Phaser Source: src/tween/Easing.js

# Source: src/tween/Easing.js

    /* jshint curly: false */

    /**
    * @author       Richard Davey <rich@photonstorm.com>
    * @copyright    2016 Photon Storm Ltd.
    * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
    */

    /**
    * A collection of easing methods defining ease-in and ease-out curves.
    *
    * @class Phaser.Easing
    */
    Phaser.Easing = {

        /**
        * Linear easing.
        *
        * @class Phaser.Easing.Linear
        */
        Linear: {

            /**
            * Linear Easing (no variation).
            *
            * @method Phaser.Easing.Linear#None
            * @param {number} k - The value to be tweened.
            * @returns {number} k.
            */
            None: function ( k ) {

                return k;

            }

        },

        /**
        * Quadratic easing.
        *
        * @class Phaser.Easing.Quadratic
        */
        Quadratic: {

            /**
            * Ease-in.
            *
            * @method Phaser.Easing.Quadratic#In
            * @param {number} k - The value to be tweened.
            * @returns {number} k^2.
            */
            In: function ( k ) {

                return k * k;

            },

            /**
            * Ease-out.
            *
            * @method Phaser.Easing.Quadratic#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} k* (2-k).
            */
            Out: function ( k ) {

                return k * ( 2 - k );

            },

            /**
            * Ease-in/out.
            *
            * @method Phaser.Easing.Quadratic#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( k ) {

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

            }

        },

        /**
        * Cubic easing.
        *
        * @class Phaser.Easing.Cubic
        */
        Cubic: {

            /**
            * Cubic ease-in.
            *
            * @method Phaser.Easing.Cubic#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

                return k * k * k;

            },

            /**
            * Cubic ease-out.
            *
            * @method Phaser.Easing.Cubic#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

                return --k * k * k + 1;

            },

            /**
            * Cubic ease-in/out.
            *
            * @method Phaser.Easing.Cubic#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( k ) {

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

            }

        },

        /**
        * Quartic easing.
        *
        * @class Phaser.Easing.Quartic
        */
        Quartic: {

            /**
            * Quartic ease-in.
            *
            * @method Phaser.Easing.Quartic#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

                return k * k * k * k;

            },

            /**
            * Quartic ease-out.
            *
            * @method Phaser.Easing.Quartic#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

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

            },

            /**
            * Quartic ease-in/out.
            *
            * @method Phaser.Easing.Quartic#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( k ) {

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

            }

        },

        /**
        * Quintic easing.
        *
        * @class Phaser.Easing.Quintic
        */
        Quintic: {

            /**
            * Quintic ease-in.
            *
            * @method Phaser.Easing.Quintic#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

                return k * k * k * k * k;

            },

            /**
            * Quintic ease-out.
            *
            * @method Phaser.Easing.Quintic#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

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

            },

            /**
            * Quintic ease-in/out.
            *
            * @method Phaser.Easing.Quintic#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            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 easing.
        *
        * @class Phaser.Easing.Sinusoidal
        */
        Sinusoidal: {

            /**
            * Sinusoidal ease-in.
            *
            * @method Phaser.Easing.Sinusoidal#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

                if (k === 0) return 0;
                if (k === 1) return 1;
                return 1 - Math.cos( k * Math.PI / 2 );

            },

            /**
            * Sinusoidal ease-out.
            *
            * @method Phaser.Easing.Sinusoidal#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

                if (k === 0) return 0;
                if (k === 1) return 1;
                return Math.sin( k * Math.PI / 2 );

            },

            /**
            * Sinusoidal ease-in/out.
            *
            * @method Phaser.Easing.Sinusoidal#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( k ) {

                if (k === 0) return 0;
                if (k === 1) return 1;
                return 0.5 * ( 1 - Math.cos( Math.PI * k ) );

            }

        },

        /**
        * Exponential easing.
        *
        * @class Phaser.Easing.Exponential
        */
        Exponential: {

            /**
            * Exponential ease-in.
            *
            * @method Phaser.Easing.Exponential#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

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

            },

            /**
            * Exponential ease-out.
            *
            * @method Phaser.Easing.Exponential#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

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

            },

            /**
            * Exponential ease-in/out.
            *
            * @method Phaser.Easing.Exponential#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            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 easing.
        *
        * @class Phaser.Easing.Circular
        */
        Circular: {

            /**
            * Circular ease-in.
            *
            * @method Phaser.Easing.Circular#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

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

            },

            /**
            * Circular ease-out.
            *
            * @method Phaser.Easing.Circular#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

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

            },

            /**
            * Circular ease-in/out.
            *
            * @method Phaser.Easing.Circular#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            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 easing.
        *
        * @class Phaser.Easing.Elastic
        */
        Elastic: {

            /**
            * Elastic ease-in.
            *
            * @method Phaser.Easing.Elastic#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( 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 ) );

            },

            /**
            * Elastic ease-out.
            *
            * @method Phaser.Easing.Elastic#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( 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 );

            },

            /**
            * Elastic ease-in/out.
            *
            * @method Phaser.Easing.Elastic#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( 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;

            }

        },

        /**
        * Back easing.
        *
        * @class Phaser.Easing.Back
        */
        Back: {

            /**
            * Back ease-in.
            *
            * @method Phaser.Easing.Back#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

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

            },

            /**
            * Back ease-out.
            *
            * @method Phaser.Easing.Back#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            Out: function ( k ) {

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

            },

            /**
            * Back ease-in/out.
            *
            * @method Phaser.Easing.Back#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( 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 );

            }

        },

        /**
        * Bounce easing.
        *
        * @class Phaser.Easing.Bounce
        */
        Bounce: {

            /**
            * Bounce ease-in.
            *
            * @method Phaser.Easing.Bounce#In
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            In: function ( k ) {

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

            },

            /**
            * Bounce ease-out.
            *
            * @method Phaser.Easing.Bounce#Out
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            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;

                }

            },

            /**
            * Bounce ease-in/out.
            *
            * @method Phaser.Easing.Bounce#InOut
            * @param {number} k - The value to be tweened.
            * @returns {number} The tweened value.
            */
            InOut: function ( k ) {

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

            }

        }

    };

    Phaser.Easing.Default = Phaser.Easing.Linear.None;
    Phaser.Easing.Power0 = Phaser.Easing.Linear.None;
    Phaser.Easing.Power1 = Phaser.Easing.Quadratic.Out;
    Phaser.Easing.Power2 = Phaser.Easing.Cubic.Out;
    Phaser.Easing.Power3 = Phaser.Easing.Quartic.Out;
    Phaser.Easing.Power4 = Phaser.Easing.Quintic.Out;