Easing - iOS Core Animation - page 213

representing something like a door that starts to swing closed and then slows to a gradual
stop instead of slamming shut.
The kCAMediaTimingFunctionEaseInEaseOut constant creates a gradual acceleration up
to full speed and then a smooth deceleration back down to a stop. This is generally how
most real-world objects move, and is the best choice for most animations. If you could only
ever use one easing function, it would be this one. Given this fact, you might wonder why
this isn't the default, and in fact when you use UIView animation methods, this is the
default, but when creating a CAAnimation , you will need to specify it yourself.
Finally, we have kCAMediaTimingFunctionDefault , which is very similar to
kCAMediaTimingFunctionEaseInEaseOut , but creates a slightly more rapid initial
acceleration up to full speed, followed by a slightly more gradual deceleration. The
difference between this and kCAMediaTimingFunctionEaseInEaseOut is almost
imperceptible, but Apple presumably felt that this was a better choice as the default for
implicit animations (although they subsequently changed their mind for UIKit, which uses
kCAMediaTimingFunctionEaseInEaseOut as the default instead). Remember that despite
the name, this is not the default value when creating an explicit CAAnimation , it is only
used as the default for implicit animations. (In other words, the default layer action
animations use kCAMediaTimingFunctionDefault as their timing function.)
You can try out these different easing functions using a simple test project (see Listing
10.1). Just adjust the timing function in the code before running the project, and then tap
anywhere to see the layer move with the specified easing.
Listing 10.1 Simple Project for Testing Easing Functions
@interface ViewController ()
@property ( nonatomic , strong ) CALayer *colorLayer;
@end
@implementation ViewController
- ( void )viewDidLoad
{
[ super viewDidLoad ];
//create a red layer
self .colorLayer = [ CALayer layer ];
self .colorLayer. frame = CGRectMake ( 0 , 0 , 100 , 100 );
self .colorLayer. position = CGPointMake ( self . view . bounds . size . width / 2.0 ,
self . view . bounds . size . height / 2.0 );
self .colorLayer. backgroundColor = [ UIColor redColor ]. CGColor ;
[ self . view . layer addSublayer : se lf .colorLayer];
}