[lilypond.git] / lily / page-layout-problem.cc

/*
  This file is part of LilyPond, the GNU music typesetter.

  Copyright (C) 2009--2010 Joe Neeman <joeneeman@gmail.com>

  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.

  LilyPond is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "page-layout-problem.hh"

#include "align-interface.hh"
#include "axis-group-interface.hh"
#include "hara-kiri-group-spanner.hh"
#include "international.hh"
#include "item.hh"
#include "output-def.hh"
#include "paper-book.hh"
#include "paper-column.hh"
#include "pointer-group-interface.hh"
#include "prob.hh"
#include "skyline-pair.hh"
#include "system.hh"

Page_layout_problem::Page_layout_problem (Paper_book *pb, SCM page_scm, SCM systems)
  : bottom_skyline_ (DOWN)
{
  Prob *page = unsmob_prob (page_scm);
  header_height_ = 0;
  footer_height_ = 0;
  header_padding_ = 0;
  footer_padding_ = 0;
  page_height_ = 100;

  if (page)
    {
      Stencil *head = unsmob_stencil (page->get_property ("head-stencil"));
      Stencil *foot = unsmob_stencil (page->get_property ("foot-stencil"));

      header_height_ = head ? head->extent (Y_AXIS).length () : 0;
      footer_height_ = foot ? foot->extent (Y_AXIS).length () : 0;
      page_height_ = robust_scm2double (page->get_property ("paper-height"), 100);
    }

  // Initially, bottom_skyline_ represents the top of the page. Make
  // it solid, so that the top of the first system will be forced
  // below the top of the printable area.
  bottom_skyline_.set_minimum_height (-header_height_);

  SCM system_system_spacing = SCM_EOL;
  SCM score_system_spacing = SCM_EOL;
  SCM markup_system_spacing = SCM_EOL;
  SCM score_markup_spacing = SCM_EOL;
  SCM markup_markup_spacing = SCM_EOL;

  // top_system_spacing controls the spring from the top of the printable
  // area to the first staff. It allows the user to control the offset of
  // the first staff (as opposed to the top of the first system) from the
  // top of the page. Similarly for last_bottom_spacing.
  SCM top_system_spacing = SCM_EOL;
  SCM last_bottom_spacing = SCM_EOL;
  if (pb && pb->paper_)
    {
      Output_def *paper = pb->paper_;
      system_system_spacing = paper->c_variable ("system-system-spacing");
      score_system_spacing = paper->c_variable ("score-system-spacing");
      markup_system_spacing = paper->c_variable ("markup-system-spacing");
      score_markup_spacing = paper->c_variable ("score-markup-spacing");
      markup_markup_spacing = paper->c_variable ("markup-markup-spacing");
      last_bottom_spacing = paper->c_variable ("last-bottom-spacing");
      top_system_spacing = paper->c_variable ("top-system-spacing");
      if (scm_is_pair (systems) && unsmob_prob (scm_car (systems)))
        top_system_spacing = paper->c_variable ("top-markup-spacing");

      // Note: the page height here does _not_ reserve space for headers and
      // footers. This is because we want to anchor the top-system-spacing
      // spring at the _top_ of the header.
      page_height_ -= robust_scm2double (paper->c_variable ("top-margin"), 0)
        + robust_scm2double (paper->c_variable ("bottom-margin"), 0);

      read_spacing_spec (top_system_spacing, &header_padding_, ly_symbol2scm ("padding"));
      read_spacing_spec (last_bottom_spacing, &footer_padding_, ly_symbol2scm ("padding"));
    }
  bool last_system_was_title = false;


  for (SCM s = systems; scm_is_pair (s); s = scm_cdr (s))
    {
      bool first = (s == systems);

      if (Grob *g = unsmob_grob (scm_car (s)))
        {
          System *sys = dynamic_cast<System*> (g);
          if (!sys)
            {
              programming_error ("got a grob for vertical spacing that wasn't a System");
              continue;
            }

