[XeTeX] Ligature unavailable in Estrangelo Antioch

[Adam Twardoch]

Sargon Hasso wrote:
>     In TTF specs, you could have
>     have more than one alternative, but, unfortunately, Microsoft did
>     not implement this ligature selection alternative in their rendering
>     engine (uniscribe). (...)
>     Unfortunately, like I mentioned above, we don't have that option in
>     the TTF implementation of Microsoft. 

Sargon,

I think this is a misrepresentation of facts. The basic level of
Uniscribe-based implementations (e.g. RichEdit or Word) indeed don't
typically have mechanisms for user-controlled (discretionary) access to
some features. They only apply those features (in appropriate contexts)
which are supposed to be "on by default" to provide linguistically
correct and generally typographically pleasing typesetting.

But more advanced Uniscribe-based applications (e.g. WPF) certainly do.
In WPF-based applications, you have this functionality out of the box
right now.

The situation you're describing clearly indicate that the three
different ligatures should be placed in the Stylistic Alternates
("salt") feature using the GSUB LookupType 3 (one-to-one-out-of-many).
In addition, you could create two Stylistic Sets ("ss01", "ss02") that
provide GSUB LookupType 1 (one-to-one) substitutions for the three
additional ligatures. Of course the lookups associated with those
features should be defined after the lookups that define the "liga" or
"rlig" features that turn on the ligatures.

Both the Stylistic Alternate feature and the Stylistic Sets features are
appropriate mechanisms for this type of selection, and they are
implemented in WPF as well as other OpenType Layout-aware applications,
such as XeTeX or Mellel. My guess is that future versions of Adobe
Creative Suite applications will also provide access to those. In fact,
they already provide the mechanism, but don't support Syriac at the moment.

Of course you're free to build additional fonts that simplify access to
those alternates by making them default. But I think that each of those
fonts should include "salt", "ss01" and "ss02" for users of environments
that support user-selectable OpenType Layout features for complex
scripts (e.g. WPF, XeTeX, Mellel).

Regards,
Adam

-- 

Adam Twardoch
| Language Typography Unicode Fonts OpenType
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