text: /* Return the closest base object intersecting the given ray, and
     the curvilinear abscissa t of the intersection point.
     Return NULL if no intersection.
     Return t = 0.0 if the viewpoint (origin of the ray) is inside an
     object. */
  
  struct object * intersect_ray(struct point * p,
                                struct vector * v,
                                struct object * obj,
                                int initial,
                                /*out*/ flt * t);
  