Re: Indentation and visual-line-mode

[Stephen Berman <stephen.berman@gmx.net>]

On Fri, 25 Nov 2011 13:52:37 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Tassilo Horn <tassilo@member.fsf.org>
>> Date: Fri, 25 Nov 2011 10:34:25 +0100
>> 
>> --8<---------------cut here---------------start------------->8---
>>   \begin{itemize}
>>   \item Foo bar baz foo
>> bar baz foo
>>   \item Bar baz foo bar
>> baz
>>   \end{itemize}
>> --8<---------------cut here---------------end--------------->8---
>> 
>> which looks pretty weird.  Is there some option that allows the wrapped
>> lines to be visually indented relative to the current logical line?
>
> I doubt that, because logical indentation and display-time wrap or
> prefixing are two very different features on two very different
> levels.  Logical indentation is actually present in the buffer, while
> display-time features are produced by the display engine on the fly,
> without any consideration of previous lines.
>
>> Checking the docs, I think something like that can be achieved using the
>> variables or text properties `line-prefix' and `wrap-prefix', but what
>> is a stretch-glyph?
>
> That's the empty space generated by the display engine when you use
> :width, :relative-width, or :align-to display specs, see the node
> "Specified Space" in the ELisp manual.  (I will clarify the text in
> the manual in this regard.)  But the variables you mention are
> supposed to have constant values, so you cannot put there a Lisp
> expression that needs to be evaluated.  Therefore, I think you will
> only be able to use them in your situation if you manually set them to
> the amount of space derived from the logical indentation, or invoke
> some hook that does that when the file is visited 

I use the following (added to a major-mode defun) to achieve the visual
effect described:

(defun srb-wrap-and-indent ()
  "Use word wrapping on long lines and indent with a wrap prefix.
The amount of indentation is given by user option `srb-indent-to-here'."
  (set (make-local-variable 'word-wrap) t)
  (set (make-local-variable 'wrap-prefix) (make-string srb-indent-to-here 32))
  (unless (member '(continuation) fringe-indicator-alist)
    (push '(continuation) fringe-indicator-alist)))

>                                                   (assuming you never
> want to change the indentation during editing).

A while ago there was a thread about implementing a minor mode to get
visual indentation with wrap-prefix using fill-context-prefix, in which
I proposed an adaptation of the above; see
<http://permalink.gmane.org/gmane.emacs.devel/125268>.  AFAIK there was
no followup to my proposal.

Steve Berman