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[css-animations-2] Specify the animation-trigger property #10128

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[css-animations-2] Specify the animation-trigger property #10128

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133f6e0
[css-animations-2] Specify the animation-trigger property
ydaniv Mar 25, 2024
f3a49ba
Fixed syntax of single-animation-trigger + some link fixes
ydaniv Mar 25, 2024
cbd4f07
More fixes to links and defs
ydaniv Mar 27, 2024
9f6464a
More fixes to links and defs
ydaniv Mar 28, 2024
912426a
Move all definitions to web-animations-1;
ydaniv Apr 17, 2024
9ae1a13
Fixed idle state definition for animation trigger state
ydaniv Apr 18, 2024
f1d2e89
Moved all new definitions from web-animations-1 to web-animations-2
ydaniv May 11, 2024
e55e476
Added a description to each property of animation-trigger;
ydaniv Jun 2, 2024
a0e90fe
Fixed some syntax errors
ydaniv Jun 6, 2024
361f5d9
Added an issue about timeline becoming idle and did-trigger resetting…
ydaniv Jun 6, 2024
efa38c7
Define animation trigger active interval
ydaniv Jun 6, 2024
085618e
Merge from main
ydaniv Jun 6, 2024
11e3138
Rewrite again according to review
ydaniv Jul 31, 2024
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279 changes: 279 additions & 0 deletions css-animations-2/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,13 @@ spec:web-animations-1; type:dfn;
text:start delay
text:target element
text:unresolved
spec:web-animations-2; type:dfn;
text:active interval; for:animation trigger
text:default range
text:exit range
spec:scroll-animations-1; type:dfn;
text:animation-range-start
text:animation-range-end
</pre>

<h2 id="delta">Delta specification</h2>
Expand Down Expand Up @@ -690,7 +697,279 @@ The 'animation' shorthand property syntax is as follows:

<span class=prod><dfn>&lt;single-animation></dfn> = <<'animation-duration'>> || <<easing-function>> || <<'animation-delay'>> || <<single-animation-iteration-count>> || <<single-animation-direction>> || <<single-animation-fill-mode>> || <<single-animation-play-state>> || [ none | <<keyframes-name>> ] || <<single-animation-timeline>></span>

<h2 id="animation-triggers">
Declaring Animation Triggers</h2>

Animation Triggers are defined using the 'animation-trigger-*' properties.
These list-valued properties,
which are all [=longhands=] of the 'animation-trigger' [=shorthand=],
form a [=coordinating list property group=]
with 'animation-name' as the [=coordinating list base property=]
and each item in the [=coordinated value list=]
defining the properties of a single animation trigger.
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If this spec doesn't explain how they work but only mentions the relevant properties, it should point to the section in the web-animations-2 spec which explains what animation triggers are and how they work. E.g. this could be as simple as having "animation triggers" link to the section in web animations, similar to how the animation composition property points to the web-animations definition of what a composite operation is.

That said, it's not uncommon to have a plain English explanation for what it means with the details and algorithms left to web-animations. E.g. to take a random property the definition of animation-fill-mode explains what it does without going into the specific algorithmic details that are in the web-animations spec.

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I like both. I guess I'll refactor the text a bit and add a link.

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done


## The 'animation-trigger-type' property ## {#animation-trigger-type}

The 'animation-trigger-type' property specifies the [=animation trigger type=]
of the [=animation trigger=].

<pre class='propdef'>
Name: animation-trigger-type
Value: <<single-animation-trigger-type>>#
Initial: once
Applies to: all elements
Inherited: no
Percentages: N/A
Computed value: list, each item a keyword as specified
Animation type: not animatable
Canonical order: per grammar
</pre>

<span class=prod><dfn>&lt;single-animation-trigger-type></dfn> = once | repeat | alternate | state</span>
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Can you add a description of what each property value means. Also we probably need a none value on this property to represent the default case right?

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I was pondering all the none/normal/auto options, and I think we currently don't need them, since the initial value is once, with a timeline value of auto, which I think is exactly what we have today.
We could also add an issue on that, in case it needs an approval from the group.

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The definition of the values is done here.
Should I add here another description? More user/less implementor facing?

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I was pondering all the none/normal/auto options, and I think we currently don't need them, since the initial value is once, with a timeline value of auto, which I think is exactly what we have today.

Yeah, I like having the default values basically explain the triggering behavior we get today and adding the ability to modify it. It makes it feel like less of an added on property and more just part of the standard animation infrastructure.

We could also add an issue on that, in case it needs an approval from the group.

I think this can be part of the general review when it's all written up.

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Can you add a description of what each property value means.

Done


The values of 'animation-trigger-type' have the following meaning
for an [=animation trigger=] that enters its [=animation trigger/active interval|active interval=]:

<dl dfn-type=value dfn-for=animation-trigger-type>
<dt><dfn>once</dfn>
<dd>
The animation is triggered and played once and only once.

<dt><dfn>repeat</dfn>
<dd>
The animation is played from the beginning each time it is triggered.
When the trigger’s [=animation trigger/active interval|active interval=] is exited the animation is reset.

