Intent to Prototype: Use the same paint-related timing values in all relevant performance entries

[Chromestatus]

Contact emails

nrose...@chromium.org, mmo...@chromium.org

Explainer

https://github.com/w3c/paint-timing/blob/main/presentation-timestamps.md

Specification

https://w3c.github.io/paint-timing/#painttimingmixin

Summary

Expose "paintTime" and "presentationTime" in event timing, element timing, LCP, long animation frames, paint timing. "paintTime" means the time when the rendering phase ended and the browser started the paint phase. "presentationTime" means the time when the "pixels reached the screen", which is somewhat implementation-defined

Blink component

Blink>PerformanceAPIs

Motivation

So far the spec defined the paint time as the time after the "rendering update", when the document hands over rendering to the UA. However, in chromium the exposed paint time (in event timing, element timing, LCP and paint-timing) was different - the approximated VSync time from the compositor, which is important in terms of UX. This created confusion and incompatibility This proposal defines both these timestamps, and exposes them in an identical way in all the relevant entries.

Initial public proposal

https://github.com/w3c/paint-timing/issues/62

TAG review

https://github.com/w3ctag/design-reviews/issues/1013

TAG review status

Pending

Risks

Interoperability and Compatibility

None

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/1110) Firefox folks took part of the WebPerfWG meeting where this was discussed/resolved.

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/426)

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?

None

Debuggability

None

Is this feature fully tested by web-platform-tests?

No

Flag name on about://flags

None

Finch feature name

None

Non-finch justification

None

Requires code in //chrome?

False

Estimated milestones

No milestones specified

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5162859838046208?gate=5141791681282048

This intent message was generated by Chrome Platform Status.