Untitled

<!DOCTYPE html>
<html>

  <head>
    <script src="http://cdnjs.cloudflare.com/ajax/libs/p5.js/0.3.0/p5.min.js"></script>
    <script>
      function setup() {
  createCanvas(640, 480);
}

function draw() {
  if (mouseIsPressed) {
    fill(0);
  } else {
    fill(255);
  }
  ellipse(mouseX, mouseY, 80, 80);
}
    </script>
  </head>

  <body>
    <h1>Hello p5.js!</h1>
  </body>

</html>