gistfile1.m

- (CGPoint)pointForPointOfInterest:(CGPoint)pointOfInterest
{
  CGPoint point;
  if ([previewLayer respondsToSelector:
          @selector(pointForCaptureDevicePointOfInterest:)]) {
    // Use the native method if available (available on iOS 6 or above.)
    point = [previewLayer pointForCaptureDevicePointOfInterest:pointOfInterest];
  } else {
    // Otherwise manually convert the point from point-of-interest coordinates
    // to preview layer coordinates. Notice we set the content gravity of the
    // preview layer to AVLayerVideoGravityResizeAspectFill.
    CGRect bounds = [previewLayer bounds];
    CGFloat width = CGRectGetHeight(bounds);
    CGFloat height = CGRectGetWidth(bounds);
    CGFloat aspectRatio = inputSize.width / inputSize.height;
    if (width / height > aspectRatio) {
      point.x = (pointOfInterest.y - 0.5) * width * aspectRatio - height / 2.0;
      point.y = pointOfInterest.x * width;
    } else {
      point.x = (1.0 - pointOfInterest.y) * height;
      point.y = (0.5 - pointOfInterest.x) * height / aspectRatio - width / 2.0;
    }
  }
  return point;
}

- (CGPoint)pointOfInterestForPoint:(CGPoint)point
{
  // Same discussion above.
  CGPoint pointOfInterest;
  if ([previewLayer respondsToSelector:
          @selector(captureDevicePointOfInterestForPoint:)]) {
    pointOfInterest = [previewLayer captureDevicePointOfInterestForPoint:point];
  } else {
    CGRect bounds = [previewLayer bounds];
    CGFloat width = CGRectGetHeight(bounds);
    CGFloat height = CGRectGetWidth(bounds);
    CGFloat aspectRatio = inputSize.width / inputSize.height;
    if (width / height > aspectRatio) {
      pointOfInterest.x = point.y / width;
      pointOfInterest.y = 0.5 + (height / 2.0 + point.x) / width / aspectRatio;
    } else {
      pointOfInterest.x = 0.5 - (width / 2.0 + point.y) / height * aspectRatio;
      pointOfInterest.y = 1.0 - point.x / height;
    }
  }
  return pointOfInterest;
}