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[1.2T-LC] 16.2.9 by 'identity'

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Wed, 1 Oct 2008 16:07:33 +0200
To: www-svg@w3.org
Message-Id: <200810011607.34022.Dr.O.Hoffmann@gmx.de>

Hello SVG WG,

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?

Received on Wednesday, 1 October 2008 14:19:33 UTC

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