          SCM spec = system_system_spacing;
          if (first)
            spec = top_system_spacing;
          else if (last_system_was_title)
            spec = markup_system_spacing;
          else if (0 == Paper_column::get_rank (sys->get_bound (LEFT)))
            spec = score_system_spacing;

          Spring spring (0, 0);
          Real padding = 0.0;
          alter_spring_from_spacing_spec (spec, &spring);
          read_spacing_spec (spec, &padding, ly_symbol2scm ("padding"));

          append_system (sys, spring, padding);
          last_system_was_title = false;
        }
      else if (Prob *p = unsmob_prob (scm_car (s)))
        {
          SCM spec = first ? top_system_spacing
            : (last_system_was_title ? markup_markup_spacing : score_markup_spacing);
          Spring spring (0, 0);
          Real padding = 0.0;
          alter_spring_from_spacing_spec (spec, &spring);
          read_spacing_spec (spec, &padding, ly_symbol2scm ("padding"));

          append_prob (p, spring, padding);
          last_system_was_title = true;
        }
      else
        programming_error ("got a system that was neither a Grob nor a Prob");
    }

  Spring last_spring (0, 0);
  Real last_padding = 0;
  alter_spring_from_spacing_spec (last_bottom_spacing, &last_spring);
  read_spacing_spec (last_bottom_spacing, &last_padding, ly_symbol2scm ("padding"));
  last_spring.ensure_min_distance (last_padding - bottom_skyline_.max_height () + footer_height_);
  springs_.push_back (last_spring);

  if (elements_.size ())
    {
      Real bottom_padding = 0;

      // TODO: junk bottom-space now that we have last-bottom-spacing?
      // bottom-space has the flexibility that one can do it per-system.
      // NOTE: bottom-space is misnamed since it is not stretchable space.
      if (Prob *p = elements_.back ().prob)
        bottom_padding = robust_scm2double (p->get_property ("bottom-space"), 0);
      else if (elements_.back ().staves.size ())
        {
          SCM details = get_details (elements_.back ());
          bottom_padding = robust_scm2double (ly_assoc_get (ly_symbol2scm ("bottom-space"),
                                                            details,
                                                            SCM_BOOL_F),
                                              0.0);
        }
      page_height_ -= bottom_padding;
    }
}

void
Page_layout_problem::set_header_height (Real height)
{
  header_height_ = height;
}

void
Page_layout_problem::set_footer_height (Real height)
{
  footer_height_ = height;
}

void
Page_layout_problem::append_system (System *sys, Spring const& spring, Real padding)
{
  Grob *align = sys->get_vertical_alignment ();
  if (!align)
    return;

  align->set_property ("positioning-done", SCM_BOOL_T);

  extract_grob_set (align, "elements", all_elts);
  vector<Grob*> elts = filter_dead_elements (all_elts);
  vector<Real> minimum_offsets = Align_interface::get_minimum_translations_without_min_dist (align, elts, Y_AXIS);

  Skyline up_skyline (UP);
  Skyline down_skyline (DOWN);
  build_system_skyline (elts, minimum_offsets, &up_skyline, &down_skyline);

  Real minimum_distance = up_skyline.distance (bottom_skyline_) + padding;

  Spring spring_copy = spring;
  spring_copy.ensure_min_distance (minimum_distance);
  springs_.push_back (spring_copy);

  bottom_skyline_ = down_skyline;
  elements_.push_back (Element (elts, minimum_offsets));

  // Add the springs for the VerticalAxisGroups in this system.

