I do suspect this was more of an oversight than a specific decision, and feedback from developers seems to align with Ane Diaz: most are having to work around this.
However, there are clients out there who now depend on this and we are reaching out to see if it's less of a total headache to fix in place or provide some pathway for compat. Because this is mostly used for logging / tooling and not for real time user experience, so far the feedback has been mostly that this would be fine to break and easy to fix -- but there are a few other consumers we want to get feedback from. On Tue, Jul 22, 2025 at 5:45 PM Rick Byers <rby...@chromium.org> wrote: > Sounds like a valuable improvement, thank you! > > I see you're talking with @mmocny on the CL > <https://chromium-review.googlesource.com/c/chromium/src/+/6624567>, > that's great. I wonder if this was just an oversight in our initial > design? Seems like a bug to me. Think we can just switch it (and put the > change on the changelog > <https://chromium.googlesource.com/chromium/src/+/refs/heads/main/docs/speed/metrics_changelog/cls.md>) > without causing compat issues? Or might we need to give devs a way to > opt-in to the new semantics? mmocny@ is the expert here though, so I'm > happy with whatever he wants to do. > > Cheers, > Rick > > On Tue, Jul 22, 2025 at 5:00 PM Ane Diaz De Tuesta <aned...@gmail.com> > wrote: > >> Hi all, >> I'd like to announce an Intent to Prototype for: >> >> >> - *Feature name:* Layout Instability Attribution in CSS Pixels >> >> >> - *Contact:* anediaz@gmail >> >> >> - *Explainer:* >> >> https://github.com/anediaz/layout-shift-attribution-in-css-pixels/blob/main/Explainer.md >> >> >> - *Summary:* The Layout Instability API currently reports attribution >> rectangles (`prevRect` and `currentRect`) in device pixels, which vary >> based on resolution and `devicePixelRatio`. This change proposes reporting >> them in CSS pixels for consistency with other layout and performance APIs. >> >> >> - *Motivation:* This will align attribution with other Web APIs, such >> as `getBoundingClientRect()` and make layout shift data easier to >> visualize, debug, and combine across devices and tools. >> >> >> - *Initial public proposal:* >> https://issues.chromium.org/issues/399058544 >> >> >> - *TAG review:* Not yet requested >> >> >> - *Risks:* None known. This change only affects how attribution data >> is reported, and is gated behind a runtime flag. >> >> >> - *Interoperability:* >> - Mozilla: No signal >> - WebKit: No signal >> >> >> - *Estimated milestones:* N/A (this is a prototype only) >> >> >> - *Footprint:* This will be implemented behind a runtime flag. >> >> >> - *Link to entry on Chrome Platform Status: * >> https://chromestatus.com/feature/5155103518228480 >> >> >> This Intent is to begin prototyping the feature and gather feedback. >> >> Thank you for your help and time. >> Cheers, >> Ane Diaz de Tuesta >> >> -- >> 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 blink-dev+unsubscr...@chromium.org. >> To view this discussion visit >> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACBGQem%2BV6_UiLktmqwDCSXC3RJaMpmNm%3DSxv%2BH6%3DY4yCk5Msg%40mail.gmail.com >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACBGQem%2BV6_UiLktmqwDCSXC3RJaMpmNm%3DSxv%2BH6%3DY4yCk5Msg%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 blink-dev+unsubscr...@chromium.org. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAEeF2TfKwzr7JRZy7jvYFbM8pz5TmO3M%3DuKVkG%2B56BUVN6dWGg%40mail.gmail.com.
