Bug 213842

Summary:

Missing tiles when tapping back arrow

Product:

WebKit

Reporter:

Philipp Metzler <pp>

Component:

Compositing

Assignee:

Simon Fraser (smfr) <simon.fraser>

Status:

ASSIGNED ---

Severity:

Normal

CC:

bfulgham, pp, simon.fraser, webkit-bug-importer, zalan

Priority:

Keywords:

InRadar

Version:

Safari 13

Hardware:

iPhone / iPad

OS:

iOS 13

URL:

https://bugreport2.zemtu.com

Attachments:

Description	Flags
Animated GIF to illustrate the problem.	none

Description Philipp Metzler 2020-07-01 06:54:37 PDT

Created attachment 403288 [details]
Animated GIF to illustrate the problem.

Steps to reproduce:

1. On Mobile Safari on iOS 13.5.1 open the URL https://bugreport2.zemtu.com
2. Touch scroll to the red rectangle and click on it
3. Press the arrow / back button
4. Some of the green rectangles on the top of the screen are no longer visible
5. Touch scroll just a little bit to make these rectangles visible again

Please retry several times as it may not occur all the time. Usually you have to try 2 - 4 times to see the problem.

This problem can also be reproduced in the XCode iOS simulator.

The problem cannot be reproduced under macOS Catalina 10.15.5 (19F101) in these browsers:
- Safari Version 13.1.1 (15609.2.9.1.2)
- Google Chrome Version 83.0.4103.116 (Offizieller Build) (64-Bit)
- Firefox 77.0.1 (64-Bit)
- Opera 68.0.3618.173
- Microsoft Edge 83.0.478.56 (Offizielles Build) (64-Bit)

Comment 1 Radar WebKit Bug Importer 2020-07-01 11:09:28 PDT

<rdar://problem/64994694>

Comment 2 Simon Fraser (smfr) 2020-07-06 13:08:51 PDT

I can reproduce on iOS 13.4.

Comment 3 Simon Fraser (smfr) 2020-07-06 13:12:16 PDT

Also reproduces in iOS 14 beta. Sometimes it fails to restore the scroll position.

Comment 4 Simon Fraser (smfr) 2020-07-06 13:35:45 PDT

The failure to restore the scroll position (which also happens on macOS) happens because we try to restore the scroll position from FrameLoader::HistoryController::restoreScrollPositionAndViewState() but this happens before we've done a layout for the new size, so we end up clamping the scroll position to zero.

Comment 5 Simon Fraser (smfr) 2020-07-06 13:40:26 PDT

The page doesn't build the new content until some time after the back(), using JS running on a timer, so we have no hope of restoring the correct scroll position.

Comment 6 Simon Fraser (smfr) 2020-07-06 13:51:53 PDT

On iOS this goes through WebFrameLoaderClient::restoreViewState().