Devanagari vowels - Alternative forms.

[John Hudson via Indic]

On 12/12/17 17:03, Shriramana Sharma via Indic wrote:
> Do I understand correctly that Open Type features need to be specified 
> as part of the standard? OTOH Graphite features don't and can just be 
> provided by the font maker.


Interoperable OpenType Layout features need to be registered, so that 
they have agreed upon behaviour and predictable results. In the case of 
variant glyph forms such as the regional historical forms of Devanagari 
letters, there are a few different ways in which these could be accessed 
using existing variant glyph substitution (GSUB) features.

1. If associated with specific orthographic use, as defined by an OTL 
Language System tag, then the Localised Forms <locl> feature can be 
used. So this is the case for the subset of variant Devanagari forms 
preferred in Marathi typography. However, in terms of historical 
regional use for Sanskrit, this option is not available because there is 
only one Language System tag associated with Sanskrit.

2. If associated as a variant set, as I understand the case to be with 
the Sanskrit vowel letter forms, then these can be implemented via a 
Stylistic Set <ss01...20> feature. A feature name can be associated with 
the feature via the font name table, and this may be exposed in some UIs.

3. Variants of individual characters can be implemented using the 
Character Variants <cv01...99> features.

Note that variants can be accessed using more than one feature, so it is 
possible for variants to be associated with Language System tags, and as 
stylistic sets, and as individual character variants.


The other way to provide variant forms, especially regional- or 
language-specific sets, is as separate fonts. This is the most robust 
mechanism, and hence why for the Murty Library typefaces we provided 
separate Murty Hindi and Murty Sanskrit fonts (we expect to add a Murty 
Marathi font in future).

JH


-- 

John Hudson
Tiro Typeworks Ltd    www.tiro.com
Salish Sea, BC        tiro at tiro.com

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