Auto Focus and Auto Exposure in Avfoundation on Custom Camera Layer

Auto Focus and Auto Exposure in AVFoundation on Custom Camera Layer

 public func captureDevicePointOfInterestForPoint(pointInLayer: CGPoint) -> CGPoint

will give you the point for the device to focus on based on the settings of your AVCaptureVideoPreviewLayer. See the docs.

Swift: autoFocus/Expose and continuousAutoFocus/Exposure at the same time?

Figured it out. First I call a method on myViewDidAppear that sets my default focus and exposure mode:

@objc func setDefaultFocusAndExposure() {

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
                device.isSubjectAreaChangeMonitoringEnabled = true
                device.focusMode = AVCaptureDevice.FocusMode.continuousAutoFocus
                device.exposureMode = AVCaptureDevice.ExposureMode.continuousAutoExposure
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }
}

The trick here was not to confuse autoFocus with continuousAutoFocus. This way by default it constantly observes the scene and sets the focus and exposure. Also isSubjectAreaChangeMonitorEnabled is a very important bit. This lets you register a notification to call a function when the scene changes focus or exposure-wise so that you can switch the focus mode. More on that soon.

In a touch on the screen can set the focus and exposure based on a point:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    let bounds = UIScreen.main.bounds

    let touchPoint = touches.first! as UITouch
    let screenSize = bounds.size
    let focusPoint = CGPoint(x: touchPoint.location(in: view).y / screenSize.height, y: 1.0 - touchPoint.location(in: view).x / screenSize.width)

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
            if device.isFocusPointOfInterestSupported {
                device.focusPointOfInterest = focusPoint
                device.focusMode = AVCaptureDevice.FocusMode.autoFocus
            }
            if device.isExposurePointOfInterestSupported {
                device.exposurePointOfInterest = focusPoint
                device.exposureMode = AVCaptureDevice.ExposureMode.autoExpose
            }
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }
}

Register the notification in viewDidLoad for setting back the focus and exposure mode to continuous. Here I'm just calling the function that sets the default settings of continuous:

    NotificationCenter.default.addObserver(self,
                                           selector: #selector(self.setDefaultFocusAndExposure),
                                           name: NSNotification.Name.AVCaptureDeviceSubjectAreaDidChange,
                                           object: nil)

Don't forget to remove observers in NotificationCenter:

deinit {
    NotificationCenter.default.removeObserver(self)
}

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