juktakshar problem in bengali font

[potasiyam]

I am developing a bengali font where i wanted to add this lookup স ্ প ্ ল -> স্প্ল (combining sa halant pa halant la).
But only স ্ প -> স্প (স্ প -> স্প) or প ্ ল -> প্ল (প্ ল -> প্ল) is posible with 'pres', not স ্ প ্ ল -> স্প্ল (স্প ্ ল -> স্প্ল or স্ প্ল -> স্প্ল)
It can not be use used with blwf and blws because of ল.
so what is the method for স্প্ল?

add:
1. I am working with 'beng', what should i change if i want to add 'bng2' support?
2. Volt comes with sample 'Mangal' font to understand the deva features. But Hindi & Bengali has lots of differences. Is there any Bengali sample font for volt?

[Andrew Glass (Microsoft)]

Perhaps you have done a half form substitution prior to pres? In which case the pres lookup should be something along the lines of: bn_half_sa bn_half_pa bn_la -> bn_s_p_la

Also be sure that this lookup comes before bn_half_pa bn_la -> bn_s_p_la.

There are two lookups that need to be changed for bng2 tags: blwf and pstf. The key difference is that for bng2 halanth has not been re-ordered. So where beng has bn_ba bn_halanth -> bn_ba_phala; bng2 has bn_halanth bn_ba -> bn_ba_phala. The same difference applies to the pstf lookup.

Unfortunately the Bengla fonts have not been licensed for distribution as a sample font for Volt.

I hope the above explanation helps!

[OldKnip]

My Bengali font has only <beng> lookups and works correctly under Word 7 though <blwf> and <pstf> features are using lookups with reordered halant!

[OldKnip]

I should perhaps have added "why?" to my last message to induce someone to give me an explanation. 
Meanwhile I've added <bng2> to my <beng> font and made a font with only <bng2>. I've tried out these 3 fonts both on a Windows XP Professional and a Windows 7 Professional machine with the following results:

- <beng>+<bng2> font works on both machines, as expected.
- <bng2> font works only under Windows 7, as expected.
- <beng> font font works on both machines, unexpected for Windows 7 (as stated in my last message).

Can anybody tell me why <bng2> should be needed?

[SpaceyT-17]

@OldKnip:
It seems that Microsoft has retained the old layout algorithm for handling the beng script tag, while also including the algorithm for bng2. It must be to preserve backward compatibility. However, I honestly can't see why the bng2 script tag was introduced at all, since the new features like cjct are called by the beng algorithm. I've tested this on the Uniscribe included with Vista SP2 some time ago, but not with the version bundled in Windows 7.

@potasiyam:
You can open the Vrinda in Fontlab Studio demo version, which can generate a human-readable listing of compiled OT data. I've used it myself to get an example.

[OldKnip]

Thanks, SpaceyT!
Meanwhile I've tested all my other Indic OT fonts under Windows 7. There were no rendering problems with (Bengali), Devanagari, Gujarati, Kannada, Oriya, Tamil and Telugu! Only Sinhala was not rendered properly; there was not even a glyph reordering with this script.

Microsoft says in its description of the new features: "While Indic fonts made according to the earlier recommendations will still function properly in the new versions of Uniscribe, font developers may choose to update their fonts, particularly if they wish to avoid certain limitations of the earlier implementation."

So it seems, that adding the new methods to the old ones is more or less superfluous. I'd like to know, what are the "certain limitations of the earlier implementation"?

[potasiyam]

Perhaps you have done a half form substitution prior to pres? In which case the pres lookup should be something along the lines of: bn_half_sa bn_half_pa bn_la -> bn_s_p_la

Also be sure that this lookup comes before bn_half_pa bn_la -> bn_s_p_la.

There are two lookups that need to be changed for bng2 tags: blwf and pstf. The key difference is that for bng2 halanth has not been re-ordered. So where beng has bn_ba bn_halanth -> bn_ba_phala; bng2 has bn_halanth bn_ba -> bn_ba_phala. The same difference applies to the pstf lookup.

Unfortunately the Bengla fonts have not been licensed for distribution as a sample font for Volt.

I hope the above explanation helps!

Thanks Andrew.
It seems your method is the right way. I solved it temporarily with adding a second pres with bn_half_sa bn_p_la -> bn_s_p_la

I have decided to add bng2 features to my font. So I need to understand all the changes from beng and totally new features. Is there any complete documentation for bng2?

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