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Re: [css-transforms] computed style of 'transform' property

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 25 Mar 2014 15:30:23 -0700
Message-ID: <CAAWBYDDQZXw7djH5E2nw5H5QsFWBkY8thc647hmrxAKC8s7tFA@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: Dirk Schulze <dschulze@adobe.com>, www-style <www-style@w3.org>, public-fx <public-fx@w3.org>
On Tue, Mar 25, 2014 at 2:29 PM, L. David Baron <dbaron@dbaron.org> wrote:
> On Monday 2013-12-16 09:20 +0000, Dirk Schulze wrote:
>> We discussed and decided in the past that the "computed style” of the ‘transform’ property must return the specified value [1]. This has been in the spec since the first WD.
>>
>> Yet, no browser ever implemented this part of the spec. For what it’s worth, all browsers seems to return a matrix()/matrix3d() string.
>>
>> Even if we had the agreement from browser implementers in the past to change the behavior, no browser ever did and users are starting to rely on a matrix as returned value.
>>
>> I suggest we specify the behavior of browsers and do not return the specified value. Implementations must return a string “matrix()” with 6 numerical values on a pure 2D matrix[2] (all transform functions multiplied as in [3]) and a string "matrix3d()” with 16 numerical values otherwise.
>
> I think you're confusing the "Computed value" field of the property
> description with the getComputedStyle() method.  The "Computed
> style" describes the conceptual computed value, which in turn is
> what is inherited and used for other things in the CSS processing
> model, such as triggering CSS transforms.  Changing this to be
> matrix() would break transitions and animations of CSS transforms,
> since all animations would operate on matrix() values.
>
> The getComputedStyle() method should indeed return matrix(), but
> that's not what the "Computed value:" line means.

In other words, the *serialization* of the computed value must use
matrix() or matrix3d(), but the computed value itself is still what
the spec says.

~TJ
Received on Tuesday, 25 March 2014 22:31:15 UTC

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