CALayer - Shadow causes a performance hit?
self.view.layer.shouldRasterize = YES;self.view.layer.rasterizationScale = UIScreen.mainScreen.scale;I was recently having some issues with slow CALayer shadows, and that simple line of code fixed up everything for me!
You should expect a slowdown from adding a shadow. A shadowRadius of 20 is very high and will be especially slow.
The other key to improve shadow rendering speed: set the shadowPath property. It can help dramatically.
Using shadowPath instead of shadowOffset.
theView.layer.shadowPath = [UIBezierPath bezierPathWithRect:theView.bounds].CGPath;Check this post: iphone - Animation's performance is very poor when view's shadow is on