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[SMIL30 LC comment] 3.6.4 Simple animation functions ...

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Wed, 15 Aug 2007 10:45:27 +0200
To: www-smil@w3.org
Message-Id: <200708151045.27991.Dr.O.Hoffmann@gmx.de>

Hello SMIL working group,


some comments on
3.6.4 Simple animation functions specified by from, to and by


'by animation'

'... This may only be used with attributes that support additive 
animation. ...'

-> What happens if a nasty author uses it anyway with non-additive attributes?
Is in such a case simply the additive behaviour ignored, the animation is
equivalent with a values animation using the two values '0' and vb and
additive="replace"? Or is the complete animation ignored as nonsense?
I suggest the first behaviour...


'Normative: A by animation with a by value vb is equivalent to the same
animation with a values list with 2 values, 0 and vb, and additive="sum". 
Any other specification of the additive attribute in a by animation is
ignored.'


-> A certain uncertainty came up for some people, what '0' means in this
paragraph. Sure, for attribute values consisting of a simple number or integer
this can be identified simply as the number zero, but for more complex values
there seems to be a gap of imagination ;o)
In SMIL this happens too for example for animateMotion, animateColor or an
animation of an attribute like viewBox. Values of animateMotion have two
components, animateColor has three color components and viewBox requires 
four numbers, therefore '0' itself is not directly applicable but has to be
replaced with a specific value related to the animated attribute.
According to my opinion, '0' in this paragraph is not simply the number zero,
it is just a generic symbol or a wild-card as vb is too. Therefore I
interpreted '0' always as a wild-card for the neutral element of addition in
the value space related to the animated attribute or property. Is this
correct?
-> If yes, I suggest to add something like this:
'Note, that '0' is used here as a generic symbol for the neutral element of
addition for the value type of the animated attribute or property. For example
for animateColor '0' is used here as a symbol to be replaced with black or
#000 or rgb(0,0,0), for animateMotion this is a symbol to be replaced with 
the value of the origin 0,0. Similar substitutions have to be done for any
attribute value.'



---

'to animation
This describes an animation in which the animation function is defined to
start with the underlying value for the attribute, and finish with the value
specified with the to attribute. Using this form, an author can describe an
animation that will start with any current value for the attribute, and will
end up at the desired to value. 

A normative definition of a to animation is given below in To animation'

-> missing a '.' at the end

-> Note that the reference still points to the informative box, not to the
normative box, this is maybe a little bit confusing within a normative
sections, because it it noted, that it references a normative definition.

'A to animation of an attribute which supports addition is a kind of mix of
additive and non-additive animation.'

-> Well, this is now indicated only as informative, this was not the case in
SMIL2.
My interpretation now is, that it is not important, if the attribute supports
addition or not, one has to follow the normative formulars below anyway? 
But then the sentence above can be shortend to avoid confusion:

-> 'A to animation of an attribute is a kind of mix of additive and
non-additive animation.'
Received on Wednesday, 15 August 2007 09:06:19 GMT

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