is_fullscreen()

[simbleau]

Summary

We have the ability to Element::request_fullscreen, but no way to detect it.

This makes it hard to show/hide a fullscreen button.

Goal: Add a sugar function to detect if the window is fullscreen.

Motivation

It's a nightmare to figure out (with browser compatability).

Detailed Explanation

This is a translation of the top stack overflow answer: https://stackoverflow.com/questions/2863351/checking-if-browser-is-in-fullscreen

(web_sys needs Window, Screen)

    // A little bit of magic to detect if already fullscreen, translated from:
    // https://stackoverflow.com/questions/2863351/checking-if-browser-is-in-fullscreen
    let is_fullscreen = {
        let screen_top = window()
            .screen()
            .and_then(|s| s.top())
            .map(|top| JsValue::from(top))
            .map(|v| v.is_falsy());
        let screen_y = window().screen_y().map(|v| v.is_falsy());
        if let (Ok(true), Ok(true)) = (screen_top, screen_y) {
            true
        } else {
            false
        }
    };

Drawbacks, Rationale, and Alternatives

Does this design have drawbacks? Are there alternative approaches? Why is this
design the best of all designs available?

• This is compatible for all browsers (according to the stack overflow article)

What prior art exists?

• Not sure

Unresolved Questions

What is not clear yet? What do we expect to clarify through implementation
and/or usage experience?

I'm not sure where this would fit, API wise. Perhaps in gloo-utils.

My proposal would be to add gloo_utils::screen which is short for gloo_utils::window().screen(). This could provide a wrapped Screen which mirrors the inner, while providing additional functions such as is_fullscreen().