W3C home > Mailing lists > Public > www-style@w3.org > December 2013

[css-transitions][css-background] Animating border-position

From: Dirk Schulze <dschulze@adobe.com>
Date: Mon, 2 Dec 2013 02:29:36 -0800
To: Alan Stearns <stearns@adobe.com>
CC: "www-style@w3.org list" <www-style@w3.org>
Message-ID: <A518139F-2A2D-4B7A-82E0-13B2D02A16F2@adobe.com>
Interpolation of <position> is currently defined in CSS Transitions. Either we prioritize the interpolation, bring it to CSS Background and Borders level 3 and remove it from CSS Transitions, or CSS Transitions needs to define the interpolation.

Adding [css-transitions] prefix to the email title.


On Nov 27, 2013, at 7:47 PM, Alan Stearns <stearns@adobe.com> wrote:

> Hey all,
> I brought up the issue of animating <position> last week, and Tab noted
> that background-position is defined incorrectly [1]. Testing interop shows
> differences in how background-position animates as well [2, point 2].
> The problem is that by default, transitions occur over computed values.
> The computed value for background-position include keywords, and there is
> no interpolation between keywords defined.
> This could be fixed by defining the computed value of background-position
> to be a list, with each item in the list containing two values of length,
> percentage or calc). This appears to be what Gecko does. But Im not sure
> its useful to have a value of right 10px be converted to calc(100% -
> 10px) in the computed value. And Fantasai raised the concern of future
> extensions to <position> that might not be reducible to calc() expressions.
> If we should leave the computed value definition as it is, then well need
> to specify some keyword interpolation.
> An interim fix would add a definition that allows interpolation between
> identical keywords - so that left top 50px could interpolate with left
> top 100px. This is what browsers appear to interopably implement. This
> would not define animating from left top 50px to right top 100px -
> which is something Blink does not do currently, but Gecko and IE11 appear
> to handle.
> A full fix would define current <position> keyword interpolation for all
> combinations.
> Thanks,
> Alan
> [1] http://lists.w3.org/Archives/Public/www-style/2013Nov/0391.html
> [2] http://lists.w3.org/Archives/Public/www-style/2013Nov/0376.html
Received on Monday, 2 December 2013 10:30:09 UTC

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