Re: merge emacs-bidi into the main tree

[Eli Zaretskii <eliz@elta.co.il>]

> From: Richard Stallman <rms@gnu.org>
> Date: Sat, 09 Aug 2003 10:21:17 -0400
> 
>     > IIRC, you were worried about the performance hit: the code as written
>     > in the display engine part required to disable all the optimizations
>     > and shortcuts that exist for the left-to-right languages, 
> 
> Does it disable the optimizations always, or only when there is
> right-to-left text?

Handa-san should give the definitive answer, but I think it was
always, as long as Emacs was told that the buffer _could_ contain
right-to-left text.  This is because Emacs doesn't know whether there
actually is right-to-left text in the buffer, and cannot do so easily
without getting a significant performance hit (what would we do?
search the buffer for certain ranges of characters after each change
to buffer's text?).

> If the change requires disabling optimizations always, even for people
> who don't use right-to-left text, that is potentially a serious
> problem.  Maybe it can be solved by adding a flag that people must set
> in order to use right-to-left text.

Such a flag indeed existed in the implementation I saw a few years
ago, when I was in Japan.  But perhaps things have changed since then.

However, it doesn't seem right to me to have an Emacs that cannot
scroll fast enough just because I've set such a flag, assuming that
Gerd's intuition is correct.  IMHO, of course.