<dt><dfn>alternate</dfn>
<dd>
The animation is played forwards, according to its [=playback direction=], each time it is triggered.
When the trigger’s [=animation trigger/active interval|active interval=] is exited the animation is reversed.

<dt><dfn>state</dfn>
<dd>
The animation is triggered and played once.
When the trigger’s [=animation trigger/active interval|active interval=] is exited the animation is paused.
When the trigger’s [=animation trigger/active interval|active interval=] is re-entered the animation is resumed.
</dl>

The behavior of each value is defined in [[web-animations-2#trigger-types]].

## The 'animation-trigger-timeline' property ## {#animation-trigger-timeline}

The 'animation-trigger-timeline' property specifies the <a>timeline</a>
of the animation’s associated [=animation trigger=].

<pre class='propdef'>
Name: animation-trigger-timeline
Value: <<single-animation-timeline>>#
Initial: auto
Applies to: all elements
Inherited: no
Percentages: N/A
Computed value: list, each item either
the keyword ''single-animation-timeline/none'',
the keyword ''single-animation-timeline/auto'',
a case-sensitive [=css identifier=],
a computed ''scroll()'' function,
or
a computed ''view()'' function
Canonical order: per grammar
Animation Type: not animatable
</pre>

The values of 'animation-trigger-timeline' have the same meaning as those of 'animation-timeline'.

Issue: Probably a trigger with timeline "none" is under-specified here. Need to clarify what it means.
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I wonder if the default timeline is the document timeline set up in a way such that the "trigger" is always active explaining the normal behavior of animations? You could imagine then using this as a way to coordinate starting an animation after some length of time, e.g. animation-trigger-range: 10s. Admittedly this has some overlap with animation-delay, but unlike animation delay could use absolute times since page load or other events I suppose?

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Well, I remember we considered this in a previous issue specifically on syncing animations, but we said there that this will be the stuff that will eventually be done via GroupEffects. That said, if you see some way of changing the definition here and keeping this more open for later extensions I'm all for it.

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but unlike animation delay could use absolute times since page load or other events I suppose?

I feel like we'll still the pseudo-selector you suggested in #8175, for example, to defer until DOM and assets are loaded. This is pretty common.

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I think we should remove the none state, I'm not sure what it even means and the initial value is auto so it's not clear what you'd use none for. With the initial value auto, as you've said it has the same meaning as values of animation-timeline and as such would map to the document timeline. I think we should try to go with this model as it explains the existing behavior.

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OK, but none here is part of the single-animation-timeline syntax. Should we remove it just here? Or entirely?


## The 'animation-trigger-range' property ## {#animation-trigger-range}

<pre class="propdef shorthand">
Name: animation-trigger-range
Value: [ <<'animation-trigger-range-start'>> <<'animation-trigger-range-end'>>? ]#
</pre>

The 'animation-trigger-range' property is a [=shorthand property|shorthand=]
that sets 'animation-trigger-range-start' and 'animation-trigger-range-end'
together in a single declaration,
specifying the [=animation trigger=]’s associated [=default range=].
It has the same syntax as the 'animation-range' property.

The behavior of 'animation-trigger-range' is defined in [[web-animations-2#trigger-ranges]].

## The 'animation-trigger-range-start' property ## {#animation-trigger-range-start}

<pre class="propdef">
Name: animation-trigger-range-start
Value: [ normal | <<length-percentage>> | <<timeline-range-name>> <<length-percentage>>? ]#
Initial: normal
Applies to: all elements
Inherited: no
Percentages: relative to the specified [=named timeline range=] if one was specified, else to the entire timeline
Computed value: list, each item either the keyword ''animation-trigger-range-start/normal'' or a timeline range and progress percentage
Animation type: not animatable
</pre>

The 'animation-trigger-range-start' property specifies the start of the [=animation trigger=]’s
associated [=default range=].

The values of 'animation-trigger-range-start' have the same meaning as those of 'animation-range-start'.

## The 'animation-trigger-range-end' property ## {#animation-trigger-range-end}

<pre class="propdef">
Name: animation-trigger-range-end
Value: [ normal | <<length-percentage>> | <<timeline-range-name>> <<length-percentage>>? ]#
Initial: normal
Applies to: all elements
Inherited: no
Percentages: relative to the specified [=named timeline range=] if one was specified, else to the entire timeline
Computed value: list, each item either the keyword ''animation-trigger-range-end/normal'' or a timeline range and progress percentage
Animation type: not animatable
</pre>

The 'animation-trigger-range-end' property specifies the end of the [=animation trigger=]’s
associated [=default range=].

The values of 'animation-trigger-range-end' have the same meaning as those of 'animation-range-end'.

## The 'animation-trigger-exit-range' property ## {#animation-trigger-exit-range}

<pre class="propdef shorthand">
Name: animation-trigger-exit-range
Value: [ <<'animation-trigger-exit-range-start'>> <<'animation-trigger-exit-range-end'>>? ]#
</pre>

The 'animation-trigger-exit-range' property is a [=shorthand property|shorthand=]
that sets 'animation-trigger-exit-range-start' and 'animation-trigger-exit-range-end'
together in a single declaration,
specifying the [=animation trigger=]’s associated [=exit range=].
It has the same syntax as the 'animation-range' property, with the addition of the ''auto'' keyword.

