createCanvas(600, 400);

}

​

function draw() {

  background(220);

  fill(255);

  rect(0, 0, width / 3, height);

  rect(width / 3, 0, width / 3, height);

  rect(width / 3, height, 0, (width / 3) * 2);

  rect((2 * width) / 3, 0, width / 3, height);

  //fill (255,0,0)

  if (mouseX <= width / 3) {

    fill(255, 0, 0);

    rect(0, 0, width / 3, height);

  } else if (mouseX <= (2 * width) / 3) {

    fill(255, 0, 0);

    rect(width / 3, 0, width / 3, height);

  } else if (mouseX <= width) {

    fill(255, 0, 0);

    rect((width * 2) / 3, 0, width / 3, height);

  }

}

​