1740164 - Transmogrify ScrollToCSSPixels to ScrollByCSSPixels even if there's no animation in APZ

Status: REOPENED

(Core :: Panning and Zooming, defect, P3)

Description

[Hiroyuki Ikezoe (:hiro)]

In bug 1692708 we are going to change ScrollToCSSPixels to a relative operation if there's any on-going animation in APZ triggered by user. In this bug we are going to apply it in the case of no animation as well.

Comment 1

[Botond Ballo [:botond]]

Do you know if this additional change is needed for the Slack case, or is bug 1692708 is sufficient for that?

Comment 2

[Hiroyuki Ikezoe (:hiro)]

I think bug 1692708 is sufficient in most cases including Slack basically. This is literally for a race condition where APZ just starts an async scrolling but the corresponding RepaintRequest hasn't yet reached to the content's main-thread, at that moment if JS on the main-thread calls scrollTop, our relative scroll machinery won't be triggered. This bug is for the race case.

So, I am thinking that we can defer this until someone reports to us there's a wobbly scrolling site in the wild.

Comment 3

[Hiroyuki Ikezoe (:hiro)]

Closing this bug as INVALID since the spec will clearly define that scrollTo operations are absolute. As far as I know the spec hasn't yet been changed though. See bug 1985143 and relevant github issues for details.

Comment 4

[Hiroyuki Ikezoe (:hiro)]

Re-opening this bug since we need this for bug 2029043, and actually Chrome does this, see 2025232 comment 7.

So for bug 1985143, now I think we just need to differentiate it internally.