react-native-vision-camera/package/ios/CameraView+Focus.swift

//
//  CameraView+Focus.swift
//  mrousavy
//
//  Created by Marc Rousavy on 19.02.21.
//  Copyright © 2021 mrousavy. All rights reserved.
//

import Foundation

extension CameraView {
  private func convertPreviewCoordinatesToCameraCoordinates(_ point: CGPoint) -> CGPoint {
    return previewView.captureDevicePointConverted(fromLayerPoint: point)
  }

  func focus(point: CGPoint, promise: Promise) {
    withPromise(promise) {
      guard let device = self.videoDeviceInput?.device else {
        throw CameraError.session(SessionError.cameraNotReady)
      }
      if !device.isFocusPointOfInterestSupported {
        throw CameraError.device(DeviceError.focusNotSupported)
      }

      // in {0..1} system
      let normalizedPoint = convertPreviewCoordinatesToCameraCoordinates(point)

      do {
        try device.lockForConfiguration()
        defer {
          device.unlockForConfiguration()
        }

        // Set Focus
        if device.isFocusPointOfInterestSupported {
          device.focusPointOfInterest = normalizedPoint
          device.focusMode = .autoFocus
        }

        // Set Exposure
        if device.isExposurePointOfInterestSupported {
          device.exposurePointOfInterest = normalizedPoint
          device.exposureMode = .autoExpose
        }

        // Remove any existing listeners
        NotificationCenter.default.removeObserver(self,
                                                  name: NSNotification.Name.AVCaptureDeviceSubjectAreaDidChange,
                                                  object: nil)

        // Listen for focus completion
        device.isSubjectAreaChangeMonitoringEnabled = true
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(subjectAreaDidChange),
                                               name: NSNotification.Name.AVCaptureDeviceSubjectAreaDidChange,
                                               object: nil)
        return nil
      } catch {
        throw CameraError.device(DeviceError.configureError)
      }
    }
  }

  @objc
  func subjectAreaDidChange(notification _: NSNotification) {
    guard let device = videoDeviceInput?.device else {
      invokeOnError(.session(.cameraNotReady))
      return
    }

    do {
      try device.lockForConfiguration()
      defer {
        device.unlockForConfiguration()
      }

      // Reset Focus to continuous/auto
      if device.isFocusPointOfInterestSupported {
        device.focusMode = .continuousAutoFocus
      }

      // Reset Exposure to continuous/auto
      if device.isExposurePointOfInterestSupported {
        device.exposureMode = .continuousAutoExposure
      }

      // Disable listeners
      device.isSubjectAreaChangeMonitoringEnabled = false
    } catch {
      invokeOnError(.device(.configureError))
    }
  }
}