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Re: [1.2T-LC] inverse and constrained transformations (ISSUE-2073)

From: Anthony Grasso <anthony.grasso@cisra.canon.com.au>
Date: Wed, 15 Oct 2008 16:29:47 +1100
Message-ID: <48F57FCB.5040105@cisra.canon.com.au>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
CC: www-svg@w3.org

Hi Dr. Hoffmann,

Dr. Olaf Hoffmann wrote:
> Anthony Grasso:
>> Please let me know if you still have problems viewing it.
> Hello,
> this works, maybe because Opera has no problems with
> it, it may occur not only with animation or zooming 
> (I think, typically zooming can be excluded, because this
> is only a scaling with a positive factor and for this an 
> inverse always exists), my suggestion would be to write 
> something like this (This way I think, it is easier to provide
> a simple method for authors, how to analyse the problem):
> "Note that the inverse of the CTM may not always exist. 
> This may cause problems for a user-agent, if the constrained 
> transformation is realised using the inverse of the CTM.
> Authors are encouraged to verify that the resultant CTM is always 
> invertable to avoid unexpected results. Mathematically it is invertable,
> if the determinant of the CTM is defined and not zero, graphically
> this is the case, if a two-dimensional shape remains two-dimensionally
> before the effect of a constrained transformation is applied."

The SVG Working Group looked again at this issue and we decided to use the above 
wording you proposed.

"The TransformRef value" section [1] of specification contains the updated wording.

Assuming you are satisfied by the new wording, I will close the issue. Please 
let us know if this does not satisfy your initial comment and I will reopen the 

Kind Regards,

Anthony Grasso

[1] http://dev.w3.org/SVG/profiles/1.2T/master/coords.html#transform-ref
Received on Wednesday, 15 October 2008 05:30:33 UTC

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