How to substitute a glyph when two characters are written

[ha-ab]

hi
how can i create a glyph that when write two characters ,so convert to it.
namely ل+ا convert to لا
or ش‌هْ convert to شهْ

thanks

[vanisaac]

This requires advanced features like OpenType, Apple Advanced Typography, or Graphite control. Microsoft Typography has fairly extensive documentation on how to make OpenType Arabic fonts in the MS Visual OpenType Layout Tool (MS VOLT), and Graphite is pretty easy to program (available from SIL, international), and AAT looks horribly complex to me, although it is quite powerful. Basically, in FCP, all you will need to do is make the ligature characters (your lam+alef, etc.) and give them postscript names. You do not need to assign mappings to these ligature characters - this will be taken care of when you create a substitution rule in OpenType/Graphite, namely lam + alef -> lam_alef_ligature. You can also make contextual forms - sin_initial, sin_medial, sin_final, sin_isolate, and use substitution rules to give you the proper forms, although this is actually easier in OpenType than Graphite - OpenType provides the context rules (ie, initial forms should follow alef, waw, dal, reh, etc.), you just need to say that sin -> sin_medial when it's medial. Any other questions?

-Van