title: Does Quartz2D test intersection of rect by line before drawing it
body: <p>I'm drawing a big scheme that consist of a lot of lines. I do it in the <code>drawRect:</code> method of <code>UIView</code>. The scheme is larger than the layer of view and I check each line and draw it only if it intersects the visible rect. But at one moment I thought, should I do this? Maybe Quartz is already doing this test?</p>
  
  <p>So the question is:
  When I use function <code>CGContextAddLineToPoint()</code> does the <code>Core Graphics</code> tests this line for intersection with layer rect or it just draw it anyway?</p>