RE: Off-Topic: Overriding

Hi Badral,
Yes, that is correct. See the attached over-ride logic.
Greg


-----Original Message-----
From: Badral S. [mailto:badral@bolorsoft.com] 
Sent: Saturday, October 31, 2015 5:32 AM
To: public-i18n-mongolian@w3.org
Subject: Re: Off-Topic: Overriding

Hi all,
@Greg,
With this example, my understanding is then exactly correct. For example NAIMA, we have to write a substitution rule like Rule1=if {VOWEL_SET|} + I.medi then sub I.medi by I.medi2 (assume that is double shilbe) to illustrate i.medi as double shilbe. Then we need to write a rule for invalidating Rule1. Like Rule2=if I.medi2 + FVS2 then sub I.medi2 by I.medi.
Please confirm.
@Richard,
You said, that the knowledge of what to render lies almost entirely in the font. It means, we have write the rules like Rule2 from above example in GSub table and we shouldn't trust that the renderer would do something/post-processing for overriding. Is it correct?
What did you mean with "a purely formal glyph"?

Badral

On 29.10.2015 10:05, Richard Wordingham wrote:
> On Thu, 29 Oct 2015 07:00:07 +0000
> Greg Eck <greck@postone.net> wrote:
>> I may be using it in a non-standard sense, but my use of the term
>> over-ride is when the standard context of the default glyph does not
>> render the default glyph but instead another glyph. An example would
>> be найма (eight) where NAIMA is rendered    with no FVS, but
>> NAI+FVS2+MA is rendered  . The FVS2 assignment is  needed to get the
>> default single-shilbe back where the context tells the shaping engine
>> to render the double-shilbe.
> Of course, all the shaping engine knows is that some characters have
> contextual variants.  The OpenType engine does not have to understand
> the specific meaning of the variation selectors, and knows nothing of
> the default shaping rules - merely their possible existence. The
> knowledge of what to render lies almost entirely in the font. There are
> two possible mechanisms:
>
> 1. Normal character plus variation selector chooses a different starting
> glyph, which is then substituted for differently to the glyph chosen
> without a variation selector.
>
> 2. A purely formal glyph is created for the variation selector, and
> combining rules then apply the intended effect of the variation
> selector.
>
> Richard.
>


-- 
Badral Sanlig, Software architect
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