Specialized Layers - iOS Core Animation - page 122

which is more suited to creating arbitrary particle effects). There is another more practical
use however: reflections.
Reflections
By using CAReplicatorLayer to apply a transform with a negative scale factor to a
single duplicate layer, you can create a mirror image of the contents of a given view (or an
entire view hierarchy), creating a real-time “reflection” effect.
Let's try implementing this idea in the form of a reusable UIView subclass called
ReflectionView that will automatically generate a reflection of its contents. The code
to create this is very simple (see Listing 6.9), and actually using the ReflectionView is
even simpler; we can just drop an instance of our ReflectionView into Interface
Builder (see Figure 6.9), and it will generate a reflection of its subviews at runtime without
the need to add any setup code to the view controller (see Figure 6.10).
Listing 6.9 Automatically Drawing a Reflection with CAReplicatorLayer
#import "ReflectionView.h"
#import <QuartzCore/QuartzCore.h>
@implementation ReflectionView
+ ( Class )layerClass
{
return [ CAReplicatorLayer class ];
}
- ( void )setUp
{
//configure replicator
CAReplicatorLayer *layer = ( CAReplicatorLayer *) self . layer ;
layer. instanceCount = 2 ;
//move reflection instance below original and flip vertically
CATransform3D transform = CATransform3DIdentity ;
CGFloat verticalOffset = self . bounds . size . height + 2 ;
transform = CATransform3DTranslate (transform, 0 , verticalOffset, 0 );
transform = CATransform3DScale (transform, 1 , - 1 , 0 );
layer. instanceTransform = transform;
//reduce alpha of reflection layer
layer. instanceAlphaOffset = - 0.6 ;
}