﻿/*
 * ============================================================================================
 * Easing Equations v2.0
 * September 1, 2003
 * (c) 2003 Robert Penner, all rights reserved.
 * This work is subject to the terms in http://www.robertpenner.com/easing_terms_of_use.html.
 * ============================================================================================
 */

/**
 * @namespace
 [lang:ja]
 * イージング関数ライブラリ.
 * {@link enchant.Easing} 以下にある関数は全て t(現在の時刻), b(初期値), c(変化後の値), d(値の変化にかける時間) の引数を取り, 指定した時刻に取る値を返す.
 * ActionScript で広く使われている Robert Penner による Easing Equations を JavaScript に移植した.
 [/lang]
 [lang:en]
 * JavaScript translation of Robert Penner's "Easing Equations" library which is widely used in ActionScript.
 * 
 * @param [t] the current time
 * @param [b] the property's initial value
 * @param [c] how much the value should change
 * @param [d] how much time should elapse before value is changed
 * 
 * @return {Number}
 [/lang]
 [lang:de]
 [/lang]
 * <br/>
 * See: <a href="http://www.robertpenner.com/easing/">
 * http://www.robertpenner.com/easing/</a>
 * <br/>
 * See: <a href="http://www.robertpenner.com/easing/penner_chapter7_tweening.pdf">
 * http://www.robertpenner.com/easing/penner_chapter7_tweening.pdf</a>
 */
enchant.Easing = {
    LINEAR: function(t, b, c, d) {
        return c * t / d + b;
    },

    SWING: function(t, b, c, d) {
        return c * (0.5 - Math.cos(((t / d) * Math.PI)) / 2) + b;
    },

    // *** quad
    QUAD_EASEIN: function(t, b, c, d) {
        return c * (t /= d) * t + b;
    },

    QUAD_EASEOUT: function(t, b, c, d) {
        return -c * (t /= d) * (t - 2) + b;
    },

    QUAD_EASEINOUT: function(t, b, c, d) {
        if ((t /= d / 2) < 1) {
            return c / 2 * t * t + b;
        }
        return -c / 2 * ((--t) * (t - 2) - 1) + b;
    },

    // *** cubic
    CUBIC_EASEIN: function(t, b, c, d) {
        return c * (t /= d) * t * t + b;
    },

    CUBIC_EASEOUT: function(t, b, c, d) {
        return c * ((t = t / d - 1) * t * t + 1) + b;
    },

    CUBIC_EASEINOUT: function(t, b, c, d) {
        if ((t /= d / 2) < 1) {
            return c / 2 * t * t * t + b;
        }
        return c / 2 * ((t -= 2) * t * t + 2) + b;
    },

    // *** quart
    QUART_EASEIN: function(t, b, c, d) {
        return c * (t /= d) * t * t * t + b;
    },

    QUART_EASEOUT: function(t, b, c, d) {
        return -c * ((t = t / d - 1) * t * t * t - 1) + b;
    },

    QUART_EASEINOUT: function(t, b, c, d) {
        if ((t /= d / 2) < 1) {
            return c / 2 * t * t * t * t + b;
        }
        return -c / 2 * ((t -= 2) * t * t * t - 2) + b;
    },

    // *** quint
    QUINT_EASEIN: function(t, b, c, d) {
        return c * (t /= d) * t * t * t * t + b;
    },

    QUINT_EASEOUT: function(t, b, c, d) {
        return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
    },

    QUINT_EASEINOUT: function(t, b, c, d) {
        if ((t /= d / 2) < 1) {
            return c / 2 * t * t * t * t * t + b;
        }
        return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
    },

    // *** sin
    SIN_EASEIN: function(t, b, c, d) {
        return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
    },

    SIN_EASEOUT: function(t, b, c, d) {
        return c * Math.sin(t / d * (Math.PI / 2)) + b;
    },

    SIN_EASEINOUT: function(t, b, c, d) {
        return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
    },

