A Face Detector using Vision

FaceDetector.swift

import Vision
import AppKit

final class FaceDetector {
    
    private enum Error: Swift.Error {
        case couldNotFindFace
        case couldNotGetCIImage
        case couldNotProcessImageRequest
        case didNotGetAnyObservation
    }
    
    private let faceDetectionRequest = VNSequenceRequestHandler()
    
    func detectFace(in image: CGImage) async throws -> FaceParameters {
        try await withCheckedThrowingContinuation { continuation in
            detectFaceWrapper(on: image) { result in
                continuation.resume(with: result)
            }
        }
    }
    
    
    private func detectFaceWrapper(on image: CGImage, completion: @escaping (Result<FaceParameters, Swift.Error>) -> Void) {
        
        let faceDetection = VNDetectFaceRectanglesRequest()
        
        DispatchQueue.global(qos: .userInteractive).async {
            do {
                try self.faceDetectionRequest.perform([faceDetection], on: image)
                if
                    let result = faceDetection.results?.first,
                    let yaw = result.yaw?.doubleValue,
                    let pitch = result.pitch?.doubleValue,
                    let roll = result.roll?.doubleValue
                {
                    let parameters = FaceParameters(
                        yaw: Utilities.rad2deg(yaw),
                        roll: Utilities.rad2deg(roll),
                        pitch: Utilities.rad2deg(pitch))
                    
                    completion(.success(parameters))
                } else {
                    completion(.failure(Error.didNotGetAnyObservation))
                }
            } catch {
                completion(.failure(Error.couldNotProcessImageRequest))
            }
        }
    }
}