W3C home > Mailing lists > Public > www-style@w3.org > July 2012

Re: [css3-positioning] z-index and pseudo-stacking contexts

From: Simon Fraser <smfr@me.com>
Date: Mon, 23 Jul 2012 18:52:59 -0700
Cc: "www-style@w3.org" <www-style@w3.org>
Message-id: <84F21310-8988-4C6B-B2D1-6AB8C19376F8@me.com>
To: fantasai <fantasai.lists@inkedblade.net>
On Jul 23, 2012, at 5:56 PM, fantasai <fantasai.lists@inkedblade.net> wrote:

> So I have two questions (non-rhetorical):
>  1. Is it desired / are there use cases for having positioned context
>     within a z-positioned element be able to escape the z-positioned
>     element's stacking context?

But then they participate with some other stacking context? What would
the rules be for depth sorting things across different stacking contexts?

Fundamentally, browsers (at least WebKit) paint things as a tree; stacking
contexts form nodes in this tree. Depth sorting is just ordering of sibling nodes.

Adding rules about things escaping from their stacking context would break this
basic painting algorithm, and I'm not sure how you'd implement it. I'd push
strongly against additional complexity in this area; the z-order tree is what
WebKit bases it's hardware-accelerated rendering on, and that's hard enough already,
what with the crazy behavior of clipping (see <http://smfr.org/misc/css/stacking/css-escher.html>).

Simon
Received on Tuesday, 24 July 2012 01:53:27 GMT

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