+MAKE_SCHEME_CALLBACK (Slur, calc_cross_staff, 1)
+SCM
+Slur::calc_cross_staff (SCM smob)
+{
+ Grob *me = unsmob_grob (smob);
+
+ extract_grob_set (me, "note-columns", cols);
+ extract_grob_set (me, "encompass-objects", extras);
+
+ for (vsize i = 0; i < cols.size (); i++)
+ {
+ if (Grob *s = Note_column::get_stem (cols[i]))
+ if (to_boolean (s->get_property ("cross-staff")))
+ return SCM_BOOL_T;
+ }
+
+ /* the separation items are dealt with in replace_breakable_encompass_objects
+ so we can ignore them here */
+ vector<Grob*> non_sep_extras;
+ for (vsize i = 0; i < extras.size (); i++)
+ if (!Separation_item::has_interface (extras[i]))
+ non_sep_extras.push_back (extras[i]);
+
+ Grob *common = common_refpoint_of_array (cols, me, Y_AXIS);
+ common = common_refpoint_of_array (non_sep_extras, common, Y_AXIS);
+
+ return scm_from_bool (common != me->get_parent (Y_AXIS));
+}