1213324 - [APZ] wheel events on subframe scrollbars target the wrong frame

Status: RESOLVED FIXED

(Core :: Panning and Zooming, defect)

Description

[Alice0775 White]

+++ This bug was initially created as a clone of Bug #1190112 +++

Build Identifier:
https://hg.mozilla.org/mozilla-central/rev/d01dd42e654b8735d86f9e7c723cc869a3b56798
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:44.0) Gecko/20100101 Firefox/44.0 ID:20151009030230

Steps To Reproduce:
1. Open http://xxsionxx.blog17.fc2.com/ or testcase attachment 8642106 [details] of Bug 1190112
2. Scroll down to the middle of page
3. Attempt to scroll element at the left side of page
   mouse over scrollbar and turn mouse wheel
4. Attempt to scroll the other element
   mouse over scrollbar and turn mouse wheel
5. Repeat step4

Actual Results:
Sometomes not scroll the element.
It seems transaction scroll timeout is broken

Expected Results:
these element should scroll properly

Bug 1190112 did not fix the problem.
It works when disable APZ

Comment 1

[Alice0775 White]

Attachment: another testcase

Steps to reproduce
1. Open the another testcase
2. Try scroll by mouse wheel on scrollbar (not on thunb)

Actual Results:
Page would not scroll

Expected Results:
Page should scroll

Disable APZ (layers.async-pan-zoom.enabled = false) fixes the problem.

Comment 2

[David Anderson [:dvander] - inactive, e-mail if emergency]

Yup, I can reproduce this on the attached test case.

Comment 3

[David Anderson [:dvander] - inactive, e-mail if emergency]

This looks like a separate problem from bug 1190112. Our layer tree looks like this:

  PaintedLayer (viewport)
  ContainerLayer (vscrollbar thumb)
    PaintedLayer (vscrollbar thumb)
  PaintedLayer (subframe)

The scrollbars are painted into the viewport layer, and non-root-content-document scrollbars are not layerized (except for the thumb). The subframe's layer does not include its scrollbars in its event regions, so a wheel event on the scrollbar track scrolls the viewport instead (which in this case, does nothing since the body's overflow:auto eats the viewport's scroll range).

A wheel event over the thumb does work, however, since nsSliderFrame happens to add a touch event listener which creates a d-t-c region.

It seems like to fix this, we will need to include d-t-c regions for inactive subframes' scrollbars. For active subframes, I guess we could either:
 (1) Always layerize the scrollbars.
 (2) Add hit regions for the scrollbars (but this would probably require another layer?)
 (3) Always add a d-t-c region for the scrollbars.

Unless I'm missing something... tn, thoughts?

Comment 4

[David Anderson [:dvander] - inactive, e-mail if emergency]

Attachment: speculative fix

This seems to fix the problem, assuming that it's the solution we want.

Comment 5

[David Anderson [:dvander] - inactive, e-mail if emergency]

Attachment: fix

Cleaned up to avoid d-t-c regions for overlay scrollbars, and added a test case.

Comment 6

[Timothy Nikkel (:tnikkel)]

Comment on attachment 8672960 [details] [diff] [review]
fix

Thanks for writing a test.

Comment 7

[David Anderson [:dvander] - inactive, e-mail if emergency]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=c895441c0f02

Comment 8

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/da38bd42a863

Comment 9

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/da38bd42a863