Even while dragging the scroll thumb, if the mouse pointer is far enough away from the scrollbar, page scroll position should back to its original position

VERIFIED FIXED in Firefox 65



5 months ago
4 months ago


(Reporter: alice0775, Assigned: kats)


(Blocks: 1 bug, {regression})

64 Branch
Windows 10
Dependency tree / graph
Bug Flags:
in-testsuite +

Firefox Tracking Flags

(firefox-esr60 unaffected, firefox63 wontfix, firefox64 wontfix, firefox65 verified)



(2 obsolete attachments)



5 months ago
Reproducible: always when WebRender is enabled

Steps To Reproduce:
1. Open long page
    --- remember original scroll position
2. Dragging scroll thumb
3. Keeping mouse down, move the mouse pointer away from the scroll bar

Actual results:
Page scroll position does tot back to its original position.

Expected Results:
Page scroll position should back to its original position. This is Windows default behavior.
Strange, this should be handled in the part of the APZ code that is shared between WR and non-WR. I can look into it if it's deemed to be a blocker.

Comment 2

5 months ago
same as bug 1501092?
Duplicate of this bug: 1501092
Yup, thanks.

Comment 5

5 months ago
Regression window:

Regressed by:	43963e011193	Kartikaya Gupta — Bug 1389000 - Turn on webrender layers-free mode by default. r=jrmuizel
Blocks: 1389000
Keywords: regression
No one sets WebRenderLayerScrollData::mVisibleRegion?
(In reply to Botond Ballo [:botond] from comment #6)
> No one sets WebRenderLayerScrollData::mVisibleRegion?

To elaborate on that: triggering the scrollbar sanp-back feature from APZ requires knowing the bounds of the scrollbar thumb node, which comes from ScrollNode::GetVisibleRegion() in APZCTreeManager::UpdateHitTestingTree().

When I fixed bug 1352863, I implemented GetVisibleRegion() for ScrollNode=WebRenderScrollDataWrapper; the value came from WebRenderLayerScrollData::mVisibleRegion which was set in WebRenderLayerScrollData::Initialize(). At the time WebRenderLayerScrollData objects were constructed from layers.

Since then, things were refactored so WebRenderLayerScrollData objects are constructed from display items, and the setting of mVisibleRegion seems to have gotten lost.

^ This would be the place to re-add the setter, if we can get an equivalent rect from the display item.
Blocks: 1386669
Priority: -- → P2
Assignee: nobody → kats
I have a fix, but I'll try to write a test to go with it.
This field is used by APZ to implement the feature where the scrollbar snaps
back to the starting position if the mouse gets too far away.
This field is used by APZ to implement the feature where the scrollbar snaps
back to the starting position if the mouse gets too far away.
Sorry, I tried evolving the changeset via prune -s but I guess phabricator didn't like that...
Attachment #9020822 - Attachment is obsolete: true
Attachment #9020843 - Attachment is obsolete: true
Depends on: 1503029

Comment 15

5 months ago
Last Resolved: 5 months ago
status-firefox65: affected → fixed
Resolution: --- → FIXED
Target Milestone: --- → mozilla65
Flags: qe-verify+
Flags: in-testsuite+
status-firefox64: affected → wontfix


5 months ago
Duplicate of this bug: 1506197

Comment 17

4 months ago
Verified on latest Nightly 65.0a1 with WebRender activated and the issue is fixed, the page scroll position goes back to its original position.
status-firefox65: fixed → verified
Flags: qe-verify+
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