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Re: Off-Topic: Overriding

From: Richard Wordingham <richard.wordingham@ntlworld.com>
Date: Thu, 29 Oct 2015 09:05:09 +0000
To: "public-i18n-mongolian@w3.org" <public-i18n-mongolian@w3.org>
Message-ID: <20151029090509.6208dabe@JRWUBU2>
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.
Received on Thursday, 29 October 2015 09:05:41 UTC

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