longlines.el problems...

longlines.el problems...

[David Kastrup]

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I just tried out longlines-mode with AUCTeX/preview-latex.  Cough,
cough.  One problem that it has is that it does not preserve markers
around spaces/newlines.

Emacs' fill modes have got this right by now, in contrast.  The main
trick is that if one replaces one kind of space with another one, that
one _first_ adds the new space, then deletes the old space.  Here is
how to do this in one case (unless I am mistaken):


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--- longlines.el	11 Jul 2005 00:37:43 +0200	1.8
+++ longlines.el	12 Jul 2005 01:32:25 +0200	
@@ -207,9 +207,10 @@
 If wrapping is performed, point remains on the line.  If the line does
 not need to be wrapped, move point to the next line and return t."
   (if (longlines-set-breakpoint)
-      (progn (backward-char 1)
-             (delete-char 1)
-             (insert-char ?\n 1)
+      (progn (insert-before-markers "\n")
+	     (backward-char 1)
+             (delete-char -1)
+	     (forward-char 1)
              nil)
     (if (longlines-merge-lines-p)
         (progn (end-of-line)

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But it looks like quite a number of other passages might need similar
fixes.

Another thing worth mentioning is that in the presence of images, font
locking with different font sizes, proportional fonts and similar, the
wrapped column should certainly be the visual column instead of
anything else.  This means, for example, that it is completely useless
to insert a newline in the middle of an image: it only makes sense to
replace such spaces that have a different visual column.
Unfortunately, current-column does not take images into account.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

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Re: longlines.el problems...

[Chong Yidong]

> I just tried out longlines-mode with AUCTeX/preview-latex.  Cough,
> cough.  One problem that it has is that it does not preserve markers
> around spaces/newlines.
>
> Here is how to do this in one case (unless I am mistaken):
> But it looks like quite a number of other passages might need similar
> fixes.

There is only one place where spaces and newlines are converted into one
another; that is the function longlines-wrap-line. So you missed only one
spot.  The following patch follows through on your suggested changes.  It
is correct as far as longlines is concerned; could you check if it does
the right thing for AUCTeX/preview-latex?

I didn't test longlines with AUCTeX/preview-latex, because I don't have
those installed.  So chances are there'll be incompatibilities :-/

> Another thing worth mentioning is that in the presence of images, font
> locking with different font sizes, proportional fonts and similar, the
> wrapped column should certainly be the visual column instead of
> anything else.  This means, for example, that it is completely useless
> to insert a newline in the middle of an image: it only makes sense to
> replace such spaces that have a different visual column.
> Unfortunately, current-column does not take images into account.

Sure, it would be nice, but (from what I remember) it's a pretty
complicated problem.  So longlines simply uses the value of fill-column. 
This is simple, plays nicely with fill-paragraph, and works just fine 99%
of the time.

If your fancy fonts make the fill-paragraph column fall short of the
screen width, it's generally not too ugly; things only start getting weird
if your fancy fonts make the fill-paragraph column extend past the screen
width.  But it'll be weird whether or not longlines is active.


*** emacs/lisp/longlines.el~	Wed Jul 13 00:05:40 2005
--- emacs/lisp/longlines.el	Wed Jul 13 00:48:19 2005
***************
*** 207,229 ****
  If wrapping is performed, point remains on the line.  If the line does
  not need to be wrapped, move point to the next line and return t."
    (if (longlines-set-breakpoint)
!       (progn (backward-char 1)
!              (delete-char 1)
!              (insert-char ?\n 1)
               nil)
      (if (longlines-merge-lines-p)
          (progn (end-of-line)
!                (delete-char 1)
       ;; After certain commands (e.g. kill-line), there may be two
       ;; successive soft newlines in the buffer.  In this case, we
       ;; replace these two newlines by a single space.  Unfortunately,
       ;; this breaks the conservation of (spaces + newlines), so we
       ;; have to fiddle with longlines-wrap-point.
!                (if (or (bolp) (eolp))
!                    (if (> longlines-wrap-point (point))
!                        (setq longlines-wrap-point
!                              (1- longlines-wrap-point)))
!                  (insert-char ?  1))
                 nil)
        (forward-line 1)
        t)))
--- 207,234 ----
  If wrapping is performed, point remains on the line.  If the line does
  not need to be wrapped, move point to the next line and return t."
    (if (longlines-set-breakpoint)
!       (progn (insert-before-markers "\n")
!              (backward-char 1)
!              (delete-char -1)
!              (forward-char 1)
               nil)
      (if (longlines-merge-lines-p)
          (progn (end-of-line)
!                (forward-char 1)
       ;; After certain commands (e.g. kill-line), there may be two
       ;; successive soft newlines in the buffer.  In this case, we
       ;; replace these two newlines by a single space.  Unfortunately,
       ;; this breaks the conservation of (spaces + newlines), so we
       ;; have to fiddle with longlines-wrap-point.
!                (if (eq (char-after) ?\n)
!                    (progn (if (> longlines-wrap-point (point))
! 			      (setq longlines-wrap-point
! 				    (1- longlines-wrap-point)))
! 			  (delete-char -1))
!                  (insert-before-markers " ")
! 		 (backward-char 1)
! 		 (delete-char -1)
! 		 (forward-char 1))
                 nil)
        (forward-line 1)
        t)))

Line wrapping during redisplay (was: longlines.el problems...)

[Kim F. Storm]

David Kastrup <dak@gnu.org> writes:

> Another thing worth mentioning is that in the presence of images, font
> locking with different font sizes, proportional fonts and similar, the
> wrapped column should certainly be the visual column instead of
> anything else.  This means, for example, that it is completely useless
> to insert a newline in the middle of an image: it only makes sense to
> replace such spaces that have a different visual column.
> Unfortunately, current-column does not take images into account.


Perhaps you would like to experiment a little with the following patch
which implements non-destructive line-wrapping during redisplay, i.e.
it automatically breaks _displayed_ lines at suitable spaces and tabs.

Contrary to other modes, it 

a) uses the actual display contents, rather than "counting characters"
   to determine wrapping boundaries.

b) does not alter buffer contents, so it works with all text.

c) does not do is filling, i.e. it never turns newlines into spaces.

About half of the patch is about adding a per-buffer wrap-column
variable and a per-window set-window-wrap-margin function.
The other half of the patch is changes to the display engine.

I have also added a indicate-continued-lines variable to be able to
avoid displaying the continuation glyphs in the fringe of wrapped lines.


It is not complete and probably has some bugs, but if someone would
like to experiment with it and see if it is useful as a complement
to (or useful for) e.g. longlines-mode, please try it and tell me
what you think.



