_getSceneDef() {
    return {
      key: 'scene',
      facade: Scene3DFacade,
      lights: this.lights,
      objects: this.objects,
      fog: this.fog,
      background: this.background,
      environment: this.environment,
      onClick: this.onBackgroundClick ? this._onBgClick : null
    }
  }
Build a normalized definition for the scene facade
@protected