Closed Bug 1146859 Opened 9 years ago Closed 9 years ago

The "lam-alif" arabic character It does not appear correctly with Tahoma font and using letter-spacing

Categories

(Core :: Graphics: Text, defect)

39 Branch
x86_64
Windows XP
defect
Not set
normal

Tracking

()

RESOLVED WONTFIX

People

(Reporter: over68, Unassigned)

References

Details

Attachments

(1 file)

The "lam-alif" character It does not appear correctly on Windows XP with the fonts Tahoma and Courier New with using letter-spacing.

Testcase https://dl.dropboxusercontent.com/u/95157096/85f61cf7/edu52um6ox.html

Screenshot https://dl.dropboxusercontent.com/u/95157096/85f61cf7/7gnobgtf8d.PNG
This bug occurs since the version 4.0b8pre (2010-11-21).

Screenshot https://dl.dropboxusercontent.com/u/95157096/85f61cf7/umtyczwlt8.png

http://hg.mozilla.org/mozilla-central/rev/be4b69a4babf
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b8pre) Gecko/20101121 Firefox/4.0b8pre
Build ID: 20101121044503
Pushlog:
http://hg.mozilla.org/mozilla-central/pushloghtml?startdate=2010-11-20&enddate=2010-11-21

Suspected:
Jonathan Kew — bug 603879 - part 2 - update harfbuzz integration to support arabic etc shaping. r=jdaggett a=blocking2.0
Blocks: 603879
Component: General → Graphics: Text
Flags: needinfo?(jfkthame)
This is a known issue, and arises because these fonts implement the lam-alef ligature using the 'liga' (common ligatures) feature, instead of using 'rlig' (required ligatures). When letter-spacing is applied, 'liga' is disabled by default, because generally speaking ligatures do not look good in letter-spaced text.

Newer fonts that correctly use 'rlig' for the lam-alef ligature should not show this problem.

Authors who want to use letter-spacing with Arabic text (which is not generally recommended), and who care about rendering with these obsolete fonts, can explicitly re-enable the liga feature if desired.
Flags: needinfo?(jfkthame)
This sounds very similar to the bug 986802.
(In reply to blinky from comment #5)
> This sounds very similar to the bug 986802.

With Arial, the issue was that a single lookup was used to implement both 'rlig' and 'liga' features; when we disabled 'liga' for letter-spacing, we failed to recognize that the still-enabled 'rlig' feature used that same lookup, and keep it active. So that was fixed.

In this case, the fonts have no 'rlig' feature at all, only 'liga'. So there's no way for harfbuzz to recognize that this particular ligature -- unlike other ligatures in the 'liga feature -- should still be applied.

So it's purely a WinXP font bug. Gecko is behaving as designed, and the results with properly-implemented fonts are correct.
Status: UNCONFIRMED → RESOLVED
Closed: 9 years ago
Resolution: --- → WONTFIX
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