// Click on the window that the p5 sketch isn't in!

function draw() {

  background(200);

  noStroke();

  fill(0, 200, 0);

  ellipse(25, 25, 50, 50);

​

  if (!focused) {

   // or "if (focused === false)"

    stroke(200, 0, 0);

    line(0, 0, 100, 100);

    line(100, 0, 0, 100);

  }

}

// https://discourse.processing.org/t/focused-in-ios-safari/12007/3

// https://p5js.org/reference/#/p5/focused