​

function setup() {

  createCanvas(400, 400);

  background(245);

}

​

function draw() {

  if (mouseIsPressed) {

    line(x1, y1, mouseX, mouseY);

  }

}

​

function mousePressed() {

  x1 = mouseX;

  y1 = mouseY;

}

​

function keyPressed(){

  background(255);

}