Re: Pango arabic engine

[Pablo Saratxaga <pablo mandrakesoft com>]

Kaixo!

On Tue, Nov 07, 2000 at 07:51:10PM -0800, Chookij Vanatham wrote:

> For the case of more than 2 arabic vowels in the consecutive sequences,
> what would the second arabic vowel be supposed to display ?
> 
> Ex:
> 
> 	U+0639 <--- arabic consonance
> 	U+064B <--- arabic vowel
> 
>   logical input:  U+0639    + U+0639    + U+064B     + U+064B      + U+0639
> 		   (cons)     (cons)      (vowel)      (vowel)       (cons)
> 		   
>   visual output: InitialForm  MiddleForm  combined     ??????        FinalForm

The first vowel should display on top of the previous consonant; and the
second (and other) should display in top of a tatweel (that horizontal
stroje used to fill blanks).

> I know that the second vowel, U+064B, is causing the invalid/in-correct
> spelling of arabic words

But Arabic script is not used only to write Arabic language.
I agree that two same vowels in a row is odd, but I have no evidence that
it is not possible in any language; two following different vowels may
be very well used somewhere.
So, I don't think it should be forbidden to type it.

> Here is my visual display for this sample.
> 
>   logical input:  U+0639    + U+0639    + U+064B     + U+064B      + U+0639
> 		   (cons)     (cons)      (vowel)      (vowel)       (cons)
> 
>   visual output: InitialForm  FinalForm  combined    SpacingForm    IsolateForm
>                               ^^^^^^^^^              ^^^^^^^^^^^    ^^^^^^^^^^^

I don't think it is good. A diacritic should not create a break in
a word; only a space, a ZWNJ, or a letter that doesn't combine, could
do it.
Remember that a word in Arabic script should look the same with or without
the diacritics; that is U+0639 + U+0639 + U+064B + U+064B + U+0639 should
give the same shaping for letters than U+0639 + U+0639 + U+0639 (well,
it could be more or less larger)

> The idea is that, for those invalid sequences,

I don't think Arabic has that notion of invalid sequences.
I think only THai and Lao have it, because they are composing alphabets
that are encoded in visual (instead of phonetic) order.
For others, the display can (and would, in most cases) be different without
need to introduce the idea of "invalid sequence".

> I believe that this idea doesn't break any concept of arabic script and,
> may be, it might be helpful. Please feel free to give me the comment.

I think it does break the concept of Arabic script; and also that is not 
needed at all.
THe reason Thai needs that concept is to be able to edit a text having "wrong
order", first to see it, then to be able to chose the righ element to delete
it for example.
With arabic, as it is written in a linear way horizontally, different
input combinations will give different output rendering; so there is no need
to play exceptions in the display engine.


-- 
Ki ça vos våye bén,
Pablo Saratxaga

http://www.srtxg.easynet.be/		PGP Key available, key ID: 0x8F0E4975