Custom easing functions for use with SpriteKit / SKAction

SpriteKitTimingFunctions.swift

//
//  SKTimingFunction.swift
//  Studious ToolKit
//
//  Created by Allan Weir on 09/01/2017.
//  Copyright © 2017 Allan Weir. All rights reserved.
//  Adapted from a JavaScript version found at https://gist.github.com/gre/1650294
//

class SpriteKitTimingFunctions {

    // no easing, no acceleration
    static var easeLinear: SKActionTimingFunction = {
        var t: Float = $0
        return t
    }
    
    // accelerating from zero velocity
    static var easeInQuad: SKActionTimingFunction = {
        var t: Float = $0
        return t*t
    }
    
    // decelerating to zero velocity
    static var easeOutQuad: SKActionTimingFunction = {
        var t: Float = $0
        return t*(2-t)
    }
    
    // acceleration until halfway, then deceleration
    static var easeInOutQuad: SKActionTimingFunction = {
        var t: Float = $0
        return t<0.5 ? 2*t*t : -1+(4-2*t)*t
    }
    
    // accelerating from zero velocity
    static var easeInCubic: SKActionTimingFunction = {
        var t: Float = $0
        return t*t*t
    }
    
    // decelerating to zero velocity
    static var easeOutCubic: SKActionTimingFunction = {
        var t: Float = $0
        return (t - 1)*t*t+1
    }
    
    // acceleration until halfway, then deceleration
    static var easeInOutCubic: SKActionTimingFunction = {
        var t: Float = $0
        return t<0.5 ? 4*t*t*t : (t-1)*(2*t-2)*(2*t-2)+1
    }
    
    // accelerating from zero velocity
    static var easeInQuart: SKActionTimingFunction = {
        var t: Float = $0
        return t*t*t*t
    }
    
    // decelerating to zero velocity
    static var easeOutQuart: SKActionTimingFunction = {
        var t: Float = $0
        return 1-(t-1)*t*t*t
    }
    
    // acceleration until halfway, then deceleration
    static var easeInOutQuart: SKActionTimingFunction = {
        var t: Float = $0
        return t<0.5 ? 8*t*t*t*t : 1-8*(t-1)*t*t*t
    }
    
    // accelerating from zero velocity
    static var easeInQuint: SKActionTimingFunction = {
        var t: Float = $0
        return t*t*t*t*t
    }
    
    // decelerating to zero velocity
    static var easeOutQuint: SKActionTimingFunction = {
        var t: Float = $0
        return 1+(t-1)*t*t*t*t
    }
    
    // acceleration until halfway, then deceleration
    static var easeInOutQuint: SKActionTimingFunction = {
        var t: Float = $0
        return t<0.5 ? 16*t*t*t*t*t : 1+16*(t-1)*t*t*t*t
    }
    
    static var easeInSin: SKActionTimingFunction = {
        var t: Float = $0
        return 1 + sin(Float.pi / 2 * t - Float.pi / 2)
    }
    
    static var easeOutSin : SKActionTimingFunction = {
        var t: Float = $0
        return sin(Float.pi / 2 * t)
    }
    
    static var easeInOutSin: SKActionTimingFunction = {
        var t: Float = $0
        return (1 + sin(Float.pi * t - Float.pi / 2)) / 2
    }
    
    // elastic bounce effect at the beginning
    static var easeInElastic: SKActionTimingFunction = {
        var t: Float = $0
        return (0.04 - 0.04 / t) * sin(25 * t) + 1
    }
    
    // elastic bounce effect at the end
    static var easeOutElastic: SKActionTimingFunction = {
        var t: Float = $0
        return 0.04 * t / (t - 1) * sin(25 * t)
    }
    
    // elastic bounce effect at the beginning and end
    static var easeInOutElastic: SKActionTimingFunction = {
        var t: Float = $0
        return (t < 0.5) ? (0.01 + 0.01 / t) * sin(50 * t) : (0.02 - 0.01 / t) * sin(50 * t) + 1
    }
    
}