let mx = [];

let my = [];

​

function setup() {

  createCanvas(720, 400);

  noStroke();

  fill(255, 153);

  for (let i = 0; i < num; i++) {

    mx.push(i);

    my.push(i);

  }

}

​

function draw() {

  background(237, 34, 93);

​

  // Cycle through the array, using a different entry on each frame.

  // Using modulo (%) like this is faster than moving all the values over.

  let which = frameCount % num;

  mx[which] = mouseX;

  my[which] = mouseY;

​

  for (let i = 0; i < num; i++) {

    // which+1 is the smallest (the oldest in the array)

    let index = (which + 1 + i) % num;

    let r = abs(map(i, 0, num, -50, 50));

    ellipse(mx[index], my[index], r);

  }

}