let rowNum = 50;

let colW, rowH;

​

function setup() {

  createCanvas(800, 800);

  colW = width / colNum;

  rowH = height / rowNum;

}

​

function draw() {

  background(200);

  for (let col = 0; col <= colNum; col++) {

    for (let row = 0; row <= rowNum; row++) {

      let x = col * colW;

      let y = row * rowH;

      let d = dist(mouseX, mouseY, x, y);

      d = map(d, 0, dist(0, 0, width, height) / 2, 0, 200);

      b = map(d, 0, dist(0, 0, width, height) / 2, 255, 0);

      if ((col % 2 == 1 && row % 2 == 1) || (col % 2 == 0 && row % 2 == 0)) {

        fill(20, d);

      } else {

        fill(255, b);

      }

      rect(x, y, colW, rowH);

    }

  }

}