/*
- 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--2008 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"
{
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);
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 */
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
programming_error ("insane spring distance requested, ignoring it");
else
{
- min_distance_ = min (min_distance_, d);
distance_ = d;
update_blocking_force ();
}
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)
{
programming_error ("insane spring constant");
else
inverse_stretch_strength_ = f;
+
+ update_blocking_force ();
}
void
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
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);
}
+