From: Peter_Constable@sil.org
Date: Wed Dec 04 2002 - 17:11:25 EST
On 12/03/2002 05:16:14 PM Antoine LECA wrote:
>This issue is of relevance to the rendering engines. For example,
>Microsoft's Uniscribe refuse to draw U+095x on top of any syllable
>which is not Devanagari. I believe this behaviour is incorrect,
>but the Script.txt file seems to assert MS position.
I don't think the Script.txt file isn't intended to imply such
implementation behaviours, though it's easy to imagine some implementers
might treat it that way.
There is a potential concern in Uniscribe/OpenType: substitution and
positioning rules in OT are organised hierarchically by script then by
individual writing system / typographic groups (the label used is
languages, but the intent is really groups of writing systems that share
common typographic behaviours). Thus, a rule that handles positioning of a
glyph for 0950 (or whatever) relative to some member of some class of
glyphs must be entered somewhere under some particular script. Now, there
is nothing that prohibits a font developer from creating multiple
positioning rules for 0950 with different classes of base glyphs and to
have a different one placed in the hierarchy under several different
scripts. But there may yet be an issue on the Uniscribe side: given a
string of characters, which it will begin by mapping into a string of
initial glyphs, it has to decide which script tag(s) to apply to portions
of the string. What I don't know is whether it generally assumes combining
marks belong to a specific script, or whether it allows combining marks to
inherit their script from the base characters with which they combine.
At least, that's my understanding of these technologies (which comes with
no guarantees).
- Peter
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Peter Constable
Non-Roman Script Initiative, SIL International
7500 W. Camp Wisdom Rd., Dallas, TX 75236, USA
Tel: +1 972 708 7485
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