createCanvas(600, 600);

  rectMode(CENTER);

  fill(255);

  stroke(255);

}

​

function draw() {

  background(0);

  const maxLevel = constrain(round(mouseX/width * 4), 0, 4);

  drawSquare(width/2, height/2, min(width, height), maxLevel);

}

​

function drawSquare(x, y, length, maxLevel, level = 0) {

  if(level == maxLevel || length <= 1) {

    square(x, y, length);

    return;

  }

  const newLength = length/3;

  for(let i = -1; i <= 1; i ++) {

    for(let j = -1; j <= 1; j ++) {

      if(i == 0 && j == 0) {

        continue;

      }

      drawSquare(x + i * newLength, y + j * newLength, newLength, maxLevel, level + 1);

    }

  }

}