Elastic.java

package it.sephiroth.android.library.easing;

public class Elastic implements Easing {

    @Override
    public double easeIn(double time, double start, double end, double duration) {
        return easeIn(time, start, end, duration, start + end, duration);
    }

    public double easeIn(double t, double b, double c, double d, double a, double p) {
        double s;
        if (t == 0) return b;
        if ((t /= d) == 1) return b + c;
        if (!(p > 0)) p = d * .3;
        if (!(a > 0) || 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;
    }

    @Override
    public double easeOut(double time, double start, double end, double duration) {
        return easeOut(time, start, end, duration, start + end, duration);
    }

    public double easeOut(double t, double b, double c, double d, double a, double p) {
        double s;
        if (t == 0) return b;
        if ((t /= d) == 1) return b + c;
        if (!(p > 0)) p = d * .3;
        if (!(a > 0) || 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);
    }

    @Override
    public double easeInOut(double t, double b, double c, double d) {
        return easeInOut(t, b, c, d, b + c, d);
    }

    public double easeInOut(double t, double b, double c, double d, double a, double p) {
        double s;

        if (t == 0) return b;
        if ((t /= d / 2) == 2) return b + c;
        if (!(p > 0)) p = d * (.3 * 1.5);
        if (!(a > 0) || a < Math.abs(c)) {
            a = c;
            s = p / 4;
        } else
            s = p / (2 * Math.PI) * Math.asin(c / a);
        if (t < 1)
            return -.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) * .5 + c + b;
    }
}