I recently had to improve the performance of a few views that utilized CALayer-based shadows on rounded-rect UIView objects. On this particular iPad application, when the device was rotated, the views rotated quite a lot slower than we would have hoped. It wasn’t a show-stopper, but the jerky rotation animation made it look cheap and unpolished. The easiest way to have our cake, and eat it too, was to set a custom CGPath to the layer’s shadowPath property. This told UIKit to set the inside of the path to opaque, reducing the amount of work the rendering engine needed to perform.
// Add background tile
UIImage*bgImage=[UIImageimageNamed:@"embedded_bg.png"];self.view.backgroundColor=[UIColorcolorWithPatternImage:bgImage];// Add the reference view
The resulting image, as you can see above, has a shadow as you’d expect. But since we’ve declared the shape the path will have, the iPad can drastically improve its rendering performance.
Through that process however, I decided to see what sort of effects I could pull off by passing in a path other than the default rectangular bounds of the layer. Since you can create any sort of path you want, I considered the different effects I could get away with by making non-rectangular paths and using them as shadows.
By carefully drawing a trapezoidal shape below and slightly beneath the view, you can give the illusion of depth.
There are plenty of other possibilities, more than can be covered here. Creating CGPathRef objects, either using UIBezierCurve or by using Quartz2D drawing methods, can easily step through composing shadows. Use a CGAffineTransform object to manipulate your path to stretch, scale, or rotate it as needed. Once you realize what your possibilities are, you can add an extra degree of polish to your application with very little effort.