From: Philippe Verdy (verdy_p@wanadoo.fr)
Date: Tue May 18 2004 - 18:05:40 CDT
From: <jcowan@reutershealth.com>
> Andrew C. West scripsit:
>
> > It does ? I thought that the whole point of much of the recent discussion
was
> > the uncertainty of how Ogham should be laid out in vertically formatted
text,
> > such as when embedded in Mongolian or vertical Chinese.
>
> What's uncertain is whether a lr or a rl progression is favored, given the
> paucity of evidence. Michael favors lr progression. There is no question
> that the text is read BTT.
This creates an interesting problem: Put in the same sentence Han (Chinese) and
Mongolian words in a vertical layout (I don't think this is unlikely, as
Mongolian is also spoken in China, and there's also a Chinese community in
Mongolia). So Chinese ideographs will be laid out vertically from top to bottom
(but not rotated, except for a few characters like ideographic punctuation marks
or symbols), and Mongolian will be laid out from bottom to top in their normal
stack orientation. Such a text is clearly bidirectional, so we would need BiDi
processing to order glyphs correctly.
Now admit that you want to present it horizontally: Han ideographs will not be
rotated but will flow on rows from left to right. Suppose you have performed the
Bidi processing according to the previous vertical presentation, then Mongolian
stacks will flow from right to left (but unlike Han ideographs, they will need
to be rotated...)
Now try including some Latin words in this text (also not unlikely: there are
lots of trademarks and people names that will need to be written with their
normal Latin characters). If the text is presented vertically, there's a
legitimate question of whever Latin should be rotated (but it will keep the Han
flow direction.); according to Japanese practices with halfwidth characters (the
standard Latin script is "half-width"), it will be rotated exactly like for
"half-width" Hiragana or Katakana, simply because "half-width" characters align
more naturally in that direction, and because the perception of character's
baseline really requires (for standard presentations of texts) that baselines
not be splitted at each character like in vertical columns of crosswords. This
would then flow Latin in the same direction as Han, but the reverse direction of
Mongolian.
But if experience shows that Mongolian would be presented horizontally with lr
direction, like with Latin, there's a problem.
So what is shown here is that Bidi properties are only accurate for horizontal
flows of text. What is missing is a separate set of Bidi properties for the
vertical direction of the same flow... We could define basically a similar
algorithm for vertical BiDi, but this would also require new BiDi properties.
May be this would not require changing the existing Bidi properties for
characters that are normally presented horizontally, but new property _values_
would be needed for those that flow normally vertically(Ogham, Mongolian)...
Plus a mapping of these new property values to the corresponding horizontal
properties when the same characters are to be presented horizontally.
If the main UCD file can hardly be changed, additional properties may be listed
elsewhere in the file of extended properties.
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