X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fnote-collision.cc;h=e84e5263c63a57160ce55f577232db2e40a40e83;hb=5e08569186d16ee6f01ea4495fe3a1510eb3cee7;hp=a3f18ab0026be756ee22c60280ea201afd0bd428;hpb=31568c504806f35aac420a394c9eab07abd9faa7;p=lilypond.git

diff --git a/lily/note-collision.cc b/lily/note-collision.cc
index a3f18ab002..e84e5263c6 100644
--- a/lily/note-collision.cc
+++ b/lily/note-collision.cc
@@ -48,7 +48,8 @@ check_meshing_chords (Grob *me,
   if (ups[0] > dps.back () + 1)
     return;
 
-  // FIXME: what's this?
+  /* Merge heads if the notes lie the same line, or if the "stem-up-note" is
+     above the "stem-down-note". */
   bool merge_possible = (ups[0] >= dps[0]) && (ups.back () >= dps.back ());
 
   /* Do not merge notes typeset in different style. */
@@ -304,7 +305,9 @@ Note_collision_interface::calc_positioning_done (SCM smob)
       if (cg[d].size ())
 	{
 	  Grob *h = cg[d][0];
-	  wid = Note_column::first_head (h)->extent (h, X_AXIS).length ();
+	  Grob *fh = Note_column::first_head (h);
+	  if (fh)
+	    wid = fh->extent (h, X_AXIS).length ();
 	}
     }
   while (flip (&d) != UP);
@@ -354,7 +357,14 @@ Note_collision_interface::get_clash_groups (Grob *me)
     {
       Grob *se = elements[i];
       if (Note_column::has_interface (se))
-	clash_groups[Note_column::dir (se)].push_back (se);
+	{
+	  if (!Note_column::dir (se))
+	    {
+	      se->programming_error ("note-column has no direction");
+	    }
+	  else
+	    clash_groups[Note_column::dir (se)].push_back (se);
+	}
     }
 
   Direction d = UP;