  // If the user has specified the offsets of the individual staves, fix the
  // springs at the given distances. Otherwise, use stretchable springs.
  SCM details = get_details (elements_.back ());
  SCM manual_dists = ly_assoc_get (ly_symbol2scm ("alignment-distances"), details, SCM_EOL);
  vsize last_spaceable_staff = 0;
  bool found_spaceable_staff = false;
  for (vsize i = 0; i < elts.size (); ++i)
    {
      if (is_spaceable (elts[i]))
        {
          // We don't add a spring for the first staff, since
          // we are only adding springs _between_ staves here.
          if (!found_spaceable_staff)
            {
              found_spaceable_staff = true;
              last_spaceable_staff = i;
              continue;
            }

          Spring spring (0.5, 0.0);
          SCM spec = elts[last_spaceable_staff]->get_property ("staff-staff-spacing");
          alter_spring_from_spacing_spec (spec, &spring);

          springs_.push_back (spring);
          Real min_distance = (found_spaceable_staff ? minimum_offsets[last_spaceable_staff] : 0) - minimum_offsets[i];
          springs_.back ().ensure_min_distance (min_distance);

          if (scm_is_pair (manual_dists))
            {
              if (scm_is_number (scm_car (manual_dists)))
                {
                  Real dy = scm_to_double (scm_car (manual_dists));

                  springs_.back ().set_distance (dy);
                  springs_.back ().set_min_distance (dy);
                  springs_.back ().set_inverse_stretch_strength (0);
                }
              manual_dists = scm_cdr (manual_dists);
            }
          last_spaceable_staff = i;
        }
    }

  // Corner case: there was only one staff, and it wasn't spaceable.
  // Mark it spaceable, because we do not allow non-spaceable staves
  // to be at the top or bottom of a system.
  if (!found_spaceable_staff && elts.size ())
    mark_as_spaceable (elts[0]);
}

void
Page_layout_problem::append_prob (Prob *prob, Spring const& spring, Real padding)
{
  Skyline_pair *sky = Skyline_pair::unsmob (prob->get_property ("vertical-skylines"));
  Real minimum_distance = 0;
  bool tight_spacing = to_boolean (prob->get_property ("tight-spacing"));

  if (sky)
    {
      minimum_distance = (*sky)[UP].distance (bottom_skyline_);
      bottom_skyline_ = (*sky)[DOWN];
    }
  else if (Stencil *sten = unsmob_stencil (prob->get_property ("stencil")))
    {
      Interval iv = sten->extent (Y_AXIS);
      minimum_distance = iv[UP] - bottom_skyline_.max_height ();

      bottom_skyline_.clear ();
      bottom_skyline_.set_minimum_height (iv[DOWN]);
    }

  Spring spring_copy = spring;
  if (tight_spacing)
    {
      spring_copy.set_min_distance (minimum_distance);
      spring_copy.set_inverse_stretch_strength (0.0);
      spring_copy.set_distance (0.0);
    }
  else
    spring_copy.ensure_min_distance (minimum_distance + padding);

  springs_.push_back (spring_copy);
  elements_.push_back (Element (prob));
}

void
Page_layout_problem::solve_rod_spring_problem (bool ragged)
{
  Simple_spacer spacer;

  for (vsize i = 0; i < springs_.size (); ++i)
    spacer.add_spring (springs_[i]);

  spacer.solve (page_height_, ragged);
  solution_ = spacer.spring_positions ();

  if (!spacer.fits ())
    warning (_f ("couldn't fit music on page: overflow is %f",
                 spacer.configuration_length(spacer.force()) - page_height_));
}

// The solution_ vector stores the position of every live VerticalAxisGroup
// and every title. From that information,
// 1) within each system, stretch the staves so they land at the right position
// 2) find the offset of each system (relative to the printable area of the page).
// TODO: this function is getting too long, maybe split it up?
SCM
Page_layout_problem::find_system_offsets ()
{
  SCM system_offsets = SCM_EOL;
  SCM *tail = &system_offsets;

  // spring_idx 0 is the top of the page. Interesting values start from 1.
  vsize spring_idx = 1;
  vector<Grob*> loose_lines;
  vector<Real> loose_line_min_distances;
  Grob *last_spaceable_line = 0;
  Real last_spaceable_line_translation = 0;
  Interval last_title_extent;
  for (vsize i = 0; i < elements_.size (); ++i)
    {
      if (elements_[i].prob)
        {
          *tail = scm_cons (scm_from_double (solution_[spring_idx]), SCM_EOL);
          tail = SCM_CDRLOC (*tail);
          Interval prob_extent = unsmob_stencil (elements_[i].prob->get_property ("stencil"))->extent (Y_AXIS);

