lily/spring.cc

   1 /*
   2   spring.cc -- declare Spring
   3
   4   source file of the GNU LilyPond music typesetter
   5
   6   (c) 2007 Joe Neeman <joeneeman@gmail.com>
   7 */
   8
   9 #include "spring.hh"
  10
  11 Spring::Spring ()
  12 {
  13   distance_ = 1.0;
  14   min_distance_ = 1.0;
  15   inverse_stretch_strength_ = 1.0;
  16   inverse_compress_strength_ = 1.0;
  17
  18   update_blocking_force ();
  19 }
  20
  21 Spring::Spring (Real dist, Real min_dist)
  22 {
  23   distance_ = 1.0;
  24   min_distance_ = 1.0;
  25
  26   set_distance (dist);
  27   set_min_distance (min_dist);
  28   set_default_strength ();
  29   update_blocking_force ();
  30 }
  31
  32 void
  33 Spring::update_blocking_force ()
  34 {
  35   if (distance_ == min_distance_)
  36     blocking_force_ = 0.0;
  37   else
  38     blocking_force_ = (min_distance_ - distance_) / inverse_compress_strength_;
  39 }
  40
  41 /* scale a spring, but in a way that doesn't violate min_distance */
  42 void
  43 Spring::operator*= (Real r)
  44 {
  45   distance_ = max (min_distance_, distance_ * r);
  46   inverse_compress_strength_ = distance_ - min_distance_;
  47   inverse_stretch_strength_ *= 0.8;
  48 }
  49
  50 bool
  51 Spring::operator> (Spring const &other) const
  52 {
  53   return blocking_force_ > other.blocking_force_;
  54 }
  55
  56 /* merge springs, basically by averaging them, but leave a little headroom
  57    above the largest minimum distance so that things don't get too cramped */
  58 Spring
  59 merge_springs (vector<Spring> const &springs)
  60 {
  61   Real avg_distance = 0;
  62   Real min_distance = 0;
  63   Real avg_stretch = 0;
  64
  65   for (vsize i = 0; i < springs.size (); i++)
  66     {
  67       avg_distance += springs[i].distance ();
  68       avg_stretch += springs[i].inverse_stretch_strength ();
  69       min_distance = max (springs[i].min_distance (), min_distance);
  70     }
  71
  72   avg_stretch /= springs.size ();
  73   avg_distance /= springs.size ();
  74   avg_distance = max (min_distance + 0.3, avg_distance);
  75
  76   Spring ret = Spring (avg_distance, min_distance);
  77   ret.set_inverse_stretch_strength (avg_stretch);
  78
  79   return ret;
  80 }
  81
  82 void
  83 Spring::set_distance (Real d)
  84 {
  85   if (d < 0 || isinf (d) || isnan (d))
  86     programming_error ("insane spring distance requested, ignoring it");
  87   else
  88     {
  89       min_distance_ = min (min_distance_, d);
  90       distance_ = d;
  91       update_blocking_force ();
  92     }
  93 }
  94
  95 void
  96 Spring::set_min_distance (Real d)
  97 {
  98   if (d < 0 || isinf (d) || isnan (d))
  99     programming_error ("insane spring min_distance requested, ignoring it");
 100   else
 101     {
 102       min_distance_ = d;
 103       distance_ = max (distance_, min_distance_);
 104       update_blocking_force ();
 105     }
 106 }
 107
 108 void
 109 Spring::set_inverse_stretch_strength (Real f)
 110 {
 111   if (isinf (f) || isnan (f) || f < 0)
 112     programming_error ("insane spring constant");
 113   else
 114     inverse_stretch_strength_ = f;
 115 }
 116
 117 void
 118 Spring::set_inverse_compress_strength (Real f)
 119 {
 120   if (isinf (f) || isnan (f) || f < 0)
 121     programming_error ("insane spring constant");
 122   else
 123     inverse_compress_strength_ = f;
 124
 125   update_blocking_force ();
 126 }
 127
 128 void
 129 Spring::set_blocking_force (Real f)
 130 {
 131   if (isinf (f) || isnan (f))
 132     {
 133       programming_error ("insane blocking force");
 134       return;
 135     }
 136
 137   blocking_force_ = -infinity_f;
 138   min_distance_ = length (f);
 139   distance_ = max (distance_, min_distance_);
 140   update_blocking_force ();
 141 }
 142
 143 void
 144 Spring::set_default_strength ()
 145 {
 146   inverse_compress_strength_ = distance_ - min_distance_;
 147   inverse_stretch_strength_ = distance_ - min_distance_;
 148 }
 149
 150 Real
 151 Spring::length (Real f) const
 152 {
 153   Real force = max (f, blocking_force_);
 154   Real inv_k = force < 0.0 ? inverse_compress_strength_ : inverse_stretch_strength_;
 155
 156   if (isinf (force))
 157     {
 158       programming_error ("cruelty to springs");
 159       force = 0.0;
 160     }
 161
 162   return distance_ + force * inv_k;
 163 }