Re: OpenType on Linux (was: Sequential Fathatan Final Form (Items 9 and 10))

[Mete Kural <metekural at yahoo dot com>]

> That means that there is an Indian group that has
> already created the
> conditions or environment that you need. After all,
> if it works with Nagari
> scripts, which heavily depend on complex glyph
> substitutions, it will
> certainly work with Arabic.

That's what I was thinking too. Just now I found this
interesting email on a Tamil discussion archive. It
discusses glyph substitution support for Indian
languages with OpenType:
http://www.infitt.org/tscii/archives/msg00675.html

Here are two links (one from Adobe and one from
Microsoft) on how glyph substitution works in
OpenType:

http://partners.adobe.com/asn/tech/type/opentype/gsub.jsp
http://www.microsoft.com/typography/OTSPEC/CHAPTER2.htm

Some quotes:

"The OpenType GSUB table fully supports glyph
substitution. To access glyph substitutes, GSUB maps
from the glyph index or indices defined in a cmap
table to the glyph index or indices of the glyph
substitutes. For example, if a font has three
alternative forms of an ampersand glyph, the cmap
table associates the ampersand's character code with
only one of these glyphs."

"The text-processing client uses the GSUB data to
manage glyph substitution actions. GSUB identifies the
glyphs that are input to and output from each glyph
substitution action, specifies how and where the
client uses glyph substitutes, and regulates the order
of glyph substitution operations. Any number of
substitutions can be defined for each script or
language system represented in a font."

Kind regards,
Mete