*** buffer.c	18 Jul 2005 22:41:31 +0200	1.486
--- buffer.c	21 Jul 2005 15:51:28 +0200	
***************
*** 4985,4990 ****
--- 4985,4991 ----
    buffer_defaults.enable_multibyte_characters = Qt;
    buffer_defaults.buffer_file_coding_system = Qnil;
    XSETFASTINT (buffer_defaults.fill_column, 70);
+   buffer_defaults.wrap_column = Qnil;
    XSETFASTINT (buffer_defaults.left_margin, 0);
    buffer_defaults.cache_long_line_scans = Qnil;
    buffer_defaults.file_truename = Qnil;
***************
*** 4998,5003 ****
--- 4999,5005 ----
    buffer_defaults.vertical_scroll_bar_type = Qt;
    buffer_defaults.indicate_empty_lines = Qnil;
    buffer_defaults.indicate_buffer_boundaries = Qnil;
+   buffer_defaults.indicate_continued_lines = Qt;
    buffer_defaults.scroll_up_aggressively = Qnil;
    buffer_defaults.scroll_down_aggressively = Qnil;
    buffer_defaults.display_time = Qnil;
***************
*** 5045,5050 ****
--- 5047,5053 ----
    XSETFASTINT (buffer_local_flags.truncate_lines, idx); ++idx;
    XSETFASTINT (buffer_local_flags.ctl_arrow, idx); ++idx;
    XSETFASTINT (buffer_local_flags.fill_column, idx); ++idx;
+   XSETFASTINT (buffer_local_flags.wrap_column, idx); ++idx;
    XSETFASTINT (buffer_local_flags.left_margin, idx); ++idx;
    XSETFASTINT (buffer_local_flags.abbrev_table, idx); ++idx;
    XSETFASTINT (buffer_local_flags.display_table, idx); ++idx;
***************
*** 5069,5074 ****
--- 5072,5078 ----
    XSETFASTINT (buffer_local_flags.vertical_scroll_bar_type, idx); ++idx;
    XSETFASTINT (buffer_local_flags.indicate_empty_lines, idx); ++idx;
    XSETFASTINT (buffer_local_flags.indicate_buffer_boundaries, idx); ++idx;
+   XSETFASTINT (buffer_local_flags.indicate_continued_lines, idx); ++idx;
    XSETFASTINT (buffer_local_flags.scroll_up_aggressively, idx); ++idx;
    XSETFASTINT (buffer_local_flags.scroll_down_aggressively, idx); ++idx;
    XSETFASTINT (buffer_local_flags.header_line_format, idx); ++idx;
***************
*** 5306,5311 ****
--- 5310,5320 ----
  		     doc: /* Default value of `fill-column' for buffers that do not override it.
  This is the same as (default-value 'fill-column).  */);
  
+   DEFVAR_LISP_NOPRO ("default-wrap-column",
+ 		     &buffer_defaults.wrap_column,
+ 		     doc: /* Default value of `wrap-column' for buffers that don't override it.
+ This is the same as (default-value 'wrap-column).  */);
+ 
    DEFVAR_LISP_NOPRO ("default-left-margin",
  		     &buffer_defaults.left_margin,
  		     doc: /* Default value of `left-margin' for buffers that do not override it.
***************
*** 5374,5379 ****
--- 5383,5393 ----
  		     doc: /* Default value of `indicate-buffer-boundaries' for buffers that don't override it.
  This is the same as (default-value 'indicate-buffer-boundaries).  */);
  
+   DEFVAR_LISP_NOPRO ("default-indicate-continued-lines",
+ 		     &buffer_defaults.indicate_continued_lines,
+ 		     doc: /* Default value of `indicate-continued-lines' for buffers that don't override it.
+ This is the same as (default-value 'indicate-continued-lines).  */);
+ 
    DEFVAR_LISP_NOPRO ("default-scroll-up-aggressively",
  		     &buffer_defaults.scroll_up_aggressively,
  		     doc: /* Default value of `scroll-up-aggressively'.
***************
*** 5475,5480 ****
--- 5489,5498 ----
  		     doc: /* *Column beyond which automatic line-wrapping should happen.
  Interactively, you can set the buffer local value using \\[set-fill-column].  */);
  
+   DEFVAR_PER_BUFFER ("wrap-column", &current_buffer->wrap_column,
+ 		     make_number (Lisp_Int),
+ 		     doc: /* *Column beyond which display-only line-wrapping should happen.  */);
+ 
    DEFVAR_PER_BUFFER ("left-margin", &current_buffer->left_margin,
  		     make_number (Lisp_Int),
  		     doc: /* *Column for the default indent-line-function to indent to.
***************
*** 5719,5724 ****
--- 5737,5748 ----
  bitmaps in right fringe.  To show just the angle bitmaps in the left
  fringe, but no arrow bitmaps, use ((top .  left) (bottom . left)).  */);
  
+   DEFVAR_PER_BUFFER ("indicate-continued-lines",
+ 		     &current_buffer->indicate_continued_lines, Qnil,
+ 		     doc: /* *Visually indicate continued lines in buffer.
+ If non-nil on window-systems, a bitmap is displayed in the right fringe
+ of continued lines, and in left fringe of continuation lines.  */);
+ 
    DEFVAR_PER_BUFFER ("scroll-up-aggressively",
  		     &current_buffer->scroll_up_aggressively, Qnil,
  		     doc: /* How far to scroll windows upward.
Index: buffer.h
===================================================================
RCS file: /cvsroot/emacs/emacs/src/buffer.h,v
retrieving revision 1.103
diff -c -r1.103 buffer.h
*** buffer.h	18 Jul 2005 21:34:33 -0000	1.103
--- buffer.h	21 Jul 2005 13:36:59 -0000
***************
*** 610,615 ****
--- 610,616 ----
    Lisp_Object case_fold_search;
    Lisp_Object tab_width;
    Lisp_Object fill_column;
+   Lisp_Object wrap_column;
    Lisp_Object left_margin;
    /* Function to call when insert space past fill column.  */
    Lisp_Object auto_fill_function;
***************
*** 738,743 ****
--- 739,747 ----

    /* Non-nil means indicate buffer boundaries and scrolling.  */
    Lisp_Object indicate_buffer_boundaries;
+
+   /* Non-nil means indicate continued rows.  */
+   Lisp_Object indicate_continued_lines;

    /* Time stamp updated each time this buffer is displayed in a window.  */
    Lisp_Object display_time;
Index: dispextern.h
===================================================================
RCS file: /cvsroot/emacs/emacs/src/dispextern.h,v
retrieving revision 1.207
diff -c -r1.207 dispextern.h
*** dispextern.h	4 Jul 2005 16:06:30 -0000	1.207
--- dispextern.h	21 Jul 2005 13:36:59 -0000
***************
*** 1950,1955 ****
--- 1950,1959 ----
       next newline; > 0 means hide lines indented more than that value.  */
    int selective;

