Re: Need help for Arabic text processing

From: Christopher Fynn (
Date: Mon Jan 24 2005 - 00:00:30 CST

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    Lokesh Joshi wrote:

    > Hi All,

    > I am very new to this group. I am working on a product which enables
    > a user to render bidir text using OTF fonts. Yet i am able to apply
    > the OTF rules to the text but some of the arabic text are not
    > appearing fine.

    > I went thru the Uniscribe text and came to know that it applies some
    > of the rules to the unicode text and dcides which feature shld be
    > applied to one glyph. I cannot use Uniscribe since we work on
    > different platforms that Windows. So can i get help/clue to the
    > following queries:

    > 1. Where are these rules stored and are these a standard. How can i
    > know which feature of OTF shld be applied to which glyph.

    > 2. Are there any open projetcs going on in this direction, which use
    > these preprocessing rules plus the OTF layout rules ?
    > thanx
    > Lokesh

    Open Type layout engines generally apply a particular sub-sets of Open Type
    features to each script. These features are also applied in a particular
    order for each script. The sub set of OpenType features used for Arabic
    script can be found in the document : "Developing Open Type fonts for
    Arabic script"
    Since Microsoft and Adobe are jointly responsible for the OpenType
    specificaation this is the defacto standard for Arabic script OpenType.

    Althouth these document refers to Uniscribe other OpenType shaping engines
    should do the same pre-processing and apply lookups under the same
    substitution and positioning features in the same order.

    The specific lookups under each OpenType feature, and the number of these
    lookups, will vary from font to font. These lookups are contained in tables
    built into the font itself.

    2. On Linux: - Qt, Pango/GTK+ and ICU all have code for OpenType shaping.

    For open source arabic script fonts see:
    For Urdu see:
    Open source fonts for other RTL scripts can be fond listed at:

    If you have specific questions about OpenType the place to ask is on the
    OpenType mailing list. For details see:

    - Chris

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