/**
 * @(#) $RCSfile: Attractor4DPull.as,v $ $Revision: 1.2 $ $Date: 2003/03/17 22:53:05 $
 *
 * Copyright 2003 Orgdot AS. All Rights Reserved.
 * http://dev.swfit.com
 *
 * 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 2
 * 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

/**
 * Compute the pull from an attractor on this particle.
 *
 * @author      Olaf Havnes
 * @version     $Revision: 1.2 $ $Date: 2003/03/17 22:53:05 $
 * @since       SWFIT1.0
 */

dx = _parent.ax - px;
dy = _parent.ay - py;
dz = _parent.az - pz;
dq = _parent.aq - pq;

// Eliminate the 4th dimension
dq = 0;

a_len_sq = dx * dx + dy * dy + dz * dz + dq * dq;
//a_len = (a_len + a_len_sq / a_len) / 2;
//a_f = _parent.pull / (a_len * a_len_sq);
a_f = _parent.pull / a_len_sq;
/**
 * The force is F = Constant / a_len_sq along the vector (dx, dy, dz, dq) / a_len
 */

vx += a_f * dx;
vy += a_f * dy;
vz += a_f * dz;
vq += a_f * dq;

px += vx;
py += vy;
pz += vz;
pq += vq;