          // Lay out any non-spaceable lines between this line and
          // the last one.
          if (loose_lines.size ())
            {
              Interval loose_extent = loose_lines.back ()->extent (loose_lines.back (), Y_AXIS);
              Real min_distance = -loose_extent[DOWN] + prob_extent[UP]; // TODO: include padding/minimum-distance

              loose_line_min_distances.push_back (min_distance);
              loose_lines.push_back (0);

              distribute_loose_lines (loose_lines, loose_line_min_distances,
                                      last_spaceable_line_translation, -solution_[spring_idx]);
              loose_lines.clear ();
              loose_line_min_distances.clear ();
            }

          last_spaceable_line = 0;
          last_spaceable_line_translation = -solution_[spring_idx];
          last_title_extent = prob_extent;
          spring_idx++;
        }
      else
        {
          // Getting this signs right here is a little tricky. The configuration
          // we return has zero at the top of the page and positive numbers further
          // down, as does the solution_ vector.  Within a staff, however, positive
          // numbers are up.
          // TODO: perhaps change the way the page 'configuration variable works so
          // that it is consistent with the usual up/down sign conventions in
          // Lilypond. Then this would be less confusing.

          // These two positions are relative to the page (with positive numbers being
          // down).
          Real first_staff_position = solution_[spring_idx];
          Real first_staff_min_translation = elements_[i].min_offsets.size () ? elements_[i].min_offsets[0] : 0;
          Real system_position = first_staff_position + first_staff_min_translation;

          // Position the staves within this system.
          Real translation = 0;
          vector<Real> const& min_offsets = elements_[i].min_offsets;
          bool found_spaceable_staff = false;
          for (vsize staff_idx = 0; staff_idx < elements_[i].staves.size (); ++staff_idx)
            {
              Grob *staff = elements_[i].staves[staff_idx];
              staff->set_property ("system-Y-offset", scm_from_double (-system_position));

              if (is_spaceable (staff))
                {
                  // this is relative to the system: negative numbers are down.
                  translation = system_position - solution_[spring_idx];
                  spring_idx++;

                  // Lay out any non-spaceable lines between this line and
                  // the last one.
                  if (loose_lines.size ())
                    {
                      loose_line_min_distances.push_back (min_offsets[staff_idx-1] - min_offsets[staff_idx]);
                      loose_lines.push_back (staff);

                      distribute_loose_lines (loose_lines, loose_line_min_distances,
                                              last_spaceable_line_translation, translation - system_position);
                      loose_lines.clear ();
                      loose_line_min_distances.clear ();
                    }
                  last_spaceable_line = staff;
                  // Negative is down but the translation is relative to the whole page.
                  last_spaceable_line_translation = -system_position + translation;

                  staff->translate_axis (translation, Y_AXIS);
                  found_spaceable_staff = true;
                }
              else
                {
                  if (loose_lines.empty ())
                    loose_lines.push_back (last_spaceable_line);

                  if (staff_idx)
                    loose_line_min_distances.push_back (min_offsets[staff_idx-1] - min_offsets[staff_idx]);
                  else
                    {
                      Real min_dist = 0;
                      if (loose_lines.back ())
                        min_dist = Axis_group_interface::minimum_distance (loose_lines.back (),
                                                                           staff,
                                                                           Y_AXIS);
                      else if (!last_title_extent.is_empty ())
                        { // distance to the preceding title
                          // TODO: add options for controlling the space between a loose line
                          // and a title/markup preceding it.
                          min_dist = staff->extent (staff, Y_AXIS)[UP] - last_title_extent[DOWN];
                        }
                      else // distance to the top margin
                        min_dist = header_padding_ + header_height_ + staff->extent (staff, Y_AXIS)[UP];

                      loose_line_min_distances.push_back (min_dist);
                    }
                  loose_lines.push_back (staff);
                }
            }

