title: How to animate CGAffineTransform smoothly as drag gesture is performed
body: <p>I understand the various ways of detecting drag gestures just fine (currently I'm using a <code>UIPanGestureRecognizer</code>), but my understanding of transformations is limited, so I'm not sure if/how this is possible.  Essentially, what I want to have is a scaling transformation applied to a UIView at the same <em>pace</em> (for lack of a better word) as the user performs a drag gesture elsewhere on the screen.  In other words, as the user drags up, I want the size of my transforming UIView to increase proportionally to the position of that gesture, and if the user then starts dragging down, it should start to shrink proportionally.  </p>
  
  <p>Hopefully that makes sense.  As a dummy example, just imagine a slider that you can adjust to change the size of a UIView in real time.  Is there a good way to make those sorts of incremental and constant size updates with <code>CGAffineTransform</code>?</p>