/*
- 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--2015 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/>.
+*/
+
+/*
+ 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"
{
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;
- else
+ // 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_)
+ 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_;
+ 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_ = distance_ - min_distance_;
- inverse_stretch_strength_ *= 0.8;
+ inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
+ 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_;
}
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_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);
ret.set_inverse_stretch_strength (avg_stretch);
+ ret.set_inverse_compress_strength (1 / avg_compress);
return ret;
}
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
blocking_force_ = -infinity_f;
min_distance_ = length (f);
- distance_ = max (distance_, min_distance_);
update_blocking_force ();
}
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_;
- return distance_ + force * inv_k;
+
+ 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);
}
+