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Re: ISSUE: current user space and <svg>

From: Jon Ferraiolo <jon.ferraiolo@adobe.com>
Date: Tue, 11 Jan 2005 00:15:13 -0800
To: Jonathan Watt <jonathan.watt@strath.ac.uk>, www-svg@w3.org
Message-id: <6.1.1.1.2.20050111000843.051fba88@mailsj-v1.corp.adobe.com>
Jonathan,
The key thing is that there are often two "current user coordinate systems" 
for a given element - the one before you process 'transform' or 'viewBox' 
and the one after you process the transformations associated with these 
attributes.

Section 7.4 of the SVG 1.1 spec 
(http://www.w3.org/TR/SVG11/coords.html#EstablishingANewUserSpace) includes 
the following snippet in the first paragraph:

----------------------
The <file://coords.html#TransformAttribute>transform and 
<file://coords.html#ViewBoxAttribute>viewBox attributes transform user 
space coordinates and lengths on sibling attributes on the given element 
(see <file://coords.html#TransformAttributeEffectOnSiblingAttributes>effect 
of the transform attribute on sibling attributes and 
<file://coords.html#ViewBoxAttributeEffectOnSiblingAttributes>effect of the 
viewBox attribute on sibling attributes) and all of its descendants.
----------------------

and further on in the same section (if you follow the link to "effect of 
the transform attribute on sibling attributes):
----------------------
The transform attribute is applied to an element before processing any 
other coordinate or length values supplied for that element. In the element

<rect x="10" y="10" width="20" height="20" transform="scale(2)"/>

the x, y, width and height values are processed after the current 
coordinate system has been scaled uniformly by a factor of 2 by the 
transform attribute
----------------------

However, I agree that it makes sense to add some additional clarifications 
to the SVG spec.

Jon

At 09:19 AM 1/10/2005, Jonathan Watt wrote:

>SVG WG,
>
>What is the "current user coordinate system" for an element defined as 
>(with emphesis on *current*, *user* and *element*)? Is it correct to say 
>that it's the coordinate system refered to by the element's "coordinate" 
>attributes (such as 'x' and 'y')?
>
>I'm specifically interested to know what the *current* user coordinate 
>system is for an 'svg' element. Is it the user coordinate system that the 
>element exists in (the one established by the 'svg' element's parent, and 
>to which it's "coordinate" attributes refer to)? Or is it the user space 
>it itself establishes via it's viewBox attribute?
>
>I don't believe this can be clearly answered from the contents of the specs.
>
>-Jonathan
Received on Tuesday, 11 January 2005 12:41:16 GMT

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