196327 2019-03-27 16:51:23 -0700 @supports(background-attachment:fixed) should say false on iOS 2024-07-08 21:11:32 -0700 1 1 1 Unclassified WebKit CSS WebKit Nightly Build Unspecified Unspecified NEW https://bugs.webkit.org/show_bug.cgi?id=234779 https://bugs.webkit.org/show_bug.cgi?id=275247 BrowserCompat, GoodFirstBug, InRadar P2 Normal --- 1 simon.fraser webkit-unassigned bramus gsnedders karlcow ntim simon.fraser webkit-bug-importer zakr oldest_to_newest 1521917 0 simon.fraser 2019-03-27 16:51:23 -0700 We don't support background-attachment:fixed on iOS, so @supports should reflect this. 1875543 1 webkit-bug-importer 2022-06-13 10:14:26 -0700 <rdar://problem/95035888> 1875547 2 gsnedders 2022-06-13 10:22:53 -0700 Is this primarily just the fact that we should be gating support on FixedBackgroundsPaintRelativeToDocument? 1875553 3 gsnedders 2022-06-13 10:29:51 -0700 Hmm, we also seem to set FixedElementsLayoutRelativeToFrame on !IOS_FAMILY 1875566 4 simon.fraser 2022-06-13 10:56:45 -0700 `FixedBackgroundsPaintRelativeToDocument` is historical artifact from iOS originally not supporting `position:fixed` at all. `We don't support background-attachment:fixed` is not supported on iOS because we didn't want scrolling to trigger a paint on every frame (and we'd still prefer to avoid it). We also can't paint fixed backgrounds synchronously such that they accurately align with the scroll position, so even if we allow them to paint, they will jiggle. 1875633 5 gsnedders 2022-06-13 15:25:16 -0700 So the conclusion having spoken to Simon offline is that yes, all that needs to be done is to gate the support (at the parser level, as we do for other conditional values) on FixedBackgroundsPaintRelativeToDocument. 1974594 6 ntim 2023-08-30 18:05:06 -0700 https://searchfox.org/wubkat/rev/015533966bd738b8d2392a8ff5f6c92f63ba1085/Source/WebCore/css/CSSProperties.json#1601 Needs to change to: ``` { "value": "fixed", "settings-flag": "fixedBackgroundsPaintRelativeToDocument" } ``` 1974595 7 ntim 2023-08-30 18:06:18 -0700 (In reply to Tim Nguyen (:ntim) from comment #6) > https://searchfox.org/wubkat/rev/015533966bd738b8d2392a8ff5f6c92f63ba1085/ > Source/WebCore/css/CSSProperties.json#1601 > > Needs to change to: > ``` > { > "value": "fixed", > "settings-flag": "fixedBackgroundsPaintRelativeToDocument" > } > ``` Actually, that settings flag needs to be flipped to work. Alternatively, we would need a custom parser function 2043332 8 zakr 2024-06-26 18:46:59 -0700 Pull request: https://github.com/WebKit/WebKit/pull/30220