title: how can I animate a CAlayer's bounds to progressively reveal an image?
body: <p>For certain reasons, I'm trying to avoid using a CAScrollLayer to do this. The effect I'm going after is to progressively reveal (from bottom to top) a CALayer's content (a png I previously loaded in). So I thought about doing this:</p>
  
  <pre><code>    layer.anchorPoint = CGPointMake(.5, 1);
      CABasicAnimation* a = [CABasicAnimation animationWithKeyPath:@"bounds.size.height"];
      a.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
      a.fillMode = kCAFillModeBoth;
      a.removedOnCompletion = NO;
      a.duration = 1;
      a.fromValue = [NSNumber numberWithFloat:0.];
      a.toValue = [NSNumber numberWithFloat:layer.bounds.size.height];
      [layer addAnimation:a forKey:nil];
  </code></pre>
  
  <p>The problem with this is you can tell the layer's content is scaled with the bounds. I was trying for the bounds to change but the content to stay always the original size, so that effectively the bounds clip the image and as I increase bounds.height, the image "Reveals" itself.</p>
  
  <p>Any ideas as to how to pull it off or what might I be missing?</p>