/*
 *   __               .__       .__  ._____.           
 * _/  |_  _______  __|__| ____ |  | |__\_ |__   ______
 * \   __\/  _ \  \/  /  |/ ___\|  | |  || __ \ /  ___/
 *  |  | (  <_> >    <|  \  \___|  |_|  || \_\ \\___ \ 
 *  |__|  \____/__/\_ \__|\___  >____/__||___  /____  >
 *                   \/       \/             \/     \/ 
 *
 * Copyright (c) 2006-2011 Karsten Schmidt
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * http://creativecommons.org/licenses/LGPL/2.1/
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

package toxi.math;

/**
 * Implements the sigmoid interpolation function with adjustable curve sharpness
 */
public class SigmoidInterpolation implements InterpolateStrategy {

    private float sharpness;

    private float sharpPremult;

    /**
     * Initializes the s-curve with default sharpness = 2
     */
    public SigmoidInterpolation() {
        this(2f);
    }

    /**
     *
     * @param s
     */
    public SigmoidInterpolation(float s) {
        setSharpness(s);
    }

    /**
     *
     * @return
     */
    public float getSharpness() {
        return sharpness;
    }

    @Override
    public double interpolate(double a, double b, double f) {
        f = 1.0 + Math.exp(-((f * 2 - 1) * sharpPremult));
        return a + (b - a) / f;
    }

    @Override
    public float interpolate(float a, float b, float f) {
        f = (float) (1.0 + Math.exp(-((f * 2 - 1) * sharpPremult)));
        return a + (b - a) / f;
    }

    private void setSharpness(float s) {
        sharpness = s;
        sharpPremult = 5 * s;
    }
}