Back.java

package it.sephiroth.android.library.easing;

public class Back implements Easing {

    @Override
    public double easeOut(double time, double start, double end, double duration) {
        return easeOut(time, start, end, duration, 0);
    }

    @Override
    public double easeIn(double time, double start, double end, double duration) {
        return easeIn(time, start, end, duration, 0);
    }

    @Override
    public double easeInOut(double time, double start, double end, double duration) {
        return easeInOut(time, start, end, duration, 0.9);
    }

    public double easeIn(double t, double b, double c, double d, double s) {
        if (s == 0) s = 1.70158;
        return c * (t /= d) * t * ((s + 1) * t - s) + b;
    }

    public double easeOut(double t, double b, double c, double d, double s) {
        if (s == 0) s = 1.70158;
        return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
    }

    public double easeInOut(double t, double b, double c, double d, double s) {
        if (s == 0) 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;
    }
}