title: CAShapeLayer Animating Path Glitches / Flickers (From Ellipse to Rect and back)
body: <p>I am running into an issue when I create an explicit animation to change the value of a CAShapeLayer's path from an ellipse to a rect.</p>
  
  <p>In my canvas controller I setup a basic CAShapeLayer and add it to the root view's layer:</p>
  
  <pre><code>CAShapeLayer *aLayer;
  aLayer = [CAShapeLayer layer];
  aLayer.frame = CGRectMake(100, 100, 100, 100);
  aLayer.path = CGPathCreateWithEllipseInRect(aLayer.frame, nil);
  aLayer.lineWidth = 10.0f;
  aLayer.strokeColor = [UIColor blackColor].CGColor;
  aLayer.fillColor = [UIColor clearColor].CGColor;
  [self.view.layer addSublayer:aLayer];
  </code></pre>
  
  <p>Then, when I animate the path I get a strange glitch / flicker in the last few frames of the animation when the shape becomes a rect, and in the first few frames when it animates away from being a rect. The animation is set up as follows:</p>
  
  <pre><code>CGPathRef newPath = CGPathCreateWithRect(aLayer.frame, nil);
  [CATransaction lock];
  [CATransaction begin];
  [CATransaction setAnimationDuration:5.0f];
  CABasicAnimation *ba = [CABasicAnimation animationWithKeyPath:@"path"];
  ba.autoreverses = YES;
  ba.fillMode = kCAFillModeForwards;
  ba.repeatCount = HUGE_VALF;
  ba.fromValue = (id)aLayer.path;
  ba.toValue = (__bridge id)newPath;
  [aLayer addAnimation:ba forKey:@"animatePath"];
  [CATransaction commit];
  [CATransaction unlock];
  </code></pre>
  
  <p>I have tried many different things like locking / unlocking the CATransaction, playing with various fill modes, etc...</p>
  
  <p>Here's an image of the glitch:
  <a href="http://www.postfl.com/outgoing/renderingglitch.png">http://www.postfl.com/outgoing/renderingglitch.png</a></p>
  
  <p>A video of what I am experiencing can be found here:
  <a href="http://vimeo.com/37720876">http://vimeo.com/37720876</a></p>