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Re: [css3-animations] multiple 'animation-name' and cascading

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 12 Apr 2011 12:53:07 -0700
Message-ID: <BANLkTi=P+2Cfo0KfmjL1YEZQJ6d7z59-8g@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: Simon Fraser <smfr@me.com>, Dean Jackson <dino@apple.com>, www-style@w3.org
On Tue, Apr 12, 2011 at 12:32 PM, L. David Baron <dbaron@dbaron.org> wrote:
> On Tuesday 2011-04-12 11:33 -0700, Simon Fraser wrote:
>> On Apr 12, 2011, at 10:29 AM, L. David Baron wrote:
>> > On Tuesday 2011-04-12 08:56 -0700, Tab Atkins Jr. wrote:
>> >> On Mon, Apr 11, 2011 at 9:09 PM, L. David Baron <dbaron@dbaron.org> wrote:
>> >>> (Alternatively, I suppose one could check for whether the property
>> >>> is specified in any keyframe -- though that's a bit more work.)
>> >>
>> >> You need to check all the keyframes.  Given a keyframe like this:
>> >>
>> >> @keyframes wobble {
>> >>   0% { left: 0; top: 0; }
>> >>  33% { top: 100px; }
>> >>  67% { top: -100px; }
>> >> 100% { left: 100px; top: 0; }
>> >> }
>> >>
>> >> In the middle third of the animation, the nearest keyframe blocks
>> >> don't have any mention of 'left', but 'left' is still being animated.
>> >
>> > The spec should perhaps mention that somewhere.
>>
>> Agreed :)
>>
>> > Additionally, it should say how that behavior interacts with timing
>> > functions specified in keyframes.
>>
>> In this case left animates exactly as if the middle two keyframes were missing:
>>
>> @keyframes wobble {
>>   0% { left: 0; top: 0; }
>> 100% { left: 100px; top: 0; }
>> }
>>
>> If the first keyframe had a timing-function, then that's the one that would apply.
>>
>> In other words, properties are interpolated between the keyframes
>> that specify them.
>
> This makes sense -- and seems better for authors -- but it surprises
> me given that (a) the spec doesn't say this and (b) the spec says
> that duplicate keyframes get dropped, which is part of what led me
> to the model that I interpreted (and implemented) from what the spec
> does say.
>
> So given this model, it seems like it would make much more sense if
> the spec also said that duplicate keyframes weren't dropped, but
> were instead cascaded, so that, with:
>
>  0% { left: 0; top: 0 }
>  50% { top: 40px; left: 40px }
>  50% { top: 25px; }
>  100% { top: 100px; left: 100px }
>
> you'd end up with top animating according to:
>  0% { top: 0 }
>  50% { top: 25px }
>  100% { top: 100px }
> and left animating according to:
>  0% { left: 0 }
>  50% { left: 40px }
>  100% { left: 100px }
> instead of having, as the spec currently says, left animating
> according to:
>  0% { left: 0 }
>  100% { left: 100px }
> because the second 50% keyframe overrides the first.
>
>
> In other words, I'd propose replacing the text:
>  # If there are any duplicates, then the last keyframe specified
>  # inside the @keyframes rule will be used to provide the keyframe
>  # information for that time. There is no cascading within a
>  # @keyframes rule if multiple keyframes specify the same keyframe
>  # selector values.
> with something that does specify cascading across different keyframe
> selectors in the @keyframes rule.

I also agree that cascading the keyframes would be nice, though
possibly for a different reason - as currently stated, you can't
animate two properties starting from the same moment with different
timing functions without silly hacks like starting one at 0% and the
next at 0.001%.

~TJ
Received on Tuesday, 12 April 2011 19:53:58 GMT

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