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Re: animate/transition height to/from auto

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Fri, 23 Nov 2012 09:31:56 -0500
Message-ID: <50AF88DC.9040709@mit.edu>
To: www-style@w3.org
On 11/23/12 4:08 AM, Michał Gołębiowski wrote:
> I meant changing height between 0 and auto. Their computed values are 0
> and auto, respectively, so this value changes. Why can't this be handled
> by transitions? What am I not seeing here?

Generally speaking, transitions perform interpolation on computed values 
right now.  So when the computed value changes from X to Y a transition 
needs to be able to figure out a computed value s*X + (1-s)*Y for all 0 
<= s <= 1.

The problem is how to do this for 0 and "auto".  What's halfway between 
the two?  For example, consider this testcase:

   <div id="outer" style="height: 0; overflow: hidden">
     <div id="middle" style="height: 50%">
       <div id="inner" style="height: 100px"></div>
     </div>
   </div>

The height of the outer div is 0, as is that of the middle div.

If the outer div had auto height, its height would be 100px, at which 
point the height of the middle div would also be 100px (because 50% of 
auto computes to auto).

What should happen halfway through a transition from 0 to auto for the 
height of the outer div?  Presumably the height of the outer div should 
be 50px?  What should the height of the middle div be: 50px or 25px, and 
why?

-Boris
Received on Friday, 23 November 2012 14:32:31 GMT

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