+   /* < INFINITY means do auto-wrap lines during redisplay for
+      this window at specified pixel position. */
+   int wrap_at_x;
+
    /* An enumeration describing what the next display element is
       after a call to get_next_display_element.  */
    enum display_element_type what;
Index: dispnew.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/dispnew.c,v
retrieving revision 1.351
diff -c -r1.351 dispnew.c
*** dispnew.c	4 Jul 2005 16:06:30 -0000	1.351
--- dispnew.c	21 Jul 2005 13:37:00 -0000
***************
*** 3475,3480 ****
--- 3475,3481 ----
        || g == '\t'
        || g == '\n'
        || g == '\r'
+       || (g == ' ' && !NILP (w->wrap_column))
        /* Give up if unable to display the cursor in the window.  */
        || w->cursor.vpos < 0
        /* Give up if we are showing a message or just cleared the message
Index: fringe.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/fringe.c,v
retrieving revision 1.28
diff -c -r1.28 fringe.c
*** fringe.c	4 Jul 2005 16:06:31 -0000	1.28
--- fringe.c	21 Jul 2005 13:37:00 -0000
***************
*** 906,912 ****
        else if (row->indicate_eob_p && EQ (boundary_bot, Qleft))
  	left = BOTTOM_LEFT_ANGLE_BITMAP;
        else if (MATRIX_ROW_CONTINUATION_LINE_P (row))
! 	left = CONTINUATION_LINE_BITMAP;
        else if (row->indicate_empty_line_p && EQ (empty_pos, Qleft))
  	left = ZV_LINE_BITMAP;
        else if (row->indicate_top_line_p && EQ (arrow_top, Qleft))
--- 906,914 ----
        else if (row->indicate_eob_p && EQ (boundary_bot, Qleft))
  	left = BOTTOM_LEFT_ANGLE_BITMAP;
        else if (MATRIX_ROW_CONTINUATION_LINE_P (row))
! 	left = (NILP (w->indicate_continued_rows)
! 		? NO_FRINGE_BITMAP
! 		: CONTINUATION_LINE_BITMAP);
        else if (row->indicate_empty_line_p && EQ (empty_pos, Qleft))
  	left = ZV_LINE_BITMAP;
        else if (row->indicate_top_line_p && EQ (arrow_top, Qleft))
***************
*** 932,938 ****
        else if (row->indicate_eob_p && EQ (boundary_bot, Qright))
  	right = BOTTOM_RIGHT_ANGLE_BITMAP;
        else if (row->continued_p)
! 	right = CONTINUED_LINE_BITMAP;
        else if (row->indicate_top_line_p && EQ (arrow_top, Qright))
  	right = UP_ARROW_BITMAP;
        else if (row->indicate_bottom_line_p && EQ (arrow_bot, Qright))
--- 934,942 ----
        else if (row->indicate_eob_p && EQ (boundary_bot, Qright))
  	right = BOTTOM_RIGHT_ANGLE_BITMAP;
        else if (row->continued_p)
! 	right = (NILP (w->indicate_continued_rows)
! 		 ? NO_FRINGE_BITMAP
! 		 : CONTINUED_LINE_BITMAP);
        else if (row->indicate_top_line_p && EQ (arrow_top, Qright))
  	right = UP_ARROW_BITMAP;
        else if (row->indicate_bottom_line_p && EQ (arrow_bot, Qright))
Index: window.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/window.c,v
retrieving revision 1.512
diff -c -r1.512 window.c
*** window.c	11 Jul 2005 21:43:10 -0000	1.512
--- window.c	21 Jul 2005 13:37:00 -0000
***************
*** 282,287 ****
--- 282,289 ----
    p->fringes_outside_margins = Qnil;
    p->scroll_bar_width = Qnil;
    p->vertical_scroll_bar_type = Qt;
+   p->wrap_column = Qnil;
+   p->indicate_continued_rows = Qt;

    Vwindow_list = Qnil;
    return val;
***************
*** 3123,3128 ****
--- 3125,3134 ----
  			       b->scroll_bar_width,
  			       b->vertical_scroll_bar_type, Qnil);

+       Fset_window_wrap_column (window,
+ 			       b->wrap_column,
+ 			       b->indicate_continued_lines);
+
        w->left_margin_cols = save_left;
        w->right_margin_cols = save_right;

***************
*** 3836,3841 ****
--- 3842,3852 ----
    p->scroll_bar_width = o->scroll_bar_width;
    p->vertical_scroll_bar_type = o->vertical_scroll_bar_type;

+   /* Duplicate line wrapping settings.  */
+
+   p->wrap_column = o->wrap_column;
+   p->indicate_continued_rows = o->indicate_continued_rows;
+
    /* Apportion the available frame space among the two new windows */

    if (!NILP (horflag))
***************
*** 5622,5631 ****
    Lisp_Object left_margin_cols, right_margin_cols;
    Lisp_Object left_fringe_width, right_fringe_width, fringes_outside_margins;
    Lisp_Object scroll_bar_width, vertical_scroll_bar_type;
  };

- #define SAVED_WINDOW_VECTOR_SIZE 24 /* Arg to Fmake_vector */
-
  #define SAVED_WINDOW_N(swv,n) \
    ((struct saved_window *) (XVECTOR ((swv)->contents[(n)])))

--- 5633,5641 ----
    Lisp_Object left_margin_cols, right_margin_cols;
    Lisp_Object left_fringe_width, right_fringe_width, fringes_outside_margins;
    Lisp_Object scroll_bar_width, vertical_scroll_bar_type;
+   Lisp_Object wrap_column, indicate_continued_rows;
  };

  #define SAVED_WINDOW_N(swv,n) \
    ((struct saved_window *) (XVECTOR ((swv)->contents[(n)])))

***************
*** 5842,5847 ****
--- 5852,5859 ----
  	  w->fringes_outside_margins = p->fringes_outside_margins;
  	  w->scroll_bar_width = p->scroll_bar_width;
  	  w->vertical_scroll_bar_type = p->vertical_scroll_bar_type;
+ 	  w->wrap_column = p->wrap_column;
+ 	  w->indicate_continued_rows = p->indicate_continued_rows;
  	  XSETFASTINT (w->last_modified, 0);
  	  XSETFASTINT (w->last_overlay_modified, 0);

