    /**
     * @class Ext.fx.Easing
     *
    This class contains a series of function definitions used to modify values during an animation.
    They describe how the intermediate values used during a transition will be calculated. It allows for a transition to change
    speed over its duration. The following options are available:

    - linear The default easing type
    - backIn
    - backOut
    - bounceIn
    - bounceOut
    - ease
    - easeIn
    - easeOut
    - easeInOut
    - elasticIn
    - elasticOut
    - cubic-bezier(x1, y1, x2, y2)

    Note that cubic-bezier will create a custom easing curve following the CSS3 [transition-timing-function][0]
    specification.  The four values specify points P1 and P2 of the curve as (x1, y1, x2, y2). All values must
    be in the range [0, 1] or the definition is invalid.

    [0]: http://www.w3.org/TR/css3-transitions/#transition-timing-function_tag

     * @markdown
     * @singleton
     */
    Ext.ns('Ext.fx');

    Ext.require('Ext.fx.CubicBezier', function() {
        var math = Math,
            pi = math.PI,
            pow = math.pow,
            sin = math.sin,
            sqrt = math.sqrt,
            abs = math.abs,
            backInSeed = 1.70158;
        Ext.fx.Easing = {
            // ease: Ext.fx.CubicBezier.cubicBezier(0.25, 0.1, 0.25, 1),
            // linear: Ext.fx.CubicBezier.cubicBezier(0, 0, 1, 1),
            // 'ease-in': Ext.fx.CubicBezier.cubicBezier(0.42, 0, 1, 1),
            // 'ease-out': Ext.fx.CubicBezier.cubicBezier(0, 0.58, 1, 1),
            // 'ease-in-out': Ext.fx.CubicBezier.cubicBezier(0.42, 0, 0.58, 1),
            // 'easeIn': Ext.fx.CubicBezier.cubicBezier(0.42, 0, 1, 1),
            // 'easeOut': Ext.fx.CubicBezier.cubicBezier(0, 0.58, 1, 1),
            // 'easeInOut': Ext.fx.CubicBezier.cubicBezier(0.42, 0, 0.58, 1)
        };

        Ext.apply(Ext.fx.Easing, {
            linear: function(n) {
                return n;
            },
            ease: function(n) {
                var q = 0.07813 - n / 2,
                    alpha = -0.25,
                    Q = sqrt(0.0066 + q * q),
                    x = Q - q,
                    X = pow(abs(x), 1/3) * (x < 0 ? -1 : 1),
                    y = -Q - q,
                    Y = pow(abs(y), 1/3) * (y < 0 ? -1 : 1),
                    t = X + Y + 0.25;
                return pow(1 - t, 2) * 3 * t * 0.1 + (1 - t) * 3 * t * t + t * t * t;
            },
            easeIn: function (n) {
                return pow(n, 1.7);
            },
            easeOut: function (n) {
                return pow(n, 0.48);
            },
            easeInOut: function(n) {
                var q = 0.48 - n / 1.04,
                    Q = sqrt(0.1734 + q * q),
                    x = Q - q,
                    X = pow(abs(x), 1/3) * (x < 0 ? -1 : 1),
                    y = -Q - q,
                    Y = pow(abs(y), 1/3) * (y < 0 ? -1 : 1),
                    t = X + Y + 0.5;
                return (1 - t) * 3 * t * t + t * t * t;
            },
            backIn: function (n) {
                return n * n * ((backInSeed + 1) * n - backInSeed);
            },
            backOut: function (n) {
                n = n - 1;
                return n * n * ((backInSeed + 1) * n + backInSeed) + 1;
            },
            elasticIn: function (n) {
                if (n === 0 || n === 1) {
                    return n;
                }
                var p = 0.3,
                    s = p / 4;
                return pow(2, -10 * n) * sin((n - s) * (2 * pi) / p) + 1;
            },
            elasticOut: function (n) {
                return 1 - Ext.fx.Easing.elasticIn(1 - n);
            },
            bounceIn: function (n) {
                return 1 - Ext.fx.Easing.bounceOut(1 - n);
            },
            bounceOut: function (n) {
                var s = 7.5625,
                    p = 2.75,
                    l;
                if (n < (1 / p)) {
                    l = s * n * n;
                } else {
                    if (n < (2 / p)) {
                        n -= (1.5 / p);
                        l = s * n * n + 0.75;
                    } else {
                        if (n < (2.5 / p)) {
                            n -= (2.25 / p);
                            l = s * n * n + 0.9375;
                        } else {
                            n -= (2.625 / p);
                            l = s * n * n + 0.984375;
                        }
                    }
                }
                return l;
            }
        });
        Ext.apply(Ext.fx.Easing, {
            'back-in': Ext.fx.Easing.backIn,
            'back-out': Ext.fx.Easing.backOut,
            'ease-in': Ext.fx.Easing.easeIn,
            'ease-out': Ext.fx.Easing.easeOut,
            'elastic-in': Ext.fx.Easing.elasticIn,
            'elastic-out': Ext.fx.Easing.elasticIn,
            'bounce-in': Ext.fx.Easing.bounceIn,
            'bounce-out': Ext.fx.Easing.bounceOut,
            'ease-in-out': Ext.fx.Easing.easeInOut
        });
    });