Jak przyciąć obraz z AVCapture do rect widocznego na wyświetlaczu

To doprowadza mnie do szału, bo nie mogę tego uruchomić. Mam następujący scenariusz:

Używam AVCaptureSession i AVCaptureVideoPreviewLayer do tworzenia własnego interfejsu kamery. Interfejs pokazuje prostokąt. Poniżej znajduje się AVCaptureVideoPreviewLayer, który wypełnia cały ekran.

Chcę, aby uchwycony obraz został przycięty w taki sposób, aby wynikowy obraz wyświetlał dokładnie zawartość widoczną w rect na wyświetlaczu.

Moja konfiguracja wygląda tak:

_session = [[AVCaptureSession alloc] init];
AVCaptureSession *session = _session;
session.sessionPreset = AVCaptureSessionPresetPhoto;

AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if (camera == nil) {
    [self showImagePicker];
    _isSetup = YES;
    return;
}
AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

captureVideoPreviewLayer.frame = self.liveCapturePlaceholderView.bounds;
[self.liveCapturePlaceholderView.layer addSublayer:captureVideoPreviewLayer];

NSError *error;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:camera error:&error];
if (error) {
    HGAlertViewWrapper *av = [[HGAlertViewWrapper alloc] initWithTitle:kFailedConnectingToCameraAlertViewTitle message:kFailedConnectingToCameraAlertViewMessage cancelButtonTitle:kFailedConnectingToCameraAlertViewCancelButtonTitle otherButtonTitles:@[kFailedConnectingToCameraAlertViewRetryButtonTitle]];
    [av showWithBlock:^(NSString *buttonTitle){
        if ([buttonTitle isEqualToString:kFailedConnectingToCameraAlertViewCancelButtonTitle]) {
            [self.delegate gloameCameraViewControllerDidCancel:self];
        }
        else {
            [self setupAVSession];
        }
    }];
}
[session addInput:input];

NSDictionary *options = @{ AVVideoCodecKey : AVVideoCodecJPEG };
_stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
[_stillImageOutput setOutputSettings:options];

[session addOutput:_stillImageOutput];

[session startRunning];
_isSetup = YES;

Zapisuję obraz jak to:

[_stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
 {
     if (error) {
         MWLogDebug(@"Error capturing image from camera. %@, %@", error, [error userInfo]);
         _capturePreviewLayer.connection.enabled = YES;
     }
     else
     {
         NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
         UIImage *image = [[UIImage alloc] initWithData:imageData];

         CGRect cropRect = [self createCropRectForImage:image];
         UIImage *croppedImage;// = [self cropImage:image toRect:cropRect];
         UIGraphicsBeginImageContext(cropRect.size);
         [image drawAtPoint:CGPointMake(-cropRect.origin.x, -cropRect.origin.y)];
         croppedImage = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();
         self.capturedImage = croppedImage;
         [_session stopRunning];             
     }
 }];

W metodzie createCropRectForImage: próbowałem różnych sposobów obliczania rect, aby wyciąć obraz, ale jak dotąd bez powodzenia.

- (CGRect)createCropRectForImage:(UIImage *)image
{
    CGPoint maskTopLeftCorner = CGPointMake(self.maskRectView.frame.origin.x, self.maskRectView.frame.origin.y);
    CGPoint maskBottomRightCorner = CGPointMake(self.maskRectView.frame.origin.x + self.maskRectView.frame.size.width, self.maskRectView.frame.origin.y + self.maskRectView.frame.size.height);

    CGPoint maskTopLeftCornerInLayerCoords = [_capturePreviewLayer convertPoint:maskTopLeftCorner fromLayer:self.maskRectView.layer.superlayer];
    CGPoint maskBottomRightCornerInLayerCoords = [_capturePreviewLayer convertPoint:maskBottomRightCorner fromLayer:self.maskRectView.layer.superlayer];
    CGPoint maskTopLeftCornerInDeviceCoords = [_capturePreviewLayer captureDevicePointOfInterestForPoint:maskTopLeftCornerInLayerCoords];
    CGPoint maskBottomRightCornerInDeviceCoords = [_capturePreviewLayer captureDevicePointOfInterestForPoint:maskBottomRightCornerInLayerCoords];

    float x = maskTopLeftCornerInDeviceCoords.x * image.size.width;
    float y = (1 - maskTopLeftCornerInDeviceCoords.y) * image.size.height;
    float width = fabsf(maskTopLeftCornerInDeviceCoords.x - maskBottomRightCornerInDeviceCoords.x) * image.size.width;
    float height = fabsf(maskTopLeftCornerInDeviceCoords.y - maskBottomRightCornerInDeviceCoords.y) * image.size.height;

    return CGRectMake(x, y, width, height);
}

To jest moja obecna wersja, ale nawet nie ma odpowiednich proporcji. Czy ktoś mógłby mi pomóc?

Próbowałem również użyć tej metody, aby przyciąć mój obraz:

- (UIImage*)cropImage:(UIImage*)originalImage toRect:(CGRect)rect{

    CGImageRef imageRef = CGImageCreateWithImageInRect([originalImage CGImage], rect);

    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
    CGContextRef bitmap = CGBitmapContextCreate(NULL, rect.size.width, rect.size.height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    if (originalImage.imageOrientation == UIImageOrientationLeft) {
        CGContextRotateCTM (bitmap, radians(90));
        CGContextTranslateCTM (bitmap, 0, -rect.size.height);

    } else if (originalImage.imageOrientation == UIImageOrientationRight) {
        CGContextRotateCTM (bitmap, radians(-90));
        CGContextTranslateCTM (bitmap, -rect.size.width, 0);

    } else if (originalImage.imageOrientation == UIImageOrientationUp) {
        // NOTHING
    } else if (originalImage.imageOrientation == UIImageOrientationDown) {
        CGContextTranslateCTM (bitmap, rect.size.width, rect.size.height);
        CGContextRotateCTM (bitmap, radians(-180.));
    }

    CGContextDrawImage(bitmap, CGRectMake(0, 0, rect.size.width, rect.size.height), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);

    UIImage *resultImage=[UIImage imageWithCGImage:ref];
    CGImageRelease(imageRef);
    CGContextRelease(bitmap);
    CGImageRelease(ref);

    return resultImage;
}

Czy ktoś ma 'właściwą kombinację' metod, aby to zadziałało? :)