}   // end of ParticleSystemManager Render()

        public void Render(Camera camera, BaseEmitter.Use usage)
        {
            for (int i = 0; i < emitterList.Count; i++)
            {
                BaseEmitter emitter = emitterList[i];
                if ((emitter != null) && emitter.HasUsage(usage))
                {
                    emitter.Render(camera);
                }
            }
        }   // end of ParticleSystemManager Render()
 /// <summary>
 /// True if the input usage matches any of this emitter's usages.
 /// </summary>
 /// <param name="usage"></param>
 /// <returns></returns>
 public bool HasUsage(BaseEmitter.Use usage)
 {
     return((this.usage & usage) != 0);
 }