X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fspring.cc;h=60bc0aec77ca736084ed1afd18430b6a4bc0d9ea;hb=e3a15ec3c1951dd16f6ee71fbd79870d9e2fb3a0;hp=679ccfa29db3f00d2f792785a950e40be85f0b6a;hpb=b80683cc94b0c22bbe3fccb94a9b2e23787fd10b;p=lilypond.git

diff --git a/lily/spring.cc b/lily/spring.cc
index 679ccfa29d..60bc0aec77 100644
--- a/lily/spring.cc
+++ b/lily/spring.cc
@@ -1,9 +1,20 @@
 /*
-  spring.cc -- declare Spring
+  This file is part of LilyPond, the GNU music typesetter.
 
-  source file of the GNU LilyPond music typesetter
+  Copyright (C) 2007--2011 Joe Neeman <joeneeman@gmail.com>
 
-  (c) 2007 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 "spring.hh"
@@ -22,6 +33,8 @@ 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);
@@ -32,10 +45,20 @@ Spring::Spring (Real dist, Real min_dist)
 void
 Spring::update_blocking_force ()
 {
-  if (distance_ == min_distance_)
-    blocking_force_ = 0.0;
+  if (min_distance_ > distance_)
+    blocking_force_ = (min_distance_ - distance_) / inverse_stretch_strength_;
   else
     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;
 }
 
 /* scale a spring, but in a way that doesn't violate min_distance */
@@ -43,8 +66,9 @@ void
 Spring::operator*= (Real r)
 {
   distance_ = max (min_distance_, distance_ * r);
-  inverse_compress_strength_ = distance_ - min_distance_;
+  inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
   inverse_stretch_strength_ *= 0.8;
+  update_blocking_force ();
 }
 
 bool
@@ -61,20 +85,24 @@ 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 /= springs.size ();
+  avg_compress /= springs.size ();
   avg_distance /= 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;
 }
@@ -86,7 +114,6 @@ Spring::set_distance (Real d)
     programming_error ("insane spring distance requested, ignoring it");
   else
     {
-      min_distance_ = min (min_distance_, d);
       distance_ = d;
       update_blocking_force ();
     }
@@ -100,11 +127,16 @@ Spring::set_min_distance (Real d)
   else
     {
       min_distance_ = d;
-      distance_ = max (distance_, min_distance_);
       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)
 {
@@ -112,6 +144,8 @@ Spring::set_inverse_stretch_strength (Real f)
     programming_error ("insane spring constant");
   else
     inverse_stretch_strength_ = f;
+
+  update_blocking_force ();
 }
 
 void
@@ -143,8 +177,21 @@ Spring::set_blocking_force (Real f)
 void
 Spring::set_default_strength ()
 {
-  inverse_compress_strength_ = distance_ - min_distance_;
-  inverse_stretch_strength_ = distance_ - min_distance_;
+  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
@@ -152,5 +199,16 @@ Spring::length (Real f) const
 {
   Real force = max (f, blocking_force_);
   Real inv_k = force < 0.0 ? inverse_compress_strength_ : inverse_stretch_strength_;
-  return distance_ + force * inv_k;
+
+  if (force == infinity_f)
+    {
+      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);
 }
+