LTR and text wrapping (Re: Internationalisation of bzr cli

[INADA Naoki]

Thank you, Eli.

I understand that problems is more difficult than I thought and
some console can handle these problems.
I'll hold in my mind about bidi, but don't implement by myself
unlsess it needed.

On Tue, May 3, 2011 at 1:44 PM, Eli Zaretskii <eliz at gnu.org> wrote:
>> From: INADA Naoki <songofacandy at gmail.com>
>> Date: Tue, 3 May 2011 12:00:32 +0900
>> Cc: Andrew Bennetts <andrew.bennetts at canonical.com>, bazaar at lists.canonical.com
>>
>> I'll implement textwrapper that take care of CJK width (one character having
>> double width).
>
> Thanks.
>
>> I want to support bidi but I don't know about bidi much.
>
> You can learn the basics here:
>
>  http://unicode.org/reports/tr9/
>
> Unless you intend to implement the full bidirectional reordering
> algorithm described there (which I don't think you need, see below),
> you can disregard most of what the above says, and just read the
> definitions and the general guidelines, to catch the spirit.  There's
> also a pointer there to a "reference implementation", which you can
> compile and play with.
>
>> When I have string "foo bar foobar FOO BAR FOOO",
>> It is shown as "OOOF RAB OOF raboof rab oof", right?
>
> No.  First, the visual appearance depends on whether the text will be
> predominantly right-to-left or left-to-right.  In the former case, the
> visual appearance will be
>
>                                           OOF RAB OOOF foo bar foobar
>
> (flushed all the way to the right margin of the display area).  In the
> latter case, it will look like this:
>
>  foo bar foobar OOF RAB OOOF
>
> IOW, the parts that use left-to-right characters are displayed as they
> normally would, while the right-to-left characters are reversed.
>
> And this is just the simplest case, with no explicit embeddings and no
> special control characters that affect reordering.  The Unicode Annex
> at the above URL has all the details.
>
> However, you don't need to implement all this complexity in bzr or in
> your wrapper; that'd be madness, IMO.  There are already terminals and
> text widgets that support bidi reordering, and you should rely on them
> to do the job.  Or we could decide that the translated strings will be
> already in the visual order, then the translator will need to take
> care of that.  In the latter case, the text should already be wrapped
> correctly, which doesn't allow dynamic wrap.
>
>> Then, when I wrap it with 8 chars, it should be shown as
>> >rab oof
>> >F raboof
>> >F RAB OO
>> >OOO
>> right?
>
> No.  Each line is reordered separately.  For example:
>
>  foo bar
>  F foobar
>  F RAB OO
>  OOO
>
> (And it is better not to break the line in the middle of a word, in
> any language; with bidi it is even worse than in English.)
>
> Note that I didn't mean to bother everyone here with this complexity.
> All I said is that we should decide early on whether the translations
> to right-to-left script will be in logical order, and we rely on
> reordering at display time by the terminal or the text widget that is
> used to display the strings; or the translations are in visual order
> and are displayed without any reordering.  Also, if the strings to be
> translated include format conversion specifiers, they need to be able
> to support change of order in the use of arguments (because the
> literal text will be reordered), like the %n$ thing in C printf
> formats.
>



-- 
INADA Naoki  <songofacandy at gmail.com>