title: ios how to make a camera circle mask
body: <p>everybody,
  I want to make the circle mask on the camera.</p>
  
  <p>i try this way:</p>
  
  <pre><code>- (void)drawRect:(CGRect)rect
  {
      // Drawing code
      CGContextRef context = UIGraphicsGetCurrentContext();
      CGContextAddArc(context, self.frame.size.width/2, self.frame.size.height/2, 200, 0, M_PI *2, 0);
      //Set the stroke color to black
      [[UIColor blackColor]setStroke];
      //Define line width and cap
      CGContextSetLineWidth(context, 200);
      CGContextSetLineCap(context, kCGLineCapButt);
      //draw it!
      CGContextDrawPath(context, kCGPathStroke);
  }
  </code></pre>
  
  <p>just set the line with enough big,but i think it can set alpha.</p>
  
  <p>thanks.</p>