1281457 - Word with "text-align: justify" moves as text selection changes

Status: RESOLVED FIXED

(Core :: DOM: Selection, defect)

Description

[Matthew Kogan]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0
Build ID: 20160604131506

Steps to reproduce:

- Open https://www.bmw-warranty.co.uk/Comprehensive#/_ComprehensiveDetails
- Start selecting text from the beginning of the second line of the paragraph underneath the bullet points, beginning "aware"
- Extend the selection slowly to the right


Actual results:

The word "number" later in that line moves slightly left and right as the selection changes.


Expected results:

No words should move.

Comment 1

[Loic]

I'm not able to reproduce it.

Does it work in safe mode?
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode


With a fresh profile?
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Comment 2

[Matthew Kogan]

I can reproduce it in safe mode and with a fresh profile.

Comment 3

[Moin Shaikh]

I could reproduce it in two different versions: Firefox Nightly 47 and Firefox Release version.

[testday-20160624]

Comment 4

[Moin Shaikh]

(In reply to Moin Shaikh from comment #3)
> I could reproduce it in two different versions: Firefox Nightly 47 and
> Firefox Release version.
> 
> [testday-20160624]

Sorry, I mean Firefox 48.0b3 not the Release version.

Comment 5

[Loic]

Ok, I'm able to reproduce it if I set back the resolution to 100%.
The <p> has "text-align: justify".

Regression range:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=d380166816dd&tochange=cbe6afcae26c

Regressed by bug:
Xidorn Quan — Bug 1063857 - Improve selecting on justified characters. r=roc

Comment 6

[Xidorn Quan [:xidorn] UTC+10]

Thanks for this great reproducible example. I eventually see where the issue is. Patch's coming.

Comment 7

[Xidorn Quan [:xidorn] UTC+10]

Attachment: Bug 1281457 - Compute justification spacing eagerly in SetupJustificationSpacing.

Before this change, SetupJustificationSpacing calls ComputeJustification
to compute how justification gaps are assigned to characters, and store
them in the PropertyProvider instance. When GetSpacing is called, those
information would be used to compute actual spacings from justification
before/after each character.

The bug is that, GetSpacing did not take gaps before the given range
into account when computing the spacing, which leads to unstable results
when range varies because of ignorance of accumulated error.

This patch changes it to eagerly computing the actual spacings inside
SetupJustificationSpacing, so that GetSpacing just queries the result
from mJustificationSpacings.

Review commit: https://reviewboard.mozilla.org/r/60770/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/60770/

Comment 8

[Jonathan Kew [:jfkthame]]

Comment on attachment 8765335 [details]
Bug 1281457 - Compute justification spacing eagerly in SetupJustificationSpacing.

https://reviewboard.mozilla.org/r/60770/#review57718

I'm not currently seeing the bug here (on OS X; may depend on platform/font details?), but the patch seems fine; thanks for including the explanation in the commit message.

Comment 9

[Xidorn Quan [:xidorn] UTC+10]

Since it depends on the natural width of the text piece, it should be font-dependent, and probably also platform-dependent. I can reproduce it on Windows, but not OS X, as well. And in most of cases, the effect is just too subtle to be noticed.

I think I did see this issue before, but didn't find a stably-reproducible example, and didn't realize this is a regression from my change...

Comment 10

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/f99734930e68
Compute justification spacing eagerly in SetupJustificationSpacing. r=jfkthame

Comment 11

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/f99734930e68