Re: 'kern': TrueType table and GPOS lookup feature

From: Steve White <stevan.white@gmail.com>
To: Hans Hagen <pragma@wxs.nl>
Cc: mailing list for ConTeXt users <ntg-context@ntg.nl>
Subject: Re: 'kern': TrueType table and GPOS lookup feature
Date: Fri, 30 Nov 2012 19:34:13 +0100	[thread overview]
Message-ID: <CAEmWKkSx0wMP3S4+C43+W5fB7LwAEyH8BHD4Hu7Btthx-cRrtg@mail.gmail.com> (raw)
In-Reply-To: <50B8D947.50003@wxs.nl>

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Hi, Hans,

Sorry about the accidental post

I'm struggling with gmail's new input interface...very hard not to top-post.

On Fri, Nov 30, 2012 at 7:15 PM, Steve White <stevan.white@gmail.com> wrote:

> Hi Hans,
>
> On Fri, Nov 30, 2012 at 5:05 PM, Hans Hagen <pragma@wxs.nl> wrote:
>
>> On 11/30/2012 10:58 AM, Steve White wrote:
>>
>>
>>  3) In most applications, the script of a run of text is determined from
>>> the Unicode.  This is the assumption made in FreeFont.  The GNU FreeFont
>>> policy starts from its essence as a Unicode font, in which no particular
>>> script is default. (Some generic features that are not specific to any
>>> script, are in {dflt,dflt}.)
>>>
>>> There was a suggestion that Latin kerns should be activated by
>>> {script,lang}={dflt,dflt}.  Let me ask, should Devanagari kerns also be
>>> activated by {dflt, dflt}?  If not, why?
>>>
>>
>> because one text can contain multiple scripts
>>
>>
>>
>> This is interesting.

There are different notions of text here, depending on point of view.

Certainly a sentence could contain a mixture of scripts.

When I said "run of text" I meant it from the point of view of how font
featues are applied to text.  Usually it is a small chunk of text, with
chunks separated by white space or other delimiters.

In web browsers, etc, if a run of text is, say, from the Armenian Unicode
range, the script is judged to be Armenian for the purposes of matching
OpenType lookups.
(The information of what *language* is meant by the text must be supplied
otherwise, in this case, in a 'lang' attribute).

Now, you could imgaine applying an OpenType lookup to, say, a Malayalam
letter immediately followed by an Arabic letter, but this is .. I think...
really pointless.

Even in text containing very mixed scripts, at least the words from the
different scripts are separated by white space (or other punctuation etc).

So the mechanism of determining the "script" of a "run of text" does
typically make good sense.

That all said:

It's not clear to me how this is implemented in ConTeXt.  I'll play with it
once I have some examples working.  My guess is, the author has to
explicitly indicate the script each run of text (by specifying the
attributes of the font to apply to the run).

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