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

Alexis Menard alexis at webkit.org
Mon Dec 3 05:31:19 PST 2012

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?

it seems like transform-origin supports something similar. I need to look at it.


> 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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Software Engineer @
Intel Open Source Technology Center

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