let speed = 0.02;

​

function setup() {

  createCanvas(windowWidth, windowHeight);

}

​

function drawCircle(radius, opacity, circleW){

  const nb = radius/2;

  const angle = Math.PI*2 / nb;

  fill(0, opacity);

  for(let i = 0; i < nb; i++){

    ellipse(width/2 + cos(angle*i) * radius, width/2 - sin(angle*i) * radius, circleW, circleW);

  }

}

​

function draw() {

  background(220, 220, 220, 100);

  noStroke();

  for(let i = 0; i < 40; i++){

      height -= speed;

      drawCircle(i*10, 100-i*3, height);

  }

  if(height < 15 || height > 30) speed = -speed;

}