Re: Bidirectional display in GUI sessions

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org,  emacs-bidi@gnu.org
> Date: Tue, 20 Apr 2010 12:19:00 -0400
> 
> > I have committed to the Emacs development trunk revno 99950, which
> > adds implementation of bidirectional display in GUI sessions (as well
> > as a few fixes for display of R2L lines on TTYs).
> 
> Thanks.

The pleasure is all mine.

> > I could only test this on MS-Windows; I have no easy access for
> > development on an X-based machine.
> 
> Sad to hear.  Is there something we could do to fix this problem?

I'm not sure it would be practical.  I could install an X server for
Windows, but I don't think we can trust it to be a faithful imitation
of a native X server.  And I don't have enough resources for
maintaining yet another box at home.

> BTW, I'm now running with (setq-default bidi-display-reordering t) and
> I recommend everyone do the same to help find bugs in that code.

Yes, please do.  The display engine has so many features that it is
virtually impossible for a single individual to test them.

Wider usage of the bidi display will also provide clear guidance for
me which missing features to work on first (those about which I will
hear more complaints ;-).

> > Last, but certainly not least: Thanks to Gerd Möllmann for his kind
> > guidance and advice which was instrumental in making this happen.
> > Without his help, I would never have found such a simple and elegant
> > solution for implementing this feature, being quite ignorant about
> > internals of the Emacs GUI display.
> 
> Would it be possible to document the design/insight of this solution
> somewhere?

Didn't you see the improved commentary at the beginning of xdisp.c,
since revno 99943?  It does tell how R2L lines are displayed, among
other things I added there.

Let me know if I need to make the description more detailed or more
clear.  That includes bidi.c, of course.