          // Corner case: even if a system has no live staves, it still takes up
          // one spring (a system with one live staff also takes up one spring),
          // which we need to increment past.
          if (!found_spaceable_staff)
            spring_idx++;

          *tail = scm_cons (scm_from_double (system_position), SCM_EOL);
          tail = SCM_CDRLOC (*tail);
        }
    }

  if (loose_lines.size ())
    {
      Grob *last = loose_lines.back ();
      Interval last_ext = last->extent (last, Y_AXIS);
      loose_line_min_distances.push_back (-last_ext[DOWN] + footer_height_ + footer_padding_);
      loose_lines.push_back (0);

      distribute_loose_lines (loose_lines, loose_line_min_distances,
                              last_spaceable_line_translation, -page_height_);

    }

  assert (spring_idx == solution_.size () - 1);
  return system_offsets;
}

// Given two lines that are already spaced (the first and last
// elements of loose_lines), distribute some unspaced lines between
// them.
// first_translation and last_translation are relative to the page.
void
Page_layout_problem::distribute_loose_lines (vector<Grob*> const &loose_lines,
                                             vector<Real> const &min_distances,
                                             Real first_translation, Real last_translation)
{
  Simple_spacer spacer;
  for (vsize i = 0; i + 1 < loose_lines.size (); ++i)
    {
      SCM spec = get_spacing_spec (loose_lines[i], loose_lines[i+1], false, 0, INT_MAX);
      Spring spring (1.0, 0.0);
      alter_spring_from_spacing_spec (spec, &spring);
      spring.ensure_min_distance (min_distances[i]);
      spacer.add_spring (spring);
    }

  // Remember: offsets are decreasing, since we're going from UP to DOWN!
  spacer.solve (first_translation - last_translation, false);

  vector<Real> solution = spacer.spring_positions ();
  for (vsize i = 1; i + 1 < solution.size (); ++i)
    {
      Real system_offset = scm_to_double (loose_lines[i]->get_property ("system-Y-offset"));
      loose_lines[i]->translate_axis (first_translation - solution[i] - system_offset, Y_AXIS);
    }
}

SCM
Page_layout_problem::solution (bool ragged)
{
  solve_rod_spring_problem (ragged);
  return find_system_offsets ();
}

// Build upper and lower skylines for a system. We don't yet know the positions
// of the staves within the system, so we make the skyline as conservative as
// possible. That is, for the upper skyline, we pretend that all of the staves
// in the system are packed together close to the top system; for the lower
// skyline, we pretend that all of the staves are packed together close to
// the bottom system.
//
// The upper skyline is relative to the top staff; the lower skyline is relative to
// the bottom staff.
void
Page_layout_problem::build_system_skyline (vector<Grob*> const& staves,
                                           vector<Real> const& minimum_translations,
                                           Skyline *up,
                                           Skyline *down)
{
  if (minimum_translations.empty ())
    return;

  assert (staves.size () == minimum_translations.size ());
  Real first_translation = minimum_translations[0];
  Real last_spaceable_dy = 0;
  Real first_spaceable_dy = 0;
  bool found_spaceable_staff = false;

  for (vsize i = 0; i < staves.size (); ++i)
    {
      Real dy = minimum_translations[i] - first_translation;
      Grob *g = staves[i];
      Skyline_pair *sky = Skyline_pair::unsmob (g->get_property ("vertical-skylines"));
      if (sky)
        {
          up->raise (-dy);
          up->merge ((*sky)[UP]);
          up->raise (dy);

          down->raise (-dy);
          down->merge ((*sky)[DOWN]);
          down->raise (dy);
        }
      if (is_spaceable (staves[i]))
        {
          if (!found_spaceable_staff)
            {
              found_spaceable_staff = true;
              first_spaceable_dy = dy;
            }
          last_spaceable_dy = dy;
        }
    }

