createCanvas(400, 400);

  let cols = 10;

  let rows = 10;

  let cellWidth = width / cols;

  let cellHeight = height / rows;

  for (let x = 0; x < cols; x++) {

    for (let y = 0; y < rows; y++) {

      let cellX = x * cellWidth;

      let cellY = y * cellHeight;

      if (mouseX > cellX && mouseX < cellX + cellWidth && mouseY > cellY && mouseY < cellY + cellHeight) {

        fill(255, 0, 0); // Highlight the cell when the mouse is over it

      } else {

        fill(255);

      }

      rect(cellX, cellY, cellWidth, cellHeight);

    }

  }

}

​

function draw() {

  background(220);

  setup(); // Continuously redraw grid

}