ShakeInterpolator.java

import android.animation.TimeInterpolator;

/**
 * Interpolator that produces a decaying sine wave oscillating around zero.
 */
public class ShakeInterpolator implements TimeInterpolator {
  
    private static final double AMP, FREQ = 5, DECAY = 6;

    static {
        // calculate AMP so that the max of the function is 1
        final double k = 2d * Math.PI * FREQ; // 31.41592653589793
        final double max = 1d / k * Math.atan(k / DECAY); // 0.04399306738001356
        AMP = 1d / (Math.sin(max * FREQ * Math.PI * 2d) / Math.exp(max * DECAY)); // 1.3256083323146437
    }

    @Override
    public float getInterpolation(float input) {
        // see http://www.motionscript.com/articles/bounce-and-overshoot.html [Overshoot in Detail]
        return (float)(AMP * Math.sin(input * 2d * Math.PI * FREQ) / Math.exp(input * DECAY));
        // y = 1.3256083323146437 * Math.sin(x * 2 * Math.PI * 5) / Math.exp(x * 6)
        // Wolfram: plot | 1.3256083323146437 sin(x 2 pi 5) / e^(x 6) | x = 0 to 1 | y = -1 to 1
    }
}