[HarfBuzz] Contextual shaping of Malayalam post(pre)/below base forms

[Suresh P]

Behdad Esfahbod wrote:
> On 13-06-11 07:29 AM, Suresh P wrote:
>> I want to know whether it is possible to prevent pref and blwf rules being
>> applied using contextual rules
> The engine doesn't do anything specific for blwf, so whatever you put in your
> (contextual) lookup is what happens.  pref is different since the engine does
> reordering.  But it only does the reordering if the virama,consonant have
> ligated.  So, again, yes, you can block the reordering using a contextual lookup.
But I find the ligation(for pref and blwf) always happen irrespective of 
the rules in the contextual lookup. The reordering issue does not arise 
at all. I want to block ligation via pref and blwf entirely for certain 
base consonants without any syllable breaking exercise. Is that possible ?

http://www.microsoft.com/typography/OpenTypeDev/malayalam/intro.htm says:

...
Note that a font may be implemented to re-order a Ra to pre-base 
position only in certain syllables and display it as a below-base or 
post-base form otherwise. This means that the Pre-base-form 
classification is not mutually exclusive with either Below-base-form or 
Post-base-form classifications. However, /all classifications are 
determined as described above using context-free substitutions/.
....