float[] x;
float[] y;
float[] z;
float[] xp;
float[] yp;
float[] vx;
float[] vy;
float[] vz;
int zcenter;
float angleX;
float angleY;
int num;
int fl;
color c;

void setup(){
  num = 10000;
  fl = 250;
  size(500, 500);
  x = new float[num];
  y = new float[num];
  z = new float[num];
  xp = new float[num];
  yp = new float[num];
  vx = new float[num];
  vy = new float[num];
  vz = new float[num];
}
void startSim(){
  angleX = 0;
  angleY = 0;
  zcenter = 300;
  for(int i=0; i<num; i++){
    x[i] = random(-100, 100);
    y[i] = random(-200, 200);
    z[i] = random(100, 200);
    vx[i] = random(1,3);
    vy[i] = 0;
    vz[i] = 0;
  }
}

void loop(){
  background(0,0,0);
  angleX += ((mouseY-250)*.015-angleX)*.05;
  angleY += ((mouseX-250)*.015-angleY)*.05;
  float cosangleX = cos(angleX);
  float sinangleX = sin(angleX);
  float cosangleY = cos(angleY);
  float sinangleY = sin(angleY);
  for(int i=0; i<num; i++){
    float distSQ = x[i]*x[i]+z[i]*z[i];
    float dist = sqrt(distSQ);
    float force = (y[i]+200)*5/distSQ;
    vx[i] -= force*x[i]/dist;
    vz[i] -= force*z[i]/dist;
    x[i] += vx[i];
    z[i] += vz[i];
    float ya = cosangleX*y[i]-sinangleX*z[i];
    float za = cosangleX*z[i]+sinangleX*y[i];
    float xb = cosangleY*x[i]-sinangleY*za;
    float zb = cosangleY*za+sinangleX*x[i];
    float sc = fl/(fl+zb+zcenter);
    float xp1 = xb * sc + 250;
    float yp1 = ya * sc + 250;
    stroke(255*sc, 255*sc, 255*sc);
    if(-zb-zcenter < fl){
      line(int(xp1), int(yp1), int(xp[i]), int(yp[i]));
      xp[i] = xp1;
      yp[i] = yp1;
    }
  }
}
void mousePressed(){
  startSim();
}
void keyPressed(){
  if(key==UP){
    zcenter-=5;
  }else if(key==DOWN){
    zcenter+=5;
  }
}