Fix bug #9218 with slow cursor motion and scrolling Org Mode buffers.

 src/dispextern.h (struct bidi_it): New member disp_prop_p.
 src/xdisp.c: Remove one-slot cache of display string positions.
 (compute_display_string_pos): Accept an additional argument
 DISP_PROP_P; callers changed. Scan at most 5K characters forward
 for a display string or property.  If found, set DISP_PROP_P
 non-zero.
 src/bidi.c (bidi_fetch_char): Accept an additional argument
 DISP_PROP_P, and pass it to compute_display_string_pos.  Only
 handle text covered by a display string if DISP_PROP_P is returned
 non-zero.  All callers of bidi_fetch_char changed.

4 files changed, 70 insertions, 64 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 59f09515829..3717924ff68 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,21 @@
+2011-08-02  Eli Zaretskii  <eliz@gnu.org>
+
+        Fix slow cursor motion and scrolling in large buffers with
+        selective display, like Org Mode buffers.  (Bug#9218)
+
+        * dispextern.h (struct bidi_it): New member disp_prop_p.
+
+        * xdisp.c: Remove one-slot cache of display string positions.
+        (compute_display_string_pos): Accept an additional argument
+        DISP_PROP_P; callers changed. Scan at most 5K characters forward
+        for a display string or property.  If found, set DISP_PROP_P
+        non-zero.
+
+        * bidi.c (bidi_fetch_char): Accept an additional argument
+        DISP_PROP_P, and pass it to compute_display_string_pos.  Only
+        handle text covered by a display string if DISP_PROP_P is returned
+        non-zero.  All callers of bidi_fetch_char changed.
+
 2011-08-02  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * keymap.c (Fdefine_key): Fix Lisp_Object/int mixup; apply some CSE.
diff --git a/src/bidi.c b/src/bidi.c
index 697ebb92856..ae5143b37e0 100644
--- a/src/bidi.c
+++ b/src/bidi.c
@@ -792,6 +792,7 @@ bidi_init_it (EMACS_INT charpos, EMACS_INT bytepos, int frame_window_p,
     bidi_it->prev_for_neutral.orig_type = UNKNOWN_BT;
   bidi_it->sor = L2R;    /* FIXME: should it be user-selectable? */
   bidi_it->disp_pos = -1;       /* invalid/unknown */
+  bidi_it->disp_prop_p = 0;
   /* We can only shrink the cache if we are at the bottom level of its
      "stack".  */
   if (bidi_cache_start == 0)
@@ -874,14 +875,16 @@ bidi_char_at_pos (EMACS_INT bytepos, const unsigned char *s, int unibyte)
    covered characters as a single character u+FFFC, and return their
    combined length in CH_LEN and NCHARS.  DISP_POS specifies the
    character position of the next display string, or -1 if not yet
-   computed.  When the next character is at or beyond that position,
-   the function updates DISP_POS with the position of the next display
-   string.  STRING->s is the C string to iterate, or NULL if iterating
-   over a buffer or a Lisp string; in the latter case, STRING->lstring
-   is the Lisp string.  */
+   computed.  DISP_PROP_P non-zero means that there's really a display
+   string at DISP_POS, as opposed to when we searched till DISP_POS
+   without findingone.  When the next character is at or beyond that
+   position, the function updates DISP_POS with the position of the
+   next display string.  STRING->s is the C string to iterate, or NULL
+   if iterating over a buffer or a Lisp string; in the latter case,
+   STRING->lstring is the Lisp string.  */
 static inline int
 bidi_fetch_char (EMACS_INT bytepos, EMACS_INT charpos, EMACS_INT *disp_pos,
-                 struct bidi_string_data *string,
+                 int *disp_prop_p, struct bidi_string_data *string,
                  int frame_window_p, EMACS_INT *ch_len, EMACS_INT *nchars)
 {
   int ch;
@@ -894,7 +897,8 @@ bidi_fetch_char (EMACS_INT bytepos, EMACS_INT charpos, EMACS_INT *disp_pos,
   if (charpos < endpos && charpos > *disp_pos)
     {
       SET_TEXT_POS (pos, charpos, bytepos);
-      *disp_pos = compute_display_string_pos (&pos, string, frame_window_p);
+      *disp_pos = compute_display_string_pos (&pos, string, frame_window_p,
+                                              disp_prop_p);
     }
 
   /* Fetch the character at BYTEPOS.  */
@@ -904,8 +908,9 @@ bidi_fetch_char (EMACS_INT bytepos, EMACS_INT charpos, EMACS_INT *disp_pos,
       *ch_len = 1;
       *nchars = 1;
       *disp_pos = endpos;
+      *disp_prop_p = 0;
     }
-  else if (charpos >= *disp_pos)
+  else if (charpos >= *disp_pos && *disp_prop_p)
     {
       EMACS_INT disp_end_pos;
 
