public function getVisiblePanels()
    {
        if ($this->visiblePanels === null) {
            $this->visiblePanels = array();

            $panels = $this->getSortedChildBlocks();
            foreach ($panels as $panel) {
                if (!$panel instanceof Sheep_Debug_Block_Panel) {
                    continue;
                }

                $this->visiblePanels[] = $panel;
            }
        }
        return $this->visiblePanels;
    }