766132 - Too much space above and below line with zero-width space (U+200B) when using specific fonts on Win XP

Status: RESOLVED DUPLICATE of bug 739804

(Core :: Layout: Text and Fonts, defect)

Description

[Loic]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20100101 Firefox/13.0.1
Build ID: 20120614114901

Steps to reproduce:

Some users reported this issue with Firefox 13 (beta & release) on Windows XP only.
When a line contains the zero-width space (U+200B) [1] with specific fonts (Times New Roman, Verdana etc), there is too much space above and below the line.

Restarting FF13 in safe mode or using a new profile doesn't fix the issue.
Downgrading to FF12 fixes the issue.
Changing the default font may fix the issue (like switching to MS Sans Serif or DejaVu Serif).

This issue is *not* reproducible with all FF13 running on Win XP (Nvidia or ATI GPUs). Maybe GDI and the font rendering are involved.
I tried to modify some settings in about:config to try to reproduce the bug on Win 7 but I failed.

I'd say it's a regression of Bug 729047.

[1] http://en.wikipedia.org/wiki/Zero-width_space

Comment 1

[Loic]

Attachment: Testcase with fonts Times New Roman, Verdana and MS Sans Serif

Testcase:

3 fonts are tested: Times New Roman, Verdana and MS Sans Serif
For each font:
+ 1st line is without the zero-width space between each sequence
+ 2nd line contains the zero-width space between each sequence

2nd line with MS Sans Serif should be normal with no extra space above and below.

Comment 2

[Loic]

Attachment: Snapshot of bug

I upload a snapshot of the bug visible on a discussion board.
Each user's nickname contains a zero-width space after the 10th letter to be cut when the browser window is shortened. You can see that nicknames with 11 letters or more have space above and below.

Comment 3

[mjh563]

This is bug 739804 I think.

Comment 4

[Loic]

(In reply to mjh563 from comment #3)
> This is bug 739804 I think.

I'm not sure because it appears (afaik) only on Win XP (and maybe with old drivers). Even with gfx.direct2d.disabled = true on Win 7, the issue is not visible.

Comment 5

[mjh563]

Is it reproducible in the current Nightly?

Comment 6

[Jonathan Kew [:jfkthame]]

The issue might not appear on Win7 because the OS ships with more complete versions of the core fonts, and so font fallback might not kick in for the ZWSP character. So it's entirely plausible that an instance of bug 739804 might show up only on WinXP, and not on Win7 even without D2D.

Comment 7

[Loic]

More info: some users tried FF16 and FF14, and the bug was fixed, so this bug is likely a dupe of bug 739804.

Comment 8

[Jonathan Kew [:jfkthame]]

Yup, I'm pretty sure this was another example of 739804. Marking as dupe.

Comment 9

[Loic]

Attachment: Times New Roman and Verdana fonts

For the record, I attached a font pack (Times New Roman and Verdana) provided by a user who's meeting this issue on Win XP SP3. They are old fonts (2001 & 2004) but on my Win 7 and XP SP3 machines, with these 2 fonts installed, I wasn't able to reproduce it, with or without D2D.