X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fspring.cc;h=d1640e72b9790fb2d96991a743cfebef63f62f81;hb=90e4d7057f3857da049dfda3d130017d4719bd6b;hp=8b137891791fe96927ad78e64b0aad7bded08bdc;hpb=ce521e79fd7669b45c8c1132e4b5693a03b5d90a;p=lilypond.git

diff --git a/lily/spring.cc b/lily/spring.cc
index 8b13789179..d1640e72b9 100644
--- a/lily/spring.cc
+++ b/lily/spring.cc
@@ -1 +1,232 @@
+/*
+  This file is part of LilyPond, the GNU music typesetter.
+
+  Copyright (C) 2007--2015 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/>.
+*/
+
+/*
+  Springs help chains of objects, such as the notes in a line of music,
+  distribute themselves evenly.
+  Each spring decides the length from the reference point of one object
+  along the line to the reference point of the next, based on a force
+  applied to the entire chain (see Spring::length() for details):
+     length = distance_ + flexibility * force
+
+  distance_  is the ideal separation between reference points
+  inverse_stretch_strength_ is the flexibility when the force is stretching
+  inverse_compress_strength_ is the flexibility when the force is compressing
+  min_distance_ sets a lower limit on length
+
+  Typically, the force applied to a list of objects ranges from about
+  -1 to about 1, though there are no set limits.
+*/
+
+#include "spring.hh"
+
+Spring::Spring ()
+{
+  distance_ = 1.0;
+  min_distance_ = 1.0;
+  inverse_stretch_strength_ = 1.0;
+  inverse_compress_strength_ = 1.0;
+
+  update_blocking_force ();
+}
+
+Spring::Spring (Real dist, Real min_dist)
+{
+  distance_ = 1.0;
+  min_distance_ = 1.0;
+  inverse_stretch_strength_ = 1.0;
+  inverse_compress_strength_ = 1.0;
+
+  set_distance (dist);
+  set_min_distance (min_dist);
+  set_default_strength ();
+  update_blocking_force ();
+}
+
+void
+Spring::update_blocking_force ()
+{
+  // blocking_force_ is the value of force
+  //   below which length(force) is constant, and
+  //   above which length(force) varies according to inverse_*_strength.
+  // Simple_spacer::compress_line() depends on the condition above.
+  // We assume inverse_*_strength are non-negative.
+  if (min_distance_ > distance_)
+    if (inverse_stretch_strength_ > 0.0)
+      blocking_force_ = (min_distance_ - distance_) / inverse_stretch_strength_;
+    else
+      // Conceptually, this should be +inf, but 0.0 meets the requirements
+      //  of Simple_spacer and creates fewer cases of 0.0*inf to handle.
+      blocking_force_ = 0.0;
+  else if (inverse_compress_strength_ > 0.0)
+    blocking_force_ = (min_distance_ - distance_) / inverse_compress_strength_;
+  else
+    blocking_force_ = 0.0;
+}
+
+/* scale a spring, but in a way that doesn't violate min_distance */
+void
+Spring::operator *= (Real r)
+{
+  distance_ = max (min_distance_, distance_ * r);
+  inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
+  inverse_stretch_strength_ *= r;
+  update_blocking_force ();
+}
+
+bool
+Spring::operator > (Spring const &other) const
+{
+  return blocking_force_ > other.blocking_force_;
+}
+
+/* merge springs, basically by averaging them, but leave a little headroom
+   above the largest minimum distance so that things don't get too cramped */
+Spring
+merge_springs (vector<Spring> const &springs)
+{
+  Real avg_distance = 0;
+  Real min_distance = 0;
+  Real avg_stretch = 0;
+  Real avg_compress = 0;
+
+  for (vsize i = 0; i < springs.size (); i++)
+    {
+      avg_distance += springs[i].distance ();
+      avg_stretch += springs[i].inverse_stretch_strength ();
+      avg_compress += 1 / springs[i].inverse_compress_strength ();
+      min_distance = max (springs[i].min_distance (), min_distance);
+    }
+
+  avg_stretch /= Real (springs.size ());
+  avg_compress /= Real (springs.size ());
+  avg_distance /= Real (springs.size ());
+  avg_distance = max (min_distance + 0.3, avg_distance);
+
+  Spring ret = Spring (avg_distance, min_distance);
+  ret.set_inverse_stretch_strength (avg_stretch);
+  ret.set_inverse_compress_strength (1 / avg_compress);
+
+  return ret;
+}
+
+void
+Spring::set_distance (Real d)
+{
+  if (d < 0 || isinf (d) || isnan (d))
+    programming_error ("insane spring distance requested, ignoring it");
+  else
+    {
+      distance_ = d;
+      update_blocking_force ();
+    }
+}
+
+void
+Spring::set_min_distance (Real d)
+{
+  if (d < 0 || isinf (d) || isnan (d))
+    programming_error ("insane spring min_distance requested, ignoring it");
+  else
+    {
+      min_distance_ = d;
+      update_blocking_force ();
+    }
+}
+
+void
+Spring::ensure_min_distance (Real d)
+{
+  set_min_distance (max (d, min_distance_));
+}
+
+void
+Spring::set_inverse_stretch_strength (Real f)
+{
+  if (isinf (f) || isnan (f) || f < 0)
+    programming_error ("insane spring constant");
+  else
+    inverse_stretch_strength_ = f;
+
+  update_blocking_force ();
+}
+
+void
+Spring::set_inverse_compress_strength (Real f)
+{
+  if (isinf (f) || isnan (f) || f < 0)
+    programming_error ("insane spring constant");
+  else
+    inverse_compress_strength_ = f;
+
+  update_blocking_force ();
+}
+
+void
+Spring::set_blocking_force (Real f)
+{
+  if (isinf (f) || isnan (f))
+    {
+      programming_error ("insane blocking force");
+      return;
+    }
+
+  blocking_force_ = -infinity_f;
+  min_distance_ = length (f);
+  update_blocking_force ();
+}
+
+void
+Spring::set_default_strength ()
+{
+  set_default_stretch_strength ();
+  set_default_compress_strength ();
+}
+
+void
+Spring::set_default_compress_strength ()
+{
+  inverse_compress_strength_ = (distance_ >= min_distance_) ? distance_ - min_distance_ : 0;
+  update_blocking_force ();
+}
+
+void
+Spring::set_default_stretch_strength ()
+{
+  inverse_stretch_strength_ = distance_;
+}
+
+Real
+Spring::length (Real f) const
+{
+  Real force = max (f, blocking_force_);
+  Real inv_k = force < 0.0 ? inverse_compress_strength_ : inverse_stretch_strength_;
+
+  if (isinf (force))
+    {
+      programming_error ("cruelty to springs");
+      force = 0.0;
+    }
+
+  // There is a corner case here: if min_distance_ is larger than
+  // distance_ but the spring is fixed, then inv_k will be zero
+  // and we need to make sure that we return min_distance_.
+  return max (min_distance_, distance_ + force * inv_k);
+}