On Wed, Feb 26, 2020 at 11:29 AM Maciej Stachowiak <m...@apple.com> wrote:
> > > On Feb 26, 2020, at 10:51 AM, Noam Rosenthal <noam.j.rosent...@gmail.com> > wrote: > > > > On Wed, Feb 26, 2020 at 8:08 PM Maciej Stachowiak <m...@apple.com> wrote: > >> >> Some quick comments: >> > >> the definition of First Contentful Paint here in the spec: < >> https://www.w3.org/TR/paint-timing/#sec-terminology> does not match the >> definition stated at <https://web.dev/first-contentful-paint/>. The >> Chrome definition on web.dev specifies that iframe content is not >> included, the spec does not have this limitation. Would an implementation >> that matches the spec match Chrome? >> > The draft version of the spec specifies that iframe content is not > included in FCP: > https://w3c.github.io/paint-timing/#sec-reporting-paint-timing, and has a > few more comprehensive details about this. I think it's a good place to > start. > > I am also not sure this matches the layout milestones that already exist >> in non-Blink browser engines. Has this spec been implemented in Gecko, for >> example, to verity that it’s not exposing a concept that only exists in >> Blink? >> > No, this has not been implemented in Gecko, I'm tracking the bug on this: > https://bugzilla.mozilla.org/show_bug.cgi?id=1518999, there was some > movement recently. > > I suggest to start from "first-paint", and to try to match chrome as much > as possible in how FCP is implemented, in the cases where the spec doesn't > give enough detail, if such places exist. I think that for the main > use-case of catching regressions for website code, it's ok (and almost > unpreventable) if the implementations have some variances between them, > what matters is that the metric is reliable for the particular browser. > I also suggest to start with "first-paint" as it's perhaps a bit less > "internal" than FCP, and can provide a performance-regression metric with a > lesser degree of risk regarding exposing internals / privacy. > > > First paint that’s not first meaningful/contentful paint is not a very > good performance metric IMO. Who cares that a paint happened if it doesn’t > have any image or text content? > > I also don’t think this exposes less. The privacy risk here is exposing > timing data that might be usable for fingerprinting. > > > >> >> Chrome team themselves have been telling web developers that First >> Contentful Paint is deprecated in favor of Largest Contentful Paint. Should >> we concerned about this? It seems even harder to define LCP in an >> engine-independent way. >> > What was deprecated was "first meaningful paint" (FMP). FCP was not > deprecated and has been in wide use for some time. > > > What’s the difference between First Meaningful and First Contentful? > There is no difference in Safari because we don't do any painting of a newly navigated until the first meaningful paint happens. - R. Niwa >> Finally, we should do a privacy review to consider whether exposing this >> info to webpages creates fingerprinting risk or otherwise exposes user data. >> > Great, what is needed for such review? > > > We will discuss with Apple’s privacy experts what they think of the > privacy risk. I’m just giving you a rain check for results of this > discussion. > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev >
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