***************
*** 6111,6116 ****
--- 6123,6131 ----
        p->fringes_outside_margins = w->fringes_outside_margins;
        p->scroll_bar_width = w->scroll_bar_width;
        p->vertical_scroll_bar_type = w->vertical_scroll_bar_type;
+       p->wrap_column = w->wrap_column;
+       p->indicate_continued_rows = w->indicate_continued_rows;
+
        if (!NILP (w->buffer))
  	{
  	  /* Save w's value of point in the window configuration.
***************
*** 6205,6211 ****
    data->saved_windows = tem;
    for (i = 0; i < n_windows; i++)
      XVECTOR (tem)->contents[i]
!       = Fmake_vector (make_number (SAVED_WINDOW_VECTOR_SIZE), Qnil);
    save_window_save (FRAME_ROOT_WINDOW (f), XVECTOR (tem), 0);
    XSETWINDOW_CONFIGURATION (tem, data);
    return (tem);
--- 6220,6226 ----
    data->saved_windows = tem;
    for (i = 0; i < n_windows; i++)
      XVECTOR (tem)->contents[i]
!       = Fmake_vector (make_number (VECSIZE (struct saved_window)), Qnil);
    save_window_save (FRAME_ROOT_WINDOW (f), XVECTOR (tem), 0);
    XSETWINDOW_CONFIGURATION (tem, data);
    return (tem);
***************
*** 6439,6444 ****
--- 6454,6512 ----

  \f
  /***********************************************************************
+ 			   Auto filling
+  ***********************************************************************/
+
+ DEFUN ("set-window-wrap-column", Fset_window_wrap_column, Sset_window_wrap_column,
+        2, 3, 0,
+        doc: /* Set display auto-wrap column of window WINDOW.
+ If WINDOW is nil, set margins of the currently selected window.
+ Second arg WRAP-COLUMN is a positive number that specifies the
+ wrap column, or nil to disable auto-wrap in window.
+ Optional thrid arg INDICATORS non-nil means to show the indicators
+ for continued lines in the fringes.  */)
+   (window, wrap_column, indicators)
+      Lisp_Object window, wrap_column, indicators;
+ {
+   struct window *w = decode_window (window);
+
+   /* Translate negative or zero widths to nil.
+      Margins that are too wide have to be checked elsewhere.  */
+
+   if (!NILP (wrap_column))
+     {
+       CHECK_NUMBER (wrap_column);
+       if (XINT (wrap_column) <= 0)
+ 	wrap_column = Qnil;
+     }
+
+   if (!EQ (w->wrap_column, wrap_column)
+       || !EQ (w->indicate_continued_rows, indicators))
+     {
+       w->wrap_column = wrap_column;
+       w->indicate_continued_rows = indicators;
+
+       ++windows_or_buffers_changed;
+     }
+
+   return Qnil;
+ }
+
+
+ DEFUN ("window-wrap-column", Fwindow_wrap_column, Swindow_wrap_column,
+        0, 1, 0,
+        doc: /* Get display auto-wrap column of window WINDOW.
+ If WINDOW is omitted or nil, use the currently selected window.  */)
+      (window)
+      Lisp_Object window;
+ {
+   struct window *w = decode_window (window);
+   return w->wrap_column;
+ }
+
+
+ \f
+ /***********************************************************************
  			   Smooth scrolling
   ***********************************************************************/

***************
*** 6721,6726 ****
--- 6789,6798 ----
  	return 0;
        if (! EQ (p1->vertical_scroll_bar_type, p2->vertical_scroll_bar_type))
  	return 0;
+       if (! EQ (p1->wrap_column, p2->wrap_column))
+ 	return 0;
+       if (! EQ (p1->indicate_continued_rows, p2->indicate_continued_rows))
+ 	return 0;
      }

    return 1;
***************
*** 7045,7050 ****
--- 7117,7124 ----
    defsubr (&Swindow_fringes);
    defsubr (&Sset_window_scroll_bars);
    defsubr (&Swindow_scroll_bars);
+   defsubr (&Swindow_wrap_column);
+   defsubr (&Sset_window_wrap_column);
    defsubr (&Swindow_vscroll);
    defsubr (&Sset_window_vscroll);
    defsubr (&Scompare_window_configurations);
Index: window.h
===================================================================
RCS file: /cvsroot/emacs/emacs/src/window.h,v
retrieving revision 1.65
diff -c -r1.65 window.h
*** window.h	4 Jul 2005 16:06:38 -0000	1.65
--- window.h	21 Jul 2005 13:37:00 -0000
***************
*** 179,184 ****
--- 179,191 ----
         no scroll bar.  A value of t means use frame value.  */
      Lisp_Object vertical_scroll_bar_type;

+     /* Non-nil means text column to automatically wrap lines
+        during redisplay.  */
+     Lisp_Object wrap_column;
+
+     /* Non-nil means to show continuation bitmaps in current window.  */
+     Lisp_Object indicate_continued_rows;
+
      /* Frame coords of mark as of last time display completed */
      /* May be nil if mark does not exist or was not on frame */
      Lisp_Object last_mark_x;
Index: xdisp.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/xdisp.c,v
retrieving revision 1.1036
diff -c -r1.1036 xdisp.c
*** xdisp.c	18 Jul 2005 20:59:41 -0000	1.1036
--- xdisp.c	21 Jul 2005 13:37:01 -0000
***************
*** 2116,2121 ****
--- 2116,2130 ----
  		       Iterator initialization
   ***********************************************************************/

+ /* Check if iterator is at a position corresponding to a valid buffer
+    position after some move_it_ call.  */
+
+ #define IT_POS_VALID_AFTER_MOVE_P(it)			\
+   ((it)->method == GET_FROM_STRING			\
+    ? IT_STRING_CHARPOS (*it) == 0			\
+    : 1)
+
+
  /* Initialize IT for displaying current_buffer in window W, starting
     at character position CHARPOS.  CHARPOS < 0 means that no buffer
     position is specified which is useful when the iterator is assigned
***************
*** 2226,2231 ****
--- 2235,2245 ----
    it->selective_display_ellipsis_p
      = !NILP (current_buffer->selective_display_ellipses);

+   it->wrap_at_x = (INTEGERP (w->wrap_column)
+ 		   ? (XFASTINT (w->wrap_column)
+ 		      * WINDOW_FRAME_COLUMN_WIDTH (w))
+ 		   : INFINITY);
+
    /* Display table to use.  */
    it->dp = window_display_table (w);

***************
*** 2410,2416 ****

    /* Don't reseat to previous visible line start if current start
       position is in a string or image.  */
!   if (it->method == GET_FROM_BUFFER && !it->truncate_lines_p)
      {
        int start_at_line_beg_p;
        int first_y = it->current_y;
--- 2424,2430 ----

