1280917 - occasional off-by-one when scrolling with position: sticky content

Status: NEW

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

Description

[Arpad Borsos [:Swatinem]]

Attachment: stickyscroll-vert.html

When vertically scrolling content with a few `position: sticky` elements, they are occasionally positioned off by one pixel.

See the attached testcase. Scroll all the way down. There is a 1px gap at the bottom after the "C" section. This is not consistently triggered. Scrolling up and down, sometimes the gap is gone. Refreshing the page (which restores the scroll position to the bottom) also removes the gap.

Comment 1

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

I don't see exactly the same manifestation of the problem. For me I occasionally see one white row of pixels at the top of the visible area while scrolling upwards, particular when the B "start" switches into fixed mode.

I can see this on Aurora and Nightly, but not Beta.

Comment 2

[David Bolter [:davidb] (NeedInfo me for attention)]

Kats I see you triaged this already. Is it minor? Shall we mark it fix-optional for 49?

Comment 3

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

Sounds good to me.

Comment 4

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

I'm not able to reproduce this in Nightly, although I still occasionally see one row of white pixels in Aurora. So maybe it's been fixed by something else. Arpad, are you still seeing this in Nightly?

Comment 5

[Arpad Borsos [:Swatinem]]

Not the newest Nightly, but with `Build ID 20160816030459` I still see a row of white pixels on the bottom sometimes. However when I click the page, it moves by one pixel and clears itself.

I also sometime see a small stutter, as if you did the switch between absolute/fixed via js onscroll event. But that also happens very seldomly.

Comment 6

[Markus Stange [:mstange]]

Attachment: different testcase

I still see this sometimes, but I couldn't reproduce it on Arpad's testcase just now. But I have been able to reproduce it on the testcase I'm attaching now.
It's really intermittent, but if it happens, it usually happens when I'm scrolled all the way to the bottom of the page.

Comment 7

[Arpad Borsos [:Swatinem]]

(In reply to Markus Stange [:mstange] from comment #6)

> It's really intermittent, but if it happens, it usually happens when I'm
> scrolled all the way to the bottom of the page.

That is also my observation. With the testing I just did it only happened at the bottom, neither on the top nor in the middle.