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Hi Stefan and others,
>> 1. Horizontal, that is, left-to-right (LTR) versus right-to-left
>> (RTL).
>> 2. Vertical, that is, top-to-bottom (TTB) versus bottom-to-top (BTT).
>> 3. Priority of direction (e.g. (LTR, TTB) versus (TTB, LTR)).
>> [...] An elaboration of the directional override mechanism to
>> handle vertical directionality would have to take priority into
>> account as well. Instead of two directionalities, LTR and RTL, the
>> Unicode Standard would have to consider eight.
This is not quite sufficient, I'm afraid. An interesting approach is,
for example, taken in the Omega typesetting system, an extension of
TeX, where they deal with a total of 32 writing directions by
describing writing directions by three variables:
1. "Top" side of the page (one out of four)
2. "Left" side of the page (one out of two, since it *does* have to be
orthogonal to 1)
3. "Top" of character (one out of four). This is needed if you want to
embed, say, RTL and LTR text in the middle of a TTB paragraph, such as
embedding other scripts in Mongolian, or rotated plain script in
vertical CJK.
This gives you 32 combinations of what is written into which
directions and how glyphs have to be aligned. It's described in a
paper on http://omega.cse.unsw.edu.au:8080/papers/directions.pdf, but
be kind to the poor server :-) The most "common" direction
combinations given there are the following eight:
TLT - Left-right scripts, horizontal CJK
TRT - Right-left scripts
RTT - Vertical CJK, upright left-right scripts in vertical CJK
RTL - Mongolian in vertical CJK
RTR - Rotated left-right scripts in vertical CJK
LTL - Mongolian [This actually depents on the orientation of Mongolian
glyphs]
LTR - Rotated left-right scripts in Mongolian
LTT - Vertical CJK in Mongolian
Even this 32-direction system does not cover cases such as Mayan where
scripts follow the rebus principle, where text gets embedded inside
other glyphs or where text is written "boustrophedon" ("as the ox
plows", i.e. line by line in both directions). Actually, this is a DTP
issue. It has very little to do with the information content of the
text, instead it's rather a presentation thing, which is why IMHO it
does not belong into Unicode, but that's a matter of discussion.
SP> As an alternative solution, the current switches could be considered LTR,
SP> TTB and RTL, TTB. Then 6 other code points would be necessary for the other
SP> directions.
As said, this is not quite enough. Admittedly, some directions are
rather arcane, but believe me, it will be possible to dig up some
ancient document or other which is written into any odd combination of
directions. If Unicode wants to achieve complete representation of any
kind of presentation of text direction here, it's going to be a pretty
rough job.
Kind regards and happy new year to everyone (at least everyone
following the Gregorian calendar, that is :-)
Philipp mailto:uzsv2k@uni-bonn.de
__________________________
Out of memory / We wish to hold the whole sky / But we never will
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This archive was generated by hypermail 2.1.2 : Sat Dec 29 2001 - 08:13:51 EST