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Re: Clarification of reset behaviour

From: Brian Birtles <birtles@gmail.com>
Date: Thu, 31 Dec 2009 11:34:35 +1100
Message-ID: <65fa1620912301634p562deacep5019a8aea6de8b8e@mail.gmail.com>
To: Sjoerd Mullender <sjoerd@acm.org>
Cc: www-smil@w3.org
Dear Jack and Sjoerd,

Thank you very much for your careful response to my queries. It is
very helpful to know that I have understood the specification
correctly on these points although I understand that the specification
cannot be changed without producing a new version.

One issue which I would like to follow up is this final comment:

Sjoerd Mullender wrote:
> Elements may begin without there being an end in sight.  This is
> equivalent to having end="indefinite".  For animations this may be
> problematic, however, since they often need some fixed duration over
> which to change a value.

I don't think I quite understand what is being said here. In
particular I would like to check my understanding of the condition
given in the pseudocode for getFirstInterval[1] and getNextInterval[2]
that if we have an end attribute specified we must match each begin to
an end or else it's a bad interval. Therefore:

  <animate begin="1s; 3s" ... />

produces two intervals as no end attribute is specified. Whereas:

  <animate begin="1s; 3s" end="2s" .../>

produces only one interval since there is no end to match the begin at
3s  (and nor does the end attribute have event conditions or an empty
end instance list). So I wonder if it's true that "elements may begin
without there being an end in sight."

I bring this up here because (a) I might have misunderstood this and
you may be able to correct me here, and (b) I suspect that in any case
this pseudocode needs review. In particular the initial three lines:

   If there was no end attribute specified
      // this calculates the active end with no end constraint
      tempEnd = calcActiveEnd( tempBegin );

would effectively mean that any calls to endElement on an animation
that lacks an end attribute would have no effect. However this seems
counter-intuitive. A script should be able to stop an animation
regardless of whether it has an end attribute specified.

(One suggestion for fixing this might be to change the first line to
read "If there was no end attribute and there are no end instances.")

Again, this may be something for a later SYMM working group to consider.

Thank you once again for your helpful feedback on this.

Best regards,

Brian

[1] http://www.w3.org/TR/SMIL3/smil-timing.html#Timing-BeginEnd-LC-Start
[2] http://www.w3.org/TR/SMIL3/smil-timing.html#Timing-BeginEnd-LC-End
Received on Thursday, 31 December 2009 00:35:30 GMT

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