Bug 181741

Summary:

Element with position:fixed stops scrolling at the bottom of the page, but is painted in the right place on Chacos.com.

Product:

WebKit

Reporter:

Stephanie Poll <stephanie.poll>

Component:

New Bugs

Assignee:

Simon Fraser (smfr) <simon.fraser>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

commit-queue, simon.fraser, thorton, webkit-bug-importer, zalan

Priority:

Keywords:

InRadar, PlatformOnly

Version:

Safari 11

Hardware:

iPhone / iPad

OS:

iOS 11

URL:

http://www.chacos.com/US/en/home

See Also:

https://bugs.webkit.org/show_bug.cgi?id=182052

Attachments:

Description	Flags
A screenshot of what happens when hovering over the element in the safari web inspector.	none
Reduction	none
Patch	none

Description Stephanie Poll 2018-01-17 07:01:59 PST

Created attachment 331492 [details]
A screenshot of what happens when hovering over the element in the safari web inspector.

If you scroll to the very bottom of the URL on an iPhone, the fixed top/chat buttons on the side stop moving down with the page, but continue to be painted in the correct place. This happens about 40 pixels from the actual bottom. This causes the click area to be shoved above where the elements appear to be. While scrolling, the element is in the correct position, but after scrolling stops, the element will jump above where it appears to be painted. For visual reference, please see the attached screenshot or watch the video at this link: https://www.screencast.com/t/dDzlXxSIZ

Comment 1 Simon Fraser (smfr) 2018-01-17 12:54:07 PST

I can reproduce.

Comment 2 Radar WebKit Bug Importer 2018-01-17 12:54:28 PST

<rdar://problem/36593581>

Comment 3 Simon Fraser (smfr) 2018-01-17 16:06:53 PST

Created attachment 331553 [details]
Reduction

Seems to happen on pages that have a viewport meta tag that triggers scaling. I'm surprised this is such a basic failure :(

Comment 4 Simon Fraser (smfr) 2018-01-17 18:46:19 PST

So this issue happens when the minimum scale is > 1. FrameView::visualViewportRect() returns a visual viewport that's too big (larger than the document) because it assumes that it can scale the visible rect by the scale (~1.3 on this page).

Comment 5 Simon Fraser (smfr) 2018-01-17 19:04:41 PST

The iOS-only code in FrameView::unscaledMaximumScrollPosition() looks suspicious.

Comment 6 Simon Fraser (smfr) 2018-01-17 19:05:42 PST

Bug 174648 is relevant.

Comment 7 Simon Fraser (smfr) 2018-01-22 13:00:58 PST

Created attachment 331953 [details]
Patch

Comment 8 WebKit Commit Bot 2018-01-23 12:11:15 PST

Comment on attachment 331953 [details]
Patch

Clearing flags on attachment: 331953

Committed r227430: <https://trac.webkit.org/changeset/227430>

Comment 9 WebKit Commit Bot 2018-01-23 12:11:17 PST

All reviewed patches have been landed.  Closing bug.