​

function setup() {

  createCanvas(windowWidth, windowHeight);

  button = createButton('clear');

  button.position(19, 19);

  button.mousePressed(clearScreen);

}

​

function draw() {

}

​

function touchStarted() {

  ellipse(mouseX, mouseY, 8, 8);

  // prevent default

  return false;

}

​

function clearScreen(){

  background(255);

}

​