function setup() {

  createCanvas(windowWidth, windowHeight);

}

​

function mousePressed() {

  if (mouseX > 0 

      && mouseX < windowWidth 

      && mouseY > 0 

      && mouseY < windowHeight) {

    let fs = fullscreen();

    fullscreen(!fs);

  }

}

​

function draw() {

  background(mouseX, mouseY, 200);

}

​

function windowResized() {

  resizeCanvas(windowWidth, windowHeight);

}