docs: function WebGLRenderGroup(gl, transparent)
  {
      this.gl = gl;
      this.root = null;
  
      this.backgroundColor = undefined;
      this.transparent = transparent === undefined ? true : transparent;
  
      this.batchs = [];
      this.toRemove = [];
      //console.log(this.transparent);
      this.filterManager = new WebGLFilterManager(this.transparent);
  }