Fullscreen() choice of return values

p5.js Beginners
1

I was playing with fullscreen() in p5.js and the prototypical way of toggling state in the reference:

let fs = fullscreen();
fullscreen(!fs);

The values returned for fs depend on the state:

  • Windowed mode… undefined
  • Full screen mode… … that is, the entire html page and contents

Applying !fs, in the first case we get true, and in the second, false.

Question 1: Why the seemingly odd values of fs? Why not use booleans instead?

Question 2: given that !fs always maps to true or false, could I use:
fullscreen(true) to enter full screen mode
fullscreen(false) to leave full screen mode

Thanks!

2

Indeed fullscreen() got a couple of poor implementation oversights:

This is my take on refactoring it:

p5.prototype.fullscreen = function(val) {
  p5._validateParameters('fullscreen', arguments);

  if (!arguments.length) // no arguments; return fullscreen or not
    return !!( // boolean type coercion
      document.fullscreenElement ||
      document.webkitFullscreenElement ||
      document.mozFullScreenElement ||
      document.msFullscreenElement
    );

  // otherwise set to fullscreen or not
  val? launchFullscreen(document.documentElement) : exitFullscreen();

  return this; // make it call-chainable
};

Absolutely! You could also toggle it like this: fullscreen(!fullscreen());

1 Like
3

Thanks @GoToLoop for the reply. Makes perfect sense.

One additional question though… entering full screen mode has to be done via a user-initiated action (e.g. clicking a button) and not programmatically, i.e. I cannot simply write fullscreen(true) inside draw() and expect that it will work. What’s the reason for this browser imposed limitation?

4

There are some browser features (sound, alerts, fullscreen, camera, microphone) that can be abused if it’s done w/o the user’s permission.

That’s why fullscreen is requested and can be denied:

5

Aha… Now I get it. As they say in Spain: “A la cama no te irás, sin saber una cosa más” equivalent to “you have to learn something new every day”… and I just did! :sunglasses: