Initial support for bidirectional editing.

 Makefile.in (obj): Include bidi.o.
 (bidi.o): New target.
 makefile.w32-in (OBJ1): Add $(BLD)/bidi.$(O).
 ($(BLD)/bidi.$(O)): New target.
 bidi.c: New file.
 buffer.h (struct buffer): New members bidi_display_reordering
 and bidi_paragraph_direction.
 buffer.c (init_buffer_once): Initialize bidi_display_reordering
 and bidi_paragraph_direction.
 (syms_of_buffer): Declare Lisp variables bidi-display-reordering
 and bidi-paragraph-direction.
 (Fbuffer_swap_text): Swap the values of
 bidi_display_reordering and bidi_paragraph_direction.
 dispextern.h (BIDI_MAXLEVEL, BIDI_AT_BASE_LEVEL): New macros.
 (bidi_type_t, bidi_dir_t): New types.
 (bidi_saved_info, bidi_stack, bidi_it): New structures.
 (struct it): New members bidi_p, bidi_it, paragraph_embedding,
 prev_stop, base_level_stop, and eol_pos.
 (bidi_init_it, bidi_get_next_char_visually): New prototypes.
 (IT_STACK_SIZE): Enlarge to 5.
 (struct glyph_row): New member reversed_p.
 <string_buffer_position>: Update prototype.
 (PRODUCE_GLYPHS): Set the reversed_p flag in the iterator's
 glyph_row if bidi_it.paragraph_dir == R2L.
 (struct glyph): New members resolved_level and bidi_type.
 dispnew.c (direct_output_forward_char): Give up if we need bidi
 processing or buffer's direction is right-to-left.
 (prepare_desired_row): Preserve the reversed_p flag.
 (row_equal_p): Compare the reversed_p attributes as well.
 xdisp.c (init_iterator): Initialize it->bidi_p.  Call
 bidi_init_it and set it->paragraph_embedding from the current
 buffer's value of bidi_paragraph_direction.
 (reseat_1): Initialize bidi_it.first_elt.
 (set_iterator_to_next, next_element_from_buffer): Use the value of
 paragraph_embedding to determine the paragraph direction.
 (set_iterator_to_next): Under bidi reordering, call
 bidi_get_next_char_visually.  Call bidi_paragraph_init if the
 new_paragraph flag is set in the bidi iterator.
 (next_element_from_buffer): If bidi_it.first_elt is set,
 initialize paragraph direction and find the first character to
 display in the visual order.  If reseated to a middle of a line,
 prime the bidi iterator starting at the line's beginning.  Handle
 the situation where we overstepped stop_charpos due to
 non-linearity of the bidi iteration.  Likewise for when we back up
 beyond the previous stop_charpos.  When moving across stop_charpos,
 record it in prev_stop.
 (display_line): Set row->end and it->start for the next row to the
 next character in logical order.  Always extend reversed_p rows to
 the end of line, even if they end at ZV.  Copy the reversed_p flag
 to the next glyph row.  Keep calling set_cursor_from_row for
 bidi-reordered rows even if we already have a possible candidate
 for cursor position.  Set row_end after all the row's glyphs have
 been produced, by looping over the glyphs.  Record the position
 after EOL in it->eol_pos, and use it to set end_pos of the last
 row produced for a continued line.
 <Qright_to_left, Qleft_to_right>: New variables.
 (syms_of_xdisp): Initialize and staticpro them.
 (string_buffer_position_lim): New function.
 (string_buffer_position): Most of code moved to
 string_buffer_position_lim.  Last argument and return value are
 now EMACS_INT; all callers changed.
 (set_cursor_from_row): Rewritten to support bidirectional text and
 reversed glyph rows.
 (text_outside_line_unchanged_p, try_window_id): Disable
 optimizations if we are reordering bidirectional text and the
 paragraph direction can be affected by the change.
 (append_glyph, append_composite_glyph)
 (produce_image_glyph, append_stretch_glyph): Set the
 resolved_level and bidi_type members of each glyph.
 (append_glyph): If the glyph row is reversed, prepend the glyph
 rather than appending it.
 (handle_stop_backwards): New function.
 (reseat_1, pop_it, push_it): Set prev_stop and base_level_stop.
 (reseat): call handle_stop_backwards to recompute prev_stop and
 base_level_stop for the new position.
 (handle_invisible_prop): Under bidi iteration, skip invisible text
 using bidi_get_next_char_visually.  If we are `reseat'ed, init the
 paragraph direction.  Update IT->prev_stop after skipping
 invisible text.
 (move_it_in_display_line_to): New variables prev_method
 and prev_pos.  Compare for strict equality in
 BUFFER_POS_REACHED_P.
 (try_cursor_movement): Examine all the candidate rows that occlude
 point, to return the best match.  If rows are bidi-reordered
 and point moved backwards, back up to the row that is not a
 continuation line, and start looking for a suitable row from
 there.
 term.c (append_glyph): Reverse glyphs by pre-pending them,
 rather than appending, if the glyph_row's reversed_p flag is set.
 Set the resolved_level and bidi_type members of each glyph.
 .gdbinit (pbiditype): New command.
 (pgx): Use it to display bidi level and type of the glyph.
 (pitx): Display some bidi information about the iterator.
 (prowlims, pmtxrows): New commands.
 files.el: Make bidi-display-reordering safe variable for boolean
 values.
 mule.texi (International): Mention support of bidirectional editing.
 (Bidirectional Editing): New section.
 HELLO: Reorder Arabic and Hebrew into logical order, and
 insert RLM before the opening paren, to make the display more
 reasonable.  Add setting for bidi-display-reordering in the local
 variables section.
 NEWS: Mention initial support for bidirectional editing.

