: commandBuffer,
                bounds:  mtkView.bounds,
                colorSpace: colorSpace)
            
            commandBuffer.present(currentDrawable)
            commandBuffer.commit()
        }
    }
}

extension UIImage {
    func blurredImage(with context: CIContext, radius: CGFloat, atRect: CGRect) -> UIImage? {
        guard let ciImg = CIImage(image: self) else { return nil }

        let cropedCiImg = ciImg.cropped(to: atRect)
        let blur = CIFilter(name: "CIGaussianBlur")
        blur?.setValue(cropedCiImg, forKey: kCIInputImageKey)
        blur?.setValue(radius, forKey: kCIInputRadiusKey)

        if let ciImgWithBlurredRect = blur?.outputImage?.composited(over: ciImg),
           let outputImg = context.createCGImage(ciImgWithBlurredRect, from: ciImgWithBlurredRect.extent) {
            return UIImage(cgImage: outputImg)
        }
        return nil
    }
}