code: function(scene, camera) {
          var renderer = this.renderer;
          if (renderer.getWidth() !== this.width || renderer.getHeight() !== this.height) {
              this.resize(renderer.width, renderer.height);
          }
  
          this._frameBuffer.attach(this._texture);
          this._frameBuffer.bind(renderer);
          this._idOffset = this.lookupOffset;
          this._setMaterial(scene);
          renderer.render(scene, camera);
          this._restoreMaterial();
          this._frameBuffer.unbind(renderer);
      }
docs: Update the picking framebuffer
  @param {number} ratio