[xep-support] Another Arabic problem (diacritics)

Peter von Kaehne refdoc at gmx.net
Thu Jun 19 08:15:31 PDT 2008


Thanks Alexei,

this is is a fascinating post and should indeed address Krister's
problem very well.

Wrt the numbers - if I replaced the Farsi numbers with Arabic numbers -
which look practically identical (but for a couple of glyphs) but occupy
a different unicode range, the bidi mechanism kicked in fine. That is
about 1 1/2 years ago and I had no need to try it again, so maybe things
are different now. I think I reported the matter at the time to RenderX

Peter

Alexei Gagarinov wrote:
> Hi Peter,
> 
>>> I have found another old post talking about diacritics:
>>> http://services.renderx.com/lists/xep-support/1812.html
>>> In this post it is suggested to use special characters. For example
>>> for alef+hamza one should use &#x623. But I can not find any special
>>> character for this combination.
>>
>> I did the same search on your behalf and came to the same conclusion.
> 
> Arabic diacritics behavior is the same as described in that post.
> 
>> A while back I had a problem with XEP not dealing with Farsi numbers
>> correctly - it ordered them RtoL instead of LtoR.
> 
> I guess, this is an issue with the using of BIDI algorithm;
> I don't remember any compliance about Farsi numbers. :)
> 
>> Taking this further would mean to me that you could use unused parts of
>> unicode (which exist for such purposes) and put customised glyphs in
>> your font on those places, bypassing in this way the rendering/glyph
>> shaping attempts by XEP.
>>
>> This would be an ugly hack and probably very tedious if it applied to
>> more than a few glyphs, but it should work fine. The numbering worked
>> for me.
> 
> If you're considering such a hack as an alternative I can suggest an
> optimization.
> XEP places glyphs according their dimensions. So you may change required
>  glyph's bounding boxes. Set a negative value for the left side and zero
> for the width. It should be enough for Arabic diacritics.
> And this approach makes the editing more easy (with GUI font tools).
> 
> 
> 
> OpenType Specification added new features for advanced typographic
> extensions.
> These features include font tables for the placement of complex glyphs
> (shifts, in the both directions, for certain sequences of glyphs and so
> on).
> I believe this would be enough for the correct rendering of alef+hamza
> and similar glyphs (if you use OpenType fonts with the correct advanced
> typographic tables, of course).
> 
> The only point here is that XEP does not support these advanced OpenType
> features.
> 
> Are you using OpenType or another type of fonts for Arabic?
> 
> Best regards,
>   Alexei Gagarinov
> RenderX
> ---
> www.renderx.com
> www.renderx.net
> 
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