@@ -972,10 +977,12 @@ bidi_fetch_char (EMACS_INT bytepos, EMACS_INT charpos, EMACS_INT *disp_pos,
 
   /* If we just entered a run of characters covered by a display
      string, compute the position of the next display string.  */
-  if (charpos + *nchars <= endpos && charpos + *nchars > *disp_pos)
+  if (charpos + *nchars <= endpos && charpos + *nchars > *disp_pos
+      && *disp_prop_p)
     {
       SET_TEXT_POS (pos, charpos + *nchars, bytepos + *ch_len);
-      *disp_pos = compute_display_string_pos (&pos, string, frame_window_p);
+      *disp_pos = compute_display_string_pos (&pos, string, frame_window_p,
+                                              disp_prop_p);
     }
 
   return ch;
@@ -1083,6 +1090,7 @@ bidi_paragraph_init (bidi_dir_t dir, struct bidi_it *bidi_it, int no_default_p)
       int ch;
       EMACS_INT ch_len, nchars;
       EMACS_INT pos, disp_pos = -1;
+      int disp_prop_p = 0;
       bidi_type_t type;
       const unsigned char *s;
 
@@ -1130,7 +1138,8 @@ bidi_paragraph_init (bidi_dir_t dir, struct bidi_it *bidi_it, int no_default_p)
         bytepos = pstartbyte;
         if (!string_p)
           pos = BYTE_TO_CHAR (bytepos);
-        ch = bidi_fetch_char (bytepos, pos, &disp_pos, &bidi_it->string,
+        ch = bidi_fetch_char (bytepos, pos, &disp_pos, &disp_prop_p,
+                              &bidi_it->string,
                               bidi_it->frame_window_p, &ch_len, &nchars);
         type = bidi_get_type (ch, NEUTRAL_DIR);
 
@@ -1157,7 +1166,8 @@ bidi_paragraph_init (bidi_dir_t dir, struct bidi_it *bidi_it, int no_default_p)
                 && bidi_at_paragraph_end (pos, bytepos) >= -1)
               break;
             /* Fetch next character and advance to get past it.  */
-            ch = bidi_fetch_char (bytepos, pos, &disp_pos, &bidi_it->string,
+            ch = bidi_fetch_char (bytepos, pos, &disp_pos,
+                                  &disp_prop_p, &bidi_it->string,
                                   bidi_it->frame_window_p, &ch_len, &nchars);
             pos += nchars;
             bytepos += ch_len;
@@ -1290,6 +1300,7 @@ bidi_resolve_explicit_1 (struct bidi_it *bidi_it)
       bidi_it->ch_len = 1;
       bidi_it->nchars = 1;
       bidi_it->disp_pos = (string_p ? bidi_it->string.schars : ZV);
+      bidi_it->disp_prop_p = 0;
     }
   else
     {
@@ -1297,8 +1308,8 @@ bidi_resolve_explicit_1 (struct bidi_it *bidi_it)
          display string, treat the entire run of covered characters as
          a single character u+FFFC.  */
       curchar = bidi_fetch_char (bidi_it->bytepos, bidi_it->charpos,
-                                 &bidi_it->disp_pos, &bidi_it->string,
-                                 bidi_it->frame_window_p,
+                                 &bidi_it->disp_pos, &bidi_it->disp_prop_p,
+                                 &bidi_it->string, bidi_it->frame_window_p,
                                  &bidi_it->ch_len, &bidi_it->nchars);
     }
   bidi_it->ch = curchar;
@@ -2032,12 +2043,13 @@ bidi_level_of_next_char (struct bidi_it *bidi_it)
       struct bidi_string_data bs = bidi_it->string;
       bidi_type_t chtype;
       int fwp = bidi_it->frame_window_p;
+      int dpp = bidi_it->disp_prop_p;
 
