Re: [csswg-drafts] [css-view-transitions-1] Define the constraints which must be satisfied by a named element during the transition (#8548)

The CSS Working Group just discussed `[css-view-transitions-1] Define the constraints which must be satisfied by a named element during the transition`, and agreed to the following:

* ``RESOLVED: If an element is involved in a transition, the `view-transition-name` constraints are enforced during the transition``
* `RESOLVED: Conditions are checked per-frame; transition is skipped if other constraints are broken`

<details><summary>The full IRC log of that discussion</summary>
&lt;JakeA> A view-transition-name value that isn't none gives an element stacking context, grouping element, backdrop root, similar to non-1 opacity, as view transitions need these constraints.<br>
&lt;emeyer> JakeA: If you give an element a transition name that isn’t none, it acts as if opacity is not 1<br>
&lt;fantasai> s/Topic:/Subtopic:/<br>
&lt;fantasai> s/Topic:/Subtopic:/<br>
&lt;fantasai> i/Subtopic: [css-view-transitions-1] Capturing/Topic: View Transitions<br>
&lt;RRSAgent> I have made the request to generate https://www.w3.org/2023/03/15-css-minutes.html fantasai<br>
&lt;emeyer> …Name is only checked during transition, but because the new view is live, we need to check constraints per frame<br>
&lt;emeyer> …If constraints are not satisfied mid-transition, element is dropped from the rest of the transition<br>
&lt;emeyer> …If an element isn’t rendered during setup, it’s ignored<br>
&lt;emeyer> …If an element becomes fragmented during transition, it’s dropped<br>
&lt;emeyer> …How do we check these conditions?<br>
&lt;emeyer> …Option 1: we assert extra conditions, then check to see if the view transition name is not none<br>
&lt;emeyer> …If a name ever becomes none, element is dropped<br>
&lt;emeyer> Option 2: We assert these all individually, regardless of name<br>
&lt;flackr> q+<br>
&lt;astearns> ack flackr<br>
&lt;emeyer> flackr: Option 3, if an element is undergoing view transition, it is subject to the constraints<br>
&lt;khush> I'd be ok with that.<br>
&lt;emeyer> JakeA: We can’t enforce rendering and we wouldn’t enforce fragmenting<br>
&lt;vmpstr> +1<br>
&lt;emeyer> flackr: Right, we could continue to enforce name-based constraints<br>
&lt;astearns> ack fantasai<br>
&lt;emeyer> TabAtkins: My preference as well<br>
&lt;emeyer> fantasai: That makes sense; other thought I had was if the name changes at all, I wouldn’t be surprised if the transition is suddenly dropped<br>
&lt;emeyer> JakeA: We avoided that because it means we can’t deal with elements that suddenly gain a transition name<br>
&lt;emeyer> fantasai: I’m not saying you’d start a new transition, I’m saying if someone messes with names, it should be dropped<br>
&lt;emeyer> JakeA: If a paragraph isn’t in a transition and halfway through JS gives it a name, should it be ignored?<br>
&lt;emeyer> …If we deal with every element changed names, then you have to check every frame<br>
&lt;emeyer> astearns: It sounds like Option 2, except names are kept throughout the transition and so need to be checked?<br>
&lt;emeyer> JakeA: I think people like flackr’s option<br>
&lt;emeyer> …I’m happy with that<br>
&lt;khush> +1<br>
&lt;emeyer> fantasai: Wouldn’t you also be enforcing that it’s not fragmented?<br>
&lt;emeyer> JakeA: We would skip the transition in that case<br>
&lt;emeyer> fantasai: What if a thing becomes fragmented partway through? Would you just ignore that?<br>
&lt;emeyer> JakeA: The new views are live and updated per frame<br>
&lt;emeyer> …If an element becomes not-renderable…<br>
&lt;emeyer> fantasai: I get it<br>
&lt;emeyer> astearns: Option3<br>
&lt;JakeA> If an element is involved in a transition, the ``view-transition-name` constraints are enforced during the transition<br>
&lt;JakeA> It's skipped if other constraints are broken<br>
&lt;JakeA> (eg rendering and now fragmenting)<br>
&lt;emeyer> RESOLVED: If an element is involved in a transition, the `view-transition-name` constraints are enforced during the transition<br>
&lt;emeyer> RESOLVED: Conditions are checked per-frame; transition is skipped if other constraints are broken<br>
</details>


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Received on Wednesday, 15 March 2023 15:50:45 UTC