title: scaling image on pinch gesture
body: <p>I'm using the jQuery <a href="https://github.com/HotStudio/touchy" rel="noreferrer">touchy</a> plugin for detecting the pinch event to give users the ability to zoom in/out on an image.  Here's the gist of my code:</p>
  
  <pre>
  var w = 800,
      h = 600;
  $('img').on('touchy-pinch', function (e, $target, data) {
      $(this).css({
          width: w * data.scale,
          height: h * data.scale
      });
  });
  </pre>
  
  <p>Where the custom data object contains the following:</p>
  
  <ul>
  <li>scale</li>
  <li>previousScale</li>
  <li>currentPoint</li>
  <li>startPoint</li>
  <li>startDistance</li>
  </ul>
  
  <p>It works fine on the first pinch, but once my fingers leave the screen and then I try to do it again, the image re-scales back up.  How can I modify my handler so that the image continues where it left off rather than re-scale?  Using the data's previousScale didn't help since the previousScale just gets reset as well.</p>