On Tue, Mar 3, 2020 at 12:31 AM Noam Rosenthal <n...@webkit.org> wrote:
> > On Tue, Mar 3, 2020 at 10:18 AM Ryosuke Niwa <rn...@webkit.org> wrote: > >> Sorry for the delay. I had other other things to take care of first. >> >> Based on the discussion we had (between Maciej, Simon, Alan, and I), we >> should take the following items into account for WebKit's first meaningful >> paint heuristics: >> >> - Background image >> >> I've filed https://bugs.webkit.org/show_bug.cgi?id=208501 and can get it > done. > Btw if there's something I'm taking on myself but Apple would rather do or > vice versa, please let me know :) > Great. I've cc'ed a few more folks. > >> - SVG images >> - "Contentful" canvas once we rigorously defined what it means: >> https://github.com/w3c/paint-timing/issues/50 >> - First frame / poster image of a video: >> https://github.com/w3c/paint-timing/issues/51 >> >> Then as Maciej pointed out there are a few spec works to do: >> >> - WebKit takes any text regardless of whether they appear within UA >> shadow root or not into account for the first meaningful paint. The spec >> needs to clarify this behavior - >> https://github.com/w3c/paint-timing/issues/52 >> - The exact timing of navigation should be defined - >> https://github.com/w3c/paint-timing/issues/19 >> - Clarify whether "first paint" or "first content paint" ever happens >> to a blank page - https://github.com/w3c/paint-timing/issues/53 >> - Clarify what happens to a page which consists of just an iframe - >> https://github.com/w3c/paint-timing/issues/54 >> - Combination of paint timing and long tasks can expose precise paint >> timing - https://github.com/w3c/paint-timing/issues/55 >> >> To supplement earlier Maciej's points, per our discussion, we don't think >> "first paint" is a good metric to expose to the Web since Safari / WebKit >> users would never see that. If any website optimize for the first paint >> metrics instead of or at the cost of first contentful paint, then such an >> optimization would only result in perceived regressions for our users. >> > I've spoken with the Wikipedia folks on this and they agree, first-paint > is not really that useful as a performance metric (I think it's useful to > catch bugs, e.g. in cases where it's vastly behind first-contentful-paint). > For now I'm focusing only on the first-contentful-paint metric, and adding > web platform tests to cover this situation (the current tests would fail in > the case where FP is not implemented). > Sounds great to me. By the way, do you know what the status / interests at Mozilla? Given WebKit's painting / navigation behavior / implementation is still pretty close to Blink, it would be a good idea to reach out to Mozilla to make sure whatever in the spec is something they can also implement. - R. Niwa
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