+/* transformation nodes */
+struct erb_node *erb_node(void);
+void erb_free_node(struct erb_node *n);
+int erb_node_addchild(struct erb_node *n, struct erb_node *c);
+int erb_node_rmchild(struct erb_node *n, struct erb_node *c);
+int erb_node_addsurf(struct erb_node *n, struct erb_surf *s);
+int erb_node_rmsurf(struct erb_node *n, struct erb_surf *s);
+
+void erb_node_setxform(struct erb_node *n, float *mat);
+void erb_node_mulxform(struct erb_node *n, float *mat);
+void erb_node_translate(struct erb_node *n, float x, float y, float z);
+/* TODO ... more ... */
+
+/* surfaces */
+struct erb_surf *erb_surface(int datasz);
+void erb_free_surface(struct erb_surf *surf);
+struct erb_surf *erb_surf_sphere(float rad);
+struct erb_surf *erb_surf_box(float xsz, float ysz, float zsz);
+
+/* utility functions */
+void erb_xform_ray(struct erb_ray *ray, float *mat);
+