[XeTeX] OT features

[Georg A. Duffner]

Am 2011-02-15 04:38, schrieb David J. Perry:
> I had the exact same problem last weekend. I constructed an OT feature
> to replace a long s with a regular s if followed by a comma, period,
> space, etc. The longs-space combination did not work. I am not a
> low-level TeX programming kind of guy, but I had learned a bit somewhere
> about TeX's "glue" and I wondered if the OT parser did not see the space
> character. Thanks to Khaled for confirming this.
>
> David
>
>
> ----- Original Message ----- From: "Khaled Hosny" <khaledhosny at eglug.org>
> To: "Unicode-based TeX for Mac OS X and other platforms" <xetex at tug.org>
> Sent: Monday, February 14, 2011 6:35 PM
> Subject: Re: [XeTeX] OT features
>
>
>> On Mon, Feb 14, 2011 at 10:24:14PM +0100, Georg A. Duffner wrote:
>>> For my font project (see www.georgduffner.at/ebgaramond) i have been
>>> playing around with some opentype features. It seems, that
>>> contextual features involving the character "space" don’t work as
>>> expected.
>>
>> AFAIK, XeTeX processes each word in isolation, so space never part of
>> context (also in TeX space is not a character/glyph but a kind of a
>> property named glue, so it does not get handled by OT layout).
>>
>> Generally speaking, using space in context is fragile and not guaranteed
>> to work everywhere.
>>
>>> I wanted to implement a feature for latin texts that
>>> replaces "u" at the beginning of a word by a letter that looks like
>>> "v". The rule looks like this:
>>
>> 'init' feature should be more suitable here, but almost all OT engine
>> supports it for few selected scripts (Arabic mainly). With 'init' it is
>> the responsibility of the engine to detect word beginning.
>>

Thanks Khaled,

I already feared such implication being the culprit. In this case, the 
solution was simple since it’s easy to reverse the lookup: replace every 
"u" by a "v"-like glyph and then make a contextual rule that changes 
them to a "u"-like one after a letter. But I don’t think I’m gonna keep 
this as default for latin but rather put it in a stylistic set.

best regards
Georg