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Re: [1.2T-LC] Comments on Last Call WD of SVG T1.2 (ISSUE-2149, ISSUE-2157)

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Sat, 18 Oct 2008 14:30:11 +0200
To: www-svg@w3.org, cyril.concolato@telecom-paristech.fr
Message-Id: <200810181430.11973.Dr.O.Hoffmann@gmx.de>


I think, this was mainly skipped, because I insisted, that 
the formula was meaningless in that sense, that it does 
not result in general in a paced change of the related 
shape/value. It is quite simple to provide samples to
show, that no behaviour fits to the definition of calcMode="paced".
This happens especially because calcMode="paced" additionally
requires, that the animation has to interpolate between the
given values. One can show, that there is no formula fitting
to all requirements of calcMode="paced" for points lists
and several other list constructions.

In general, there is no meaningful distance definition for
lists of numbers related to a paced changes, if these lists 
have more than one list item (a scalar) or cannot be 
identified with a vector. Vectors can always be identified 
to have an absolute value and a direction, lists and other 
constructions typically have no absolute value and no 
direction. Distances between scalars (numbers with optional
units) are no problem too.
Therefore there is a well known and meaningful behaviour 
for scalars and vectors for a paced animation, which fits
to the definition of calcMode="paced".
There is no for lists in general and none for path data
and none for mixed data sets like that of transform
rotate with a changed rotation center.

Up to now, nobody even tried to explain, how some
(current or previous) formulas in the list are related 
to a paced animation or how or which formula is related 
to a somehow meaningful behaviour related to the word 
'paced' for lists in general.
If someone is able to do it for example for a points list
of for a list of XXX in general, this would be interesting 
to discuss ;o) 
I cannot see a reason, why the specify meaningless
formulas not related to the definition of calcMode="paced"
to be related, if they are not related or not explainable
to be related.

My current position is: Give me a formula for paced
behaviour of lists and I will be able to provide a simple
example, showing, that the behaviour is not related
to a paced change of the animated entity.
The other way round, for several constructions I will be
able to simulate something looking like a paced change
of this construction without fitting to the definition of
calcMode="paced" ;o)
Not everything is meaningful or relevant or related
somehow to 'reality', just because it can be computed 
or implemented or it is asserted that it is related to
an already defined construction.


Because it is possible to have some singular samples
and circumstances, one can have something like a 
paced behaviour for even more complex constructions,
however this cannot be generalised, but authors can
simply use calcMode="linear" and keyTimes to describe
such timing without problems (requires only some number
crunching). Indeed, because of the 'SVG confusion' about 
this issue in the past, for compatibility and predictable 
behaviour in different viewers and versions, authors
need to do it anyway for everything different than a
color or a scalar.

Additionally, if it is important to indicate, that such
an author defined behaviour is considered to be
paced somehow, an author can indicate this simply
by a description in the desc element or even 
simpler by using the new role attribute with
a (safe) CURIE:

attributeName="points" calcMode="linear" keyTimes="..." values="..."
 dur="..." />

This approach could be even improved with an additional fragment identifier
for the defintion of calcMode="paced" in the draft itself to help authors
to use propper CURIEs.

Of course, authors can reference other sources of wisdom too with a
CURIE to indicate, to what the timing is related and giving it a specific
meaning, if required.
For example, if this applies (what is only the case for very specific samples
of animations of the points attribute):
(such a motion is in many cases even 'more uniform and paced' as
calcMode="paced" in general provides, it is a subset of calcMode="paced").

Received on Saturday, 18 October 2008 12:37:48 UTC

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