line_count related patches in a single commit for review

lily/rest-collision.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 1997--2012 Han-Wen Nienhuys <hanwen@xs4all.nl>
 
   LilyPond is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
 
@@ skipping 232 matching lines @@
                   else
                     programming_error ("Note_column without first_head()");
                 }
               else
                 notedim.unite (notes[i]->extent (common, Y_AXIS));
             }
 
           Real y = dir * max (0.0,
                               -dir * restdim[-dir] + dir * notedim[dir] + minimum_dist);
 
-          int stafflines = Staff_symbol_referencer::line_count (me);
-          if (!stafflines)
-            {
-              programming_error ("no staff line count");
-              stafflines = 5;
-            }
-
           // move discretely by half spaces.
           int discrete_y = dir * int (ceil (y / (0.5 * dir * staff_space)));
 
+          Interval staff_span = Staff_symbol_referencer::staff_span (rest);
+          staff_span.widen (1);
           // move by whole spaces inside the staff.
-          if (fabs (Staff_symbol_referencer::get_position (rest)
-                    + discrete_y) < stafflines + 1)
+          if (staff_span.contains
+              (Staff_symbol_referencer::get_position (rest) + discrete_y))
             {
               discrete_y = dir * int (ceil (dir * discrete_y / 2.0) * 2.0);
             }
 
           Rest::translate (rest, discrete_y);
           if (rcount[dir]++)
             rest->warning (_ ("too many colliding rests"));
         }
     }
   return SCM_BOOL_T;
 }
 
 ADD_INTERFACE (Rest_collision,
                "Move ordinary rests (not multi-measure nor pitched rests)"
                " to avoid conflicts.",
 
                /* properties */
                "minimum-distance "
                "positioning-done "
                "elements "
               );