title: UIGraphicsBeginImageContext with parameters
body: <p>I am taking a screenshot in my application.  I am able to take the screenshot.</p>
  
  <p>Now I want to take the screenshot by specifying the x and y coordinate.  Is that possible?</p>
  
  <pre><code>UIGraphicsBeginImageContext( self.view.bounds.size );
  [self.view.layer renderInContext:UIGraphicsGetCurrentContext(  )];
  UIImage* aImage = UIGraphicsGetImageFromCurrentImageContext(  );
  </code></pre>