[XeTeX] xetex arabic fonts issue

[Jonathan Kew]

On 26 Jun 2010, at 16:46, Khaled Hosny wrote:

> On Sat, Jun 26, 2010 at 03:04:05PM -0700, wodzicki at math.berkeley.edu wrote:
>> 
>>> My guess is that you have an old version of the font installed somewhere.
>>> Having to different version of the same font installed is known to cause
>>> this kind of issues with xetex, deleting the old version(s) is enough
>>> to solve this issue.
>>> 
>>> Regards,
>>> Khaled
>> 
>> "an old version" should not be understood literally. Two identical copies
>> of the exactly same font: one, say, in the system fonts directory, and
>> another one in the TeX distribution tree -- will cause this behavior.

I have not seen any evidence that this is so, and would be very surprised if this happens.

>> This
>> is a very frustrating and well attested bug in XeTeX (which for some
>> reason has been ignored so far by the XeTeX creator and maintainer).
> 
> Theoretically, if my previous "analysis" of this issue was correct, two
> identical copies should not cause any problems, since both will have
> the same glyph IDs. I should have said a different instead of old copy,
> though.

Indeed. The problem may occur if two *different* versions of the "same" font (i.e., with the same font names, but different versions or different formats -- e.g., type 1 vs truetype) are installed. As I believe I have explained previously, it's possible that xetex will find one font during formatting, but then xdvipdfmx finds the other at PDF generation time, and the glyph IDs don't match.

Obviously, it would be better if the two programs were guaranteed to always find the same font for a given name, but ensuring this for all configurations and environments may not be as simple as it sounds. For now, at least, the *strong* recommendation is to have only ONE version of any given font installed.

JK