RE: [Indic-computing-devel] Testing OpenType support

[Keyur S. <key...@ya...>]

--- Arun M <ar...@fr...> wrote:

> 
> My knowledge of OpenType is very limited. Here is the issue.
> http://www.microsoft.com/typography/otfntdev/indicot/features.htm
> 
> It says for some consonants (eg NNA) halant form will be represented by
> chillaksharam. My understanding is <NNA><virama>  will form chillu NNA. 
> <NNA><virama><ZWNJ> will make virama visible as it is and consonant will
> be in base form. 
> 
> How does NNA+virama and NNA+virama+ZWNJ should differ ?
> 

This has been the issue pending since long ago. Unfortunately, Unicode
remains almost silent about this confusion :-(. I think some clarification
is required in Unicode Indic-FAQ when some consensus has been reached.

We want use virama sign in three different cases. 

(A) chillu form, 
(B) virama (halant) form, and  
(C) ligature (or consonant conjuct).

A scheme should be able to support all 3 possible kind of rendering when
using halant in Malayalam.

It seems that there are two approaches to select alternate forms at
present; using ZWJ and/or using ZWNJ. It is general belief (I may be wrong
;-)) that ZWJ becomes part of the syllable and ZWNJ forces termination of a
syllable.


Approach-1:
----------

A1. <C1><virama> will produce Chillu form (if any).
A2. <C1><virama><ZWNJ> will produce halant form of C1.
A3. <C1><virama><C2> will produce a ligature if <C1> doesn't have chillu
form.
A4. <C1><virama><ZWJ><C2> will produce a ligature if <C1> has chillu form. 

A4 has been given to answer the question:
"How to produce <C1-chillu><C2> sequence if <C1><virama><C2> produce a
ligature". As a result the rule A3 should be used when there is no chillu
form of <C1> and A4 should be used when there is a chillu form of the
consonant <C1>.

The issue with this approach is that we have to use ZWJ in conjunct
formation when <C1> has chillu form.


Approach-2:
----------

B1. <C1><virama><ZWJ> will produce Chillu form (if any).
B2. <C1><virama> will produce halant form if <C1> is not part of a
ligature.
B3. <C1><virama><ZWNJ> will also produce halant form of <C1>.
B4. <C1><virama><C2> will produce a ligature (or consonant conjunct).

The issue here is that people generally believe that ZWJ is used to join
the consonant preceding it with the consonant immediately following ZWJ.
Thus, ZWJ virtually becomes part of the syllable. Here we are using it to
terminate the syllable.


However, I am not a Malayalam expert :-) My observations are based on my
discussion with a Malayalam font designer. It is better if you once again
raise this issue on Unicode list.

- Keyur


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