let rowNum = 5;

let colW;

let rowH;

​

function setup() {

  createCanvas(500, 500);

  colW = width / colNum;

  rowH = height / rowNum;

}

​

function draw() {

  background(220);

  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, 200, 0)

      // if (mouseX > col * colW && mouseX < (col + 1) * colW && mouseY > row * rowH && mouseY < (row + 1) * rowH) {

      fill(d);

      rect(x, y, colW, rowH);

      // }

    }

  }

}