SpriteKit-Spring is a set of extensions to perform spring animations with SpriteKit.

If you need to support iOS 7, you can just drop SpriteKit-Spring.swift in your project.

If you support iOS 8 only, you can install SpriteKit-Spring as a framework with CocoaPods (version 0.36 or above) by adding the following lines to your Podfile:

use_frameworks!

pod 'SpriteKit-Spring'

You then need to import SpriteKit-Spring wherever you want to use it:

import SpriteKit_Spring

#import <SpriteKit_Spring/SpriteKit_Spring-Swift.h>

In iOS 7, Apple introduced spring animations in UIKit by adding a new animation method on UIView (see WWDC video and UIView documentation).

This library replicates this feature by adding a spring variant to most factory methods of SKAction. The parameters usingSpringWithDamping: and initialSpringVelocity: have the same meaning as their UIKit counterpart. See below for examples.

let move = SKAction.moveByX(0, y: 200, 
  duration: 5, delay: 5,
  usingSpringWithDamping: 0.2, initialSpringVelocity: 0)
  
node.runAction(move)

let scale = SKAction.scaleXTo(2, y: 0.5,
  duration: 5, delay: 5,
  usingSpringWithDamping: 0.2, initialSpringVelocity: 0)
  
node.runAction(scale)

let rotate = SKAction.rotateByAngle(CGFloat(M_PI/2),
  duration: 5, delay: 5,
  usingSpringWithDamping: 0.2, initialSpringVelocity: 0)
  
node.runAction(rotate)

• Because they use customActionWithDuration:actionBlock:, none of these actions is reversible (the reverse action performs the same animation).
• All these factory methods are based on the lower level animateKeyPath:byValue:duration:delay:usingSpringWithDamping:initialSpringVelocity: and animateKeyPath:toValue:duration:delay:usingSpringWithDamping:initialSpringVelocity: methods, which can animate any CGFloat key path. If you have a SKNode subclass with a fancy CGFloat property that you'd like to animate, feel free to use these methods!

• Alexis Taugeron (@ataugeron)

SpriteKit-Spring is released under the Apache 2 license. See LICENSE for details.