Gets vertical skylines from grob stencils

lily/staff-performer.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 1997--2012 Jan Nieuwenhuizen <janneke@gnu.org>
 
   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 227 matching lines @@
 
   instrument_string_ = ly_scm2string (minstr);
 
   return instrument_string_;
 }
 
 int
 Staff_performer::get_channel (string instrument)
 {
   SCM channel_mapping = get_property ("midiChannelMapping");
-  map<string, int>& channel_map
+  map<string, int> &channel_map
     = (channel_mapping != ly_symbol2scm ("instrument"))
       ? channel_map_
       : static_channel_map_;
 
   if (channel_mapping == ly_symbol2scm ("staff")
       && channel_ >= 0)
     return channel_;
 
   map<string, int>::const_iterator i = channel_map.find (instrument);
   if (i != channel_map.end ())
@@ skipping 61 matching lines @@
               dynamic_map_[voice] = d;
               // Output volume as velocity: must disable Midi_dynamic output
               d->silent_ = true;
             }
         }
       Audio_staff *audio_staff = get_audio_staff (voice);
       audio_staff->add_audio_item (ai);
     }
 }