Re: Basic question: types of diacritics marks

Date: Fri Jul 19 2002 - 09:58:54 EDT

On 07/18/2002 07:08:07 PM John Hudson wrote:

>In an OpenType font, it is possible for the combining diacritics to
>actually be spacing glyphs...

>It is necessary to provide
>separate glyphs for the spacing and combining forms, since the kind of
>glyph processing lookups you will want to involve them in will differ.
>Of course, the combining diacritic can be a composite of the spacing form,
>placed on a zero width.

One other factor to consider is what behaviour you want when people copy
from, say, a PDF file: a font could have a single GID for 00B4 and 02CA --
i.e. the cmap maps both these USVs to the same GID -- but then that would
create a problem for text being copied from PDF. We have decided to have
each and every USV map to a unique GID in our cmaps. At that point, the
glyf entry for one GID might be a composite glyph description that simply
points to another to get the outline, in effect causing both characters to
use the same outline data -- or all three characters, for that matter.

- Peter

Peter Constable

Non-Roman Script Initiative, SIL International
7500 W. Camp Wisdom Rd., Dallas, TX 75236, USA
Tel: +1 972 708 7485
E-mail: <>

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