Thursday, 10 November 2011

Firefox's HTML full-screen API enabled in Nightly builds

A few days ago I enabled the HTML full-screen API in Firefox nightly builds. This enables developers to make an arbitrary HTML element "full-screen", hiding the browser's UI and stretching the element to encompass the entire screen. This will be particularly useful for HTML5 video and games.

If all goes well, this feature will ship in Firefox 10 at the end of January.

The API has changed slightly since I last blogged about it. The current API is Mozilla-specific, but is similar to the W3C's Fullscreen draft specification.

To enter full-screen mode, call the following method on the HTML Element you'd like to enter full-screen:
  • void mozRequestFullScreen() : posts an asynchronous request to make the HTML element the full-screen element. If the request is granted, some time later a bubbling "mozfullscreenchange" event is dispatched to the element which requested full-screen. If the request is denied, a "mozfullscreenerror" event is dispatched to the element's owning document. We only grant requests for full-screen when:
    • mozRequestFullScreen() is called in a user-generated event handler, e.g. a mouse click handler, and
    • the requesting element is in its document, and
    • there are no windowed plugins present in any document/iframe in the current page, and
    • all iframes containing the requesting element (if any) have the mozallowfullscreen attribute.
We added the following method and attributes to HTML Document:
  • void mozCancelFullScreen() : exits the document from full-screen mode. This dispatches a "mozfullscreenchange" event to the document containing the (now former) full-screen element. Note that the "mozfullscreenchange" event which is dispatched when you enter full-screen is targeted at the full-screen element, so if you want to receive the "mozfullscreenchange" on both entering and exiting full-screen in the same listener you should add your listener to the document, rather than the full-screen element.
  • readonly attribute boolean mozFullScreen : true when the document is in full-screen mode.
  • readonly attribute Element mozFullScreenElement : reference to the current full-screen element.
  • readonly attribute boolean mozFullScreenEnabled : returns true if calls to mozRequestFullScreen() would be granted in the current document. This returns false if there are any windowed plugins present in any document/iframe in the current page, or if any iframes containing this document don't have the mozallowfullscreen attribute present, or if the user has disabled the API by preference. If this returns false you may want to not show the user your enter-full-screen button in your page, since you know it won't work!
We also added the :-moz-full-screen css pseudo class, which applies to the full-screen element while in full-screen mode.

We added the mozallowfullscreen attribute to iframe elements. Without this, full-screen requests made by script in the iframe's content (i.e embedded ads, or a YouTube player in an iframe for that matter) will be denied.

While in full-screen mode, the user can press the ESC key (or F11) to exit. Alpha-numeric keyboard input while in full-screen mode causes a warning message to pop-up to guard against phishing attacks. The only key input which doesn't cause the warning message to pop up are: left, right, up, down, space, shift, control, alt, page up, page down, end, home, tab, and meta.

Navigating, changing tab, changing app (ALT+TAB) while in full-screen mode will cause full-screen mode to exit.

Here's about a simple example, which will work in current Firefox nightly builds:

(Press ESC to exit full-screen)

The code for that button's onclick handler is simply:

How is Firefox's full-screen API different from Webkit/Chrome/Safari's full-screen API? Firefox's API adds a "width: 100%; height: 100%;" CSS rule to the element which requests full-screen, so that it's stretched to occupy the entire screen. Chrome's API does not do this, but instead it centers the full-screen element in the window and blacks-out the underlying webpage. So the full-screen element won't occupy the entire screen with Chrome's API unless you specify a "width: 100%; height: 100%;" rule yourself. Conversely if you want to vertically and horizontally center something while in full-screen with Firefox's API, you need to make the containing element of your desired centered element full-screen instead, and apply CSS rules to vertically and horizontally center the contained element.

For a cross-browser full-screen API example, see's full-screen demo.

Edit: 11 Nov 2011, clarified Document.mozCancelFullScreen() and Document.mozFullScreenEnabled, fixed typos.