/*
* __ .__ .__ ._____.
* _/ |_ _______ __|__| ____ | | |__\_ |__ ______
* \ __\/ _ \ \/ / |/ ___\| | | || __ \ / ___/
* | | ( <_> > <| \ \___| |_| || \_\ \\___ \
* |__| \____/__/\_ \__|\___ >____/__||___ /____ >
* \/ \/ \/ \/
*
* Copyright (c) 2006-2011 Karsten Schmidt
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* http://creativecommons.org/licenses/LGPL/2.1/
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
*/
package toxi.physics2d;
import toxi.geom.Vec2D;
/**
* Implements a spring whose maximum relaxation distance at every time step can
* be limited to achieve better (if physically incorrect) stability of the whole
* spring system.
*/
public class VerletConstrainedSpring2D extends VerletSpring2D {
/**
* Maximum relaxation distance for either end of the spring in world units
* (by default unlimited until set by user)
*/
public float limit = Float.MAX_VALUE;
/**
* @param a
* @param b
* @param len
* @param str
*/
public VerletConstrainedSpring2D(VerletParticle2D a, VerletParticle2D b,
float len, float str) {
super(a, b, len, str);
}
/**
* @param a
* @param b
* @param len
* @param str
* @param limit
*/
public VerletConstrainedSpring2D(VerletParticle2D a, VerletParticle2D b,
float len, float str, float limit) {
super(a, b, len, str);
this.limit = limit;
}
protected void update(boolean applyConstraints) {
Vec2D delta = b.sub(a);
// add minute offset to avoid div-by-zero errors
float dist = delta.magnitude() + EPS;
float normDistStrength = (dist - restLength)
/ (dist * (a.invWeight + b.invWeight)) * strength;
if (!a.isLocked && !isALocked) {
a.addSelf(delta.scale(normDistStrength * a.invWeight).limit(limit));
if (applyConstraints) {
a.applyConstraints();
}
}
if (!b.isLocked && !isBLocked) {
b.subSelf(delta.scale(normDistStrength * b.invWeight).limit(limit));
if (applyConstraints) {
b.applyConstraints();
}
}
}
}