1662800 - Scrollbar thumbs inside div element don't respond to mouse dragging when certain css rules applied

Status: VERIFIED FIXED

(Core :: Graphics: WebRender, defect)

Description

[nederland074]

Attachment: test.html

User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36

Steps to reproduce:

1. Open the attached file test.html.
2. Try to drag the scrollbar thumbs inside the div element with a mouse.

Actual results:

The scrollbar thumbs (both vertical and horizontal) do not respond to mouse dragging.

Expected results:

The scrollbar thumbs should be draggable by mouse and scroll the content inside the div element accordingly.

Comment 1

[nederland074]

Attachment: test.mp4

Video showcasing the issue under Windows 10.

Comment 2

[nederland074]

Attachment: test.log

Log with results from mozregression. Apparently, it worked in Firefox 64.0a1.

Comment 3

[nederland074]

Also, I can reproduce this issue on Windows 10, but it's not reproduceable for me on Linux Ubuntu 18.04.

Comment 4

[BugBot [:suhaib / :marco/ :calixte]]

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Comment 5

[Alice0775 White]

I can reproduce the issue on Nightly82.0a1 Windows10 if WebRender is enabled.
However, I cannot reproduce the issue if WebRender is disabled.

Comment 6

[Timothy Nikkel (:tnikkel)]

The div has a transform but the scrollthumbs drag as if the div is at it's not-transformed position.

Comment 7

[Jim Mathies [:jimm]]

I can reproduce this, Win10 Nightly.

Comment 8

[Clara Guerrero ( Need Info Brindusa Tot Please)]

I can reproduce in firefox release 81.0.1 (64-bit), beta 82.0b6 (64-bit) , nightly 83.0a1 (2020-10-02) (64-bit). I will update flags accordingly and check "has regression range" as per comment 2 thanks for providing the range. Not reproducible in Chrome.
Best,
Clara

Comment 9

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

The regression range in comment 2 contains this changeset: https://hg.mozilla.org/mozilla-central/rev/f1da54a2d166d6370d485d2b3d2f5b386a6af177 which is probably what caused the original reporter to start seeing the problem as WR got turned on for them. That might also explain why they're not seeing it on Linux (WR might be disabled). I can repro a similar problem on macOS, the scrollbar immediately jumps to the end of the range.

It seems similar to previous bugs I've fixed with the WR scroll data, I can take a look.

Comment 10

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

(And thank you for the reduced test case, that will be super helpful!)

Comment 11

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

I investigated this and found the problem, which is simply combining these two matrices in the wrong order. If the two matrices were pure translation then it doesn't matter, but in this case one has a scale and so it matters if we pre-multiply or post-multiply, and apparently I got it wrong when I wrote the code.

Comment 12

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

https://treeherder.mozilla.org/jobs?repo=try&group_state=expanded&revision=d340d8cc9e67dc535bc30d0011297d3d014c611a

Comment 13

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

Attachment: Bug 1662800 - Make the WebRenderScrollData dump nicer. r?botond

This makes the WebRenderScrollData dump more analogous to the layer tree dump,
in that it prints the layer entries one per line showing in-order nested tree
structure. It also omits printing things if they're not important.

Depends on D96196

Comment 14

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

Attachment: Bug 1662800 - Fix WR display list dumping in cases with reused items. r?miko

I was running with gfx.webrender.dl.dump-content enabled and it hit the assertion
at https://searchfox.org/mozilla-central/rev/96e2c6e14998f38e419850d55d8a3d32a3fc244a/gfx/wr/webrender_api/src/display_list.rs#703
because the iterator wasn't provided with a cache. This seems to fix it.

Comment 15

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

Attachment: Bug 1662800 - Fix matrix multiplication order. r?botond

When combining transform matrices for deferred transforms, we were multiplying
them in the wrong order. This caused incorrect behaviour when one of the matrices
had a scale factor.

Depends on D96198

Comment 16

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

Attachment: Bug 1662800 - Make the WebRenderScrollData dump nicer. r?botond

This makes the WebRenderScrollData dump more analogous to the layer tree dump,
in that it prints the layer entries one per line showing in-order nested tree
structure. It also omits printing things if they're not important.

Comment 17

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/77c19223a20f
Make the WebRenderScrollData dump nicer. r=botond
https://hg.mozilla.org/integration/autoland/rev/93582e247339
Fix WR display list dumping in cases with reused items. r=miko
https://hg.mozilla.org/integration/autoland/rev/a86cc0d29dc0
Fix matrix multiplication order. r=botond

Comment 18

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/77c19223a20f
https://hg.mozilla.org/mozilla-central/rev/93582e247339
https://hg.mozilla.org/mozilla-central/rev/a86cc0d29dc0

Comment 19

[Alexandru Trif, Desktop Test Engineering [:atrif] [PTO 22 Dec-9 Jan, please ni? :mboldan]]

Reproduced the issue using Firefox 82.0a1 (20200902215721) on Windows 10x64.
The issue is verified fixed with Firefox 84.0b3 (20201119195818) on Windows 10x64, macOS 10.12, and Ubuntu 18.04. The scroll bar from the test case can be dragged using the mouse with WebRender.