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Re: [css3-2d-transforms][css3-images] <position> grammar is duplicated or points to the wrong spec

From: L. David Baron <dbaron@dbaron.org>
Date: Mon, 23 Jan 2012 09:20:43 -0800
To: Aryeh Gregor <ayg@aryeh.name>
Cc: Lea Verou <leaverou@gmail.com>, www-style list <www-style@w3.org>
Message-ID: <20120123172043.GA3342@pickering.dbaron.org>
On Monday 2012-01-23 11:04 -0500, Aryeh Gregor wrote:
> On Sat, Jan 21, 2012 at 11:01 AM, L. David Baron <dbaron@dbaron.org> wrote:
> > In 3-D transforms, on the other hand, the syntax is actually
> > different since it allows a 3-D point (a value in x, y, and z).
> > It's not necessarily clear to me how this should interact with the
> > new background-position syntax -- it's perhaps a bad result of the
> > suggestion I made to use the same syntax for both (when I was
> > thinking only about 2-D).
> >
> > That said, I'm not sure transform-origin really needs to allow a 3-D
> > point, given that transform-origin doesn't actually add
> > functionality -- it just makes it easier to think about transforms
> > in different ways -- the same effects can always be done using
> > translate.
> 
> This might have been a reasonable argument at one point -- although
> all the functionality of the enhanced 2D transform-origin can be
> obtained with calc(), right?  But Gecko and WebKit both implement the
> transform-origin from the 3D draft, so the ship has sailed.  The 2D
> draft should drop the three- and four-argument versions.

I don't think that means the ship has sailed.

> (Also, the background-position syntax doesn't make sense to me.  It
> allows "left 10% bottom 10%", which is the same as "10% 90%"; but
> doesn't allow "10% 5px 10% 5px", which is an effect that's not
> obtainable without using calc().  Nor does it allow things like "10%
> bottom 5px" to mean "10% calc(100% - 5px)".  "[ left | right |
> <percentage> ] [ <length> ]?" would make more sense to me than "[ left
> | right ] [ <percentage> | <length> ]?".  But that's a side point.)

What's not obtainable using calc()?  Gecko's implementation of
calc(10% + 5px) for background-position positions the 10% point of
the image 5px to the left of the 10% point in the container.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂
Received on Monday, 23 January 2012 17:21:09 GMT

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