1414874 - When page-scrolling on pages with position: sticky items, reduce page scroll amount to maintain visible overlap

Status: NEW

(Core :: Layout, defect, P3)

Description

[Asif Youssuff]

Attachment: scroll-position-sticky2.mov

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20171106100122

Steps to reproduce:

1. Navigate to https://belen-albeza.github.io/scroll-demos/sticky.html
2. Use spacebar or pagedown to scroll


Actual results:

The position scrolled to does not contain any of the previous page. 


Expected results:

New position after scroll should show the last line or two of text in the previous page. 

See video; Chromium does this correctly. In Firefox, highlighted the word "voices", which does not appear in new scrolled position; in Chrome, highlighted "where", which appears in the new scroll position.

Comment 1

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

We should probably deal with this the same way we do fixed-pos items. That is, in the function at [1], figure out if there are any sticky elements attached to the edges of the viewport (zero-margin sticky elements) and that are in their "sticky" mode, and deal with the same way as the fixed items.

[1] http://searchfox.org/mozilla-central/rev/5a60492a53667fc61a62af1847d005a210b7a4f6/layout/generic/nsGfxScrollFrame.cpp#4216

Comment 2

[Asif Youssuff]

Sorry guys, apparently Chrome *doesn't* do this correctly, but that's not a reason why Firefox shouldn't. :)

Comment 3

[jonjohnjohnson]

Keep in mind interactions with impending 'scroll-padding' -> https://www.w3.org/TR/css-scroll-snap-1/#scroll-padding

Comment 4

[jonjohnjohnson]

CSSWG desicion about scroll-padding interactions with heuristics of keypress scrolling -> https://github.com/w3c/csswg-drafts/issues/2929