Intent to Ship: First Paint Timing API
Shubhie Panicker
Contact emails
pani...@chromium.org, tdre...@chromium.org, igri...@google.com
Spec
https://github.com/wicg/paint-timing
Tag review: https://github.com/w3ctag/design-reviews/issues/177
Summary
No single moment in time completely captures the user’s "loading experience". To give developers better insight into the loading experience, we will expose two new key progress metrics that capture the key moments during pageload: First Paint (FP) and First Contentful Paint (FCP).
For detailed motivation for First Paint, see the Why First Paint doc.
(In the future, we may expose more such key moments — for example, time to first meaningful paint, time to interactive, etc. — to help developers better understand and optimize the loading experience.)
Also, the non-standardized first-paint API (chrome.loadTimes’ firstPaint) has high usage ~0.97%, we cannot deprecate and remove this API without shipping the standardized API.
Link to “Intent to Implement” blink-dev discussion
https://discourse.wicg.io/t/expose-first-paint-timing-in-performance-observer/1868/2
The primary feedback we got was to make the timing more accurate by capturing the cost of the rendering pipeline (compositing, rasterization) -- we have now updated the timing to include time up to the swap.
Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?
Yes.
Interoperability and Compatibility Risk
Compat risk is none, the event is exposed via well-defined Performance Observer interface.
Interop risk is moderate to low: the cost of the rendering pipeline is implementation-dependent on different browsers.
Edge: Public support
Firefox: No signals
Safari: Public support
Web developers: Positive (SOASTA, Facebook, AMP)
Is this feature fully tested by web-platform-tests?
Layout tests not yet upstreamed
OWP launch tracking bug
Entry on the feature dashboard
https://www.chromestatus.com/feature/5688621814251520
Chris Harrelson
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TAMURA, Kent
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Software Engineer, Google
Jochen Eisinger
LGTM2.
LGTM1
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----TAMURA Kent
Software Engineer, Google
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