createCanvas(400, 400);

}

​

function draw() {

  background(220);

​

  stroke("pink");

  grid(width / 10);

​

  stroke("black");

  verticalLine(width / 10);

  horizontalLine(height / 10);

​

  stroke("red");

  verticalLine(mouseX);

​

  stroke("blue");

  horizontalLine(mouseY);

}

// draws a vertical line spanning the canvas

function verticalLine(x) {

  line(x, 0, x, height);

}

// horizontal line spaning the canvas

function horizontalLine(y) {

  line(0, y, width, y);

}

// creates a grid spanning the whole canvas

function grid(stepGrid) {

  for (x = 0; x < width; x += stepGrid) {

    for (y = 0; y < height; y += stepGrid) {

      verticalLine(x);

      horizontalLine(y);

    }

  }

}