var lastY = 0;

var lastXX = 0;

var lastYY = 0;

function setup() {

  let w = 4095 / 8;

  let h = 255;

  lastYY = h;

  createCanvas(w, h);

  background(220);

}

​

function mouseDragged() {

  let xx = mouseX;

  let yy = mouseY;

  let x = round(xx);

  let y = round(height - yy);

  if (x > lastX && y <= 255) {

    print(str(x) + "    " + str(y));

    line(lastXX, lastYY, xx, yy);

  }

  lastX = x;

  lastY = y;

  lastXX = xx;

  lastYY = yy;

}

​