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[css-view-transitions-1] Display live image when element is outside the snapshot containing block in old state #10587

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[css-view-transitions-1] Display live image when element is outside the snapshot containing block in old state #10587

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[css-view-transitions-1] Display live image when old content is outsi…
noamr Jul 17, 2024
5574fd5
Account for null
noamr Jul 17, 2024
0070f5e
Use bounding box
noamr Jul 17, 2024
a17eee8
Refactor to use boolean instead of variant
noamr Jul 17, 2024
cab151d
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noamr Jul 19, 2024
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27 changes: 20 additions & 7 deletions css-view-transitions-1/Overview.bs
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Expand Up @@ -1172,7 +1172,7 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;

<dl dfn-for="captured element">
: <dfn>old image</dfn>
:: an 2D bitmap or null. Initially null.
:: a 2D bitmap, "`live`" or null. Initially null.
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Since old image is supposed to be a 2D bitmap data type, making it also "live" is odd. Can we track this state using a separate bool?

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What would old image hold in the live case then? I actually think this is a good way to represent it and it's common in other standards (e.g. fetch callbacks pass failure, a network error, or a response).

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What would old image hold in the live case then?

The old image can stay null, since we didn't capture anything. And a bool on captured element like, "should display new live image for old pseudo".

I find the pattern of strongly typed data types in the spec makes it more readable, could be my C++ brain. 😅 So would prefer it unless you feel strongly otherwise.

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No worries. Actually I need to do this anyway because once we update from the actual live snapshot that live enum is replaced with an image anyway.

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Hmm actually trying to refactor this makes it so that I have to check for this boolean in multiple places (where we check for old image is null). I think the variant approach is a lot cleaner...

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Maybe the bool can be "should generate old pseudo"? That's what old image != null implies which we want to change right. Then we'd only use old image when we need the pixels.

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Fine, done.


: <dfn>old width</dfn>
: <dfn>old height</dfn>
Expand Down Expand Up @@ -1368,11 +1368,13 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;

1. Let |capture| be a new [=captured element=] struct.

1. Set |capture|'s [=old image=] to the result of [=capturing the image=] of |element|.

1. Let |originalRect| be [=snapshot containing block=] if |element| is the [=document element=],
otherwise, the element|'s [=border box=].

1. If |originalRect| does not intersect with [=snapshot containing block=], then set |capture|'s [=old image=] to "`live`".
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We need to use the ink overflow rect here, instead of border box.

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Was this in the resolution?

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We didn't explicitly state that in the resolution. It's in the notes here:

<TabAtkins> khush: first, how to define offscreen
<TabAtkins> khush: related to the reference rect discussion, we want ink overflow, and i think that's sufficinetly specced now

The last comment was from the discussion here where the conclusion was that ink overflow is sufficiently spec'd to be used by VT or IntersectionObserver.


1. Otherwise, set |capture|'s [=old image=] to the result of [=capturing the image=] of |element|.

1. Set |capture|'s [=captured element/old width=] to |originalRect|'s {{DOMRect/width}}.

1. Set |capture|'s [=captured element/old height=] to |originalRect|'s {{DOMRect/height}}.
Expand Down Expand Up @@ -1469,9 +1471,11 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;
1. If |capturedElement|'s [=captured element/old image=] is not null, then:

1. Let |old| be a new ''::view-transition-old()'',
with its [=view transition name=] set to |transitionName|,
displaying |capturedElement|'s [=captured element/old image=]
as its [=replaced element|replaced=] content.
with its [=view transition name=] set to |transitionName|.

1. If |capturedElement|'s [=captured element/old image=] is not "`live`", then
set |old|'s [=replaced element|replaced=] content to |capturedElement|'s
[=captured element/old image=].

1. Append |old| to |imagePair|.

Expand Down Expand Up @@ -1903,11 +1907,19 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface;

Note: The above code example contains variables to be replaced.

1. Let |liveSnapshot| be the result of [=capturing the image=] of |capturedElement|'s [=new element=].

1. If |capturedElement|'s [=new element=] is not null, then:

1. Let |new| be the ''::view-transition-new()'' with the [=view transition name=] |transitionName|.

1. Set |new|'s [=replaced element=] content to the result of [=capturing the image=] of |capturedElement|'s [=new element=].
1. Set |new|'s [=replaced element=] content to |liveSnapshot|.

1. If |capturedElement|'s [=old image=] is "`live`", then:

1. Let |old| be the ''::view-transition-old()'' with the [=view transition name=] |transitionName|.

1. Set |old|'s [=replaced element=] content to |liveSnapshot|.

This algorithm must be executed to update styles in [=user-agent origin=] if its effects can be observed by a web API.

Expand Down Expand Up @@ -1979,6 +1991,7 @@ Changes from <a href="https://www.w3.org/TR/2023/WD-css-view-transitions-1-20230
* Fix algorithm for dispatching updateDOMCallback promise.
* Scope view transition names to matching tree context. See <a href="https://github.com/w3c/csswg-drafts/issues/10145">issue 10145</a>.
* Fix scoping to match name instead of element. See <a href="https://github.com/w3c/csswg-drafts/issues/10145">issue 10145</a>.
* Show live contents if the old element is captured when outside the viewport. See <a href="https://github.com/w3c/csswg-drafts/issues/8282">issue 8282</a>.

<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>
Expand Down