Re: Mixed L2R and R2L paragraphs and horizontal scroll

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 30 Jan 2010 18:22:27 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: emacs-devel@gnu.org, emacs-bidi@gnu.org
> 
>  > Why should it change from what it returns now?
> 
> Because it's no more a window but a line property, IIUC.  When, after
> scrolling the first line, you move `point' to show another portion of
> the second line like this
> 
>        +---------+---------+-------------------+
>        |$ijk     |abcdefgh$|abcdefghijk        |
>        |KJIHGFED$|$HGFEDCBA|        KJIHGFEDCBA|
>        |         |         |                   |
>        +---------+---------+-------------------+
> 
> you get two different non-zero values of `window-hscroll'.

No, you don't necessarily get two different values.  The value from
the second line defines a scroll from the right margin, not from the
left.  (Which probably means it's not a good idea to have
window-hscroll return a negative value in that case.)

>  > Or are you saying that we should scroll the R2L lines to the right by
>  > as much as we scroll the L2R lines to the left?  That is, are you
>  > saying we should display the last example as
>  >
>  >
>  >       +---------+---------+-------------------+
>  >       |$ijk     |abcdefgh$|abcdefghijk        |
>  >       |     KJI$|$HGFEDCBA|        KJIHGFEDCBA|
>  >       |         |         |                   |
>  >       +---------+---------+-------------------+
>  >
>  > Is this what you are suggesting?
> 
> This would be needlessly inconvenient.

Why inconvenient?  That's what would happen if the second line was
displayed at the left margin, like this:

      +---------+---------+-------------------+
      |$ijk     |abcdefgh$|abcdefghijk        |
      |$IJK     |$HGFEDCBA|        KJIHGFEDCBA|
      |         |         |                   |
      +---------+---------+-------------------+

The advantage is that all the lines scroll in lockstep, albeit in two
different directions, and `window-hscroll' can still return a single
value whose meaning is well defined.

> Hence, `window-hscroll' should probably return the value for the
> line `window-point' is on.

That's also possible.  Are the users of this function normally
interested only in the amount of scroll of the current line?