X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fspring.cc;h=f4123b9891527abc9c8633c7abe3f48a1c77fd6f;hb=9e781b7dc83b60a543ce218aa1a5f139f74c760f;hp=60bc0aec77ca736084ed1afd18430b6a4bc0d9ea;hpb=55ac733b69643a6bc6a83b706c65cb56efd388ef;p=lilypond.git

diff --git a/lily/spring.cc b/lily/spring.cc
index 60bc0aec77..f4123b9891 100644
--- a/lily/spring.cc
+++ b/lily/spring.cc
@@ -1,7 +1,7 @@
 /*
   This file is part of LilyPond, the GNU music typesetter.
 
-  Copyright (C) 2007--2011 Joe Neeman <joeneeman@gmail.com>
+  Copyright (C) 2007--2014 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
@@ -17,6 +17,23 @@
   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 ()
@@ -45,34 +62,36 @@ Spring::Spring (Real dist, Real min_dist)
 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_)
-    blocking_force_ = (min_distance_ - distance_) / inverse_stretch_strength_;
-  else
+    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_;
-
-  // If the spring is fixed, it's not clear what the natural value
-  // of blocking_force_ would be (because it always blocks).
-  // -infinity_f works fine for now.
-  // If inverse_stretch_strength > 0, the spring is not fixed (because it can stretch).
-  if (isnan (blocking_force_) || blocking_force_ == infinity_f)
-    blocking_force_ = (inverse_stretch_strength_ > 0) ? 0.0 : -infinity_f;
-
-  if (blocking_force_ >= 0)
-    inverse_compress_strength_ = 0;
+  else
+    blocking_force_ = 0.0;
 }
 
 /* scale a spring, but in a way that doesn't violate min_distance */
 void
-Spring::operator*= (Real r)
+Spring::operator *= (Real r)
 {
   distance_ = max (min_distance_, distance_ * r);
   inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
-  inverse_stretch_strength_ *= 0.8;
+  inverse_stretch_strength_ *= r;
   update_blocking_force ();
 }
 
 bool
-Spring::operator> (Spring const &other) const
+Spring::operator > (Spring const &other) const
 {
   return blocking_force_ > other.blocking_force_;
 }
@@ -95,9 +114,9 @@ merge_springs (vector<Spring> const &springs)
       min_distance = max (springs[i].min_distance (), min_distance);
     }
 
-  avg_stretch /= springs.size ();
-  avg_compress /= springs.size ();
-  avg_distance /= springs.size ();
+  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);
@@ -200,7 +219,7 @@ Spring::length (Real f) const
   Real force = max (f, blocking_force_);
   Real inv_k = force < 0.0 ? inverse_compress_strength_ : inverse_stretch_strength_;
 
-  if (force == infinity_f)
+  if (isinf (force))
     {
       programming_error ("cruelty to springs");
       force = 0.0;