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/*
This file is part of LilyPond, the GNU music typesetter.
Copyright (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"
Spring::Spring ()
{
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 ()
{
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. -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;
}
/* 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_ *= 0.8;
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 /= springs.size ();
avg_compress /= springs.size ();
avg_distance /= 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);
distance_ = max (distance_, min_distance_);
update_blocking_force ();
}
void
Spring::set_default_strength ()
{
inverse_compress_strength_ = (distance_ >= min_distance_) ? distance_ - min_distance_ : 0;
inverse_stretch_strength_ = distance_;
update_blocking_force ();
}
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)
{
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);
}
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