/*
 * Tween.js - Licensed under the MIT license
 * https://github.com/tweenjs/tween.js
 */

/**
 * Easing Function :<br>
 * <p>
 * Easing.Linear.None<br>
 * Easing.Quadratic.In<br>
 * Easing.Quadratic.Out<br>
 * Easing.Quadratic.InOut<br>
 * Easing.Cubic.In<br>
 * Easing.Cubic.Out<br>
 * Easing.Cubic.InOut<br>
 * Easing.Quartic.In<br>
 * Easing.Quartic.Out<br>
 * Easing.Quartic.InOut<br>
 * Easing.Quintic.In<br>
 * Easing.Quintic.Out<br>
 * Easing.Quintic.InOut<br>
 * Easing.Sinusoidal.In<br>
 * Easing.Sinusoidal.Out<br>
 * Easing.Sinusoidal.InOut<br>
 * Easing.Exponential.In<br>
 * Easing.Exponential.Out<br>
 * Easing.Exponential.InOut<br>
 * Easing.Circular.In<br>
 * Easing.Circular.Out<br>
 * Easing.Circular.InOut<br>
 * Easing.Elastic.In<br>
 * Easing.Elastic.Out<br>
 * Easing.Elastic.InOut<br>
 * Easing.Back.In<br>
 * Easing.Back.Out<br>
 * Easing.Back.InOut<br>
 * Easing.Bounce.In<br>
 * Easing.Bounce.Out<br>
 * Easing.Bounce.InOut
 * </p>
 * @public
 * @constant
 * @enum {Function}
 * @name Easing
 * @memberof Tween
 */
export let Easing = {

    Linear: {
        /** @ignore */
        None: function (k) {

            return k;

        }

    },

    Quadratic: {
        /** @ignore */
        In: function (k) {

            return k * k;

        },
        /** @ignore */
        Out: function (k) {

            return k * (2 - k);

        },
        /** @ignore */
        InOut: function (k) {

            if ((k *= 2) < 1) return 0.5 * k * k;
            return - 0.5 * (--k * (k - 2) - 1);

        }

    },

    Cubic: {
        /** @ignore */
        In: function (k) {

            return k * k * k;

        },
        /** @ignore */
        Out: function (k) {

            return --k * k * k + 1;

        },
        /** @ignore */
        InOut: function (k) {

            if ((k *= 2) < 1) return 0.5 * k * k * k;
            return 0.5 * ((k -= 2) * k * k + 2);

        }

    },

    Quartic: {
        /** @ignore */
        In: function (k) {

            return k * k * k * k;

        },
        /** @ignore */
        Out: function (k) {

            return 1 - (--k * k * k * k);

        },
        /** @ignore */
        InOut: function (k) {

            if ((k *= 2) < 1) return 0.5 * k * k * k * k;
            return - 0.5 * ((k -= 2) * k * k * k - 2);

        }

    },

    Quintic: {
        /** @ignore */
        In: function (k) {

            return k * k * k * k * k;

        },
        /** @ignore */
        Out: function (k) {

            return --k * k * k * k * k + 1;

        },
        /** @ignore */
        InOut: function (k) {

            if ((k *= 2) < 1) return 0.5 * k * k * k * k * k;
            return 0.5 * ((k -= 2) * k * k * k * k + 2);

        }

    },

    Sinusoidal: {
        /** @ignore */
        In: function (k) {

            return 1 - Math.cos(k * Math.PI / 2);

        },
        /** @ignore */
        Out: function (k) {

            return Math.sin(k * Math.PI / 2);

        },
        /** @ignore */
        InOut: function (k) {

            return 0.5 * (1 - Math.cos(Math.PI * k));

        }

    },

    Exponential: {
        /** @ignore */
        In: function (k) {

            return k === 0 ? 0 : Math.pow(1024, k - 1);

        },
        /** @ignore */
        Out: function (k) {

            return k === 1 ? 1 : 1 - Math.pow(2, - 10 * k);

        },
        /** @ignore */
        InOut: function (k) {

            if (k === 0) return 0;
            if (k === 1) return 1;
            if ((k *= 2) < 1) return 0.5 * Math.pow(1024, k - 1);
            return 0.5 * (- Math.pow(2, - 10 * (k - 1)) + 2);

        }

    },

    Circular: {
        /** @ignore */
        In: function (k) {

            return 1 - Math.sqrt(1 - k * k);

        },
        /** @ignore */
        Out: function (k) {

            return Math.sqrt(1 - (--k * k));

        },
        /** @ignore */
        InOut: function (k) {

            if ((k *= 2) < 1) return - 0.5 * (Math.sqrt(1 - k * k) - 1);
            return 0.5 * (Math.sqrt(1 - (k -= 2) * k) + 1);

        }

    },

    Elastic: {
        /** @ignore */
        In: function (k) {
            if (k === 0) {
                return 0;
            }
            if (k === 1) {
                return 1;
            }
            return -Math.pow(2, 10 * (k - 1)) * Math.sin((k - 1.1) * 5 * Math.PI);
        },
        /** @ignore */
        Out: function (k) {
            if (k === 0) {
                return 0;
            }
            if (k === 1) {
                return 1;
            }
            return Math.pow(2, -10 * k) * Math.sin((k - 0.1) * 5 * Math.PI) + 1;

        },
        /** @ignore */
        InOut: function (k) {
            if (k === 0) {
                return 0;
            }
            if (k === 1) {
                return 1;
            }
            k *= 2;
            if (k < 1) {
                return -0.5 * Math.pow(2, 10 * (k - 1)) * Math.sin((k - 1.1) * 5 * Math.PI);
            }
            return 0.5 * Math.pow(2, -10 * (k - 1)) * Math.sin((k - 1.1) * 5 * Math.PI) + 1;
        }

    },

    Back: {
        /** @ignore */
        In: function (k) {

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

        },
        /** @ignore */
        Out: function (k) {

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

        },
        /** @ignore */
        InOut: function (k) {

            const 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);

        }

    },

    Bounce: {
        /** @ignore */
        In: function (k) {

            return 1 - Easing.Bounce.Out(1 - k);

        },
        /** @ignore */
        Out: function (k) {

            if (k < (1 / 2.75)) {

                return 7.5625 * k * k;

            } else if (k < (2 / 2.75)) {

                return 7.5625 * (k -= (1.5 / 2.75)) * k + 0.75;

            } else if (k < (2.5 / 2.75)) {

                return 7.5625 * (k -= (2.25 / 2.75)) * k + 0.9375;

            } else {

                return 7.5625 * (k -= (2.625 / 2.75)) * k + 0.984375;

            }

        },
        /** @ignore */
        InOut: function (k) {

            if (k < 0.5) return Easing.Bounce.In(k * 2) * 0.5;
            return Easing.Bounce.Out(k * 2 - 1) * 0.5 + 0.5;

        }

    }

};
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