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Re: [css3-transitions] transitioning to/from auto value

From: Simon Fraser <smfr@me.com>
Date: Tue, 27 Apr 2010 13:36:52 -0700
Cc: Brad Kemper <brad.kemper@gmail.com>, www-style list <www-style@w3.org>
Message-id: <16A57A18-A63D-42EB-9045-5D046C37F89C@me.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
On Apr 27, 2010, at 11:16 AM, Tab Atkins Jr. wrote:

> On Mon, Apr 26, 2010 at 11:36 AM, Brad Kemper <brad.kemper@gmail.com> wrote:
>> On Apr 26, 2010, at 10:56 AM, Simon Fraser <smfr@me.com> wrote:
>> 
>>> The main issue is that, when transitioning to an 'auto' height, the user
>>> agent would have to do a layout for the page in its final state in order to
>>> determine the destination height of the element. And, of course, that height
>>> may depend on all sorts of other style rules, some of which themselves may
>>> be animating, and which could also change for other reasons while the
>>> transition is running.
>> 
>> I figured that was the issue, but I think that even the transition was based
>> on a snapshot of the used values at the beginning or end of the transition,
>> that would be huge, and be closer to what JavaScript animation libraries can
>> do.
> 
> I suspect that this would be sufficient as well.  We definitely need
> the ability to transition to auto in some manner, and I think just
> doing a single tentative layout to establish an end-point for the
> transition will be "good enough".

I'm very reluctant to put something in a specification for which a correct implementation would be extremely difficult, and for which a "reasonable" implementation would show glitches in many common situations. I know that if we ended up implementing your suggestion in WebKit, it would not be long before we get a bug about transitioning to an 'auto' value using the wrong target size.

Simon
Received on Tuesday, 27 April 2010 20:37:32 GMT

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