    /* Don't reseat to previous visible line start if current start
       position is in a string or image.  */
!   if (IT_POS_VALID_AFTER_MOVE_P (it) && !it->truncate_lines_p)
      {
        int start_at_line_beg_p;
        int first_y = it->current_y;
***************
*** 2422,2427 ****
--- 2436,2442 ----
        if (!start_at_line_beg_p)
  	{
  	  int new_x;
+ 	  int last_x = min (it->wrap_at_x, it->last_visible_x);

  	  reseat_at_previous_visible_line_start (it);
  	  move_it_to (it, CHARPOS (pos), -1, -1, -1, MOVE_TO_POS);
***************
*** 2437,2446 ****
  	  if (it->current_x > 0
  	      && !it->truncate_lines_p /* Lines are continued.  */
  	      && (/* And glyph doesn't fit on the line.  */
! 		  new_x > it->last_visible_x
  		  /* Or it fits exactly and we're on a window
  		     system frame.  */
! 		  || (new_x == it->last_visible_x
  		      && FRAME_WINDOW_P (it->f))))
  	    {
  	      if (it->current.dpvec_index >= 0
--- 2452,2461 ----
  	  if (it->current_x > 0
  	      && !it->truncate_lines_p /* Lines are continued.  */
  	      && (/* And glyph doesn't fit on the line.  */
! 		  new_x > last_x
  		  /* Or it fits exactly and we're on a window
  		     system frame.  */
! 		  || (new_x == last_x
  		      && FRAME_WINDOW_P (it->f))))
  	    {
  	      if (it->current.dpvec_index >= 0
***************
*** 4737,4742 ****
--- 4752,4758 ----
  	  pos = --IT_CHARPOS (it2);
  	  --IT_BYTEPOS (it2);
  	  it2.sp = 0;
+ 	  it2.string_from_display_prop_p = 0;
  	  if (handle_display_prop (&it2) == HANDLED_RETURN
  	      && !NILP (val = get_char_property_and_overlay
  			(make_number (pos), Qdisplay, Qnil, &overlay))
***************
*** 4884,4889 ****
--- 4900,4906 ----
    IT_STRING_CHARPOS (*it) = -1;
    IT_STRING_BYTEPOS (*it) = -1;
    it->string = Qnil;
+   it->string_from_display_prop_p = 0;
    it->method = GET_FROM_BUFFER;
    /* RMS: I added this to fix a bug in move_it_vertically_backward
       where it->area continued to relate to the starting point
***************
*** 5873,5887 ****
  	     Moving an iterator without producing glyphs
   ***********************************************************************/

- /* Check if iterator is at a position corresponding to a valid buffer
-    position after some move_it_ call.  */
-
- #define IT_POS_VALID_AFTER_MOVE_P(it)			\
-   ((it)->method == GET_FROM_STRING			\
-    ? IT_STRING_CHARPOS (*it) == 0			\
-    : 1)
-
-
  /* Move iterator IT to a specified buffer or X position within one
     line on the display without producing glyphs.

--- 5890,5895 ----
***************
*** 5922,5932 ****
--- 5930,5947 ----
  {
    enum move_it_result result = MOVE_UNDEFINED;
    struct glyph_row *saved_glyph_row;
+   struct it wrap_it, atpos_it;
+   int may_wrap;
+   int last_x = min (it->wrap_at_x, it->last_visible_x);

    /* Don't produce glyphs in produce_glyphs.  */
    saved_glyph_row = it->glyph_row;
    it->glyph_row = NULL;

+   wrap_it.sp = -1;
+   atpos_it.sp = -1;
+   may_wrap = 0;
+
  #define BUFFER_POS_REACHED_P()					\
    ((op & MOVE_TO_POS) != 0					\
     && BUFFERP (it->object)					\
***************
*** 5946,5951 ****
--- 5961,5978 ----
  	  && it->method == GET_FROM_BUFFER
  	  && IT_CHARPOS (*it) > to_charpos)
  	{
+ 	  if (it->wrap_at_x == INFINITY || wrap_it.sp < 0)
+ 	    {
+ 	      result = MOVE_POS_MATCH_OR_ZV;
+ 	      break;
+ 	    }
+ 	  /* Must continue to see if we wrap after pos */
+ 	  if (atpos_it.sp < 0)
+ 	    atpos_it = *it;
+ 	}
+
+       if (!get_next_display_element (it))
+ 	{
  	  result = MOVE_POS_MATCH_OR_ZV;
  	  break;
  	}
***************
*** 5954,5965 ****
           We used to stop here when TO_CHARPOS reached as well, but that is
           too soon if this glyph does not fit on this line.  So we handle it
           explicitly below.  */
!       if (!get_next_display_element (it)
! 	  || (it->truncate_lines_p
! 	      && BUFFER_POS_REACHED_P ()))
  	{
! 	  result = MOVE_POS_MATCH_OR_ZV;
! 	  break;
  	}

        /* The call to produce_glyphs will get the metrics of the
--- 5981,5997 ----
           We used to stop here when TO_CHARPOS reached as well, but that is
           too soon if this glyph does not fit on this line.  So we handle it
           explicitly below.  */
!       if (it->truncate_lines_p
! 	  && BUFFER_POS_REACHED_P ())
  	{
! 	  if (it->wrap_at_x == INFINITY || wrap_it.sp < 0)
! 	    {
! 	      result = MOVE_POS_MATCH_OR_ZV;
! 	      break;
! 	    }
! 	  /* Must continue to see if we wrap after pos */
! 	  if (atpos_it.sp < 0)
! 	    atpos_it = *it;
  	}

        /* The call to produce_glyphs will get the metrics of the
***************
*** 5976,5981 ****
--- 6008,6026 ----
  	  descent = it->max_descent;
  	}

+       if (it->what == IT_CHARACTER && (it->c == ' ' || it->c == '\t'))
+ 	may_wrap = (it->wrap_at_x != INFINITY);
+       else if (may_wrap) {
+ 	/* We are done if to_pos is found before a possible wrap point.  */
+ 	if (atpos_it.sp >= 0)
+ 	  {
+ 	    *it = atpos_it;
+ 	    goto buffer_pos_reached;
+ 	  }
+ 	wrap_it = *it;
+ 	may_wrap = 0;
+       }
+
        PRODUCE_GLYPHS (it);

