lily/simple-spacer-scheme.cc

   1 /*
   2   simple-spacer-scheme.cc -- implement Simple_spacer
   3
   4   source file of the GNU LilyPond music typesetter
   5
   6   (c) 2005--2009 Han-Wen Nienhuys <hanwen@xs4all.nl>
   7 */
   8
   9 #include <cstdio>
  10
  11 #include "paper-column.hh"
  12 #include "spring.hh"
  13 #include "warn.hh"
  14 #include "simple-spacer.hh"
  15
  16 LY_DEFINE (ly_solve_spring_rod_problem, "ly:solve-spring-rod-problem",
  17            4, 1, 0, (SCM springs, SCM rods, SCM length, SCM ragged),
  18            "Solve a spring and rod problem for @var{count} objects, that"
  19            " are connected by @var{count}-1 @var{springs}, and an arbitrary"
  20            " number of @var{rods}.  @var{count} is implicitly given by"
  21            " @var{springs} and @var{rods}.  The @var{springs} argument has"
  22            " the format @code{(ideal, inverse_hook)} and @var{rods} is of"
  23            " the form @code{(idx1, idx2, distance)}.\n"
  24            "\n"
  25            "@var{length} is a number, @var{ragged} a boolean.\n"
  26            "\n"
  27            "The function returns a list containing the force (positive for"
  28            " stretching, negative for compressing and @code{#f} for"
  29            " non-satisfied constraints) followed by @var{spring-count}+1"
  30            " positions of the objects.")
  31 {
  32   int len = scm_ilength (springs);
  33   if (len == 0)
  34     return scm_list_2 (scm_from_double (0.0), scm_from_double (0.0));
  35
  36   SCM_ASSERT_TYPE (len >= 0, springs, SCM_ARG1, __FUNCTION__, "list of springs");
  37   SCM_ASSERT_TYPE (scm_ilength (rods)  > 0, rods, SCM_ARG1, __FUNCTION__, "list of rods");
  38   LY_ASSERT_TYPE (scm_is_number, length, 3);
  39
  40   bool is_ragged = ragged == SCM_BOOL_T;
  41   Simple_spacer spacer;
  42   for (SCM s = springs; scm_is_pair (s); s = scm_cdr (s))
  43     {
  44       Real ideal = scm_to_double (scm_caar (s));
  45       Real inv_hooke = scm_to_double (scm_cadar (s));
  46
  47       Spring sp (ideal, 0.0);
  48       sp.set_inverse_compress_strength (inv_hooke);
  49       sp.set_inverse_stretch_strength (inv_hooke);
  50
  51       spacer.add_spring (sp);
  52     }
  53
  54   for (SCM s = rods; scm_is_pair (s); s = scm_cdr (s))
  55     {
  56       SCM entry = scm_car (s);
  57       int l = scm_to_int (scm_car (entry));
  58       int r = scm_to_int (scm_cadr (entry));
  59       entry = scm_cddr (entry);
  60
  61       Real distance = scm_to_double (scm_car (entry));
  62       spacer.add_rod (l, r, distance);
  63     }
  64
  65   spacer.solve (scm_to_double (length), is_ragged);
  66
  67   vector<Real> posns = spacer.spring_positions ();
  68
  69   SCM force_return = spacer.fits () ? scm_from_double (spacer.force ()) : SCM_BOOL_F;
  70
  71   SCM retval = SCM_EOL;
  72   for (vsize i = posns.size (); i--;)
  73     retval = scm_cons (scm_from_double (posns[i]), retval);
  74
  75   retval = scm_cons (force_return, retval);
  76   return retval;
  77 }