phaser/todo/TS Source/tweens/easing/Back.ts

/// <reference path="../../_definitions.ts" />

/**
* @author       Richard Davey <rich@photonstorm.com>
* @author       sole (http://soledadpenades.com), tween.js
* @copyright    2013 Photon Storm Ltd.
* @license      https://github.com/photonstorm/phaser/blob/master/license.txt  MIT License
* @module       Phaser
*/
module Phaser.Easing {

    /**
    * Back easing methods.
    *
    * @class Back
    */
    export class Back {

        /**
        * The In ease method.
        *
        * @method In
        * @param {Number} k The value to ease.
        * @return {Number} The eased value.
        */
        public static In(k) {

            var s = 1.70158;
            return k * k * ((s + 1) * k - s);

        }

        /**
        * The Out ease method.
        *
        * @method Out
        * @param {Number} k The value to ease.
        * @return {Number} The eased value.
        */
        public static Out(k) {

            var s = 1.70158;
            return --k * k * ((s + 1) * k + s) + 1;

        }

        /**
        * The InOut ease method.
        *
        * @method InOut
        * @param {Number} k The value to ease.
        * @return {Number} The eased value.
        */
        public static InOut(k) {

            var s = 1.70158 * 1.525;
            if ((k *= 2) < 1) return 0.5 * (k * k * ((s + 1) * k - s));
            return 0.5 * ((k -= 2) * k * ((s + 1) * k + s) + 2);

        }

    }

}