X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fspring.cc;h=f57695bfd732ec50f821465a570a088547eaf9d8;hb=794dcbdb52faf4292036cd1b0270a956cf4316a3;hp=1f250546db354d31f41a7cfb344a011281af7524;hpb=157d98c1870868bf59c1691577444e3c3d533bc4;p=lilypond.git

diff --git a/lily/spring.cc b/lily/spring.cc
index 1f250546db..f57695bfd7 100644
--- a/lily/spring.cc
+++ b/lily/spring.cc
@@ -3,7 +3,7 @@
 
   source file of the GNU LilyPond music typesetter
 
-  (c) 2007 Joe Neeman <joeneeman@gmail.com>
+  (c) 2007--2009 Joe Neeman <joeneeman@gmail.com>
 */
 
 #include "spring.hh"
@@ -32,10 +32,18 @@ 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. -infinity_f works fine for now.
+  if (isnan (blocking_force_) || blocking_force_ == infinity_f)
+    blocking_force_ = -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 +51,9 @@ 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
@@ -90,7 +99,6 @@ 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 ();
     }
@@ -104,11 +112,16 @@ 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)
 {
@@ -116,6 +129,8 @@ Spring::set_inverse_stretch_strength (Real f)
     programming_error ("insane spring constant");
   else
     inverse_stretch_strength_ = f;
+
+  update_blocking_force ();
 }
 
 void
@@ -147,8 +162,9 @@ Spring::set_blocking_force (Real f)
 void
 Spring::set_default_strength ()
 {
-  inverse_compress_strength_ = distance_ - min_distance_;
-  inverse_stretch_strength_ = distance_ - min_distance_;
+  inverse_compress_strength_ = (distance_ >= min_distance_) ? distance_ - min_distance_ : 0;
+  inverse_stretch_strength_ = distance_;
+  update_blocking_force ();
 }
 
 Real
@@ -157,11 +173,15 @@ 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))
+  if (force == infinity_f)
     {
       programming_error ("cruelty to springs");
       force = 0.0;
     }
 
-  return distance_ + force * inv_k;
+  // 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);
 }
+