Incorrect rendering in Devanagari forms in some fonts

1 Sep 2021

      Dear All,

I have encountered a strange problem using certain Devanagari fonts for the 
Sanskrit languagein ConTeXt, wherein the rakaar ligatures are not rendered 
properly in some glyphs/conjuncts. The problem is not too easy to describe so 
please pardon this long email.

The fonts I am using are as follows: 
  • Shobhika – https://github.com/Sandhi-IITBombay/Shobhika
  • Murty Sanskrit – https://murtylibrary.com/mcli-fonts.php

I had previously posted about this issue on TeX SE and Ulrike Fischer was 
kind enough to suggest that the problem might have something to do with the 
font rendering (since I have no issues in XeLaTeX (using Harfbuzz)): 

https://tex.stackexchange.com/questions/612634/devanagari-forms-in-context-u...

My ConTeXt (LMTX) version is: 2021.08.30 19:56

I am using the following typescript for Murty:

\starttypescript [serif] [murty]
  \definefontsynonym 
        [Serif] 
        [name:murtysanskritregular] 
        [features=devanagari-two]
\stoptypescript

\starttypescript [murty]
  \definetypeface [murty] [rm] [serif] [murty] [default]
\stoptypescript 

and the following for Shobhika:

\starttypescript [serif] [shobhika]
  \definefontsynonym 
        [Serif] 
        [name:shobhikaregular] 
        [features=devanagari-two]
  \definefontsynonym 
        [SerifBold] 
        [name:shobhikabold]
        [features=devanagari-two]
\stoptypescript

\starttypescript [shobhika]
  \definetypeface [shobhika] [rm] [serif] [shobhika]
\stoptypescript

Below is the test file I am using to demonstrate the problem:

\setupbodyfont[shobhika]
\starttext
\startcolumns
ट्रा ट्रि ट्री ट्रु द्रू ट्रे ट्रै ट्रो ट्रौ

ठ्रा ठ्रि ठ्री ठ्रु ठ्रू ठ्रे ठ्रै ठ्रो ठ्रौ

ड्रा ड्रि ड्री ड्रु ड्रू ड्रे ड्रै ड्रो ड्रौ

ढ्रा ढ्रि ढ्री ढ्रु ढ्रू ढ्रे ढ्रै ढ्रो ढ्रौ

छ्रा छ्रि छ्री छ्रु छ्रू छ्रे छ्रै छ्रो छ्रौ

\column
क्र ख्र ग्र घ्र ण्र 

च्र छ्र ज्र झ्र ञ्र

च्रे छ्रे ज्रे झ्रे ञ्रे

त्रे थ्रे द्रे ध्रे न्रे 

प्र फ्र ब्र भ्र म्र

य्र ल्र व्र स्र श्र ष्र ह्र 
\stopcolumns
\stoptext

When I use the 'devanagari-two' feature set, which sets the script tag to 
'dev2', the rakaar forms (provided by the features 'rkrf=yes' and 'blwf=yes') 
do not render properly for some glyphs, namely the glyphs in the right column, 
enclosed in a red rectangle in the file 'devanagari-two-forms-shobhika.png' 
attached in the Drive folder here.

When I switch to using the 'devanagari-one' 
feature set (in the foregoing typescript definitions), which sets the script 
tag to 'deva', the rakaar forms in the left column are rendered incorrectly  
in 
the file 'devanagari-one-forms-shobhika.png' attached in the Drive folder here.

Analogous problems occur with the Murty font. Further, in the Murty font, one 
other conjunct, namely
त् +‌ त 
does not render properly. I have highlighted this in the file 
'murty-conjuct.png'.

The sample images demonstrating the issues are available in the following 
public Google Drive folder: 

https://drive.google.com/drive/folders/1aOmPKqBzB5usVvT9g-Bxk87exyiQn7ax

I must mention once again that I have no such problems using either of these 
fonts in XeLaTeX. 

What I am noticing is that this problem only occurs with consonant forms that 
have a 'circular base', i.e., have no danda (the vertical line) next to the 
character. For what it is worth, I have noticed also that I am able to 
'circumvent' this issue if I write 

छ्र‌ +‌ ZWS + Devanagari vowel sign

where ZWS is the zero-width space U+200B. Unfortunately, this quickly becomes 
very untenable in large documents. Since I was new to ConTeXt I did not 
venture 
to ask earlier on since I had not read much of the documentaion. Now, after 
having read quite a bit, I have mustered up the courage to ask here. As a 
stop-gap solution, I defined another font alternative with
\definefontalternative[rk]
and used that with a font synonym using 'devanagari-two' where necessary. 

I have completely migrated (away from (Xe)LaTeX )to ConTeXt for all my 
university work which is in English with lots of mathematics. I am by no means 
an expert but I have learned very much about ConTeXt by reading the excellent 
wiki, documentation and mailing list. I have no issues using ConTeXt on an 
everyday basis for my English-language based work. It is only when I tried to 
use it for my work in Indian-languages that I ran into this issue.

I request your kind help in this matter. I really want to be able to use 
ConTeXt for these Indic works. I will be grateful for any help and/or 
guidance.

Many thanks,
kauśika

kauśika cittūr

kauśika cittūr

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