    // *** circ
    CIRC_EASEIN: function(t, b, c, d) {
        return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
    },

    CIRC_EASEOUT: function(t, b, c, d) {
        return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
    },

    CIRC_EASEINOUT: function(t, b, c, d) {
        if ((t /= d / 2) < 1) {
            return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
        }
        return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
    },

    // *** elastic
    ELASTIC_EASEIN: function(t, b, c, d, a, p) {
        if (t === 0) {
            return b;
        }
        if ((t /= d) === 1) {
            return b + c;
        }

        if (!p) {
            p = d * 0.3;
        }

        var s;
        if (!a || a < Math.abs(c)) {
            a = c;
            s = p / 4;
        } else {
            s = p / (2 * Math.PI) * Math.asin(c / a);
        }
        return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
    },

    ELASTIC_EASEOUT: function(t, b, c, d, a, p) {
        if (t === 0) {
            return b;
        }
        if ((t /= d) === 1) {
            return b + c;
        }
        if (!p) {
            p = d * 0.3;
        }
        var s;
        if (!a || a < Math.abs(c)) {
            a = c;
            s = p / 4;
        } else {
            s = p / (2 * Math.PI) * Math.asin(c / a);
        }
        return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b);
    },

    ELASTIC_EASEINOUT: function(t, b, c, d, a, p) {
        if (t === 0) {
            return b;
        }
        if ((t /= d / 2) === 2) {
            return b + c;
        }
        if (!p) {
            p = d * (0.3 * 1.5);
        }
        var s;
        if (!a || a < Math.abs(c)) {
            a = c;
            s = p / 4;
        } else {
            s = p / (2 * Math.PI) * Math.asin(c / a);
        }
        if (t < 1) {
            return -0.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
        }
        return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * 0.5 + c + b;
    },

    // *** bounce
    BOUNCE_EASEOUT: function(t, b, c, d) {
        if ((t /= d) < (1 / 2.75)) {
            return c * (7.5625 * t * t) + b;
        } else if (t < (2 / 2.75)) {
            return c * (7.5625 * (t -= (1.5 / 2.75)) * t + 0.75) + b;
        } else if (t < (2.5 / 2.75)) {
            return c * (7.5625 * (t -= (2.25 / 2.75)) * t + 0.9375) + b;
        } else {
            return c * (7.5625 * (t -= (2.625 / 2.75)) * t + 0.984375) + b;
        }
    },

    BOUNCE_EASEIN: function(t, b, c, d) {
        return c - enchant.Easing.BOUNCE_EASEOUT(d - t, 0, c, d) + b;
    },

    BOUNCE_EASEINOUT: function(t, b, c, d) {
        if (t < d / 2) {
            return enchant.Easing.BOUNCE_EASEIN(t * 2, 0, c, d) * 0.5 + b;
        } else {
            return enchant.Easing.BOUNCE_EASEOUT(t * 2 - d, 0, c, d) * 0.5 + c * 0.5 + b;
        }

    },

    // *** back
    BACK_EASEIN: function(t, b, c, d, s) {
        if (s === undefined) {
            s = 1.70158;
        }
        return c * (t /= d) * t * ((s + 1) * t - s) + b;
    },

    BACK_EASEOUT: function(t, b, c, d, s) {
        if (s === undefined) {
            s = 1.70158;
        }
        return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
    },

    BACK_EASEINOUT: function(t, b, c, d, s) {
        if (s === undefined) {
            s = 1.70158;
        }
        if ((t /= d / 2) < 1) {
            return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;
        }
        return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;
    },

    // *** expo
    EXPO_EASEIN: function(t, b, c, d) {
        return (t === 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;
    },

    EXPO_EASEOUT: function(t, b, c, d) {
        return (t === d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;
    },

    EXPO_EASEINOUT: function(t, b, c, d) {
        if (t === 0) {
            return b;
        }
        if (t === d) {
            return b + c;
        }
        if ((t /= d / 2) < 1) {
            return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
        }
        return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
    }
};
