CIImage做滤镜，Metal显示。
格式不太好，当做记录吧...
整体代码如下：

// capture
var captureSession : AVCaptureSession!
var backCamera : AVCaptureDevice!
var backInput : AVCaptureInput!
var videoOutput : AVCaptureVideoDataOutput!
var photoOutput : AVCapturePhotoOutput!
var captureImage : UIImage!

// metal
var metalDevice : MTLDevice!
var metalCommandQueue : MTLCommandQueue!
    
// core image
var ciContext : CIContext!
var currentCIImage : CIImage?
let transferFilter = CIFilter(name: "CIPhotoEffectTransfer")

// view
let captureImageButton : UIButton = {
    let button = UIButton()
    button.backgroundColor = .white
    button.tintColor = .white
    button.layer.cornerRadius = 25
    button.translatesAutoresizingMaskIntoConstraints = false
    return button
}()
    
let mtkView = MTKView()

override func viewDidLoad() {
    super.viewDidLoad()
    setupView()
    checkPermissions()
    checkAlbum()
    setupMetal()
    setupCoreImage()
    setupAndStartCaptureSession()
}

界面初始化

func setupView() {
    view.backgroundColor = .black
    mtkView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(mtkView)
    view.addSubview(captureImageButton)
        
    NSLayoutConstraint.activate([
        captureImageButton.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor),
        captureImageButton.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
        captureImageButton.widthAnchor.constraint(equalToConstant: 50),
        captureImageButton.heightAnchor.constraint(equalToConstant: 50),
            
        mtkView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        mtkView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        mtkView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        mtkView.topAnchor.constraint(equalTo: view.topAnchor)
    ])
        
    captureImageButton.addTarget(self, action: #selector(captureImageClick(_:)), for: .touchUpInside)
}

相机权限

// 相机权限
func checkPermissions() {
    let cameraAuthStatus = AVCaptureDevice.authorizationStatus(for: AVMediaType.video)
    switch cameraAuthStatus {
        case .notDetermined:
        AVCaptureDevice.requestAccess(for: AVMediaType.video) { (authorized) in
            if (!authorized) {
                abort()
            }
        }
        case .restricted:
            abort()
        case .denied:
            abort()
        case .authorized:
            return
        @unknown default:
            fatalError()
    }
}

相册权限

// 相册权限
func checkAlbum() {
    let authorStatus:PHAuthorizationStatus? = PHPhotoLibrary.authorizationStatus(for: PHAccessLevel.readWrite)
    switch authorStatus {
    case .notDetermined:
        PHPhotoLibrary.requestAuthorization(for: .readWrite) { status in
                
        }
        break
    case .authorized:
            
        break
    case .restricted:

        break
    case .denied:

        break
    case .limited:
            
        break
    default:
        break
    }
}

Metal初始化

// metal
func setupMetal() {
    metalDevice = MTLCreateSystemDefaultDevice()
    mtkView.device = metalDevice
    mtkView.isPaused = true
    mtkView.delegate = self
    mtkView.framebufferOnly = false
        
    metalCommandQueue = metalDevice.makeCommandQueue()
}

CoreImage

// core image
func setupCoreImage() {
    ciContext = CIContext(mtlDevice: metalDevice)
}

func applyFilters(inputImage image: CIImage) -> CIImage? {
    var filteredImage : CIImage?
        
    transferFilter?.setValue(image, forKeyPath: kCIInputImageKey)
    filteredImage = transferFilter?.outputImage
        
    return filteredImage
}

CaptureSession

// camera
func setupAndStartCaptureSession() {
    DispatchQueue.global(qos: .userInitiated).async {
        self.captureSession = AVCaptureSession()
        self.captureSession.beginConfiguration()
        if self.captureSession.canSetSessionPreset(.photo) {
            self.captureSession.sessionPreset = .photo
        }
        self.captureSession.automaticallyConfiguresCaptureDeviceForWideColor = true
            
        self.setupInputs()
        self.setupOutput()
            
        self.captureSession.commitConfiguration()
        self.captureSession.startRunning()
    }
}

func setupInputs() {
    if let device = AVCaptureDevice.default(.builtInWideAngleCamera, for: .video, position: .back) {
        backCamera = device
    } else {
        fatalError("no back camera")
    }
        
    guard let bInput = try? AVCaptureDeviceInput(device: backCamera) else {
        fatalError()
    }
        
    backInput = bInput
    if !captureSession.canAddInput(backInput) {
        fatalError()
    }
        
    captureSession.addInput(backInput)
}

func setupOutput() {
    videoOutput = AVCaptureVideoDataOutput()
    let videoQueue = DispatchQueue(label: "videoQueue")
    videoOutput.setSampleBufferDelegate(self, queue: videoQueue)
        
    if captureSession.canAddOutput(videoOutput) {
        captureSession.addOutput(videoOutput)
    } else {
        fatalError()
    }
        
    videoOutput.connections.first?.videoOrientation = .portrait
    photoOutput = AVCapturePhotoOutput()
        
    if captureSession.canAddOutput(photoOutput) {
        captureSession.addOutput(photoOutput)
    }
}

画面渲染

extension ViewController : AVCaptureVideoDataOutputSampleBufferDelegate {
    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        guard let cvBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
            return
        }
        
        let ciImage = CIImage(cvImageBuffer: cvBuffer)
        
        guard let filteredCIImage = applyFilters(inputImage: ciImage) else {
            return
        }
        self.currentCIImage = filteredCIImage
        
        mtkView.draw()
    }
}

extension ViewController : MTKViewDelegate {
    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {
    }
    
    func draw(in view: MTKView) {
        guard let commandBuffer = metalCommandQueue.makeCommandBuffer() else {
            return
        }
        
        guard let ciImage = currentCIImage else {
            return
        }
        
        guard let currentDrawable = view.currentDrawable else {
            return
        }
        
        let heightOfciImage = ciImage.extent.height
        let heightOfDrawable = view.drawableSize.height
        let yOffsetFromBottom = (heightOfDrawable - heightOfciImage)/2
        
        self.ciContext.render(ciImage, to: currentDrawable.texture, commandBuffer: commandBuffer, bounds: CGRect(origin: CGPoint(x: 0, y: -yOffsetFromBottom), size: view.drawableSize), colorSpace: CGColorSpaceCreateDeviceRGB())
        
        commandBuffer.present(currentDrawable)
        commandBuffer.commit()
    }
}

图片输出

extension ViewController : AVCapturePhotoCaptureDelegate {
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
        // you can do something
        guard let photoData = photo.fileDataRepresentation() else {
            return
        }
        
        guard let ciImage = CIImage(data: photoData) else {
            return
        }
        
        guard let filteredCIImage = applyFilters(inputImage: ciImage) else {
            return
        }
        
        self.captureImage = UIImage(ciImage: filteredCIImage)
    }
    
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishCaptureFor resolvedSettings: AVCaptureResolvedPhotoSettings, error: Error?) {
        if self.captureImage == nil {
            return
        }
        // save
    }
}

Click

@objc func captureImageClick(_ sender: UIButton?) {
    let settings = AVCapturePhotoSettings(format: [AVVideoCodecKey:AVVideoCodecType.jpeg])
    settings.flashMode = .off
    photoOutput.capturePhoto(with: settings, delegate: self)
}