phaser/todo/TS Source/tweens/easing/Elastic.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 {

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

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

            var s, a = 0.1, p = 0.4;
            if (k === 0) return 0;
            if (k === 1) return 1;
            if (!a || a < 1) { a = 1; s = p / 4; }
            else s = p * Math.asin(1 / a) / (2 * Math.PI);
            return -(a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));

        }

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

            var s, a = 0.1, p = 0.4;
            if (k === 0) return 0;
            if (k === 1) return 1;
            if (!a || a < 1) { a = 1; s = p / 4; }
            else s = p * Math.asin(1 / a) / (2 * Math.PI);
            return (a * Math.pow(2, -10 * k) * Math.sin((k - s) * (2 * Math.PI) / p) + 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, a = 0.1, p = 0.4;
            if (k === 0) return 0;
            if (k === 1) return 1;
            if (!a || a < 1) { a = 1; s = p / 4; }
            else s = p * Math.asin(1 / a) / (2 * Math.PI);
            if ((k *= 2) < 1) return -0.5 * (a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));
            return a * Math.pow(2, -10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p) * 0.5 + 1;

        }

    }

}