package org.openpixi.pixi.physics.collision.algorithms;
import java.util.ArrayList;
import org.openpixi.pixi.physics.collision.util.Pair;
import org.openpixi.pixi.physics.force.Force;
import org.openpixi.pixi.physics.particles.Particle;
import org.openpixi.pixi.physics.solver.Solver;
public class SimpleCollision extends CollisionAlgorithm{
public SimpleCollision() {
super();
}
private void doCollision(Particle p1, Particle p2) {
//distance between the particles
double distance = Math.sqrt((p1.getX() - p2.getX()) * (p1.getX() - p2.getX()) + (p1.getY() - p2.getY()) * (p1.getY() - p2.getY()));
//finding the unit distance vector
double dnX = (p1.getX() - p2.getX()) / distance;
double dnY = (p1.getY() - p2.getY()) / distance;
//finding the minimal distance if the ball are overlapping
double minDistanceX = dnX * (p1.getRadius() + p2.getRadius() - distance);
double minDistanceY = dnY * (p1.getRadius() + p2.getRadius() - distance);
//moving the balls if they are overlapping (if not, the minimal distance is equal to zero)
p1.setX(p1.getX() + minDistanceX * p2.getMass() / (p1.getMass() + p2.getMass()));
p1.setY(p1.getY() + minDistanceY * p2.getMass() / (p1.getMass() + p2.getMass()));
p2.setX(p2.getX() - minDistanceX * p1.getMass() / (p1.getMass() + p2.getMass()));
p2.setY(p2.getY() - minDistanceY * p1.getMass() / (p1.getMass() + p2.getMass()));
//defining variables for cleaner calculation
double m21 = p2.getMass() / p1.getMass();
double x21 = p2.getX() - p1.getX();
double y21 = p2.getY() - p1.getY();
double vx21 = p2.getVx() - p1.getVx();
double vy21 = p2.getVy() - p1.getVy();
//avoiding dividing with zero
double helpCoef = 1.0e-5 * Math.abs(y21);
if(Math.abs(x21) < helpCoef) {
if(x21 < 0) {
helpCoef = - helpCoef;
}
x21 = helpCoef;
}
//doing the calculation
double angle = y21 / x21;
double dvx2 = -2 * (vx21 + angle * vy21) / ((1 + angle * angle) * (1 + m21)) ;
p2.setVx(p2.getVx() + dvx2);
p2.setVy(p2.getVy() + angle * dvx2);
p1.setVx(p1.getVx() - m21 * dvx2);
p1.setVy(p1.getVy() - angle * m21 * dvx2);
}
public void collide(ArrayList<Pair<Particle, Particle>> pairs, Force f, Solver s, double step) {
for(int i = 0; i < pairs.size(); i++) {
Particle p1 = (Particle) pairs.get(i).getFirst();
Particle p2 = (Particle) pairs.get(i).getSecond();
double distanceSquare = ((p1.getX() - p2.getX()) * (p1.getX() - p2.getX()) + (p1.getY() - p2.getY()) * (p1.getY() - p2.getY()));
if(distanceSquare <= ((p1.getRadius() + p2.getRadius()) * (p1.getRadius() + p2.getRadius()))) {
s.complete(p1, f, step);
s.complete(p2, f, step);
doCollision(p1, p2);
s.prepare(p1, f, step);
s.prepare(p2, f, step);
}
}
}
}