  // Leave the up skyline at a position relative
  // to the top spaceable staff.
  up->raise (-first_spaceable_dy);

  // Leave the down skyline at a position
  // relative to the bottom spaceable staff.
  down->raise (-last_spaceable_dy);
}

Interval
Page_layout_problem::prob_extent (Prob *p)
{
  Stencil *sten = unsmob_stencil (p->get_property ("stencil"));
  return sten ? sten->extent (Y_AXIS) : Interval (0, 0);
}

Interval
Page_layout_problem::first_staff_extent (Element const& e)
{
  if (e.prob)
    return prob_extent (e.prob);
  else if (e.staves.size ())
    return e.staves[0]->extent (e.staves[0], Y_AXIS);

  return Interval (0, 0);
}

Interval
Page_layout_problem::last_staff_extent (Element const& e)
{
  if (e.prob)
    return prob_extent (e.prob);
  else if (e.staves.size ())
    return e.staves.back ()->extent (e.staves.back (), Y_AXIS);

  return Interval (0, 0);
}

SCM
Page_layout_problem::get_details (Element const& elt)
{
  if (elt.staves.empty ())
    return SCM_EOL;

  return get_details (elt.staves.back ()->get_system ());
}

SCM
Page_layout_problem::get_details (Grob *g)
{
  Grob *left_bound = dynamic_cast<Spanner*> (g)->get_bound (LEFT);
  return left_bound->get_property ("line-break-system-details");
}

bool
Page_layout_problem::is_spaceable (Grob *g)
{
  return !scm_is_number (g->get_property ("staff-affinity"));
}

void
Page_layout_problem::mark_as_spaceable (Grob *g)
{
  g->set_property ("staff-affinity", SCM_BOOL_F);
}

bool
Page_layout_problem::read_spacing_spec (SCM spec, Real* dest, SCM sym)
{
  SCM pair = scm_sloppy_assq (sym, spec);
  if (scm_is_pair (pair) && scm_is_number (scm_cdr (pair)))
    {
      *dest = scm_to_double (scm_cdr (pair));
      return true;
    }
  return false;
}

// If there is a forced, fixed spacing between BEFORE and AFTER, return it.
// Otherwise, return -infinity_f.
// If after is spaceable, it is the (spaceable_index + 1)th spaceable grob in
// its alignment.
Real
Page_layout_problem::get_fixed_spacing (Grob *before, Grob *after, int spaceable_index, bool pure, int start, int end)
{
  SCM spec = Page_layout_problem::get_spacing_spec (before, after, pure, start, end);
  Real ret = -infinity_f;
  Real stretchability = 0;
  if (Page_layout_problem::read_spacing_spec (spec, &stretchability, ly_symbol2scm ("stretchability"))
      && stretchability == 0)
    Page_layout_problem::read_spacing_spec (spec, &ret, ly_symbol2scm ("space"));

  // If we're pure, then paper-columns have not had their systems set,
  // and so elts[i]->get_system () is unreliable.
  System *sys = pure ? Grob::get_system (before) : before->get_system ();
  Grob *left_bound = sys ? sys->get_maybe_pure_bound (LEFT, pure, start, end) : 0;

  if (is_spaceable (before) && is_spaceable (after) && left_bound)
    {
      SCM details = left_bound->get_property ("line-break-system-details");
      SCM manual_dists = ly_assoc_get (ly_symbol2scm ("alignment-distances"), details, SCM_EOL);
      if (scm_is_pair (manual_dists))
        {
          SCM forced = robust_list_ref (spaceable_index - 1, manual_dists);
          if (scm_is_number (forced))
            ret = max (ret, scm_to_double (forced));
        }
    }
  return ret;
}

static SCM
add_stretchability (SCM alist, Real stretch)
{
  if (!scm_is_pair (scm_sloppy_assq (ly_symbol2scm ("stretchability"), alist)))
    return scm_acons (ly_symbol2scm ("stretchability"), scm_from_double (stretch), alist);

  return alist;
}

// We want to put a large stretch between a non-spaceable line and its
// non-affinity staff. We want to put an even larger stretch between
// a non-spaceable line and the top/bottom of the page. That way,
// a spacing-affinity UP line at the bottom of the page will still be
// placed close to its staff.
const double LARGE_STRETCH = 10e5;
const double HUGE_STRETCH = 10e7;

