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Re: [1.2T-LC] 16.2.9 by 'identity' (ISSUE-2093, ACTION-2319)

From: Doug Schepers <schepers@w3.org>
Date: Fri, 17 Oct 2008 21:41:13 -0400
Message-ID: <48F93EB9.8040400@w3.org>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
CC: www-svg@w3.org

Hi, Dr. Olaf-

Dr. Olaf Hoffmann wrote (on 10/1/08 10:07 AM):
> 
> in 16.2.9 it is mentioned:
> 
> ##
> If a 'by' value is used on a non-scalar data type ( such as color or
> transform ), the starting 0 delta value is to be conceptually 
> considered as 'identity'.
> ##
> 
> If this is to be interpreted within some algebraic relation, it is required to
> define or to specify the binary operation a value is considered the
> 'identity' for. Luckily already in SMIL is defined, that this type of
> animation is only available, if additive animation is supported. 
> The SMIL 3 CR already explains in more detail, that the starting '0' is 
> "the neutral element for addition for the domain of the target attribute".
> Therefore the binary operation must be the addition (even or especially
> because not explictly mentioned), this means if X is a value, then 
> X + 'identity' = X, with '+' beeing an additive operation for the space 
> X belongs to.
> For example for RGB-colors this means the 'identity' is black, #000,
> rgb(0,0,0) etc; 
> for vector like types this is the origin (zero length, any direction); 
> for lists of numbers (lengths etc) it might be a list of zeros 
> - right?

Yes, that is the idea.

In our offlist exchange, you seemed to indicate that this is already
clarified in SMIL3.  Is there any need for a change in SVG 1.2 Tiny, in
that case?  If there is a contradiction, we will certainly look at
changing it, so please give us the details.

If there is no need for a change and your comment is satisfied, please
let us know.

Regards-
-Doug
Received on Saturday, 18 October 2008 01:41:22 GMT

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