RE: 2d vs 3d transform-origin

I'm a little fuzzy on the expected user experience here, but I think simplifying is probably your best bet.

Some options...


Option A

Add a fixed string or character (such as 'z') before the z parameter.

<transform-origin-3d> = <transform-origin-2d> [z <length>]?



Option B

Restrict the 3 dimensional grammar to exclude ambiguity by disallowing the problematic 4 parameter cases.  In my grammar below, I also require {x,y,z} ordering for simplicity.
<transform-origin-3d> =
                <transform-origin-2d>
                |
                <transform-origin-3d-3>
                |
                <transform-origin-3d-4>
                |
                <transform-origin-3d-5>

/* x-param y-param z-param */
<transform-origin-3d-3> =
                [ <percentage> | <length> | left | center | right ]   [ <percentage> | <length> | top | center | bottom ]   <length>

/* center yanchor yoffset zoffset */
/* xanchor xoffset center zoffset */
<transform-origin-3d-4> =
center   [ [ top | bottom ] [ <percentage> | <length> ] ]   <length>
|
[ [ left | right ] [ <percentage> | <length> ] ]   center   <length>

/* xanchor xoffset yanchor yoffset zoffset */
<transform-origin-3d-5> =
                [ left | right ] [ <percentage> | <length> ]   [ top | bottom ] [ <percentage> | <length> ]   <length>




As I looked back at Option B, specifically the <transform-origin-3d-5> something struck me - Z needs anchor keywords.

Perhaps the Z anchor should use { in, center, out } or { back, center, front }.  That leads to...



Option C

CSS4 (Consider)
<transform-origin-3d> = <transform-origin-2d>     [ center   |   [ back | front ] [<percentage> | <length>]? ]?

CSS3 (Simplified)
<transform-origin-3d> = <transform-origin-2d>     [ front [<percentage> | <length>]? ]?

In short, the CSS3 recommendation is to use the same approach as Option A but use a future-looking keyword.


From: Simon Fraser [mailto:smfr@me.com]
Sent: Monday, October 31, 2011 4:09 PM
To: Jennifer Yu
Cc: www-style@w3.org
Subject: Re: 2d vs 3d transform-origin

On Oct 31, 2011, at 2:30 PM, Jennifer Yu wrote:


Hi guys,

It looks like the ED version of the 2D Transforms spec was updated in March 2010 to align transform-origin with background-position. This is great, except that the 3D Transforms ED had no accommodating update and now clashes with the 2D Transforms spec. For instance, is 'transform-origin: left bottom 20px' specifying a 2D (left, bottom 20px) or 3D (left, bottom, 20px) transform origin?

Good point. I filed <http://www.w3.org/Bugs/Public/show_bug.cgi?id=14647>

I'm not sure how to resolve this, other than invent a new syntax for transform-origin, or to break out transform-origin-z into a separate property.

Simon