title: Draw on a CGContext from a CGImage
body: <p>I would like to draw on a <code>CGContext</code> by using tiles from <code>CGImage</code> that I would like to draw in a specified order.</p>
  
  <p>According to documentation <a href="http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Reference/CGContext/Reference/reference.html" rel="nofollow">here</a> it seems that the only method to draw an image in a graphic context is </p>
  
  <pre><code>void CGContextDrawImage (
     CGContextRef c,
     CGRect rect,
     CGImageRef image
  );
  </code></pre>
  
  <p>But this doesn't take in account the case in which I want to draw just a <code>CGRect</code> of the source image. Do I have to do some tricks to make this work?</p>