title: iphone camera show focus rectangle
body: <p>I am cloning Apple's camera app using AVCaptureSession based on Apple's AppCam app sample.
  The problem is I cannot see focus rectangle in the video preview screen.
  I used following code for setting focus, but still focus rectangle is not shown.</p>
  
  <pre><code>  AVCaptureDevice *device = [[self videoInput] device];
  if ([device isFocusModeSupported:focusMode] &amp;&amp; [device focusMode] != focusMode) {
      NSError *error;
  
        printf(" setFocusMode    \n");
      if ([device lockForConfiguration:&amp;error]) {
          [device setFocusMode:focusMode];
          [device unlockForConfiguration];
      } else {
          id delegate = [self delegate];
          if ([delegate respondsToSelector:@selector(acquiringDeviceLockFailedWithError:)]) {
              [delegate acquiringDeviceLockFailedWithError:error];
          }
      }    
  }
  </code></pre>
  
  <p>When I use UIImagePickerController, auto focus, tap focus are supported by default, and can see focus rectangle.
  Is there no way to show focus rectangle in the video preview layer using AVCaptureSession?</p>