// Returns the spacing spec connecting BEFORE to AFTER.
SCM
Page_layout_problem::get_spacing_spec (Grob *before, Grob *after, bool pure, int start, int end)
{
  // If there are no spacing wishes, return a very flexible spring.
  // This will occur, for example, if there are lyrics at the bottom of
  // the page, in which case we don't want the spring from the lyrics to
  // the bottom of the page to have much effect.
  if (!before || !after)
    return add_stretchability (SCM_EOL, HUGE_STRETCH);

  if (is_spaceable (before))
    {
      if (is_spaceable (after))
        return before->get_maybe_pure_property ("staff-staff-spacing", pure, start, end);
      else
        {
          Direction affinity = to_dir (after->get_maybe_pure_property ("staff-affinity", pure, start, end));
          return (affinity == DOWN)
            ? add_stretchability (after->get_maybe_pure_property ("nonstaff-unrelatedstaff-spacing", pure, start, end),
                                  LARGE_STRETCH)
            : after->get_maybe_pure_property ("nonstaff-relatedstaff-spacing", pure, start, end);
        }
    }
  else
    {
      if (is_spaceable (after))
        {
          Direction affinity = to_dir (before->get_maybe_pure_property ("staff-affinity", pure, start, end));
          return (affinity == UP)
            ? add_stretchability (before->get_maybe_pure_property ("nonstaff-unrelatedstaff-spacing", pure, start, end),
                                  LARGE_STRETCH)
            : before->get_maybe_pure_property ("nonstaff-relatedstaff-spacing", pure, start, end);
        }
      else
        {
          Direction before_affinity = to_dir (before->get_maybe_pure_property ("staff-affinity", pure, start, end));
          Direction after_affinity = to_dir (after->get_maybe_pure_property ("staff-affinity", pure, start, end));
          if (after_affinity > before_affinity)
            {
              warning (_ ("staff-affinities should only decrease"));
              after_affinity = before_affinity;
            }
          if (before_affinity != UP)
            return before->get_maybe_pure_property ("nonstaff-nonstaff-spacing", pure, start, end);
          else if (after_affinity != DOWN)
            return before->get_maybe_pure_property ("nonstaff-nonstaff-spacing", pure, start, end);
          return add_stretchability (before->get_maybe_pure_property ("nonstaff-unrelatedstaff-spacing", pure, start, end),
                                     LARGE_STRETCH);
        }
    }

  assert (0);
  return SCM_BOOL_F;
}

void
Page_layout_problem::alter_spring_from_spacing_spec (SCM spec, Spring* spring)
{
  Real space;
  Real stretch;
  Real min_dist;
  if (read_spacing_spec (spec, &space, ly_symbol2scm ("space")))
    spring->set_distance (space);
  if (read_spacing_spec (spec, &min_dist, ly_symbol2scm ("minimum-distance")))
    spring->set_min_distance (min_dist);
  spring->set_default_strength ();

  if (read_spacing_spec (spec, &stretch, ly_symbol2scm ("stretchability")))
    {
      spring->set_inverse_stretch_strength (stretch);
      spring->set_inverse_compress_strength (stretch);
    }
}

vector<Grob*>
Page_layout_problem::filter_dead_elements (vector<Grob*> const& input)
{
  vector<Grob*> output;
  for (vsize i = 0; i < input.size (); ++i)
    {
      if (Hara_kiri_group_spanner::has_interface (input[i]))
        Hara_kiri_group_spanner::consider_suicide (input[i]);

      if (input[i]->is_live ())
        output.push_back (input[i]);
    }

  return output;
}