title: OPENCV how to speed up imshow?
body: <p>I'm developing a little program in which there is a circle handled by the mouse pointer that moves in real time over an image.</p>
  
  <p>I achieved to do that using 
      <code>cvSetMouseCallback()</code>
  but it works fine only when the window is set as
      <code>CV_WINDOW_AUTOSIZE</code>
  and the image size is not too big (less then 400x400). I realized that the problem is in the
      <code>imShow()</code>
  function that wastes to much time.
  I wanted to use
     <code>cv::updateWindow()</code>
  function to force the window updating but I get 
      <code>undefined reference to</code>
  error. What can I do to speed up my application? Any suggestion?</p>
  
  <p>Thank you in advance.</p>