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[css-view-transitions-1] Defer restoring persisted state until after capturing old state #9676

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[css-view-transitions-1] Defer restoring persisted state until after capturing old state #9676

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[css-view-transitions-1] Defer restoring persisted state until after…
noamr Dec 4, 2023
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noamr Dec 4, 2023
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noamr Dec 13, 2023
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noamr Dec 18, 2023
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39 changes: 39 additions & 0 deletions css-view-transitions-1/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,9 @@ spec:css-display-4; type: dfn; text:invisible;
urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
text: NavigateEvent
text: signal; for: NavigateEvent; url: #ref-for-dom-navigateevent-signal①
urlPrefix: https://html.spec.whatwg.org/multipage/; spec: html; type: dfn;
text: restore persisted state; url: #restore-persisted-state
text: active session history entry; url: #nav-active-history-entry
</pre>

<script async type="module" src="diagrams/resources/scaler.js"></script>
Expand Down Expand Up @@ -1094,6 +1097,18 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
Initially null.

Note: this is used for cross-document view transitions.

: <dfn>persisted state restoration</dfn>
:: One of the following, initially "`defer`":
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Do we have scroll restoration in the spec for cross-document navigations?


1. "`defer`".
1. "`pending`".
1. "`immediate`".

Note: this is used to defer automatic restoration of persisted state, e.g. scroll position,
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Can you add what immediate implies as well?

to be performed after the old state is captured. When in the "`defer`" mode, persisted state
is not yet requested, but should be deferred if requested. When in the "`pending`" mode,
persisted state restoration is requested and should be performed once the old state is captured.
</dl>

A {{ViewTransition}} must never have both an [=ViewTransition/update callback=] and a [=ViewTransition/process old state captured=].
Expand Down Expand Up @@ -1252,10 +1267,16 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
If failure is returned, then [=skip the view transition=] for |transition| with an "{{InvalidStateError}}" {{DOMException}} in |transition|'s [=relevant Realm=],
and return.

1. [=Resolve persisted state restoration=] for |transition|.
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We should do this in the skip case as well.


1. If |transition|'s [=ViewTransition/process old state captured=] is not null, then call [=ViewTransition/process old state captured=] and return.

1. Set |document|'s [=document/rendering suppression for view transitions=] to true.

1. Set |transition|'s [=ViewTransition/persisted state restoration=] to "`immediate`".

Note: Now that the old state is captured, synchronous restoring persisted state should behave as normal.

1. [=Queue a global task=] on the [=DOM manipulation task source=],
given |transition|'s [=relevant global object=],
to execute the following steps:
Expand Down Expand Up @@ -1912,6 +1933,23 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
1. Set |document|'s [=document/active view transition=] to null.
</div>

## [=persisted state restoration=] ## {#persisted-state-restoration-algorithm}

<div algorithm>
To <dfn export>potentially defer persisted state restoration</dfn> for a {{Document}} |document|:

1. Let |transition| be |document|'s [=active view transition=].
1. If |transition| is null or its [=ViewTransition/persisted state restoration=] is "`immediate`", then return "`proceed`".
1. Set |transition|'s [=ViewTransition/persisted state restoration=] to "`pending`".
1. Return "`defer`".
</div>

<div algorithm>
To <dfn>resolve persisted state restoration</dfn> for a {{ViewTransition}} |transition|:
1. If |transition|'s [=ViewTransition/persisted state restoration=] is "`pending`", then
[=restore persisted state=] given |transition|'s [=associated document=]'s [=node navigable=]'s [=active session history entry=].
1. Set |transition|'s [=ViewTransition/persisted state restoration=] to "`immediate`".
</div>
<h2 id="priv" class="no-num">Privacy Considerations</h2>

This specification introduces no new privacy considerations.
Expand Down Expand Up @@ -1940,6 +1978,7 @@ Changes from <a href="https://www.w3.org/TR/2023/WD-css-view-transitions-1-20230
* Copy `color-scheme` from DOM element to ''::view-transition-group()''. See <a href="https://github.com/w3c/csswg-drafts/issues/9276">issue 9276</a>.
* Expose [=auto-skip view transition=] for a {{Document}}, to allow having outbound cross-document transitions preceed programmatic view transiitons. see <a href="https://github.com/w3c/csswg-drafts/issues/9512">issue 9512</a>.
* Add a note about why 'view-transition-name' should be animatable.
* Export an algorithm and add mechanism to defer restoring scroll/persisted state.
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Is there a link to an html or csswg issue where this was discussed?


<h3 id="changes-since-2022-05-25">
Changes from <a href="https://www.w3.org/TR/2023/WD-css-view-transitions-1-20230525/">2022-05-25 Working Draft</a>
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