+MAKE_SCHEME_CALLBACK (Span_bar,brew_molecule,1);
+
+/*
+ Limitations/Bugs:
+
+ (1) Elements from 'me->get_grob_property ("elements")' must be
+ ordered according to their y coordinates relative to their common
+ axis group parent. Otherwise, the computation goes mad.
+
+ (TODO:
+ apply a sort algorithm that ensures this precondition.) However,
+ until now, I have seen no case where lily has not fulfilled this
+ precondition.
+
+ (2) This method depends on bar_engraver not being removed from
+ staff context. If bar_engraver is removed, the size of the staff
+ lines is evaluated as 0, which results in a solid span bar line
+ with faulty y coordinate.
+ */
+
+/*
+ This routine was originally by Juergen Reuter, but it was a on the
+ bulky side. Rewritten by Han-Wen.
+ */
+SCM
+Span_bar::brew_molecule (SCM smobbed_me)
+{
+ Grob *me = unsmob_grob (smobbed_me);
+ SCM first_elt = me->get_grob_property ("elements");
+
+ // compute common refpoint of elements
+ Grob *refp = me;
+ for (SCM elts = first_elt; gh_pair_p (elts); elts = ly_cdr (elts))
+ {
+ SCM smobbed_staff_bar = ly_car (elts);
+ Grob *staff_bar = unsmob_grob (smobbed_staff_bar);
+ refp = staff_bar->common_refpoint (refp, Y_AXIS);
+ }
+
+ Span_bar::evaluate_glyph(me);
+ SCM glyph = me->get_grob_property ("glyph");
+
+ /*
+ glyph may not be a string, when ME is killed by Hara Kiri in
+ between.
+ */
+ if (!gh_string_p (glyph))
+ return SCM_EOL;
+
+ String glyph_string = ly_scm2string (glyph);
+
+ // compose span_bar_mol
+ Molecule span_bar_mol;
+
+ Interval prev_extent;
+ for (SCM elts = first_elt; gh_pair_p (elts); elts = ly_cdr (elts))
+ {
+ SCM smobbed_staff_bar = ly_car (elts);
+ Grob *staff_bar = unsmob_grob (smobbed_staff_bar);
+ Interval ext = staff_bar->extent (refp, Y_AXIS);
+ if (ext.empty_b ())
+ continue;
+
+ if (!prev_extent.empty_b ())
+ {
+ Interval l(prev_extent [UP],
+ ext[DOWN]);
+
+ if (l.empty_b ())
+ {
+ /* there is overlap between the bar lines. We do nothign here.
+ */
+ }
+ else
+ {
+ Molecule interbar
+ = Bar_line::compound_barline (staff_bar, glyph_string, l.length());
+ interbar.translate_axis (l.center (), Y_AXIS);
+ span_bar_mol.add_molecule (interbar);
+ }
+ }
+ prev_extent = ext;
+ }
+
+ span_bar_mol.translate_axis (- me->relative_coordinate (refp, Y_AXIS), Y_AXIS);
+
+ return span_bar_mol.smobbed_copy ();
+}
+
+MAKE_SCHEME_CALLBACK (Span_bar,width_callback,2);