bug#7939: 24.0.50; bidi-display-reordering has problems with truncate-lines

[Eli Zaretskii]

> From: Eli Zaretskii <eliz@gnu.org>
> Date: Sun, 30 Jan 2011 06:03:38 -0500
> Cc: 7939@debbugs.gnu.org
> 
> > From: Michael Welsh Duggan <md5i@md5i.com>
> > Date: Sun, 30 Jan 2011 01:34:52 -0500
> > Cc: 
> > 
> > emacs -Q
> > 
> > The following lines are to be typed in the resulting *scratch* buffer:
> > 
> > M-x toggle-truncate-lines RET
> > (setq bidi-display-reordering t) C-j
> > C-u 82 a
> > C-a
> > 
> > The cursor will move not to the last "a" on the line,
>                               ^^^^^^^^^^^^
> You mean "the FIRST a", right?
> 
> > but rather to the newline of the first line in the window.
> 
> It's a cursor-positioning problem (see "C-x =").

In fact, it was a fundamental flaw in design of displaying hscrolled
lines.  Thanks for uncovering it.

I think I fixed this now, hopefully without breaking anything else.
Please try with the latest trunk, and if you still see some problems,
feel free to reopen this bug (or file a new one if something else
became broken).