int particleNum = 1000;
Particle[] p = new Particle[particleNum];

void setup(){
  size(400, 400, JAVA2D);
  smooth();
  int col;
  float s;
  for (int i = 0; i<particleNum; i++){
     if ((int)random(2) == 1){
      col = 0; 
     }else{
      col = 255;
     }
     s = random(20);
     if ((int)random(1000) == 1){
        s = 100;
        col = 100;
     }
     p[i] = new Particle(width / 2, height / 2, col, s); 
  }
}


void draw(){
    fill(0,30);
    rect(-10,-10,width+20, height+20);
    noFill();
 
    for (int i = 0; i<particleNum; i++){
     p[i].run();
   }
}

class Particle{
   float x, y, sx, sy;
   float vx=0, vy=0;
   int col;
   float s;
   Particle(float x, float y, int col, float s){
     sx = this.x = x;
     sy = this.y = y;
     this.col = col;
     this.s = s;
     reset();
   } 
   void reset(){
     x = sx;
     y = sy;
     vx = random(-4, 4) ;
     vy = random(-4, 4);
   }
   
   void run(){
      if (x < -s || y < -s || x > width + s || y > height + s){
        reset();
      }
      x += vx;
      y += vy;
      strokeWeight(s);
      stroke(col);
      point(x, y);
   } 
}