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

Dirk Schulze dschulze at adobe.com
Mon Dec 3 05:19:01 PST 2012

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.

That said, great work regarding the interoperability with other browsers.


> 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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