let particles;

let numTotalParticles, numParticlesOnline;

class Particle {

  constructor(x,y) {

    this.position = createVector(x, y);

    this.velocity = createVector(0, random(0.5,2));

  }

  update() {

    // noStroke()

    // fill(0);

    // circle(this.position.x, this.position.y,2);

    this.position.x += this.velocity.x;

    this.position.y += this.velocity.y;

  }

  draw() {

    stroke(255);

    point(this.position.x, this.position.y);

  }

}

​

function setup() {

  numTotalParticles = 10000;

  numParticlesOnline = 1000;

  particles = [];

  createCanvas(400, 400);

  background(0);

  for (let i = 0; i < numParticlesOnline; i++) {

    particles.push(new Particle(random(1,width-1), random(-height,0)));

  }

  numTotalParticles -= numParticlesOnline;

}

​

function draw() {

  background(0);

  loadPixels();

  for (let i = particles.length-1; i >= 0; i--) {

    particles[i].update();

    particles[i].draw();

    if (particles[i].position.x < 0 || particles[i].position.x > width || particles[i].position.y > height) {

      particles.splice(i, 1);

      particles.push(new Particle(random(1,width-1), random(-height,0)));

      numTotalParticles--;

    }

  }

  if (numTotalParticles <= 0) {

    console.log("done");

    noLoop();

  }

  //background(220);

}