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non-additive to-animations?

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Sat, 1 Jul 2006 14:25:21 +0200
To: www-smil@w3.org
Message-Id: <200607011425.21931.Dr.O.Hoffmann@gmx.de>

Hello,

I tried to find something about a to-animation 
(without) from for a non-additive attribute, 
but I could not find much about it. If it
is mentioned, it would be already helpful to
know in which section.
But as far as I have seen, this is not completely clear
from the recommendation what to do with this.

Old recommendation 04-September-2001 
notes about to-animation in general:

'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.
The last two forms "by animation" and "to animation" have 
additional semantic constraints when combined with other 
animations. 
The details of this are described below in the section 
How from, to and by attributes affect additive behavior.
'

This is already sufficient if there is no lower priority
animation, even for non-additive attributes or properties.
Anyway it is not mentioned, what happens if the behaviour
cannot be additive sum, but has to be replace in the case 
with a lower priority animation.
Is it correct, that in this case the to-animation will
replace all lower priority animations, just starting 
with the underlying value directly from the animated 
attribute too? 
This would be one possible interpretation of this 
paragraph concerning non-additve attributes or 
properties.
The other one is: If c(begin) is the current (time 
dependent) underlying value from lower priority animations
at the begin of the higer priority to-animation, and
f is the final value given by the to-animation, this 
is the same visual effect as using values="c(begin); f".
Which interpretation is correct or what is the correct
behaviour if none of them is correct?


Even if this is clearified for SVG1.0 and SVG1.1 using the
old recommendation, SMIL2.1 changes description:
'
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
'

Well, the first part is the same but seems to be changed
to something just informative, not normative, but the 
second refers to a section defining only the behaviour 
of additive attributes and properties. 
Therefore correct behaviour of non-additive attributes 
seems to be completely undefined, even if there
is no lower priority animation.

Therefore: Is it intended to change the previously 
defined behaviour? 
Which behaviour is correct in these cases with 
SMIL2.1?
For example in SVG there is the attribute 'rotate' of 
the 'text' element defined to be non-additive and the
property 'stroke-dasharray'.
If we take this as an example:

<text x="200" y="400" rotate="-30" stroke="#ccc">?
<animate
        attributeName="rotate" 
        attributeType="XML"
        to="30"
        dur="3s" />
</text>


Is this the same visual effect as using:
1. values="-30;30"
or
2. values="30" or
   instead of animate 
   <set 
        attributeName="rotate" 
        attributeType="XML"
        to="30"
        dur="5s" />
or  
3. values="-30;30" calcMode="discrete"
or 
4. authors should not use to-animations for non-additive 
   attributes or properties, viewers should ignore an 
   animation like this.
or 
5. something different?  

Is it correct in a general case to assume, that the
animation of highest priority will overwrite other
animations in this case, that therefore the chosen
alternative from 1. to 5. is always applicable for
the animation with highest priority?
Or is the replacement values="c(begin); f" as
mentioned above the correct general interpretation?


A related question: If fill is freeze, the general
rule for none-additive attributes is applied and not
the special rule for frozen to-animations?



 
Grateful for any information about this

Olaf Hoffmann
Received on Saturday, 1 July 2006 12:24:33 GMT

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