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RE: [css3-transitions] under what transition-duration/delay conditions should there be a transition?

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Fri, 20 Apr 2012 00:37:58 +0000
To: "L. David Baron" <dbaron@dbaron.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <3C4041FF83E1E04A986B6DC50F0178290994EB94@TK5EX14MBXC295.redmond.corp.microsoft.com>

[L. David Baron:]
> In http://lists.w3.org/Archives/Public/www-style/2012Mar/0013.html

> we agreed to accept my proposal in
> http://lists.w3.org/Archives/Public/www-style/2012Feb/1083.html for
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=15838 :  that is, we agreed
> that when transition-duration and transition-delay are both 0s that there
> should be no transition (and thus no events).
> However, we didn't agree whether that was the only case.  I realized that
> there are a set of other cases where there probably shouldn't be a
> transition:  in particular, when transition delay is as negative or more
> negative than transition duration is positive.  In these cases the
> transition end event would have a firing time at or before the time the
> transition started, which suggests to me that maybe it shouldn't fire at
> all.
> Thus, I've written:
>   # When the computed value of a property changes, implementations
>   # must start transitions based on the relevant item (see the
>   # definition of ‘transition-property’) in the computed value of
>   # ‘transition-property’. Corresponding to this item there are
>   # values of ‘transition-duration’ and ‘transition-delay’ (see the
>   # rules on matching lists). Define the combined duration of the
>   # transition as the sum of max(‘transition-duration’, ‘0s’) and
>   # ‘transition-delay’. When the combined duration is greater than
>   # ‘0s’, then a transition starts based on the values of
>   # ‘transition-duration’, ‘transition-delay’, and
>   # ‘transition-timing-function’; in other cases transitions do not
>   # occur.
> Does this seem reasonable to others?
My apologies for catching this so late; I agree with the resolution and had
only one minor editorial question: is the "max(‘transition-duration’, ‘0s’)" 
expression needed in this prose given that transition-duration explicitly maps 
negative <time> values to 0s? Or is this just an editorial reminder to the reader?

Received on Friday, 20 April 2012 00:38:33 UTC

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