createCanvas(400, 400);

  background(100);

}

​

function draw() {

  if (mouseIsPressed) {

    brush(mouseX, mouseY);

  }

}

​

function brush(X, Y) {

  noStroke();

  triangle(X, Y, X+10,Y+10, X-10,Y+10);

  if (mouseX > 200) {

    fill(0);

  }

  else {

    fill(255);

  }

}

​