/*

Gravit - A gravity simulator
Copyright 2003-2005 Gerald Kaszuba

Gravit 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.

Gravit 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 Gravit; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/

#include "gravit.h"

void processFramePP(int start, int amount) {

	int i,j;
	particle_t *p1;
	particle_t *p2;
	particleDetail_t *pd1;
	particleDetail_t *pd2;

	VectorNew(dv);
	VectorNew(dv2);

	float inverseSquareDistance;
	float force;

	// apply gravity to every specified velocity
	for (i = start; i < amount; i++) {

		p1 = state.particleHistory + state.particleCount*state.frame + i;
		pd1 = state.particleDetail + i; 

		for (j = 0; j < state.particleCount; j++) {

			if (i == j) {

				continue;

			}

			p2 = state.particleHistory + state.particleCount*state.frame + j;
			pd2 = state.particleDetail + j; 

			dv[0] = p1->pos[0] - p2->pos[0];
			dv[1] = p1->pos[1] - p2->pos[1];
			dv[2] = p1->pos[2] - p2->pos[2];

			dv2[0] = pow(dv[0], 2);
			dv2[1] = pow(dv[1], 2);
			dv2[2] = pow(dv[2], 2);

			// get distance^2 between the two
			inverseSquareDistance = dv2[0] + dv2[1] + dv2[2];

			force = state.g * pd1->mass * pd2->mass / inverseSquareDistance;

			p1->vel[0] += dv[0] * force;
			p1->vel[1] += dv[1] * force;
			p1->vel[2] += dv[2] * force;

		}

	}

}