let width, height;

​

function setup() {

  width = window.innerWidth;

  height = window.innerHeight;

  createCanvas(width, height);

}

​

function draw() {

  clear();

  background(255);

  for(let x = 0; x < width; x+=boxSize) {

    for(let y = 0; y < height; y+=boxSize) {

      rect(x, y, boxSize);

    }

  }

}