ios AVFoundation tap to focus

Question

I am trying to create a camera app which, would act like the default camera app more or less. The thing, which is not working for me at the moment, is tap to focus. I want the camera to focus and do whatever it does on my touched point, just like the real camera app does.

Here's my viewDidLoad

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Session
    _session = [[AVCaptureSession alloc] init];
    _session.sessionPreset = AVCaptureSessionPresetPhoto;

    // Input
    _videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    _videoInput = [AVCaptureDeviceInput deviceInputWithDevice:_videoDevice error:nil];

    // Output
    _frameOutput = [[AVCaptureVideoDataOutput alloc] init];
    _frameOutput.videoSettings = [NSDictionary dictionaryWithObject:AVVideoCodecJPEG forKey:AVVideoCodecKey];

    [_frameOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
    [_session addInput:_videoInput];
    [_session addOutput:_frameOutput];
    [_session startRunning];
};

And here's the method that should make my camera focus stuff on click.

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    [touches enumerateObjectsUsingBlock:^(id obj, BOOL *stop) {
        UITouch *touch = obj;
        CGPoint touchPoint = [touch locationInView:touch.view];
        focusLayer.frame = CGRectMake((touchPoint.x-25), (touchPoint.y-25), 50, 50);

        if ([_videoDevice isFocusPointOfInterestSupported]) {
            NSError *error;
            if ([_videoDevice lockForConfiguration:&error]) {
                [_videoDevice setFocusPointOfInterest:touchPoint];
                [_videoDevice setExposurePointOfInterest:touchPoint];

                [_videoDevice setFocusMode:AVCaptureFocusModeAutoFocus];
                if ([_videoDevice isExposureModeSupported:AVCaptureExposureModeAutoExpose]){
                    [_videoDevice setExposureMode:AVCaptureExposureModeAutoExpose];
                }
                [_videoDevice unlockForConfiguration];
            }
        }


        // NSLog(@"x = %f, y = %f", touchPoint.x, touchPoint.y);
    }];
}

Nothing really happens once I click on the screen.

Answer 1

You have to adjust the touchPoint to a range of [0,1] using something like the following code:

    CGRect screenRect = [[UIScreen mainScreen] bounds];
    screenWidth = screenRect.size.width;
    screenHeight = screenRect.size.height;  
    double focus_x = thisFocusPoint.center.x/screenWidth;
    double focus_y = thisFocusPoint.center.y/screenHeight;

    [[self captureManager].videoDevice lockForConfiguration:&error];
    [[self captureManager].videoDevice setFocusPointOfInterest:CGPointMake(focus_x,focus_y)];
    [[self captureManager].videoDevice unlockForConfiguration];

The documentation on this can be found in Apple - AV Foundation Programming Guidelines - see section Media Capture where you will find information on Focus Modes:

If it’s supported, you set the focal point using focusPointOfInterest. You pass a CGPoint where {0,0} represents the top left of the picture area, and {1,1} represents the bottom right in landscape mode with the home button on the right—this applies even if the device is in portrait mode.