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Re: [css3-transitions] transitions and rendering objects vs. DOM nodes

From: David Hyatt <hyatt@apple.com>
Date: Sat, 27 Jun 2009 16:37:25 -0500
Cc: www-style@w3.org
Message-id: <16B4C56E-22BC-48D5-94C6-5414644AACCA@apple.com>
To: "L. David Baron" <dbaron@dbaron.org>
In WebKit, at the moment we do transitions on rendering objects (and  
yes this means changes to display:none just kill transitions).  We  
don't allow transitions to occur on pseudo elements.  Not sure if this  
is the right decision though, but it's what we have done so far.

dave
(hyatt@apple.com)

On Jun 26, 2009, at 6:44 PM, L. David Baron wrote:

> I have another question about transitions that I think ought to be
> addressed in the spec ( http://dev.w3.org/csswg/css3-transitions/ ),
> though in this case I'm not exactly sure how it should be addressed
> in the spec.
>
> This is the question of whether transition should be associated with
> a change in style on a content node, or a change in style on a
> rendering object (a box).  Either solution poses a bunch of
> problems.
>
> If transitions are associated with the style on an element (DOM
> node), then we have problems in any case where a content node has
> more than one style.  The main case of this I can think of is
> pseudo-elements.  For example, I think it's hard to do something
> sensible with:
>  p { color: gray; }
>  p::first-line { color: black; }
>  p:hover { color: blue; }
>  p:hover::first-line { color: aqua; }
>  a { transition: 3s color; }
> then it's really not clear what the transition on the anchor should
> be when the p goes into the :hover state (either when the anchor is
> split between the first line and the second, or when the anchor is
> entirely in the first line).
>
> On the other hand, if transitions are associated with the style on a
> rendering object, you end up with transitions not occurring when
> there's also a change in 'display' or some other property that
> changes what rendering objects are present.
>
> I think the specification should define more precisely how
> transitions interact with pseudo-elements and when they should occur
> so that this distinction is clear.
>
> -David
>
> -- 
> L. David Baron                                 http://dbaron.org/
> Mozilla Corporation                       http://www.mozilla.com/
>
Received on Saturday, 27 June 2009 21:38:07 GMT

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