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'prev' Keyword And Id Restrictions

From: Doug Schepers <doug@schepers.cc>
Date: Sun, 6 Nov 2005 19:21:40 -0500
To: <www-svg@w3.org>
Message-Id: <20051107002143.8AA88109EAA@pilfer.dreamhost.com>

Hi, SVG-WG-

When I was working on my SmilScript lib, I started wondering where the
'prev' keyword is specified. I've used it many times in my SMIL animations,
but when I actually looked for it in the W3C Recommendations [1][2][3][4], I
couldn't find it. I did find mention of it [5] in the "Synchronized
Multimedia Integration Language (SMIL) Boston Specification" (3-August-1999)
[6], but that's not just a Working Draft, not a Recommendation.

Is this actually a part of the SVG SMIL Rec, or is it an Adobe-specific
extension? Is it just something that was assumed to be in SMIL, but dropped
without anyone noticing? In any case, I would like to see it made explicit
in the new SVG1.2 Spec if it is indeed part of SVG.

I think it's a valuable keyword, but there is a problem with it. Is it
permitted to have an animation with an id="prev"? If so, how can that be
resolved with the syntax 
 begin="myAnimationId.begin"
It's probably much too late to address this, but it really makes much more
sense (and more consistent) to have something that uses XLink syntax, like: 
 begin="#myAnimationId.begin"
or 
 begin="url(#myAnimationId).begin".

The example below illustrates this problem:

<svg xmlns='http://www.w3.org/2000/svg'
xmlns:xlink='http://www.w3.org/1999/xlink'>

   <circle id='circle_1' cx='25' cy='25' r='20' fill='gold'>
      <animateMotion to='100, 100' begin='1s' dur='2s' fill='freeze'
repeatCount='1'/>
      <set attributeName='fill' to='blue' begin='prev.end' />
   </circle>

   <circle id='circle_2' cx='125' cy='25' r='20' fill='gold'>
      <animateMotion id='prev' to='100, 100' begin='1s' dur='2s'
fill='freeze' repeatCount='1'/>
   </circle>

   <circle id='circle_2' cx='225' cy='25' r='20' fill='gold'>
      <animateMotion id='prev1' to='100, 100' begin='1s' dur='2s'
fill='freeze' repeatCount='1'/>
   </circle>

   <circle id='circle_3' cx='125' cy='25' r='10' fill='red'>
      <set attributeName='fill' to='lime' begin='prev.end' />
   </circle>

   <circle id='circle_4' cx='225' cy='25' r='10' fill='red'>
      <set attributeName='fill' to='lime' begin='prev1.end' />
   </circle>
</svg>

[1] http://www.w3.org/TR/SVG/animate.html (and the equivalent in SVG1.0)
[2] http://www.w3.org/TR/2001/REC-smil-animation-20010904/
[3] http://www.w3.org/TR/1998/REC-smil-19980615/
[4] http://www.w3.org/TR/2005/REC-SMIL2-20050107/smil20.html
[5]
http://www.w3.org/1999/08/WD-smil-boston-19990803/Animation/smil-animation#F
illAndRepeat
[6]
http://www.w3.org/1999/08/WD-smil-boston-19990803/Overview.html#generalTOC

Regards-
Doug

doug.schepers@vectoreal.com
www.vectoreal.com ...for scalable solutions.
Received on Monday, 7 November 2005 00:21:56 GMT

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