1478339 - unexpected scrollbar on vk.com

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P3)

Description

[she357]

Attachment: firebug.jpg

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0
Build ID: 20180724223402

Steps to reproduce:

Having webrender enabled, go to any vk.com. Open the overflow music player and play a song.


Actual results:

There will appear Windows' scrollbar next to the music player box.


Expected results:

It isn't supposed to be there and won't appear if webrender is disabled.

Comment 1

[Darkspirit]

Thank you!

STR:
1. Open https://vk.com/audios-13623631?section=playlists&z=audio_playlist-13623631_7871567
2. Click on "Play all".
3. Click on the top-left VK logo.
4. Click on the music player on the top and scroll its content a bit down.

Doesn't happen without WebRender. Ask me if you want to get account data.

Comment 2

[Darkspirit]

mozregression --good 2018-04-15 --bad 2018-07-25 --pref gfx.webrender.all:true -a https://bit.ly/2AjjQ4X
> 10:35.65 INFO: Last good revision: d08944831e26fc9ec613e1fa2dc35d00332586ac
> 10:35.65 INFO: First bad revision: 5b15326286d466b5cf4889160cc09b59bdde08fd
> 10:35.65 INFO: Pushlog:
> https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=d08944831e26fc9ec613e1fa2dc35d00332586ac&tochange=5b15326286d466b5cf4889160cc09b59bdde08fd

> 5b15326286d4	Martin Robinson — Bug 1465058 - Update for API change in WR PR 2756. r=kats
> ccda83410bf4	Kartikaya Gupta — Bug 1465058 - Update reftest annotations for WR PR 2784. r=Gankro
> a3f7b4a6d494	Kartikaya Gupta — Bug 1465058 - Update webrender to commit 8e697f8cb1f1aab2e5f6b9b903eb7191340b10c5. r=Gankro

https://github.com/servo/webrender/compare/3829687ffbe8d55885d71a3d5e5e79216251548f...8e697f8cb1f1aab2e5f6b9b903eb7191340b10c5

Comment 3

[Martin Robinson (email:[e-mail])]

I'm not sure I'm going to have cycles to look at this, but I'm almost certain that scrollbars in Firefox are handled outside of WebRender (unless you are seeing a WebRender scrollbar).

Comment 4

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

I reproduced this using Jan's login credentials on my mac. Some notes:

- There is a <div class="ui_scroll_outer"> that is the relevant scrolling div
- This div has a 50px right-margin, which pushes the "real" Gecko scrollbar out 50px, which is why it appears misplaced
- The scrollbar that *appears* to be the regular scrollbar is actually created in the content itself and adjusted based on scroll events

i.e. the page is doing that trick where it has a scrollable div, reimplements the scrollbar in content, and makes the div wider than it appears so that the real scrollbar is clipped out

- However, in this case the real scrollbar still gets rendered (this is the bug)
- Also, the scrollbar disappears once the displayport expires (adjustable by apz.displayport_expiry_ms).

Comment 5

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

Attachment: Reduced testcase

Here's a reduced testcase. Mouse over the gradient box and scroll

Comment 6

[Darkspirit]

Fixed by https://github.com/servo/webrender/pull/3315.