[whatwg] Fullscreen changes to support <dialog>

Ian Hickson ian at hixie.ch
Tue Apr 3 16:14:43 PDT 2012

So based on our discussions on IRC and in person earlier today, I think 
the following additions to the Fullscreen specification would provide the 
necessary infrastructure to support <dialog>:

- Add a new stacking layer to the CSS 2.1 Appendix E layering model, 
  after the current layer 10. Let's call this new layer the "top" layer.

  This layer consists of a stack of elements, which each CSS viewport 
  maintains. These stacks are initially empty. When the layer is painted, 
  the elements in the stack are rendered in the order that they were added 
  to the stack, with the most recently added being rendered closest to the 
  user. The 'z-index' property is ignored for this stacking layer.

  An element in this layer is rendered in the CSS model as an atomic unit 
  that is a sibling to the root element; overflow, opacity, masks, clips, 
  etc, of ancestor elements do not affect it. Outlines must be rendered in 
  their non-layer-10 position if they are specified on an element with an 
  ancestor-or-self that is in such a stack.

  An element in this layer that has an ancestor-or-self that is 
  display:none does not get rendered.

  The 'position' property for elements in one of these stacks computes to 
  'absolute', 'fixed', or 'center' if that is its specifed value, and to 
  'absolute' if the specified value is anything else.

  The containing block for such an element is the initial containing 
  block, same as for the root element. The static position for left, 
  right, and top are zero, unless overridden by another specification. 
  (The <dialog> spec will override the static position for top.)

- Define an algorithm to "push an element onto the top layer", which adds 
  a given element to this element's browsing context's viewport's stack, 
  if the element is in a document.

- Define an algorithm to "yank an element from the top layer", which 
  removes the given element from the stack it is in.

  When an element is removed from a document, it must be yanked from the 
  top layer.

- Define a new pseudo-element ::backdrop which applies to any element in 
  such a stack; it addresses a box that exactly covers the viewport 
  immediately below the element in the stack, in the same stacking layer, 
  whose only applicable properties are the 'background' properties. 
  (Alternatively, make it a generic box with properties initially set to 
  have position:fixed and positioned to exactly cover the viewport, but 
  I don't see much point in letting people fiddle with this box's 
  positioning, display type, etc.)

Fullscreen then defines that when you make an element fullscreen, it's 
"pushed onto the top layer", and when an element is unfullscreened, it's 
"yanked from the top layer". The user "emergency escape" UI yanks all 
fullscreened elements from the top layer (but leaves any other elements in 
it; we wouldn't want dialogs to disappear when exiting full screen mode).

If this works, then I'll use this for <dialog>.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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