[webkit-dev] Adding CSS3 background-position offsets.

[Dirk Schulze]

On Dec 3, 2012, at 5:31 AM, Alexis Menard <alexis at webkit.org> wrote:

> On Mon, Dec 3, 2012 at 10:19 AM, Dirk Schulze <dschulze at adobe.com> wrote:
>> 
>> On Dec 3, 2012, at 4:51 AM, Alexis Menard <alexis at webkit.org> wrote:
>> 
>>> Hi everyone,
>>> 
>>> I wanted to let you know that I have added the new CSS3
>>> background-position offsets support to WebKit.
>>> 
>>> This support is behind the ENABLE_CSS3_BACKGROUND feature define and
>>> it's disabled by default on all ports. I took the conservative
>>> approach despite it's a cool feature.
>>> 
>>> Long story short, it allows you to specify three or four values to
>>> background-position. It's a nice addition as you can now position the
>>> images using length or values in relation to any of the four corners
>>> of elements, not just the top left corner.
>>> 
>>> Opera, IE10 and Firefox implements this feature already (though the
>>> latter returns weird results using getComputedStyle).
>>> 
>>> It is tracked by https://bugs.webkit.org/show_bug.cgi?id=37514 and the
>>> two patches landed (parsing and rendering) are
>>> http://trac.webkit.org/changeset/135632 and
>>> http://trac.webkit.org/changeset/136378.
>>> 
>>> I believe the <position> type (3-4 values) could be/or is used in
>>> other cases so we can reuse the parsing code for four/three values if
>>> needed. I will investigate this afterwards and make appropriate
>>> patches.
>> 
>> I really hope that we don't use it any where else again (with the exception of -webkit-mask-position which should have same behavior as background-position). This is the use case for the calc() function. Sadly the calc() function came to late for CSS3 Backgrounds.
> 
> -webkit-mask-position should behave the same way as
> background-position? Even if I add feature to the latter? Why so?

Because -webkit-mask and background share the same properties and syntax. Why should it be different on -webkit-mask-position? (Btw. CSS Masking already adapted the background-position syntax for mask-position[1])

> 
> it seems like transform-origin supports something similar. I need to look at it.
> 
> http://www.w3.org/TR/css3-transforms/#transform-origin-property

It definitely does not :)

Greetings,
Dirk

[1] http://dvcs.w3.org/hg/FXTF/raw-file/tip/masking/index.html#the-mask-position

> 
>> 
>> That said, great work regarding the interoperability with other browsers.
>> 
>> Greetings,
>> Dirk
>> 
>> 
>>> 
>>> I plan to enable it by default on Qt and EFL ports this week. If
>>> somebody wants me to enable it on their ports please tell me, I'll be
>>> happy to do it.
>>> 
>>> Looking forward to your comments.
>>> 
>>> Spec : http://www.w3.org/TR/css3-background/#the-background-position
>>> 
>>> --
>>> Software Engineer @
>>> Intel Open Source Technology Center
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>>> webkit-dev mailing list
>>> webkit-dev at lists.webkit.org
>>> http://lists.webkit.org/mailman/listinfo/webkit-dev
>> 
> 
> 
> 
> -- 
> Software Engineer @
> Intel Open Source Technology Center
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