code: public void moveAndFadeInAndOut (Path path, long pathDuration, float fadePortion)
      {
          move(path);
  
          setAlpha(0.0f);
  
          _pathDuration = pathDuration;
          _fadeInDuration = _fadeOutDuration = (long)(pathDuration * fadePortion);
      }
docs: Puts this sprite on the specified path, fading it in over the specified duration at the
  beginning and fading it out at the end.
  
  @param path the path to move along
  @param pathDuration the duration of the path
  @param fadePortion the portion of time to spend fading in/out, from 0.0f (no time) to 1.0f
  (the entire time)