The [=exit range=] replaces the [=default range=] once the [=animation trigger=]’s
[=animation trigger/active interval|active interval=] is entered,
and redefines the extent of the [=animation trigger=]’s [=animation trigger/active interval|active interval=].
It is used to extend the [=default range=], for example,
in cases where exiting the [=animation trigger/active interval|active interval=]
may create a visual jump that needs to be avoided.

The behavior of 'animation-trigger-exit-range' is further defined in [[web-animations-2#trigger-ranges]].

## The 'animation-trigger-exit-range-start' property ## {#animation-trigger-exit-range-start}

<pre class="propdef">
Name: animation-trigger-exit-range-start
Value: [ auto | normal | <<length-percentage>> | <<timeline-range-name>> <<length-percentage>>? ]#
Initial: auto
Applies to: all elements
Inherited: no
Percentages: relative to the specified [=named timeline range=] if one was specified, else to the entire timeline
Computed value: list, each item either the keyword ''animation-trigger-exit-range-start/normal'' or a timeline range and progress percentage
Animation type: not animatable
</pre>

The 'animation-trigger-exit-range-start' property specifies the start of the [=animation trigger=]’s
associated [=exit range=].

The values of 'animation-trigger-exit-range-start' have the following meaning:

<dl dfn-for="animation-trigger-exit-range-start" dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
The start of the trigger’s [=exit range=]
is equal to the start of its [=default range=].

<dt><dfn>normal</dfn>
<dd>
The start of the trigger’s [=exit range=]
is the start of its associated [=timeline=];
the start of the trigger’s [=animation trigger/active interval|active interval=]
is determined as normal.

<dt><dfn><<length-percentage>></dfn>
<dd>
The [=exit range=] starts
at the specified point on the [=timeline=]
measuring from the start of the timeline.

<dt><dfn><<timeline-range-name>> <<length-percentage>>?</dfn>
<dd>
The [=exit range=] starts
at the specified point on the [=timeline=]
measuring from the start of the specified [=named timeline range=].
If the <<length-percentage>> is omitted,
it defaults to 0%.
</dl>

## The 'animation-trigger-exit-range-end' property ## {#animation-trigger-exit-range-end}

<pre class="propdef">
Name: animation-trigger-exit-range-end
Value: [ auto | normal | <<length-percentage>> | <<timeline-range-name>> <<length-percentage>>? ]#
Initial: auto
Applies to: all elements
Inherited: no
Percentages: relative to the specified [=named timeline range=] if one was specified, else to the entire timeline
Computed value: list, each item either the keyword ''animation-trigger-exit-range-end/normal'' or a timeline range and progress percentage
Animation type: not animatable
</pre>

The 'animation-trigger-exit-range-end' property specifies the end of the [=animation trigger=]’s
associated [=exit range=].

The values of 'animation-trigger-exit-range-start' have the following meaning:

<dl dfn-for="animation-trigger-exit-range-end" dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
The end of the trigger’s [=exit range=]
is equal to the end of its [=default range=].

<dt><dfn>normal</dfn>
<dd>
The end of the trigger’s [=exit range=]
is the end of its associated [=timeline=];
the end of the trigger’s [=animation trigger/active interval|active interval=]
is determined as normal.

<dt><dfn><<length-percentage>></dfn>
<dd>
The [=exit range=] ends
at the specified point on the [=timeline=]
measuring from the start of the timeline.

<dt><dfn><<timeline-range-name>> <<length-percentage>>?</dfn>
<dd>
The [=exit range=] ends
at the specified point on the [=timeline=]
measuring from the start of the specified [=named timeline range=].
If the <<length-percentage>> is omitted,
it defaults to 100%.
</dl>

## The 'animation-trigger' property ## {#animation-trigger}
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The 'animation-trigger' property is a [=shorthand property|shorthand=]
that sets 'animation-trigger-type', 'animation-trigger-timeline',
'animation-trigger-range-start', 'animation-trigger-range-end',
'animation-trigger-exit-range-start', and 'animation-trigger-exit-range-end'
together in a single declaration,
specifying the [=animation trigger=] for an animation.

<pre class='propdef'>
Name: animation-trigger
Value: <<single-animation-trigger>>#
Initial: see individual properties
Applies to: all elements
Inherited: no
Percentages: N/A
Computed value: see individual properties
Canonical order: per grammar
Animation Type: not animatable
</pre>

<pre class=prod>
<dfn>&lt;single-animation-trigger></dfn> = <<single-animation-trigger-type>> || [ none | auto | [ [ <<dashed-ident>> | <<scroll()>> | <<view()>> ] [ normal | <<length-percentage>> | <<timeline-range-name>> <<length-percentage>>? ]{0,4} ] ]
</pre>

# Animation Events # {#events}

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