Gets vertical skylines from grob stencils

lily/beam.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 1997--2012 Han-Wen Nienhuys <hanwen@xs4all.nl>
   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 830 matching lines @@
   this routine should take into account the stemlength scoring
   of a possible knee/nonknee beam.
 */
 void
 Beam::consider_auto_knees (Grob *me)
 {
   SCM scm = me->get_property ("auto-knee-gap");
   if (!scm_is_number (scm))
     return;
 
-  Interval_set gaps;
-
-  gaps.set_full ();
+  vector<Interval> forbidden_intervals;
 
   extract_grob_set (me, "normal-stems", stems);
 
   Grob *common = common_refpoint_of_array (stems, me, Y_AXIS);
   Real staff_space = Staff_symbol_referencer::staff_space (me);
 
   vector<Interval> head_extents_array;
   for (vsize i = 0; i < stems.size (); i++)
     {
       Grob *stem = stems[i];
@@ skipping 13 matching lines @@
           head_extents += stem->pure_relative_y_coordinate (common, 0, INT_MAX);
 
           if (to_dir (stem->get_property_data ("direction")))
             {
               Direction stemdir = to_dir (stem->get_property ("direction"));
               head_extents[-stemdir] = -stemdir * infinity_f;
             }
         }
       head_extents_array.push_back (head_extents);
 
-      gaps.remove_interval (head_extents);
+      forbidden_intervals.push_back (head_extents);
     }
 
   Interval max_gap;
   Real max_gap_len = 0.0;
 
-  for (vsize i = gaps.allowed_regions_.size () - 1; i != VPOS; i--)
-    {
-      Interval gap = gaps.allowed_regions_[i];
+  vector<Interval> allowed_regions
+    = Interval_set::interval_union (forbidden_intervals).complement ().intervals ();
+  for (vsize i = allowed_regions.size () - 1; i != VPOS; i--)
+    {
+      Interval gap = allowed_regions[i];
 
       /*
         the outer gaps are not knees.
       */
       if (isinf (gap[LEFT]) || isinf (gap[RIGHT]))
         continue;
 
       if (gap.length () >= max_gap_len)
         {
           max_gap_len = gap.length ();
@@ skipping 448 matching lines @@
     }
 
   /* In stems with several heads, use the one closest to the beam. */
   Direction beamdir = get_grob_direction (beam);
   Real shift = min (max ( (Stem::head_positions (left)[beamdir]
                            + Stem::head_positions (right)[beamdir]) / 2.0,
                           rest_max_pos[DOWN]),
                     rest_max_pos[UP]
                    ) * ss / 2.0
                - previous;
+
+  // So that ceil below kicks in for rests that would otherwise brush
+  // up against a beam quanted to a ledger line, add a bit of space
+  // between the beam and the rest.
+  shift += (0.01 * beamdir);
+
   /* Always move by a whole number of staff spaces */
   shift = ceil (fabs (shift / ss)) * ss * sign (shift);
 
   return scm_from_double (previous + shift);
 }
 
 bool
 Beam::is_knee (Grob *me)
 {
   SCM k = me->get_property ("knee");
@@ skipping 121 matching lines @@
                "least-squares-dy "
                "neutral-direction "
                "normal-stems "
                "positions "
                "quantized-positions "
                "shorten "
                "skip-quanting "
                "stems "
                "X-positions "
               );