Fix bug #9610 with slow cursor motion in buffers with invisible text.

 src/xdisp.c (handle_invisible_prop): If invisible text ends on a
 newline, reseat the iterator instead of bidi-iterating there one
 character at a time.  (Bug#9610)
 (BUFFER_POS_REACHED_P, move_it_in_display_line_to): Bail when past
 TO_CHARPOS if the bidi iterator is at base embedding level.

2 files changed, 75 insertions, 32 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 59169bdcf9f..dd2e7256476 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2011-09-27  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (handle_invisible_prop): If invisible text ends on a
+        newline, reseat the iterator instead of bidi-iterating there one
+        character at a time.  (Bug#9610)
+        (BUFFER_POS_REACHED_P, move_it_in_display_line_to): Bail when past
+        TO_CHARPOS if the bidi iterator is at base embedding level.
+
 2011-09-27  Andreas Schwab  <schwab@linux-m68k.org>
 
         * lread.c (readevalloop): Use correct code for NBSP.
diff --git a/src/xdisp.c b/src/xdisp.c
index a556236835c..75f266ff739 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4056,40 +4056,67 @@ handle_invisible_prop (struct it *it)
           /* The position newpos is now either ZV or on visible text.  */
           if (it->bidi_p && newpos < ZV)
             {
-              /* With bidi iteration, the region of invisible text
-                 could start and/or end in the middle of a non-base
-                 embedding level.  Therefore, we need to skip
-                 invisible text using the bidi iterator, starting at
-                 IT's current position, until we find ourselves
-                 outside the invisible text.  Skipping invisible text
-                 _after_ bidi iteration avoids affecting the visual
-                 order of the displayed text when invisible properties
-                 are added or removed.  */
-              if (it->bidi_it.first_elt && it->bidi_it.charpos < ZV)
+              EMACS_INT bpos = CHAR_TO_BYTE (newpos);
+
+              if (FETCH_BYTE (bpos) == '\n'
+                  || (newpos > BEGV && FETCH_BYTE (bpos - 1) == '\n'))
                 {
-                  /* If we were `reseat'ed to a new paragraph,
-                     determine the paragraph base direction.  We need
-                     to do it now because next_element_from_buffer may
-                     not have a chance to do it, if we are going to
-                     skip any text at the beginning, which resets the
-                     FIRST_ELT flag.  */
-                  bidi_paragraph_init (it->paragraph_embedding,
-                                       &it->bidi_it, 1);
+                  /* If the invisible text ends on a newline or the
+                     character after a newline, we can avoid the
+                     costly, character by character, bidi iteration to
+                     newpos, and instead simply reseat the iterator
+                     there.  That's because all bidi reordering
+                     information is tossed at the newline.  This is a
+                     big win for modes that hide complete lines, like
+                     Outline, Org, etc.  (Implementation note: the
+                     call to reseat_1 is necessary, because it signals
+                     to the bidi iterator that it needs to reinit its
+                     internal information when the next element for
+                     display is requested.  */
+                  struct text_pos tpos;
+
+                  SET_TEXT_POS (tpos, newpos, bpos);
+                  reseat_1 (it, tpos, 0);
                 }
-              do
+              else      /* Must use the slow method.  */
                 {
-                  bidi_move_to_visually_next (&it->bidi_it);
+                  /* With bidi iteration, the region of invisible text
+                     could start and/or end in the middle of a
+                     non-base embedding level.  Therefore, we need to
+                     skip invisible text using the bidi iterator,
+                     starting at IT's current position, until we find
+                     ourselves outside the invisible text.  Skipping
+                     invisible text _after_ bidi iteration avoids
+                     affecting the visual order of the displayed text
+                     when invisible properties are added or
+                     removed.  */
+                  if (it->bidi_it.first_elt && it->bidi_it.charpos < ZV)
+                    {
+                      /* If we were `reseat'ed to a new paragraph,
+                         determine the paragraph base direction.  We
+                         need to do it now because
+                         next_element_from_buffer may not have a
+                         chance to do it, if we are going to skip any
+                         text at the beginning, which resets the
+                         FIRST_ELT flag.  */
+                      bidi_paragraph_init (it->paragraph_embedding,
+                                           &it->bidi_it, 1);
+                    }
+                  do
+                    {
+                      bidi_move_to_visually_next (&it->bidi_it);
+                    }
+                  while (it->stop_charpos <= it->bidi_it.charpos
+                         && it->bidi_it.charpos < newpos);
+                  IT_CHARPOS (*it) = it->bidi_it.charpos;
+                  IT_BYTEPOS (*it) = it->bidi_it.bytepos;
+                  /* If we overstepped NEWPOS, record its position in
+                     the iterator, so that we skip invisible text if
+                     later the bidi iteration lands us in the
+                     invisible region again. */
+                  if (IT_CHARPOS (*it) >= newpos)
+                    it->prev_stop = newpos;
                 }
-              while (it->stop_charpos <= it->bidi_it.charpos
-                     && it->bidi_it.charpos < newpos);
-              IT_CHARPOS (*it) = it->bidi_it.charpos;
-              IT_BYTEPOS (*it) = it->bidi_it.bytepos;
-              /* If we overstepped NEWPOS, record its position in the
-                 iterator, so that we skip invisible text if later the
-                 bidi iteration lands us in the invisible region
-                 again. */
-              if (IT_CHARPOS (*it) >= newpos)
-                it->prev_stop = newpos;
             }
           else
             {
@@ -7880,7 +7907,9 @@ move_it_in_display_line_to (struct it *it,
   ((op & MOVE_TO_POS) != 0                                      \
    && BUFFERP (it->object)                                      \
    && (IT_CHARPOS (*it) == to_charpos                           \
-       || (!it->bidi_p && IT_CHARPOS (*it) > to_charpos)        \
+       || ((!it->bidi_p                                         \
+            || BIDI_AT_BASE_LEVEL (it->bidi_it))                \
+           && IT_CHARPOS (*it) > to_charpos)                    \
        || (it->what == IT_COMPOSITION                           \
            && ((IT_CHARPOS (*it) > to_charpos                   \
                 && to_charpos >= it->cmp_it.charpos)            \
@@ -7912,7 +7941,13 @@ move_it_in_display_line_to (struct it *it,
       if ((op & MOVE_TO_POS) != 0
           && BUFFERP (it->object)
           && it->method == GET_FROM_BUFFER
-          && ((!it->bidi_p && IT_CHARPOS (*it) > to_charpos)
+          && (((!it->bidi_p
+                /* When the iterator is at base embedding level, we
+                   are guaranteed that characters are delivered for
+                   display in strictly increasing order of their
+                   buffer positions.  */
+                || BIDI_AT_BASE_LEVEL (it->bidi_it))
+               && IT_CHARPOS (*it) > to_charpos)
               || (it->bidi_p
                   && (prev_method == GET_FROM_IMAGE
                       || prev_method == GET_FROM_STRETCH