        if (it->area != TEXT_AREA)
***************
*** 6017,6040 ****
  	      if ((op & MOVE_TO_X) && new_x > to_x)
  		{
  		  if (BUFFER_POS_REACHED_P ())
! 		    goto buffer_pos_reached;
  		  it->current_x = x;
  		  result = MOVE_X_REACHED;
  		  break;
  		}
! 	      else if (/* Lines are continued.  */
! 		       !it->truncate_lines_p
! 		       && (/* And glyph doesn't fit on the line.  */
! 			   new_x > it->last_visible_x
! 			   /* Or it fits exactly and we're on a window
! 			      system frame.  */
! 			   || (new_x == it->last_visible_x
! 			       && FRAME_WINDOW_P (it->f))))
  		{
  		  if (/* IT->hpos == 0 means the very first glyph
  			 doesn't fit on the line, e.g. a wide image.  */
  		      it->hpos == 0
! 		      || (new_x == it->last_visible_x
  			  && FRAME_WINDOW_P (it->f)))
  		    {
  		      ++it->hpos;
--- 6062,6092 ----
  	      if ((op & MOVE_TO_X) && new_x > to_x)
  		{
  		  if (BUFFER_POS_REACHED_P ())
! 		    {
! 		      if (it->wrap_at_x == INFINITY || wrap_it.sp < 0)
! 			goto buffer_pos_reached;
! 		      /* Must continue to see if we wrap after pos */
! 		      if (atpos_it.sp < 0)
! 			atpos_it = *it;
! 		    }
  		  it->current_x = x;
  		  result = MOVE_X_REACHED;
  		  break;
  		}
!
! 	      if (/* Lines are continued.  */
! 		  !it->truncate_lines_p
! 		  && (/* And glyph doesn't fit on the line.  */
! 		      new_x > last_x
! 		      /* Or it fits exactly and we're on a window
! 			 system frame.  */
! 		      || (new_x == last_x
! 			  && FRAME_WINDOW_P (it->f))))
  		{
  		  if (/* IT->hpos == 0 means the very first glyph
  			 doesn't fit on the line, e.g. a wide image.  */
  		      it->hpos == 0
! 		      || (new_x == last_x
  			  && FRAME_WINDOW_P (it->f)))
  		    {
  		      ++it->hpos;
***************
*** 6074,6087 ****
  		      it->max_descent = descent;
  		    }

  		  TRACE_MOVE ((stderr, "move_it_in: continued at %d\n",
  			       IT_CHARPOS (*it)));
  		  result = MOVE_LINE_CONTINUED;
  		  break;
  		}
! 	      else if (BUFFER_POS_REACHED_P ())
! 		goto buffer_pos_reached;
! 	      else if (new_x > it->first_visible_x)
  		{
  		  /* Glyph is visible.  Increment number of glyphs that
  		     would be displayed.  */
--- 6126,6153 ----
  		      it->max_descent = descent;
  		    }

+ 		  if (wrap_it.sp >= 0)
+ 		    {
+ 		      *it = wrap_it;
+ 		      atpos_it.sp = -1;
+ 		    }
+
  		  TRACE_MOVE ((stderr, "move_it_in: continued at %d\n",
  			       IT_CHARPOS (*it)));
  		  result = MOVE_LINE_CONTINUED;
  		  break;
  		}
!
! 	      if (BUFFER_POS_REACHED_P ())
! 		{
! 		  if (it->wrap_at_x == INFINITY || wrap_it.sp < 0)
! 		    goto buffer_pos_reached;
! 		  /* Must continue to see if we wrap after pos */
! 		  if (atpos_it.sp < 0)
! 		    atpos_it = *it;
! 		}
!
! 	      if (new_x > it->first_visible_x)
  		{
  		  /* Glyph is visible.  Increment number of glyphs that
  		     would be displayed.  */
***************
*** 6096,6112 ****

  	  if (result != MOVE_UNDEFINED)
  	    break;
  	}
!       else if (BUFFER_POS_REACHED_P ())
  	{
! 	buffer_pos_reached:
! 	  it->current_x = x;
! 	  it->max_ascent = ascent;
! 	  it->max_descent = descent;
! 	  result = MOVE_POS_MATCH_OR_ZV;
! 	  break;
  	}
!       else if ((op & MOVE_TO_X) && it->current_x >= to_x)
  	{
  	  /* Stop when TO_X specified and reached.  This check is
  	     necessary here because of lines consisting of a line end,
--- 6162,6187 ----

  	  if (result != MOVE_UNDEFINED)
  	    break;
+ 	  goto glyphs_done;
  	}
!
!       if (BUFFER_POS_REACHED_P ())
  	{
! 	  if (it->wrap_at_x == INFINITY || wrap_it.sp < 0)
! 	    {
! 	    buffer_pos_reached:
! 	      it->current_x = x;
! 	      it->max_ascent = ascent;
! 	      it->max_descent = descent;
! 	      result = MOVE_POS_MATCH_OR_ZV;
! 	      break;
! 	    }
! 	  /* Must continue to see if we wrap after pos */
! 	  if (atpos_it.sp < 0)
! 	    atpos_it = *it;
  	}
!
!       if ((op & MOVE_TO_X) && it->current_x >= to_x)
  	{
  	  /* Stop when TO_X specified and reached.  This check is
  	     necessary here because of lines consisting of a line end,
***************
*** 6117,6122 ****
--- 6192,6198 ----
  	  break;
  	}

+     glyphs_done:
        /* Is this a line end?  If yes, we're done.  */
        if (ITERATOR_AT_END_OF_LINE_P (it))
  	{
***************
*** 6156,6161 ****
--- 6232,6242 ----

  #undef BUFFER_POS_REACHED_P

+   /* If we scanned beyond to_pos and didn't find a point to wrap at,
+      return iterator at to_pos.  */
+   if (atpos_it.sp >= 0)
+     *it = atpos_it;
+
    /* Restore the iterator settings altered at the beginning of this
       function.  */
    it->glyph_row = saved_glyph_row;
***************
*** 6627,6634 ****
  	    break;
  	  /* If start of line is still in string or image,
  	     move further back.  */
! 	  back_to_previous_visible_line_start (it);
! 	  reseat (it, it->current.pos, 1);
  	  dvpos--;
  	}

--- 6708,6714 ----
  	    break;
  	  /* If start of line is still in string or image,
  	     move further back.  */
! 	  reseat_at_previous_visible_line_start (it);
  	  dvpos--;
  	}

***************
*** 12777,12782 ****
--- 12857,12907 ----
    /* Initialize iterator and info to start at POS.  */
    start_display (&it, w, pos);

