Hi, I was the one who originally implemented scroll anchoring in Firefox and just want to say that I agree with Emilio here.
Scroll anchoring is a cool feature and would be great to have, but these difficulties that Emilio has mentioned have been here since day-1. It would be great to find a path forward here, but so far I haven't seen a clear option that avoids the need for heuristics (hacks). If it's decided to remove this feature from Gecko, it might be worth taking a step back and trying to finding an alternative way to reduce layout jank. Thanks, Ryan On Fri, Sep 27, 2019, at 8:08 AM, Emilio Cobos Álvarez wrote: > And, to be clear, we _can_ fix these compat issues, some way or another. > > One thought is to limit the amount of scroll adjustments without user > scrolling or stuff like that, which would prevent the "you get stuck on > the page". > > Making anchoring opt-in rather than opt-out is another option, but that > defeats most of the purpose of the feature, I guess. > > See also some of the Chromium docs on the compat issues they found[1] > and how were they trying to fix them before adding the > "layout-affecting-property changed" heuristic, which is what is on the > spec right now and what they implement. > > I just think that these are very hacky heuristics that are just going to > bring a lot of compat pain and developer confusion. > > It doesn't help that all these things can break or not depending on the > speed at which the user scrolls, the amount of scroll events that the > user dispatches, the timing of these events relative to other events, etc... > > -- Emilio > > [1]: > https://docs.google.com/document/d/1nQAO4MYCDMn0rTkn_-WI6gjumk3Qi2Bn-MGuB3NlVxE/edit > > On 9/27/19 2:23 PM, Emilio Cobos Álvarez wrote: > > Hi, > > > > (cc'ing webkit-dev@ and blink-dev@ in case they have feedback or > > opinions, as WebKit is the only engine which does not implement scroll > > anchoring, though I don't know if they plan to, and Blink is the only > > other engine that does implement it. Please reply to dev-platform@ though.) > > > > TLDR: Scroll anchoring is really a mess. > > > > I didn't do the initial implementation of the feature in Gecko, but I've > > done a ton of work over the last few months to fix compat issues in our > > implementation (see all the bugs blocking [1]). > > > > At this point, our implementation is mostly compatible with Blink, but > > even with a bug-for-bug compatible implementation, we did get compat > > issues because of different content being served for different browsers, > > or because our anti-tracking protections changing the final content of > > the page slightly ([2] is an example of bug which only reproduces with > > ETP enabled only, but whose reduced test-case renders the site unusable > > in Chrome as well). > > > > If you hit one of the broken cases as a user you think the browser is > > completely broken, and the site is just unusable. > > > > I've fixed those by tweaking the heuristics Gecko uses. Those extra > > heuristics have also caused other compat issues, like [3], reported > > today, which will require other adjustments to the heuristics, etc... > > > > On top of that, the spec is not in a good state, with ton of open issues > > without feedback from the editors [4]. > > > > So right now I'm at a stage where I think that the feature is just not > > worth it. It doesn't behave predictably enough for developers, and you > > have no guarantee of it behaving consistently unless you test a > > particular browser, with a particular content in a particular viewport > > size... That's not great given the current dominant position of > > Chromium-based browsers. > > > > On top, issues with scroll anchoring are pretty hard to diagnose unless > > you're aware of the feature. > > > > All in all, it doesn't seem like the kind of feature that benefits a > > diverse web (nor web developers for that matter), and I think we should > > remove the feature from Gecko. > > > > Does anyone have strong opinions against removing scroll anchoring from > > Gecko, based on the above? > > > > Thanks, > > > > -- Emilio > > > > [1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1519644 > > [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1561450 > > [3]: https://bugzilla.mozilla.org/show_bug.cgi?id=1584499 > > [4]: https://github.com/w3c/csswg-drafts/labels/css-scroll-anchoring-1 > > _______________________________________________ > > dev-platform mailing list > > dev-platform@lists.mozilla.org > > https://lists.mozilla.org/listinfo/dev-platform > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform > _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
