Proposal for BiDi in terminal emulators

[Martin J. Dürst via Unicode]

On 2019/01/31 07:02, Richard Wordingham via Unicode wrote:
> On Wed, 30 Jan 2019 15:33:38 +0100
> Frédéric Grosshans via Unicode <unicode at unicode.org> wrote:
> 
>> Le 30/01/2019 à 14:36, Egmont Koblinger via Unicode a écrit :
>>> - It doesn't do Arabic shaping. In my recommendation I'm arguing
>>> that in this mode, where shuffling the characters is the task of
>>> the text editor and not the terminal, so should it be for Arabic
>>> shaping using presentation form characters.
>>
>> I guess Arabic shaping is doable through presentation form
>> characters, because the latter are character inherited from legacy
>> standards using them in such solutions.
> 
> So long as you don't care about local variants, e.g. U+0763 ARABIC
> LETTER KEHEH WITH THREE DOTS ABOVE.  It has no presentation form
> characters.

Same also for characters used for other languages than Arabic.

> Basic Arabic shaping, at the level of a typewriter, is straightforward
> enough to leave to a terminal emulator, as Eli has suggested.  Lam-alif
> would be trickier - one cell or two?

Same for other characters. A medial Beh/Teh/Theh/... (ببب) in any 
reasonably decent rendering should take quite a bit less space than a 
Seen or Sheen (سسس). I remember that the multilingual Emacs version 
mostly written by Ken'ichi Handa (was it called mEmacs or nEmacs or 
something like that?) had different widths only just for Arabic. In 
Thunderbird, which is what I'm using here, I get hopelessly 
stretched/squeezed glyph shapes, which definitely don't look good.

Regards,   Martin.