W3C home > Mailing lists > Public > www-svg@w3.org > January 2005

Re: ISSUE: current user space and <svg>

From: Guy de Pourtalès <depourtales@vtxnet.ch>
Date: Tue, 11 Jan 2005 08:36:35 +0100
Message-Id: <8566D183-63A3-11D9-A68C-000A958D21B8@vtxnet.ch>
Cc: www-svg@w3.org
To: Jonathan Watt <jonathan.watt@strath.ac.uk>


Le 10 janv. 05, à 18:19, Jonathan Watt a écrit :

> 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')?

No, as the specs says in chapter 7 "Coordinate systems, transformations 
and units" of SVG11, the current user coordinate system is the new user 
space specified by the transformation  matrices and/or new viewport of 
the target element relative to its parent element transformations. 
Thus, the need of matrices concatenation.

> 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?

The initial viewport is negotiated by the user agent (for example the 
svg viewer) and its parent user agent (for example the browser) to meet 
the conditions specified in chapter 7.1 and 7.2 of SVG11. Furthermore, 
chapter 7.3 of SVG11 says that the topmost user coordinate system 
(before any transform) is identical to the initial viewport.

By the way,  remember that the viewbox attribute acts like a window you 
use to look at a specific region of a coordinate space, but does not 
change it.

> I don't believe this can be clearly answered from the contents of the 
> specs.
> -Jonathan
Received on Tuesday, 11 January 2005 07:37:08 UTC

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