Link.java

/*
 * Copyright (C) 2013-2015 F(X)yz, 
 * Sean Phillips, Jason Pollastrini and Jose Pereda
 * All rights reserved.
 *
 * This program 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.
 *
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.fxyz.shapes.complex.cloth;

import java.util.logging.Logger;
import org.fxyz.geometry.Point3D;
import org.fxyz.utils.Constraint;

/**
 *
 * @author Jason Pollastrini aka jdub1581
 */
public class Link implements Constraint {
    private static final Logger log = Logger.getLogger(Link.class.getName());

    private final double distance, stiffness, damping = 0.75;
    private final WeightedPoint p1, p2;

    public Link(WeightedPoint p1, WeightedPoint p2, double distance, double stiffness) {
        this.p1 = p1;
        this.p2 = p2;
        this.distance = distance;
        this.stiffness = stiffness;
    }

    /* Option 2
        // Pseudo-code to satisfy (C2)
        delta = x2-x1;
        deltalength = sqrt(delta*delta);
        diff = (deltalength-restlength)
              /(deltalength*(invmass1+invmass2));
        x1 -= invmass1*delta*diff;
        x2 += invmass2*delta*diff;
    */
    
    @Override
    public void solve() {
        
        //calculate the distance between the two PointMasss
        Point3D diff = new Point3D(
                p1.getPosition().x - p2.getPosition().x,
                p1.getPosition().y - p2.getPosition().y,
                p1.getPosition().z - p2.getPosition().z
        );

        double d = diff.magnitude();
                
        double difference =(distance - d) / d;        
        
        double im1 = 1 / p1.getMass();
        double im2 = 1 / p2.getMass();
        double scalarP1 = (im1 / (im1 + im2)) * stiffness;
        double scalarP2 = stiffness - scalarP1;

        synchronized (this) {
            p1.position.x += ((float)(diff.x * scalarP1 * difference));
            p1.position.y += ((float)(diff.y * scalarP1 * difference));
            p1.position.z += ((float)(diff.z * scalarP1 * difference));

            p2.position.x -= ((float)(diff.x * scalarP2 * difference));
            p2.position.y -= ((float)(diff.y * scalarP2 * difference));
            p2.position.z -= ((float)(diff.z * scalarP2 * difference));
        }
            
    }

    public WeightedPoint getAnchorPoint() {
        return p1;
    }

    public WeightedPoint getAttachedPoint() {
        return p2;
    }

    @Override
    public String toString() {
        return "PointLink{" + "distance=" + distance + ", stiffness=" + stiffness + ", p1=" + p1 + ", p2=" + p2 + '}';
    }

}