Re: Mixed L2R and R2L paragraphs and horizontal scroll

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Stallman <rms@gnu.org>
> Date: Mon, 01 Feb 2010 16:05:19 -0500
> Cc: emacs-bidi@gnu.org, emacs-devel@gnu.org
> 
>  
>     > Horizontal scrolling should apply to the whole window contents
>     > in a rigid fashion.
> 
>     But that cannot be done in this case, because the second line cannot
>     be scrolled to the left without moving its first character A from the
>     right margin.
> 
> Horizontal scrolling does whatever we make it do.  The question
> is what behavior is best.
> 
> I'm saying that horizontal scrolling should move the window contents
> rigidly left or right, just as vertical scrolling moves the contents
> rigidly up or down.

That can be done, but then we will probably need to introduce some new
display features to indicate that the first character is scrolled off
the margin.  Otherwise, the display will look confusing wrt where each
line begins.  For example, we could draw special glyphs at the left
margin in L2R lines and on the right margin in R2L lines, or we might
use something similar to trailing-whitespace display.

> The definition of hscroll is not the same as how we number columns for
> indentation purposes.

That's true, but the effect of hscroll is defined in terms of columns,
so I think it's best not to break the relation between column
numbering and hscroll.