Re: Arabic-Emacs questions

[Nadim Shaikli <shaikli at yahoo dot com>]

On Fri, 12 Jul 2002 16:08:33 +0900 (JST),
  "TAKAHASHI Naoto" <ntakahas m17n org> wrote:
> Nadim Shaikli writes:
> 
> > Is the 'composition-lock-mode' (ie. Arabic shaping; even without
> > bidi) being slated to be included to emacs' proper source tree ?
> 
> As far as I know, not decided yet.  However, since the current version
> of comp-lock is far from perfect, it requires improvements to be
> included in the main tree.
> 
> Nonetheless, a glyph shaping mechanism like comp-lock is useful not
> only for Arabic but also for many Indian scripts.  I believe the
> forthcoming Unicode-based Emacs will provide something like comp-lock
> to handle those scripts.

Great; don't hesitate to let us know if help is needed in pushing this
through by showing its importance to our community.

> > But if I have say DAL (0x062f) followed by any of the tanween
> > characters (FATHATAN .. SUKUN -- 0x064b .. 0x0652) the cursor upon a
> > search ends up being placed in such a manner that it shifts to the
> > left the tanween characters (which looks rather odd).  It would be
> > more natural to highlight and to move the cursor in such a manner to
> > include the tanween unless a person included a tanween him/herself
> > in the search to exclude others.
> 
> I do not understand.  I created a file that contains four lines of
> 
> > DAL-FATHATAN-NOON
> > DAL-MEEM
> > DAL-NOON
> > DAL-KASRA-NOON
> 
> and hit C-s ] ("]" for DAL).  Then
> 
> 1. The DAL-FATHATAN composion is temporarily released.

The "release" is the issue -- I don't think its natural to see this
release.

> 2. The first DAL is highlighted.
> 3. The DAL in the second line, one in the third line, and the
>    DAL-KASRA composition in the fourth line are highlighted with a
>    different colour.
> 4. The cursor is placed on the temporarily released FATHATAN.

I would tend to think that it would look more natural to include the
FATHATAN and have the cursor be placed on the NOON (ie. not to break
that tanween composition bond).

> 5. When I hit C-s repeatedly to move the corsor to the fourth line,
>    the DAL-KASRA composition is temporarily released as in 1. above.
> 
> These are expected hehaviour, arn't they?

Technically yes, but it looks and feels odd.  I would tend to think
a more natural solution would be what I had suggested.  Include all
the tanweens in the searches unless a tanween is included in the
search string itself upon which time a more selective search would
ensue.

> > so if I do a search for DAL-NOON, emacs should highlight and move
> > the cursor (when the cursor is moved to that character-combo, the
> > cursor ought to sit past the "NOON") for all of a,c,d.
> 
> Are you saying that incremental-search should behave as if tanweens do
> not exist in the buffer?

Yes, unless the user includes a tanween in his/her own search.  Tanweens
are emphasis characters and unless a person includes them in his/her
search, I would tend to think it would be more natural to ignore 'em
(visually though, they ought to be included and highlighted; the "release"
should not happen).

> > Along the same lines, when doing a search only for a tanween
> > character (0x064b - 0x0652), emacs doesn't do any highlighting
> > although it works properly.
> 
> Thank you for pointing it out.  This is a bug we have not noticed.  It
> may take some time to fix it.

No problem.

> > Don't know what would seem natural here, but some highlight would be
> > nice.
> 
> Perhaps a temporary release of the composition as I described above is
> acceptable.

I would agree.  If a user searches for tanweens stand-alone then
a "release" would make sense since the tanweens would have to consume
their own location on the display, otherwise you'd be highlighting
erroneous characters as well.

> > This might generate some debate, but I thought I'd mention it.  It
> > "might" be useful to have search ignore repeated TATWEEL (0x0640)
> > unless the user specifies it.
> 
> Again, are you saying that TATWEEL should be invisible (like tanweens)
> for incremental-search unless the user explicitly specifies?

Yes; they should be highlighted though.  If the user, on the other
hand, specifies tatweel as part of his/her search then the search
should be a "strict" search in which tatweels ought not be ignored.

> > Any comments on the bidi addition (pseudo code) noted earlier to
> > base line direction according to the first character in the line ?
> 
> As I wrote before, the current Emacs cannot change the screen
> orientation ("base line direction", in your term) in a window.  Thus
> your idea is technically impossible to implement.

Ah, so the "toggle-displaying-orientation" is an all or none
(ie. it affects the entire buffer and can't affect individual
lines), right ?  If that is the case, then I understand.

Thanks.

 - Nadim


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