code: public void moveAndFadeOut (Path path, long pathDuration, float fadePortion)
      {
          move(path);
  
          setAlpha(1.0f);
  
          _fadeStamp = 0;
          _pathDuration = pathDuration;
          _fadeOutDuration = (long)(pathDuration * fadePortion);
          _fadeDelay = _pathDuration - _fadeOutDuration;
      }
docs: Puts this sprite on the specified path and fades it out over the specified duration.
  
  @param path the path to move along
  @param pathDuration the duration of the path
  @param fadePortion the portion of time to spend fading out, from 0.0f (no time) to 1.0f
  (the entire time)