+ virtual Vector get_node() const;
+ virtual bool is_visible() const { return true; }
+
+ Msp::GL::Matrix get_matrix() const;
+ virtual void setup_render(Msp::GL::Renderer &, const Msp::GL::Tag &) const;
+ virtual void finish_render(Msp::GL::Renderer &, const Msp::GL::Tag &) const;
+private:
+ void link_changed(unsigned, Track *);