1 files changed, 29 insertions, 10 deletions

diff --git a/src/buffer.c b/src/buffer.c
index a0acad309af..0c6e57d45be 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2279,6 +2279,8 @@ DEFUN ("buffer-swap-text", Fbuffer_swap_text, Sbuffer_swap_text,
   swapfield (undo_list, Lisp_Object);
   swapfield (mark, Lisp_Object);
   swapfield (enable_multibyte_characters, Lisp_Object);
+  swapfield (bidi_display_reordering, Lisp_Object);
+  swapfield (bidi_paragraph_direction, Lisp_Object);
   /* FIXME: Not sure what we should do with these *_marker fields.
      Hopefully they're just nil anyway.  */
   swapfield (pt_marker, Lisp_Object);
@@ -5206,7 +5208,9 @@ init_buffer_once ()
   buffer_defaults.truncate_lines = Qnil;
   buffer_defaults.word_wrap = Qnil;
   buffer_defaults.ctl_arrow = Qt;
+  buffer_defaults.bidi_display_reordering = Qnil;
   buffer_defaults.direction_reversed = Qnil;
+  buffer_defaults.bidi_paragraph_direction = Qnil;
   buffer_defaults.cursor_type = Qt;
   buffer_defaults.extra_line_spacing = Qnil;
   buffer_defaults.cursor_in_non_selected_windows = Qt;
@@ -5291,7 +5295,9 @@ init_buffer_once ()
   XSETFASTINT (buffer_local_flags.syntax_table, idx); ++idx;
   XSETFASTINT (buffer_local_flags.cache_long_line_scans, idx); ++idx;
   XSETFASTINT (buffer_local_flags.category_table, idx); ++idx;
+  XSETFASTINT (buffer_local_flags.bidi_display_reordering, idx); ++idx;
   XSETFASTINT (buffer_local_flags.direction_reversed, idx); ++idx;
+  XSETFASTINT (buffer_local_flags.bidi_paragraph_direction, idx); ++idx;
   XSETFASTINT (buffer_local_flags.buffer_file_coding_system, idx);
   /* Make this one a permanent local.  */
   buffer_permanent_local_flags[idx++] = 1;
@@ -5548,11 +5554,6 @@ This is the same as (default-value 'abbrev-mode).  */);
                      doc: /* Default value of `ctl-arrow' for buffers that do not override it.
 This is the same as (default-value 'ctl-arrow).  */);
 
-  DEFVAR_LISP_NOPRO ("default-direction-reversed",
-                     &buffer_defaults.direction_reversed,
-                     doc: /* Default value of `direction-reversed' for buffers that do not override it.
-This is the same as (default-value 'direction-reversed).  */);
-
   DEFVAR_LISP_NOPRO ("default-enable-multibyte-characters",
                      &buffer_defaults.enable_multibyte_characters,
                      doc: /* *Default value of `enable-multibyte-characters' for buffers not overriding it.
@@ -5809,11 +5810,29 @@ The variable `coding-system-for-write', if non-nil, overrides this variable.
 
 This variable is never applied to a way of decoding a file while reading it.  */);
 
-  DEFVAR_PER_BUFFER ("direction-reversed", &current_buffer->direction_reversed,
-                     Qnil,
-                     doc: /* *Non-nil means lines in the buffer are displayed right to left.  */);
-
-  DEFVAR_PER_BUFFER ("truncate-lines", &current_buffer->truncate_lines, Qnil,
+  DEFVAR_PER_BUFFER ("direction-reversed",
+                     &current_buffer->direction_reversed, Qnil,
+                     doc: /* Non-nil means set beginning of lines at the right edge of the window.
+See also the variable `bidi-display-reordering'.  */);
+
+  DEFVAR_PER_BUFFER ("bidi-display-reordering",
+                     &current_buffer->bidi_display_reordering, Qnil,
+                     doc: /* Non-nil means reorder bidirectional text for display in the visual order.
+See also the variable `direction-reversed'.  */);
+
+  DEFVAR_PER_BUFFER ("bidi-paragraph-direction",
+                     &current_buffer->bidi_paragraph_direction, Qnil,
+                     doc: /* *If non-nil, forces directionality of text paragraphs in the buffer.
+                             
+If this is nil (the default), the direction of each paragraph is
+determined by the first strong directional character of its text.
+The values of `right-to-left' and `left-to-right' override that.
+Any other value is treated as nil.
+                             
+This variable has no effect unless the buffer's value of
+\`bidi-display-reordering' is non-nil.  */);
+
+ DEFVAR_PER_BUFFER ("truncate-lines", &current_buffer->truncate_lines, Qnil,
                      doc: /* *Non-nil means do not display continuation lines.
 Instead, give each line of text just one screen line.