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ISSUE-2083 (Paced-anim-complex): Paced animation and complex types [Last Call: SVG 1.2 Tiny ]

From: SVG Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Wed, 1 Oct 2008 14:15:01 +0000 (GMT)
To: public-svg-wg@w3.org
Message-Id: <20081001141501.52B006B62B@tibor.w3.org>

ISSUE-2083 (Paced-anim-complex): Paced animation and complex types [Last Call: SVG 1.2 Tiny ]


Raised by: Doug Schepers
On product: Last Call: SVG 1.2 Tiny 

Dr. Olaf Hoffmann
16.2.7 Paced animation and complex types 
notes now for <list-of-points>, that 'There is no defined formula to pace a
list of points. The request to pace should be ignored and the value of linear 
used instead.'
This is understandable and fine because
'Distance is defined for types which can be expressed as a list of values,
where each value is a vector of scalars in an n-dimensional space. For
example, an angle value is a list of one value in a 1-dimensional space 
and a color is a list of 1 value in a 3-dimensional space.'
and even more relevant:
Defines interpolation to produce an even pace of change across the animation. 
This is only supported for values that define a linear numeric range, and for
which some notion of "distance" between points can be calculated (e.g. 
position, width, height, etc.)."

And a list is not always a vector (a vector has an absolute value and a 
direction) - <list-of-points> - no vector, no formula for a distance,
therefore no paced animation defined in general. And there is no way 
to get an interpolation with an even pace for such a list.

1. Surprisingly  there are (still) formulas given for <list-of-lengths>,
<list-of-coordinates>, <list-of-numbers>, <path-data>.
These lists are no vectors either, <path-data> is not even a list which can 
be confused with a vector. Especially <list-of-points> is equivalent to a
subset of <path-data> - and if the  equivalence of a subset of <path-data> 
has no formula for a distance as identified already correctly, obviously the
currently given formula for <path-data> results in nonsense and in
general not into an interpolation with an even pace.
The same applies for the other lists, because they do not represent vectors
with one absolute value and one direction. Therefore there should be no
formula too and authors should be discouraged to use calcMode paced with 
such types, because if there are already some formulas implemented due to 
SVG 1.1 or previous drafts, this will result in nonsense anyway.

Note, that the related sample(s) in the test suite need to be fixed/removed
too, for example animate-elem-53 (calcMode paced for points, <list-of-points>
as already excluded in the current draft)

2. transform type scale is pretty fine now (according to the curent formula it
is more one 2-dimensional value, not two 1-dimensional values) as translate 
is and skewX/Y.
rotate is more critical, but the new formula is already a big improvement
compared to previous attempts. If the rotation center is not changed within
the animation, this results indeed in a paced animation ;o)
But it should be at least noted for authors, that it exists in general no
paced animation, if the rotation center changes within the animation, 
neither with the given formula nor with any other or whatever is already
implemented in previous viewer versions or noted in SVG 1.1. 

Note, that in the test suite animate-elem-82 describes still the (wrong)
behaviour of SVG 1.1 for paced animateTransform and paced translate
animateTransform is still insensitive to  implemented timing and 
therefore useless (see long discussion from last year about this test
including a provided alternative).
Received on Wednesday, 1 October 2008 14:15:35 UTC

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