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Re: [whatwg] (X)HTML + SMIL?

From: Bjoern Hoehrmann <derhoermi@gmx.net>
Date: Sat, 27 Dec 2008 22:06:31 +0100
To: robert@ocallahan.org
Cc: www-style@w3.org
Message-ID: <v10dl4ts0ghbvb5qgo170hbomtr93juh8u@hive.bjoern.hoehrmann.de>

* Robert O'Callahan wrote:
>CSS Transitions and SMIL Animations are actually quite different. CSS
>Transitions provide for smooth transitions whenever the computed value of a
>CSS property changes; they provide no way to actually *cause* a change in a
>property value. SMIL can cause changes in property values (changes that
>occur during the cascade and therefore can be inherited etc), but it can't
>automatically smooth transitions whenever a CSS computed value changes.

It is not possible to directly change property values, except by manipu-
lating style sheets--and both CSS Transitions and SMIL animations do so.
That is necessarily so, if they would not change style sheets the compu-
ted value of properties and hence the rendering would not change either.

You also can't look at "CSS Transitions" in isolation here, you have to
consider style sheets as a whole, and if you compare

  #example       { color: blue   }
  #example:focus { color: orange }

to

  <set begin='0s' ... example ... color ... blue ...
  <set begin='example.focusin' end='example.focusout' ... orange ...

then it is quite easy to see that this is mere syntactic difference,
and either both snippets "change property values", or neither does. It's
only because writing much of your style sheet effectively in SMIL syntax
is rather undesirable that "CSS Transitions" are being proposed.

I note by the way that the "CSS Transitions" still lacks a complete de-
finition of exactly when a transition begins, and from which old state
to which new state it should go, and what happens once it has reached
it. For example, from the incomplete and informal suggestions it seems
that changes trigger transitions, and transitions trigger changes; that
process does not terminate by itself. Similarily other changes may occur
while a transition is in progress, what happens then is not clear at all
absent such definitions.
-- 
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Am Badedeich 7 · Telefon: +49(0)160/4415681 · http://www.bjoernsworld.de
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Received on Saturday, 27 December 2008 21:07:10 GMT

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