451641 - Scrollbar resizing from 56488 is fragile; in some cases, gaps appear under the scrollbar

Status: NEW

(Core :: Layout, defect, P3)

Description

[Markus Stange [:mstange]]

My fix for bug 56488 doesn't seem to work too well...

This bug only shows on Mac OS X in resizable windows.

Steps to reproduce:
1. Open a Firefox window with only one tab.
2. Turn off the status bar.
3. Load a long page in the tab.
4. Open the preferences, go to the "Tabs" pane and toggle the "Always show
   the tab bar" pref several times.

Expected results:
The scrollbar should always have the right size - leaving just enough space for the resizer.

Actual results:
The scrollbar leaves either too much or not enough space.

There are other ways to trigger this bug, e.g. closing a notification bar.

I suspect this is what's going on when the tab bar is hidden:
1. The content scroll view is at its original position.
2. It realizes that it will soon be bigger and resizes itself to the new size
   without moving its upper edge upwards. Now the lower edge is further down
   than it will be when the layout is finished.
3. The scrollbar is resized to the size that would be right it stayed at
   that position.
4. The content scroll view is moved upwards to where it belongs.
Now the scrollbar is too short.

Can I do anything about this, roc?

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Try doing your fixup in nsGfxScrollFrameInner::ReflowFinished?

Comment 7

[Alex Faaborg [:faaborg] (Firefox UX)]

This bug's priority relative to the set of other polish bugs is:
P4 - Polish issue that is rarely encountered, and is easily identifiable.

It sounds like once this happens it is pretty obvious there is a problem, but the steps to reproduce lead me to believe that it doesn't really happen that often.

Comment 8

[Fabian]

Please remember that it also happens when you simply hide the toolbar. While not everybody uses that feature in OSX, it is by no means rare among people with small screens.

Comment 9

[Johnathan Nightingale [:johnath]]

A blocker was resolved as a duplicate of this one -> blocking1.9.2

Comment 10

[Markus Stange [:mstange]]

I talked this through with roc; it's pretty hard to fix without rewriting the scrollbar code (which is on my list, but there's no way it can make 1.9.2). The only easy way to fix this bug would be to back out bug 56488.

However, I think that bug 56488 is far worse than this bug. This bug means that scrollbars are too small in some edge cases, but you can still access them. Reintroducing bug 56488 means that you can't click the down scroll arrow in a very common case (hiding the status bar).

Also, the number of duplicates per year in bug 56488 is higher than in this bug.

Comment 11

[Johnathan Nightingale [:johnath]]

Okay, putting this back in the queue then - bug 494301 was marked blocking, and subsequently dup'd to this one.

My opinion is that bug 494301 looks pretty bad, but I think it's roc's call as to whether the cure is more dangerous than the disease, here. Are there ways we can reduce or better understand the risk of fixing this (scoping down, better tests, beta exposure, some kind of protective rubber cushioning device)?

Comment 12

[Robert O'Callahan (:roc) (email my personal email if necessary)]

We can do an easy quick and dirty fix for bug 494301. So let's un-dup that one, do the quick fix there, and leave this open for the general fix.

Comment 13

[Sylvestre Ledru [:Sylvestre]]

Moving to p3 because no activity for at least 1 year(s).
See https://github.com/mozilla/bug-handling/blob/master/policy/triage-bugzilla.md#how-do-you-triage for more information

Comment 14

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

The severity field for this bug is relatively low, S3. However, the bug has 4 duplicates.
:dholbert, could you consider increasing the bug severity?

For more information, please visit auto_nag documentation.

Comment 15

[BugBot (nomail) [:suhaib / :marco/ :calixte]]

The last needinfo from me was triggered in error by recent activity on the bug. I'm clearing the needinfo since this is a very old bug and I don't know if it's still relevant.