code: function (attachment, target) {
          // TODO depth extension check ?
          this._textures[attachment] = null;
          if (this._boundRenderer) {
              var cache = this._cache;
              cache.use(this._boundRenderer.__uid__);
              this._doDetach(this._boundRenderer.gl, attachment, target);
          }
      }
docs: Detach a texture
  @param  {number} [attachment=gl.COLOR_ATTACHMENT0]
  @param  {number} [target=gl.TEXTURE_2D]