Just to be clear: anchored elements *will* respond to transform changes on the anchor, and be re-laid out if necessary, but during animations, layout may "lag behind", as laying out synchronously would prevent the animation from running on the compositor thread.
'Emilio Cobos Álvarez' via blink-dev <[email protected]> writes: > It does not at the expense of correctness AIUI. That doesn't seem a great > trade-off? > > -- Emilio > > On 10/28/25 6:44 PM, Philip Jägenstedt wrote: >> LGTM1 >> There is some discussion in https://github.com/mozilla/standards- >> positions/issues/1302 <https://github.com/mozilla/standards-positions/ >> issues/1302> about whether this feature triggers more layouts, which it does >> not IIUC. But if there is more feedback from Mozilla on this and some changes >> are needed for Gecko to avoid extra layout work, we should adjust the spec >> and >> implementation as needed. >> On Thu, Oct 23, 2025 at 8:16 AM Morten Stenshorne <[email protected] >> <mailto:[email protected]>> wrote: >> *Contact emails* >> [email protected] <mailto:[email protected]> >> *Explainer* >> /No information provided/ >> *Specification* >> https://drafts.csswg.org/css-anchor-position-1/#anchor-position-size >> <https://drafts.csswg.org/css-anchor-position-1/#anchor-position-size> >> *Summary* >> When an anchor-positioned element is tethered against an anchor that >> has a transform (or is contained by something with a transform), >> resolve anchor() and anchor-size() functions against the bounding >> box of the transformed anchor. >> *Blink component* >> Blink>Layout <https://issues.chromium.org/issues? >> q=customfield1222907:%22Blink%3ELayout%22> >> *Web Feature ID* >> anchor-positioning <https://webstatus.dev/features/anchor-positioning> >> *Motivation* >> https://drafts.csswg.org/css-anchor-position-1/#anchor-position-size >> <https://drafts.csswg.org/css-anchor-position-1/#anchor-position- >> size> says that transform effects on an anchor should affect the >> anchor box, so that anchor-positioned elements may be positioned >> with regards to where an anchor is on screen. This chimes well with >> how scroll offsets are also taken into account. https:// >> drafts.csswg.org/css-anchor-position-1/#scroll <https:// >> drafts.csswg.org/css-anchor-position-1/#scroll> This behavior is >> crucial for creating sophisticated UI effects where elements need to >> remain logically connected while one of them is being transformed. >> Consider a tooltip that points to a button. If the button rotates or >> scales on hover, you want the tooltip to move along with it, >> maintaining its relative position. >> *Initial public proposal* >> /No information provided/ >> *TAG review* >> /No information provided/ >> *TAG review status* >> Pending >> *Risks* >> *Interoperability and Compatibility* >> /No information provided/ >> /Gecko/: No signal (https://github.com/mozilla/standards-positions/ >> issues/1302 <https://github.com/mozilla/standards-positions/ >> issues/1302>) >> /WebKit/: No signal (https://github.com/WebKit/standards-positions/ >> issues/558 <https://github.com/WebKit/standards-positions/issues/558>) >> /Web developers/: No signals >> /Other signals/: >> *WebView application risks* >> Does this intent deprecate or change behavior of existing APIs, such >> that it has potentially high risk for Android WebView-based >> applications? >> /No information provided/ >> *Debuggability* >> /No information provided/ >> *Will this feature be supported on all six Blink platforms (Windows, >> Mac, Linux, ChromeOS, Android, and Android WebView)?* >> Yes >> *Is this feature fully tested by web-platform-tests <https:// >> chromium.googlesource.com/chromium/src/+/main/docs/testing/ >> web_platform_tests.md>?* >> Yes >> https://wpt.fyi/results/css/css-anchor-position? >> label=master&label=experimental&aligned <https://wpt.fyi/results/ >> css/css-anchor-position?label=master&label=experimental&aligned> >> *Flag name on about://flags* >> /No information provided/ >> *Finch feature name* >> CSSAnchorWithTransforms >> *Rollout plan* >> Will ship enabled for all users >> *Requires code in //chrome?* >> False >> *Tracking bug* >> https://issues.chromium.org/issues/382294252 <https:// >> issues.chromium.org/issues/382294252> >> *Estimated milestones* >> Shipping on desktop 144 >> Shipping on Android 144 >> Shipping on WebView 144 >> *Anticipated spec changes* >> Open questions about a feature may be a source of future web compat >> or interop issues. Please list open issues (e.g. links to known >> github issues in the project for the feature specification) whose >> resolution may introduce web compat/interop risk (e.g., changing to >> naming or structure of the API in a non-backward-compatible way). >> /No information provided/ >> *Link to entry on the Chrome Platform Status* >> https://chromestatus.com/feature/5201048700583936? >> gate=5152239350054912 <https://chromestatus.com/ >> feature/5201048700583936?gate=5152239350054912> >> *Links to previous Intent discussions* >> Intent to Prototype: https://groups.google.com/a/chromium.org/d/ >> msgid/blink-dev/ >> CAKWZFm6cenwaNiH0YEpJae2n%3DfWz7O553%3D9fKSukBL_KhvUK0A%40mail.gmail.com >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAKWZFm6cenwaNiH0YEpJae2n%3DfWz7O553%3D9fKSukBL_KhvUK0A%40mail.gmail.com> >> This intent message was generated by Chrome Platform Status >> <https://chromestatus.com/>. >> -- You received this message because you are subscribed to the Google >> Groups "blink-dev" group. >> To unsubscribe from this group and stop receiving emails from it, >> send an email to [email protected] <mailto:blink- >> [email protected]>. >> To view this discussion visit https://groups.google.com/a/ >> chromium.org/d/msgid/blink-dev/CAKWZFm7qjp6xQ2TX2jSFaXszEZnyBSKA- >> DSddU4B2P4mKLU4GQ%40mail.gmail.com <https://groups.google.com/a/ >> chromium.org/d/msgid/blink-dev/CAKWZFm7qjp6xQ2TX2jSFaXszEZnyBSKA- >> DSddU4B2P4mKLU4GQ%40mail.gmail.com?utm_medium=email&utm_source=footer>. >> -- You received this message because you are subscribed to the Google Groups >> "blink-dev" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <mailto:blink- >> [email protected]>. >> To view this discussion visit https://groups.google.com/a/chromium.org/ >> d/msgid/blink-dev/ >> CAARdPYdb6iroDcWtbBDUNPoTF8aPQ24%3D8tex2_L%3DUPJVMDBhLg%40mail.gmail.com >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/ >> CAARdPYdb6iroDcWtbBDUNPoTF8aPQ24%3D8tex2_L%3DUPJVMDBhLg%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- Morten Stenshorne, Software developer, Blink/Layout, Google, Oslo, Norway -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/877bwdx679.fsf%40bro.lan.
