public static Tween sineStep(Tween... delegates) {
        if (delegates.length == 1) {
            return new Curve(delegates[0], SINE);
        }
        return new Curve(sequence(delegates), SINE);
    }
Creates a tween that uses a sine function to smooth step the time value
for the specified delegate tween or tweens.  These 'curved' wrappers
can be used to smooth the interpolation of another tween.

@param delegates the desired sequence of tweens
@return a new instance
jme3-core/src/main/java/com/jme3/anim/tween/Tweens.java