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RE: when do transitions occur?

From: Brian Manthos <brianman@microsoft.com>
Date: Wed, 14 Sep 2011 17:48:45 +0000
To: "L. David Baron" <dbaron@dbaron.org>, Tab Atkins Jr. <jackalmage@gmail.com>
CC: Jennifer Yu <Jennifer.Yu@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <9710FCC2E88860489239BE0308AC5D1715FDD1@TK5EX14MBXC266.redmond.corp.microsoft.com>
L. David Baron:
> Tab Atkins Jr.:
> > Jennifer Yu:
> > > And what happens when a shorthand property is changed and a
> transition is
> > > kicked off? Is it a single transition with 1 event thrown for the
> shorthand,
> > > or are the longhands transitioning with an event thrown for each?
> Or are
> > > they all transitioning, with 1 event thrown for the shorthand and
> an event
> > > thrown for each transitioning longhand?
> >
> > Not sure about the intent of this one.
> 
> There should be events for each longhand.  The starting of
> transitions is based on detecting changes in computed values, which
> is past the point where there's a distinction between longhands and
> shorthands.
> 
> And there are also plenty of cases where it doesn't make sense to
> distinguish.  For example, changing an element so that it switches
> from applying these declarations:
>   border-bottom: medium solid green;
> to these:
>   border-bottom-width: thin;
>   border-bottom-style: dashed;
>   border-bottom-color: blue;
> is changing both shorthands and longhands, but there's only one set
> of computed values changing.


1. Are there any scenarios where an event should fire for the shorthand due to transitioning?
2. Or are component longhands the only events that ever fire for transitioning?
3. If 2, should longhands that are unchanged in value but members of a shorthand that is explicitly transitioned be excluded from the events?


Example A:
	from	background: blue;
	to	background: transparent;
A1: background
A2: background-color
A3: background-image
A4: background-* (all 8)
A5: A2 and A3
A6: A1, A2, and A3
A7: A1 and A4
A8: something else

My evaluation of each event set option:
A1: it's the author-aligned delta
A2: (doesn't make sense in isolation)
A3: (doesn't make sense in isolation)
A4: all longhands are involved in the delta, no culling of unchanged properties
A5: all longhands are involved in the delta, only include changed properties
A6: same reasons as A1 and A5, both apply
A7: same reasons as A1 and A4, both apply
A8: (tbd)
Received on Wednesday, 14 September 2011 17:49:15 GMT

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