I'm designing a FOSS Indic font and have run into some problems. My font works almost as expected, except that when ligatures formed by GSUB rules combine with certain marks, they break down. One example is
 
 feature blwf { # Below-base Forms
  script orya; # Oriya
     sub or_halant or_ta by or_ta_phalaa;
 }blwf
 
 feature pres { # Pre-base Substitutions
  script orya; # Oriya
     sub or_ta' or_ta_phalaa by or_ta.pres
 }pres

feature blws { # Below-base Substitutions
  script orya; # Oriya
     sub or_ta.pres or_ta_phalaa by or_t_ta
 }pres
 
 So when I want the glyph "or_t_ta" it forms fine. But when I combine it with "or_reph" or "or_ikaar" marks, the 2nd or 3rd substitution (pres or blws) is ignored and I get "or_ta + or_ta_phalaa + or_ikaar". (ତ୍ତ is the ligature. ର୍ତ୍ତ or ତ୍ତି breaks down). To simplify further it is like this
    c b -> d
    b' d -> b.pres

    b.pres d -> e
Gives
    b+c+b -> e
    b+c+b+f -> b d f

Any ideas why this might be happening? If you want to take a look at my ttf file, I've attached it and it's also on github https://github.com/coldbreeze16/Lekhani/blob/master/Lekhani.ttf

I'm a student with limited means, but I'll recompense you for your time if price is right.

Lekhani.ttf

This may have something to do with the sequence ordering of your lookups.

For example if you have:

f + f > ff

before

f + f + i > ffi

then ffi ligature will never appear, only ff followed by i. This is even more critical in Indic as there are often more than a two levels of substitution lookups.

 

On 12/8/2015 at 1:17 PM, coldbreeze16 said:

I'm designing a FOSS Indic font

Have you fixed your problems? :) How is Lekhani going? Would you like to add it to Google Fonts?

I'm developing some new contribution guidelines for Google Fonts here:

https://github.com/google/fonts/blob/master/CONTRIBUTING.md

https://github.com/googlefonts/gf-docs/blob/master/ProjectChecklist.md