1276361 - Detect position change from requestAnimationFrame callback as scroll-linked effect

Status: REOPENED

(Core :: Panning and Zooming, defect)

Description

[Botond Ballo [:botond]]

In bug 1229052, we implemented detection of "scroll-linked effects", that is, effects that update a positioning property of an element in response to a "scroll" event. In bug 1246290, we then leveraged this to optionally disable APZ for pages with scroll-linked effects.

Some pages have scroll-linked effects where a positioning property of an element is updated not in response to a "scroll" event, but in response to an input event, such as "mousewheel", that triggers a "scroll" event. From a user's point of view, these are still scroll-linked effects.

Comment 1

[Botond Ballo [:botond]]

Kats, was it a conscious decision not to include events such as "mousewheel", or was this an oversight / something we just didn't get to yet?

Comment 2

[Kartikaya Gupta (email:[e-mail])]

It hadn't really occurred to me, honestly. Thinking about now I'm not sure how valuable it would be - in most cases when pages listen to the wheel events they are also doing preventDefault on them and reimplementing scrolling, so there shouldn't be any APZ lag in those cases. If there are sites that do element repositioning based on wheel events, does the APZ lag that results also manifest in other browsers?

Comment 3

[Botond Ballo [:botond]]

(In reply to Kartikaya Gupta (email:[e-mail]) from comment #2)
> It hadn't really occurred to me, honestly. Thinking about now I'm not sure
> how valuable it would be - in most cases when pages listen to the wheel
> events they are also doing preventDefault on them and reimplementing
> scrolling, so there shouldn't be any APZ lag in those cases. If there are
> sites that do element repositioning based on wheel events, does the APZ lag
> that results also manifest in other browsers?

Deeper investigation revealed that the site in question is not changin the position from a wheel event handler after all; it's doing so from a requestAnimationFrame callback.

Kats suggested on IRC detecting a scroll-linked effect if a position is changed from a requestAnimationCallback. I'm going to re-purpose this bug for that.

Comment 4

[Kartikaya Gupta (email:[e-mail])]

Considering the scroll-linked effect stuff is disabled by default I'm going to wontfix this for now. We can come back to if it things change.

Comment 5

[Hiroyuki Ikezoe (:hiro)]

We could detect scroll linked position changes in rAF callbacks if the rAF are registered inside scroll events such as;

element.addEventListener("scroll", () => {
    requestAnimationFrame(() => {
       anotherElement.style.top = element.scrollTop;
    });
});

This is exactly the case of bug 1738838.

Reopening.