1403762 - background-attachment: fixed incorrectly scrolls in nested scrollers

Status: RESOLVED INVALID

(Core :: Layout, defect)

Description

[Philip Rogers]

Attachment: fixedtest.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3223.8 Safari/537.36

Steps to reproduce:

Open http://jsbin.com/ketiwux/quiet (or the attached testcase).

Background-attachment fixed should be fixed to the viewport but it is not if there's a nested scroller. Both Blink and Webkit have a similar bug (https://crbug.com/754094) but Edge does this correctly.

This is similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1352915 which deals with background-attachment fixed in transforms and references a spec change and discussion (https://github.com/w3c/csswg-drafts/issues/1199). This bug is different because no transforms are present.

Comment 1

[Jet Villegas (inactive)]

The happy face that's not supposed to move doesn't move in either Firefox or Chrome. Are there other steps to reproduce?

Comment 2

[Philip Rogers]

I apologize, in preparing this for uploading I minimized it too far.

I have updated the testcase so it fails in both Chrome and Firefox: http://output.jsbin.com/ketiwux/quiet

The missing piece was will-change: transform.

Comment 3

[Philip Rogers]

Attachment: Updated to actually fail

Comment 4

[Timothy Nikkel (:tnikkel)]

I think this is actually according to spec, see bug 735857, comment 1.

Comment 5

[Philip Rogers]

Thinking about this more... I think Firefox is implementing the spirit of the spec. I recommend we close this as invalid or wontfix.

The spec has a special case for "elements that are effected by a transform", but I think it really means elements with any compositing trigger (e.g., will-change: transform, opacity, scrolling, etc).