Merge branch 'master' of git://git.savannah.gnu.org/lilypond.git

[lilypond.git] / lily / spring.cc

diff --git a/lily/spring.cc b/lily/spring.cc
index fd8e0147cbd5accf74879376ad00f344c46eae5e..c576da374329bf22b196982c3276343587b56fbb 100644 (file)
--- 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--2009 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);
@@ -32,16 +45,23 @@ 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_;
+    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
-    blocking_force_ = (min_distance_ - distance_) / inverse_compress_strength_;
-
-  if (isnan (blocking_force_) || blocking_force_ == infinity_f)
-    blocking_force_ = 0;
-
-  if (blocking_force_ >= 0)
-    inverse_compress_strength_ = 0;
+    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 */
@@ -51,6 +71,7 @@ Spring::operator*= (Real r)
   distance_ = max (min_distance_, distance_ * r);
   inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
   inverse_stretch_strength_ *= 0.8;
+  update_blocking_force ();
 }
 
 bool
@@ -126,6 +147,8 @@ Spring::set_inverse_stretch_strength (Real f)
     programming_error ("insane spring constant");
   else
     inverse_stretch_strength_ = f;
+
+  update_blocking_force ();
 }
 
 void
@@ -156,8 +179,21 @@ Spring::set_blocking_force (Real f)
 
 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_;
 }
 
@@ -167,11 +203,15 @@ 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 (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);
 }
+