title: Setting A CGContext Transparent Background
body: <p>I am still struggling with drawing a line with CGContext.  I have actually go to line to draw, but now I need the background of the Rect to be transparent so the existing background shows thru.  Here's my test code: </p>
  
  <pre><code>(void)drawRect:(CGRect)rect
  {
      CGContextRef context = UIGraphicsGetCurrentContext();
      CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
      CGContextSetAlpha(context,0.0);
      CGContextFillRect(context, rect);
  
      CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
      CGContextSetLineWidth(context, 5.0);
      CGContextMoveToPoint(context, 100.0,0.0);
      CGContextAddLineToPoint(context,100.0, 100.0);
      CGContextStrokePath(context);
  }
  </code></pre>
  
  <p>Any ideas?</p>