From: Andrew C. West (andrewcwest@alumni.princeton.edu)
Date: Fri May 14 2004 - 12:07:06 CDT
For vertically laid out Chinese books, the front cover corresponds to the back
cover of an English book, and the back cover corresponds to the front cover of
an English book, so from a Western perspective such books appear to be read
backwards. Traditionally-bound bilingual Manchu-Chinese books are read the same
way as Western books ... which is backwards from a Chinese perspective.
As to newspapers, these normally follow Western newspaper page order, regardless
of whether the content is laid out horizontally, vertically or mixed horizontal
and vertical.
> > As I suggested in a recent thread on mixed horizontal/vertical layout, if you
> > did have mixed Top-To-Bottom (TTB) and Bottom-To-Top (BTT) scripts such as
> > Mongolian and Ogham [...] then you
> > could deal with their conflicting directionality as if they were rotated LTR
> and
> > RTL scripts by means of LRO, RLO and PDF control codes [202C..202D].
>
> Surely that's not enough: you'd need to implement the full implicit bidi
> algorithm, giving Ogham a nonce bidi type of R. Either that, or run the
> Ogham T2B instead of the normal direction.
>
Have a look at the attached images which show Mongolian text with embedded Ogham
(laid out horizontally).
In "Mongolian with embedded LTR Ogham" both Mongolian and Ogham are LTR by
default.
In "Mongolian with embedded RTL Ogham" Mongolian is LTR by default, but the
Ogham has been made RTL by sandwiching it between an RLO control code and a PDF
control code (i.e. <202E, 1680, 1692, 1682, 1689, 1690, 168C, 1685, 1694, 1680,
202C>). Thanks to Uniscribe this magically has the effect of reversing the flow
of the embedded Ogham text. This does not quite work, however, as although the
glyph order has been reversed the glyphs have not been rotated 180 degrees, with
the result that they are the wrong way round. But an Ogham font that was
specifically designed for RTL/BTT usage would have glyphs that are rotated 180
degrees compared with those in the Unicode code chart, and with such a font this
embedded RTL Ogham test text would be rendered correctly. Now all you would need
is a text editor that rotated the whole thing 90 degrees, and you would have BTT
Ogham embedded in TTB Mongolian ... with no messy fiddling with the bidi
algorithm.
And if you really wanted to be clever, you could perform the same trick by
embedding LTR Ogham in RTL Mongolian (using an RTL Mongolian font ... which do
exist, although I don't know of any Unicode RTL Mongolian fonts yet), and
rotating the whole thing 270 degrees ... I think ... my head's started to spin
at this point ...
Andrew
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