-/*
- spring.cc -- implement Spring
-
- source file of the GNU LilyPond music typesetter
-
- (c) 1999--2001 Han-Wen Nienhuys <hanwen@cs.uu.nl>
-
- */
+/*
+ This file is part of LilyPond, the GNU music typesetter.
+
+ 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
+ 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"
-#include "debug.hh"
-#include "item.hh"
-#include "spaceable-grob.hh"
-#include "paper-column.hh"
Spring::Spring ()
{
- item_l_drul_[LEFT] =item_l_drul_[RIGHT] =0;
- distance_f_ =0.;
- strength_f_ =1.0;
+ distance_ = 1.0;
+ min_distance_ = 1.0;
+ inverse_stretch_strength_ = 1.0;
+ inverse_compress_strength_ = 1.0;
+
+ update_blocking_force ();
+}
+
+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);
+ set_default_strength ();
+ update_blocking_force ();
+}
+
+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_)
+ 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)
+{
+ distance_ = max (min_distance_, distance_ * r);
+ inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
+ inverse_stretch_strength_ *= r;
+ update_blocking_force ();
+}
+
+bool
+Spring::operator > (Spring const &other) const
+{
+ return blocking_force_ > other.blocking_force_;
+}
+
+/* merge springs, basically by averaging them, but leave a little headroom
+ above the largest minimum distance so that things don't get too cramped */
+Spring
+merge_springs (vector<Spring> const &springs)
+{
+ 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 /= 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;
+}
+
+void
+Spring::set_distance (Real d)
+{
+ if (d < 0 || isinf (d) || isnan (d))
+ programming_error ("insane spring distance requested, ignoring it");
+ else
+ {
+ distance_ = d;
+ update_blocking_force ();
+ }
+}
+
+void
+Spring::set_min_distance (Real d)
+{
+ if (d < 0 || isinf (d) || isnan (d))
+ programming_error ("insane spring min_distance requested, ignoring it");
+ else
+ {
+ min_distance_ = d;
+ 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)
+{
+ if (isinf (f) || isnan (f) || f < 0)
+ programming_error ("insane spring constant");
+ else
+ inverse_stretch_strength_ = f;
+
+ update_blocking_force ();
+}
+
+void
+Spring::set_inverse_compress_strength (Real f)
+{
+ if (isinf (f) || isnan (f) || f < 0)
+ programming_error ("insane spring constant");
+ else
+ inverse_compress_strength_ = f;
+
+ update_blocking_force ();
+}
+
+void
+Spring::set_blocking_force (Real f)
+{
+ if (isinf (f) || isnan (f))
+ {
+ programming_error ("insane blocking force");
+ return;
+ }
+
+ blocking_force_ = -infinity_f;
+ min_distance_ = length (f);
+ update_blocking_force ();
}
void
-Spring::add_to_cols ()
+Spring::set_default_strength ()
{
- Spaceable_grob::add_spring (item_l_drul_[LEFT]->column_l (),
- item_l_drul_[RIGHT]->column_l (),
- distance_f_, strength_f_);
+ 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 ();
+}
-Column_spring::Column_spring ()
+void
+Spring::set_default_stretch_strength ()
{
- other_l_ = 0;
- distance_f_ =0;
- strength_f_ =1.0;
+ 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 (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);
+}
projects / lilypond.git / blobdiff