661157 - inaccurate horizontal alignment (deviation 2px)

Status: RESOLVED WONTFIX

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

Description

[Stefan]

User-Agent:       
Build Identifier: Mozilla/5.0 (X11; Linux x86_64; rv:7.0a1) Gecko/20110601 Firefox/7.0a1

The left border of the third column (dd.mm.yy hh:mm) is not accurately left aligned if hh is "11". 

Reproducible: Always

Steps to Reproduce:
1. open url
2. scroll and check the horizontal alignment of the third column

Actual Results:  
Columns misaligned by 2px if hh = "11"

Expected Results:  
Display all columns left aligned as in FF 3.5, 3.6 and FF 4 up to at least 4.0b8pre (2010-11-22-03-mozilla-central).

Comment 1

[Stefan]

Attachment: screenshot

Comment 2

[Stefan]

Attachment: The width of "1" deviates from the widths of other numerals.

Comment 3

[Stefan]

I took a look into the font file. It seems that there is a kerning pair due to which the letter spacing between to 1s is reduces. FF 3.5 and 3.6 do not take this kerning into account (unless you zoom in),

Comment 4

[(mostly gone) XtC4UaLL [:xtc4uall]]

Thanks for the Testcase!

Regression Range against WinXP:
http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=f47972d05473&tochange=dc2939f2640d
=> Harfbuzz defaulting.

The Regression Range is the same as in Bug 605043 if you force "gfx.font_rendering.harfbuzz.level" to "1":
http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=beab39d49de9&tochange=b26489e73818

Comment 5

[Jonathan Kew [:jfkthame]]

(In reply to comment #3)
> I took a look into the font file. It seems that there is a kerning pair due
> to which the letter spacing between to 1s is reduces.

Sounds like this is not a bug, then - Firefox is rendering the text correctly according to the font. There's no expectation that digits will be monospaced in every font; if you want them to be monospaced, you need to choose a font that specifically provides this.

> FF 3.5 and 3.6 do not
> take this kerning into account (unless you zoom in),

This was a limitation in earlier versions - for small text sizes, it used a "quick-and-dirty" text rendering path that didn't fully take account of layout features in the fonts.

Comment 6

[Stefan]

(In reply to comment #5)
> Sounds like this is not a bug, then - Firefox is rendering the text
> correctly according to the font.

I agree. Nonetheless the behavior is unexpected.

> There's no expectation that digits will be monospaced in every font; 

There is obviously such an expectation but there's no such guarantee.

> if you want them to be monospaced, you need to
> choose a font that specifically provides this.

The arial family (as the tnr) provides numerals with same width, but they also have a single inter-numeral kerning pair (one-one). In order to prevent this kerning one can let some zero-width space (e.g. ZWJ = U+200D) drop between the ones. But then one runs into issues with FF 3.5 and 3.6 (see zl.html).

For the sake of completeness: Safari on iPad, konqueor and google chrome all behave as "expected".

Comment 7

[Stefan]

Attachment: effect of zero width characters and letter spacing

Comment 8

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

That's because Webkit doesn't do kerning unless you ask for it.