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Re: Some thoughts on css transforms in svg

From: Dean Jackson <dino@apple.com>
Date: Fri, 12 Mar 2010 06:27:42 +1100
Cc: "public-fx@w3.org" <public-fx@w3.org>, www-svg <www-svg@w3.org>
Message-Id: <5FB41E2E-6F81-45E9-9C65-81A05BA3A822@apple.com>
To: Erik Dahlstrom <ed@opera.com>

On 12/03/2010, at 5:48 AM, Erik Dahlstrom wrote:

> Hi,
> 
> just trying to gather some of my thoughts on css transforms in svg.
> 
> - 'transform' in svg is defined to be an attribute, not a property
> - transform animation using animateTransform (defined in SVG) affects the transform attribute currently
> - there's nothing like the transform-ref[1] in css2d transforms, how should that be mapped?
> 
> Here are some possible ways of adding support for css transforms in svg:
> 
> 1. Treat it as any of the other CSS properties that SVG share with HTML/CSS (e.g 'display'), basically same as overriding the attribute
> Advantage(s): mostly consistent with the model (possibly with the exception of 'none')

I like this one.

> Notes: What 'transform: none' means in css2d transforms isn't clearly defined,
> for svg it would have to mean that the attribute is used, otherwise backwards compatibility is lost. Should there be an 'auto' initial value to deal with these cases?

That sounds reasonable to me.

I think the postmultiplying solutions, including/especially Tab's followup suggestion, are too confusing. 

Dean

> 
> 2. Treat it such that it applies the css transform by postmultiplying it to the transform attribute before presentation.
> Advantage(s): no need to duplicate transforms on a case-by-case basis in css that are already in the markup when something needs to be tweaked. Easily fits into the model. Preserves backwards compatibility.
> Disadvantage(s): Not possible to ignore a transform attribute by using css. Slightly different from the model used for other props in svg.
> 
> 3. Treat it such that if it's not 'none' it applies the css transform by postmultiplying it to the transform attribute before presentation.
> Advantage(s): possible to override transform attribute with 'none' keyword. preserves backwards compat.
> Disadvantage(s): you might want to ignore attribute and then add some transform in css. inconsistent with model (where css props override attributes).
> 
> Thoughts?
> 
> 
> [1] http://www.w3.org/TR/SVGTiny12/coords.html#transform-ref
> 
> -- 
> Erik Dahlstrom, Core Technology Developer, Opera Software
> Co-Chair, W3C SVG Working Group
> Personal blog: http://my.opera.com/macdev_ed
> 
Received on Thursday, 11 March 2010 19:28:19 GMT

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