/*
This file is part of LilyPond, the GNU music typesetter.
- Copyright (C) 2007--2010 Joe Neeman <joeneeman@gmail.com>
+ Copyright (C) 2007--2015 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
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 ()
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. -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;
+ 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_;
}
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);
blocking_force_ = -infinity_f;
min_distance_ = length (f);
- distance_ = max (distance_, min_distance_);
update_blocking_force ();
}
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;
- inverse_stretch_strength_ = distance_;
update_blocking_force ();
}
+void
+Spring::set_default_stretch_strength ()
+{
+ inverse_stretch_strength_ = distance_;
+}
+
Real
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;