+
+void
+Spanner::derived_mark () const
+{
+ Direction d = LEFT;
+ do
+ if (spanned_drul_[d])
+ scm_gc_mark (spanned_drul_[d]->self_scm ());
+ while (flip (&d) != LEFT)
+ ;
+
+ for (vsize i = broken_intos_.size (); i--;)
+ scm_gc_mark (broken_intos_[i]->self_scm ());
+}
+
+/*
+ Set left or right bound to IT.
+
+ Warning: caller should ensure that subsequent calls put in ITems
+ that are left-to-right ordered.
+*/
+void
+add_bound_item (Spanner *sp, Grob *it)
+{
+ if (!sp->get_bound (LEFT))
+ sp->set_bound (LEFT, it);
+ else
+ sp->set_bound (RIGHT, it);
+}
+
+MAKE_SCHEME_CALLBACK (Spanner, set_spacing_rods, 1);
+SCM
+Spanner::set_spacing_rods (SCM smob)
+{
+ Grob *me = unsmob_grob (smob);
+ SCM num_length = me->get_property ("minimum-length");
+ if (scm_is_number (num_length))
+ {
+ Rod r;
+ Spanner *sp = dynamic_cast<Spanner *> (me);
+ System *root = get_root_system (me);
+ Drul_array<Item*> bounds (sp->get_bound (LEFT),
+ sp->get_bound (RIGHT));
+ if (!bounds[LEFT] || !bounds[RIGHT])
+ return SCM_UNSPECIFIED;
+
+ vector<Item*> cols (root->broken_col_range (bounds[LEFT]->get_column (),
+ bounds[RIGHT]->get_column ()));
+
+ if (cols.size ())
+ {
+ Rod r ;
+ r.item_drul_[LEFT] = sp->get_bound (LEFT);
+ r.item_drul_[RIGHT] = cols[0]->find_prebroken_piece (LEFT);
+ r.distance_ = robust_scm2double (num_length, 0);
+ r.add_to_cols ();
+
+ r.item_drul_[LEFT] = cols.back ()->find_prebroken_piece (RIGHT);
+ r.item_drul_[RIGHT] = sp->get_bound (RIGHT);
+ r.add_to_cols ();
+ }
+
+ r.distance_ = robust_scm2double (num_length, 0);
+ r.item_drul_[LEFT] = sp->get_bound (LEFT);
+ r.item_drul_[RIGHT] = sp->get_bound (RIGHT);
+ r.add_to_cols ();
+ }
+
+ return SCM_UNSPECIFIED;
+}
+
+/*
+ Return I such that SP == SP->ORIGINAL ()->BROKEN_INTOS_[I].
+*/
+int
+broken_spanner_index (Spanner const *sp)
+{
+ Spanner *parent = dynamic_cast<Spanner *> (sp->original ());
+ /* ugh: casting */
+ return find (parent->broken_intos_, (Spanner*) sp) - parent->broken_intos_.begin ();
+}
+
+Spanner *
+unsmob_spanner (SCM s)
+{
+ return dynamic_cast<Spanner *> (unsmob_grob (s));
+}
+
+MAKE_SCHEME_CALLBACK (Spanner, bounds_width, 1);
+SCM
+Spanner::bounds_width (SCM grob)
+{
+ Spanner *me = unsmob_spanner (grob);
+
+
+ Grob *common = me->get_bound (LEFT)->common_refpoint (me->get_bound (RIGHT), X_AXIS);
+
+ Interval w (me->get_bound (LEFT)->relative_coordinate (common, X_AXIS),
+ me->get_bound (RIGHT)->relative_coordinate (common, X_AXIS));
+
+ w -= me->relative_coordinate (common, X_AXIS);
+
+ return ly_interval2scm (w);
+}
+
+ADD_INTERFACE (Spanner,
+ "Some objects are horizontally spanned between objects. For"
+ " example, slurs, beams, ties, etc. These grobs form a subtype"
+ " called @code{Spanner}. All spanners have two span points"
+ " (these must be @code{Item} objects), one on the left and one"
+ " on the right. The left bound is also the X@tie{}reference"
+ " point of the spanner.",
+
+ /* properties */
+ "minimum-length "
+ "to-barline "
+ );
+