Re: [emacs-bidi] Bidi - will it happen ?

[Eli Zaretskii]

On Sun, 16 Jun 2002, Tzafrir Cohen wrote:

> fribidi is a library that mainly provides a method for converting logical
> Hebrew text to visual Hebrew text (in conformance with the unicode
> standard, and efficiently).
> 
> Actually, from what I understand, a similar algorithm has already been
> implemented in elisp by Eli.

Not exactly.  Handa-san wrote a batch-style Lisp implementation of bidi 
reordering, and demonstrated it 3 years ago.  However, Gerd Moellmann, 
who write the current Emacs display engine, was very unhappy with that 
implementation, and asked for something that doesn't work on large 
batches of characters (for fear that it will slow donw redisplay to an 
unbearable speed).

So I wrote a prototype of a sequential implementation of UAX#9, in C, 
which could be plugged directly into the Emacs display code.  The next 
step is to take that C code and actually put it into Emacs, making the 
necessary changes in the redisplay code as you go.

> Using fribidi or a similar library probably means patching emacs itself.
> It also requires porting to various emacs ports. elisp is probably more
> portable, although has some penalty in performance.

I don't believe an efficient solution for bidi can be coded in Lisp, 
since the redisplay works on the C level.