public void playScene(int sceneNumber) {
   Scene scene = scenes.get(sceneNumber);
   if (scene != null) {
     scene.setupScene();
     processScene(scene);
   }
 }
 public void nextScene() {
   if (currentSceneIndex < scenes.size() - 1) {
     currentSceneIndex++;
     Scene scene = scenes.get(currentSceneIndex);
     scene.setupScene();
     processScene(scene);
   } else {
     // do it accurately!
     // may be I should add loopback mode?
     // after the last scene there should be the first?
   }
 }
  public void previousScene() {

    if (currentSceneIndex > 0) {
      currentSceneIndex--;
      Scene scene = scenes.get(currentSceneIndex);
      scene.setupScene();
      processScene(scene);
    } else {
      // we try to think what to do
      // some kind of exception or something?
      // how would it be in the javascript?
    }
  }