+ #if 0
+   /* Move iterator before (partial) overlay strings and images at start
+      of window start line. */
+   if (IT_CHARPOS (it) > BEGV)
+     {
+       struct it it2 = it;
+       struct it it3;
+
+       while (IT_CHARPOS (it2) > BEGV)
+ 	{
+ 	  int start_pos = IT_CHARPOS (it2);
+ 	  reseat_at_previous_visible_line_start (&it2);
+ 	  it3 = it2;
+ 	  it3.vpos = 0;
+ 	  move_it_to (&it3, CHARPOS (pos), -1, -1, it3.vpos + 1,
+ 		      MOVE_TO_POS | MOVE_TO_VPOS);
+ 	  if (it3.vpos)
+ 	    {
+ 	      it2 = it3;
+ 	      break;
+ 	    }
+ 	  IT_CHARPOS (it2) = max (BEGV, min (start_pos, IT_CHARPOS (it2))) - 1;
+ 	  it2.sp = 0;
+ 	}
+
+       it2.current_x = 0;
+       it3.current_x = -1;
+       while (!IT_POS_VALID_AFTER_MOVE_P (&it2)
+ 	     || (it2.method == GET_FROM_BUFFER
+ 		 && IT_CHARPOS (it2) < CHARPOS (pos)))
+ 	{
+ 	  it3 = it2;
+ 	  move_it_to (&it2, CHARPOS (pos), -1, -1, it2.vpos + 1,
+ 		      MOVE_TO_POS | MOVE_TO_VPOS);
+ 	}
+
+       if (it3.current_x == 0 && it2.current_x > 0)
+ 	{
+ 	  it = it3;
+ 	  it.current_y = 0;
+ 	  it.vpos = 0;
+ 	}
+     }
+ #endif
+
    /* Display all lines of W.  */
    while (it.current_y < it.last_visible_y)
      {
***************
*** 15097,15102 ****
--- 15222,15233 ----
  {
    struct glyph_row *row = it->glyph_row;
    Lisp_Object overlay_arrow_string;
+   struct it wrap_it;
+   int may_wrap = 0, wrap_x;
+   int wrap_row_used = -1, wrap_row_ascent, wrap_row_height;
+   int wrap_row_phys_ascent, wrap_row_phys_height;
+   int wrap_row_extra_line_spacing;
+   int last_x = min (it->wrap_at_x, it->last_visible_x);

    /* We always start displaying at hpos zero even if hscrolled.  */
    xassert (it->hpos == 0 && it->current_x == 0);
***************
*** 15199,15204 ****
--- 15330,15352 ----
  	  phys_descent = it->max_phys_descent;
  	}

+       if (it->area == TEXT_AREA)
+ 	{
+ 	  if (it->what == IT_CHARACTER && (it->c == ' ' || it->c == '\t'))
+ 	    may_wrap = (it->wrap_at_x != INFINITY);
+ 	  else if (may_wrap) {
+ 	    wrap_it = *it;
+ 	    wrap_x = x;
+ 	    wrap_row_used = row->used[TEXT_AREA];
+ 	    wrap_row_ascent = row->ascent;
+ 	    wrap_row_height = row->height;
+ 	    wrap_row_phys_ascent = row->phys_ascent;
+ 	    wrap_row_phys_height = row->phys_height;
+ 	    wrap_row_extra_line_spacing = row->extra_line_spacing;
+ 	    may_wrap = 0;
+ 	  }
+ 	}
+
        PRODUCE_GLYPHS (it);

        /* If this display element was in marginal areas, continue with
***************
*** 15232,15238 ****
        if (/* Not a newline.  */
  	  nglyphs > 0
  	  /* Glyphs produced fit entirely in the line.  */
! 	  && it->current_x < it->last_visible_x)
  	{
  	  it->hpos += nglyphs;
  	  row->ascent = max (row->ascent, it->max_ascent);
--- 15380,15386 ----
        if (/* Not a newline.  */
  	  nglyphs > 0
  	  /* Glyphs produced fit entirely in the line.  */
! 	  && it->current_x < last_x)
  	{
  	  it->hpos += nglyphs;
  	  row->ascent = max (row->ascent, it->max_ascent);
***************
*** 15258,15266 ****
  	      if (/* Lines are continued.  */
  		  !it->truncate_lines_p
  		  && (/* Glyph doesn't fit on the line.  */
! 		      new_x > it->last_visible_x
  		      /* Or it fits exactly on a window system frame.  */
! 		      || (new_x == it->last_visible_x
  			  && FRAME_WINDOW_P (it->f))))
  		{
  		  /* End of a continued line.  */
--- 15406,15414 ----
  	      if (/* Lines are continued.  */
  		  !it->truncate_lines_p
  		  && (/* Glyph doesn't fit on the line.  */
! 		      new_x > last_x
  		      /* Or it fits exactly on a window system frame.  */
! 		      || (new_x == last_x
  			  && FRAME_WINDOW_P (it->f))))
  		{
  		  /* End of a continued line.  */
***************
*** 15297,15302 ****
--- 15445,15452 ----
  				}
  			    }
  #endif /* HAVE_WINDOW_SYSTEM */
+ 			  if (wrap_row_used > 0)
+ 			    goto back_to_wrap;
  			}
  		    }
  		  else if (CHAR_GLYPH_PADDING_P (*glyph)
***************
*** 15336,15341 ****
--- 15486,15507 ----
  		      row->continued_p = 1;
  		      glyph->pixel_width = it->last_visible_x - x;
  		      it->starts_in_middle_of_char_p = 1;
+ 		    }
+ 		  else if (wrap_row_used > 0)
+ 		    {
+ 		    back_to_wrap:
+ 		      *it = wrap_it;
+ 		      it->continuation_lines_width += wrap_x;
+ 		      row->used[TEXT_AREA] = wrap_row_used;
+ 		      row->ascent = wrap_row_ascent;
+ 		      row->height = wrap_row_height;
+ 		      row->phys_ascent = wrap_row_phys_ascent;
+ 		      row->phys_height = wrap_row_phys_height;
+ 		      row->extra_line_spacing = wrap_row_extra_line_spacing;
+ 		      row->continued_p = 1;
+ 		      row->ends_at_zv_p = 0;
+ 		      row->exact_window_width_line_p = 0;
+ 		      it->continuation_lines_width += x;
  		    }
  		  else
  		    {

--
Kim F. Storm <storm@cua.dk> http://www.cua.dk

Re: Line wrapping during redisplay

[David Kastrup]

storm@cua.dk (Kim F. Storm) writes:

> David Kastrup <dak@gnu.org> writes:
>
>> Another thing worth mentioning is that in the presence of images,
>> font locking with different font sizes, proportional fonts and
>> similar, the wrapped column should certainly be the visual column
>> instead of anything else.  This means, for example, that it is
>> completely useless to insert a newline in the middle of an image:
>> it only makes sense to replace such spaces that have a different
>> visual column.  Unfortunately, current-column does not take images
>> into account.
>
>
> Perhaps you would like to experiment a little with the following
> patch which implements non-destructive line-wrapping during
> redisplay, i.e.  it automatically breaks _displayed_ lines at
> suitable spaces and tabs.

Actually, since I am a cleartext guy, I want my texts wrapped in their
files.  Those are almost always TeX files, and TeX does not like 50000
character lines, anyway.  Also, I have syntactical indentation in
AUCTeX, and this sort of display-induced wrapping would not help
much.

So I am not really much of a customer of longlines.el, anyway.  Your
display-based approach would probably have the advantage that the line
numbers in the source still correspond with the line numbers on file,
making error messages turn out correctly.

Personally, I think one should "just" be able to place something like

'(display (when (> (+ current-goal-pixel current-space-width)
                   current-frame-pixel-width)
                "\n"))

into the display table at the position of space, and that's that.  Oh
wait.  This would always break too late.

