createCanvas(500, 500);

}

​

function draw() {

  background(255);

  drawGrid();

  noStroke();

  fill(0);

  circle(mouseX, mouseY, 15);

  text("X = "+mouseX+"   Y = "+ mouseY, mouseX-50, mouseY-20);

}

​

// ------------------------------

​

function drawGrid(){

  stroke(150);

  // vertical lines

  line(100, 0, 100, height);

  line(200, 0, 200, height);

  line(300, 0, 300, height);

  line(400, 0, 400, height);

  // horizontal lines

  line(0, 100, width, 100);

  line(0, 200, width, 200);

  line(0, 300, width, 300);

  line(0, 400, width, 400);

}