title: How to tell how much of a UITableViewCell is visible
body: <p>UITableView has methods for determining which cells are currently visible. What I'm trying to find out is how much of a cell is visible.</p>
  
  <p>For instance, as you drag a table down the 'newly visible' cell at the top of the table doens't just appear but appears a (pixel) line at a time until the whole cell is visible. How can I tell how much of that cell is visible at any given moment as the table view is dragged. </p>
  
  <p>My final aim is, as the user drags on the table, to change the appearing view within the cell dependent on how much of it is visible at any given time. </p>
  
  <p>Any suggestions?</p>