Magnet magnet;
int rows = 120;
int cols = 120;
field[][] fields = new field[rows][cols]; // field is a grid.
// there is a distinct force of every cell according to the 
// distance of magnet and that cell's distance
Particle[] particles = new Particle[300];
Vector3D[] currentForce = new Vector3D[300];
void setup() {

  size(500,500);
  framerate(30);
   colorMode(RGB,250);
 smooth();
  magnet = new Magnet(new Vector3D(width/2,height/2),new Vector3D(0,0));
  float size = width/rows; 
  for(int x = 0; x < rows; x++) {
    for(int y = 0; y < cols; y++) {
      float xpos = x*size;
      float ypos = y*size;
      fields[x][y] = new field(new Vector3D(xpos,ypos), new Vector3D(0,0), size);
      fields[x][y].calcForce(magnet.getLoc());
    }
  }
  for (int i = 0; i < 300; i++) {
    particles[i] = new Particle(new Vector3D(cos(i)*100.0, sin(i)*100.0),new Vector3D(5,0),1);

}
}



void draw() {
  background(250);
  int size = width/rows;
 for (int k = 0; k < 300; k++) { 
  float x = particles[k].loc.x/size;
  float y = particles[k].loc.y/size;
  int i = constrain(int(x),0,rows-1);
  int j = constrain(int(y),0,cols-1);
  // println("i: " + i);
  currentForce[k] = fields[i][j].force;
  particles[k].add_force(currentForce[k]);
  particles[k].run();
  particles[k].render();
  particles[k].changeColor();
  }
  
}

  void mouseDragged(){
   for (int k = 0; k < 300; k++) { 
  particles[k].loc.setXYZ(mouseX, mouseY,0);
  }
}