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[css-transforms-1] Should will-change: transform be treated as transform for background-attachment:fixed? #6951

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wangxianzhu opened this issue Jan 14, 2022 · 2 comments
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[css-transforms-1] Should will-change: transform be treated as transform for background-attachment:fixed? #6951

wangxianzhu opened this issue Jan 14, 2022 · 2 comments
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Closed as Question Answered Used when the issue is more of a question than a problem, and it's been answered. css-transforms-1 Current Work

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@wangxianzhu
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The current spec says:

Fixed backgrounds on the root element are affected by any transform specified for that element. For all other elements that are effected by a transform (i.e. have a transform applied to them, or to any of their ancestor elements), a value of fixed for the background-attachment property is treated as if it had a value of scroll. The computed value of background-attachment is not affected.

It doesn't mention will-change:transform. However, if we don't treat will-change:transform as transform, future change of transform from initial to non-identity will cause jump of the background.

Current browser behaviors about treating will-change:transform as transform for background-attachment-fixed:
Merged
chromium-wpt-export-bot pushed a commit to web-platform-tests/wpt that referenced this issue Jan 14, 2022
@wangxianzhu @chromium-wpt-export-bot
Include will-change:transform as transform for background-attachment:…
188313e 
…fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
aarongable pushed a commit to chromium/chromium that referenced this issue Jan 14, 2022
@wangxianzhu
Include will-change:transform as transform for background-attachment:…
2ed5364 
…fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3385337
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959058}
chromium-wpt-export-bot pushed a commit to web-platform-tests/wpt that referenced this issue Jan 14, 2022
@wangxianzhu @chromium-wpt-export-bot
Include will-change:transform as transform for background-attachment:…
a0d7109 
…fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3385337
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959058}
chromium-wpt-export-bot pushed a commit to web-platform-tests/wpt that referenced this issue Jan 14, 2022
@wangxianzhu @chromium-wpt-export-bot
Include will-change:transform as transform for background-attachment:…
a04b6be 
…fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3385337
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959058}
@SelenIT
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SelenIT commented Jan 14, 2022

I believe that this paragraph from [css-will-change] applies here:

If any non-initial value of a property would cause rendering differences on the element (...), the user agent should use that alternate rendering when the property is specified in will-change

(given that [css-transforms] explicitly states that "Transforms affect the rendering of backgrounds on elements with a value of fixed for the background-attachment property"). So the current behavior of Firefox and planned behavior of Chrome are correct.

@wangxianzhu
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I think SelenIT's explanation makes sense. Closing this issue.

@tabatkins tabatkins added Closed as Question Answered Used when the issue is more of a question than a problem, and it's been answered. css-transforms-1 Current Work labels Jan 18, 2022
moz-v2v-gh pushed a commit to mozilla/gecko-dev that referenced this issue Feb 5, 2022
@wangxianzhu @moz-wptsync-bot
Bug 1749932 [wpt PR 32360] - Include will-change:transform as transfo…
08eeb7f 
…rm for background-attachment:fixed, a=testonly

Automatic update from web-platform-tests
Include will-change:transform as transform for background-attachment:fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3385337
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959058}

--

wpt-commits: a04b6be3ebaeea3fd79b82e9447ba1e0b864babe
wpt-pr: 32360
jamienicol pushed a commit to jamienicol/gecko that referenced this issue Feb 7, 2022
@wangxianzhu @moz-wptsync-bot
Bug 1749932 [wpt PR 32360] - Include will-change:transform as transfo…
6729fdd 
…rm for background-attachment:fixed, a=testonly

Automatic update from web-platform-tests
Include will-change:transform as transform for background-attachment:fixed

This is to prevent jump of background when an element with will-change:
transform changes transform from initial to non-identity. This is not in
the spec yet, so the test case is tentative with a css-transforms-1 bug
is filed at w3c/csswg-drafts#6951. Firefox
already has this behavior.

Bug: 1286593
Change-Id: I4247824b5af28613644bcd334832ff22b9483384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3385337
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959058}

--

wpt-commits: a04b6be3ebaeea3fd79b82e9447ba1e0b864babe
wpt-pr: 32360
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