Allows glissandi to span multiple lines. (issue4564042)

[mtsolo]

Reviewers: ,

Message:
Hey all,

A colleague of mine is working on a piece where he needs glissandi to
span multiple lines.  I made this change and it seems to work.  Lemme
know if you think it may break something else.  I'll run regtests today
or tomorrow.

To test this patch, do:


\relative c''' { \override Staff . Glissando #'breakable = ##t
<< { s2 a2 \glissando \break s1 \break s1 \break s1 \pageBreak \break s2
c,2 } \\
{ c1 \glissando \break s1 \break s1 \break s1 \pageBreak \break e,1 } >>
}


Cheers,
MS

Description:
Allows line spanners to span multiple lines.

Please review this at http://codereview.appspot.com/4564042/

Affected files:
  M lily/line-spanner.cc


Index: lily/line-spanner.cc
diff --git a/lily/line-spanner.cc b/lily/line-spanner.cc
index  
0235243628b0dc1a74a9cab08c1d462b14a3bb42..9ef93b099fcd3b58c818f90a74029b3026c1352c  
100644
--- a/lily/line-spanner.cc
+++ b/lily/line-spanner.cc
@@ -125,48 +125,16 @@ Line_spanner::calc_bound_info (SCM smob, Direction  
dir)
       Grob *common_y = me->common_refpoint (me->get_bound (dir), Y_AXIS);
       if (me->get_bound (dir)->break_status_dir ())
        {
-         Spanner *next_sp = me->broken_neighbor (dir);
-         Item *next_bound = next_sp->get_bound (dir);
-
-         if (next_bound->break_status_dir ())
-           {
-	      programming_error ("no note heads for the line spanner on neighbor  
line?"
-                                " Confused.");
-             me->suicide ();
-             return SCM_EOL;
-           }
-
-         Spanner *next_bound_parent = parent_spanner (next_bound);
-         Interval next_ext = next_bound->extent (next_bound_parent, Y_AXIS);
-
-         /*
-           We want to know what would be the y-position of the next
-           bound (relative to my y-parent) if it belonged to the
-           same system as this bound.  We rely on the fact that the
-           y-parent of the next bound is a spanner (probably the
-           VerticalAxisGroup of a staff) that extends over the break.
-         */
-         Spanner *next_bound_parent_on_this_line =
-           next_bound_parent->broken_neighbor (other_dir (dir));
-
-         if (next_bound_parent_on_this_line)
-           {
-	      Grob *common = me->common_refpoint (next_bound_parent_on_this_line,  
Y_AXIS);
-	      Real bound_offset =  
next_bound_parent_on_this_line->relative_coordinate (common, Y_AXIS);
-	      y = next_ext.center () + bound_offset - me->relative_coordinate  
(common, Y_AXIS);
-           }
-         else
-           {
-             /*
-               We fall back to assuming that the distance between
-               staves doesn't change over line breaks.
-             */
-	      programming_error ("next-bound's parent doesn't extend to this  
line");
-             Grob *next_system = next_bound->get_system ();
-             Grob *this_system = me->get_system ();
-	      y = next_ext.center () + next_bound_parent->relative_coordinate  
(next_system, Y_AXIS)
-               - me->relative_coordinate (this_system, Y_AXIS);
-           }
+          Grob *orig = me->original ();
+          if (!orig)
+            {
+              programming_error ("Cannot find a good Y refpoint for a line  
spanner.");
+              me->suicide ();
+              return SCM_EOL;
+            }
+          Spanner *orig_s = dynamic_cast<Spanner *> (orig);
+          y = orig_s->get_bound (dir)->extent (common_y, Y_AXIS).center ();
+	  details = scm_acons (ly_symbol2scm ("common-Y"), common_y->self_scm (),  
details);
        }
       else
        {