/** Helper structure for rendering the queue contents. */
    class render_helper
    {
    public:
        friend class drawing_queue;

        /**
         * Constructor.
         *
         * @param priority           Draw order for this element. Higher values will be drawn later.
         * @param texture            The texture to render.
         * @param src_rect           Source rect. If nullptr entire texture will be rendered.
         * @param dst_rect           Destination rect. If nullptr texture will be stretched to fill the current
         *                           rendering target.
         * @param clp_rect           Clipping rect. If nullptr no render clipping will be applied.
         */
        render_helper(const int priority,
                const texture& texture,
                const SDL_Rect* src_rect = nullptr,
                const SDL_Rect* dst_rect = nullptr,
                const SDL_Rect* clp_rect = nullptr)
            : priority_(priority)
            , textures_(1, texture)
            , src_rect_(src_rect)
            , dst_rect_(dst_rect)
            , clp_rect_(clp_rect)
        {
        }

        render_helper(const int priority,
                const std::vector<texture>& textures,
                const SDL_Rect* src_rect = nullptr,
                const SDL_Rect* dst_rect = nullptr,
                const SDL_Rect* clp_rect = nullptr)
            : priority_(priority)
            , textures_(textures)
            , src_rect_(src_rect)
            , dst_rect_(dst_rect)
            , clp_rect_(clp_rect)
        {
        }

        bool operator<(const render_helper& rhs) const
        {
            return priority_ < rhs.priority_;
        }

    private:
        const int priority_;

        std::vector<texture> textures_;

        SDL_Rect* src_rect_;

        SDL_Rect* dst_rect_;

        SDL_Rect* clp_rect_;
    };