Well, but the idea is fun.

For preview-latex+AUCTeX, one would want preferably want to wrap such
that

a) the file does not contain lines longer than fill-width
b) the screen does not contain material wider than the frame edge

Since AUCTeX should usually provide source-text WYSIWYG (namely: you
should retain full control over the formatting of your source file,
including the newlines), this means a combination of wrapping at
unadorned text columns and screen positions.

So a solution completely encapsulated in the display engine would not
be sufficiently lovable.  There might be a market for largely
decoupled file and display wrapping, but I don't feel too comfortable
about the idea.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

Re: Line wrapping during redisplay

[Chong Yidong]

> Actually, since I am a cleartext guy, I want my texts wrapped in their
> files.  Those are almost always TeX files, and TeX does not like 50000
> character lines, anyway.  Also, I have syntactical indentation in
> AUCTeX, and this sort of display-induced wrapping would not help
> much.
>
> So I am not really much of a customer of longlines.el, anyway.  Your
> display-based approach would probably have the advantage that the line
> numbers in the source still correspond with the line numbers on file,
> making error messages turn out correctly.

A relatively easy way to extend longlines.el is to write a function that
intelligently converts a buffer full of hard newlines into a longlines
buffer.  The simplest (but probably not the best) heuristic is to make
"\n\n" hard newlines, and single "\n" characters soft newlines.  Then you
can have a file full of newlines that plays well with latex, and other
programs that expect newlines.  When the file is loaded into Emacs, you
can use this function to turn into a longlines buffer, so you get the line
wrapping functionality.  Error message line numbers would correspond to
the line numbers in the buffer.  (With the display-based approach, even
though the line numbers turn out correctly, it may be hard to find the
error; for example, "line 3" may be a paragraph that takes up 50 screen
lines.)

One thing that longlines.el is unlikely ever to accomplish is support for
proportional fonts and images.  That is the big advantage of Kim's
approach (which makes the planned "longlines-2" obsolete, so it's a good
thing I haven't done much work on it ;-)  Another advantage of the
display-based approach is that it will never screw up font-lock
highlighting, as longlines.el often does.

Re: Line wrapping during redisplay

[Richard M. Stallman]

    When the file is loaded into Emacs, you
    can use this function to turn into a longlines buffer, so you get the line
    wrapping functionality.

Could it do the reverse transformation automatically when writing a
file, too?  That would provide, in effect, the functionality of longlines
for a file of ordinary filled text.

    One thing that longlines.el is unlikely ever to accomplish is support for
    proportional fonts and images.

What about this is hard?

It seems to me that all we need is to finish the TODO entry of writing
the variable-width equivalents of current-column and move-to-column.
They could be called current-pixel-column and move-to-pixel-column.
We need these anyway.  Given these, won't it be easy enough?

Re: Line wrapping during redisplay (was: longlines.el problems...)

[Richard M. Stallman]

    Perhaps you would like to experiment a little with the following patch
    which implements non-destructive line-wrapping during redisplay, i.e.
    it automatically breaks _displayed_ lines at suitable spaces and tabs.

With this approach, the commands that operate on lines in the buffer
will all treat the paragraph as one line, even though it appears as
several.  That is extremely inconvenient.  There is a package that
redefines the most common commands, but there are others, including
M-x occur.  User programs also look at lines.

I strongly prefer the approach in longlines.el, because the line
breaks are there in the buffer, so that all sorts of commands that
look for line breaks will see them where the user sees them.

Here's a peculiar idea.  Make it possible for an overlay to make a
space "appear" as a newline or vice versa.  The result is a change in
the apparent contents of the buffer, for display purposes and for some
commands.  But killing and yanking would not copy these overlays
(since they don't copy any overlays).

Re: Line wrapping during redisplay

[Kim F. Storm]

"Richard M. Stallman" <rms@gnu.org> writes:

>     Perhaps you would like to experiment a little with the following patch
>     which implements non-destructive line-wrapping during redisplay, i.e.
>     it automatically breaks _displayed_ lines at suitable spaces and tabs.
>
> With this approach, the commands that operate on lines in the buffer
> will all treat the paragraph as one line, even though it appears as
> several.  That is extremely inconvenient.  There is a package that
> redefines the most common commands, but there are others, including
> M-x occur.  User programs also look at lines.

It is no different from how continued lines are handled in the
current code.  The only real difference is that continued lines
break at spaces rather than at some arbitrary column which happens
to be the width of the window.

So although it is not useful for line wrapping in general, 
perhaps it could be useful for a nicer way to handle continued lines.

For example, we could have a setting wrap-column = t which means
to use the actual width of the window for wrapping -- to get the
effect of continuation lines, but with a "human touch" to where 
redisplay actually breaks continued lines.

I don't claim that the wrap-column functionality would replace any
of the existing packages -- but it may be useful for some things...

>
> I strongly prefer the approach in longlines.el, because the line
> breaks are there in the buffer, so that all sorts of commands that
> look for line breaks will see them where the user sees them.

I am not against the approach of longlines -- if it can be fixed to
work with proportional-width fonts, images, overlays, etc.

But IIRC longlines also has some problems with line movement -- wasn't
that what longlines-2 should fix ... ?

>
> Here's a peculiar idea.  Make it possible for an overlay to make a
> space "appear" as a newline or vice versa.  The result is a change in
> the apparent contents of the buffer, for display purposes and for some
> commands.  But killing and yanking would not copy these overlays
> (since they don't copy any overlays).

Would it have the same problems with line movement being out of sync
with what's displayed in the window...

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk

Re: Line wrapping during redisplay

[Richard M. Stallman]

    It is no different from how continued lines are handled in the
    current code.  The only real difference is that continued lines
    break at spaces rather than at some arbitrary column which happens
    to be the width of the window.

That is true.  And this mode of continuation could be better in some
cases than the current one.

What I am saying is that this new mode of continuation doesn't do the
job that longlines is trying to do, and doesn't make the use of
one-line-per-paragaph a desirable mode of operation.

    I don't claim that the wrap-column functionality would replace any
    of the existing packages -- but it may be useful for some things...

It could be so.

    > Here's a peculiar idea.  Make it possible for an overlay to make a
    > space "appear" as a newline or vice versa.  The result is a change in
    > the apparent contents of the buffer, for display purposes and for some
    > commands.  But killing and yanking would not copy these overlays
    > (since they don't copy any overlays).

    Would it have the same problems with line movement being out of sync
    with what's displayed in the window...

The ideas is that most commands that examine the buffer contents would
see the result of the overlays.  So cursor motion commands would treat
the apparent newline as a real newline, and treat the apparent space
as a real space.  Only things that copy text (including kill and yank,
and file I/O) would ignore them.