       if (bidi_it->nchars <= 0)
         abort ();
       do {
-        ch = bidi_fetch_char (bpos += clen, cpos += nc, &disp_pos, &bs, fwp,
-                              &clen, &nc);
+        ch = bidi_fetch_char (bpos += clen, cpos += nc, &disp_pos, &dpp, &bs,
+                              fwp, &clen, &nc);
         if (ch == '\n' || ch == BIDI_EOB /* || ch == LINESEP_CHAR */)
           chtype = NEUTRAL_B;
         else
diff --git a/src/dispextern.h b/src/dispextern.h
index dc44c698164..2e245479a81 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -1868,6 +1868,8 @@ struct bidi_it {
   bidi_dir_t paragraph_dir;     /* current paragraph direction */
   EMACS_INT separator_limit;    /* where paragraph separator should end */
   EMACS_INT disp_pos;           /* position of display string after ch */
+  int disp_prop_p;              /* if non-zero, there really is a
+                                   `display' property/string at disp_pos */
   unsigned first_elt : 1;       /* if non-zero, examine current char first */
   unsigned new_paragraph : 1;   /* if non-zero, we expect a new paragraph */
   unsigned frame_window_p : 1;  /* non-zero if displaying on a GUI frame */
@@ -3035,7 +3037,8 @@ extern Lisp_Object lookup_glyphless_char_display (int, struct it *);
 extern int calc_pixel_width_or_height (double *, struct it *, Lisp_Object,
                                        struct font *, int, int *);
 extern EMACS_INT compute_display_string_pos (struct text_pos *,
-                                             struct bidi_string_data *, int);
+                                             struct bidi_string_data *,
+                                             int, int *);
 extern EMACS_INT compute_display_string_end (EMACS_INT,
                                              struct bidi_string_data *);
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 9d3e501787b..fa4b3c4f9ab 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3134,13 +3134,10 @@ next_overlay_change (EMACS_INT pos)
   return endpos;
 }
 
-/* Record one cached display string position found recently by
-   compute_display_string_pos.  */
-static EMACS_INT cached_disp_pos;
-static EMACS_INT cached_prev_pos = -1;
-static struct buffer *cached_disp_buffer;
-static int cached_disp_modiff;
-static int cached_disp_overlay_modiff;
+/* How many characters forward to search for a display property or
+   display string.  Enough for a screenful of 100 lines x 50
+   characters in a line.  */
+#define MAX_DISP_SCAN 5000
 
 /* Return the character position of a display string at or after
    position specified by POSITION.  If no display string exists at or
@@ -3152,57 +3149,33 @@ static int cached_disp_overlay_modiff;
    on a GUI frame.  */
 EMACS_INT
 compute_display_string_pos (struct text_pos *position,
-                            struct bidi_string_data *string, int frame_window_p)
+                            struct bidi_string_data *string,
+                            int frame_window_p, int *disp_prop_p)
 {
   /* OBJECT = nil means current buffer.  */
   Lisp_Object object =
     (string && STRINGP (string->lstring)) ? string->lstring : Qnil;
-  Lisp_Object pos, spec;
+  Lisp_Object pos, spec, limpos;
   int string_p = (string && (STRINGP (string->lstring) || string->s));
   EMACS_INT eob = string_p ? string->schars : ZV;
   EMACS_INT begb = string_p ? 0 : BEGV;
   EMACS_INT bufpos, charpos = CHARPOS (*position);
+  EMACS_INT lim =
+    (charpos < eob - MAX_DISP_SCAN) ? charpos + MAX_DISP_SCAN : eob;
   struct text_pos tpos;
   struct buffer *b;
 
+  *disp_prop_p = 1;
+
   if (charpos >= eob
       /* We don't support display properties whose values are strings
          that have display string properties.  */
       || string->from_disp_str
       /* C strings cannot have display properties.  */
       || (string->s && !STRINGP (object)))
-    return eob;
-
-  /* Check the cached values.  */
-  if (!STRINGP (object))
     {
-      if (NILP (object))
-        b = current_buffer;
-      else
-        b = XBUFFER (object);
-      if (b == cached_disp_buffer
-          && BUF_MODIFF (b) == cached_disp_modiff
-          && BUF_OVERLAY_MODIFF (b) == cached_disp_overlay_modiff
-          && !b->clip_changed)
-        {
-          if (cached_prev_pos >= 0
-              && cached_prev_pos < charpos && charpos <= cached_disp_pos)
-            return cached_disp_pos;
-          /* Handle overstepping either end of the known interval.  */
-          if (charpos > cached_disp_pos)
-            cached_prev_pos = cached_disp_pos;
-          else  /* charpos <= cached_prev_pos */
-            cached_prev_pos = max (charpos - 1, 0);
-        }
-
-      /* Record new values in the cache.  */
-      if (b != cached_disp_buffer)
-        {
-          cached_disp_buffer = b;
-          cached_prev_pos = max (charpos - 1, 0);
-        }
-      cached_disp_modiff = BUF_MODIFF (b);
-      cached_disp_overlay_modiff = BUF_OVERLAY_MODIFF (b);
+      *disp_prop_p = 0;
+      return eob;
     }
 
   /* If the character at CHARPOS is where the display string begins,
@@ -3221,22 +3194,24 @@ compute_display_string_pos (struct text_pos *position,
       && handle_display_spec (NULL, spec, object, Qnil, &tpos, bufpos,
                               frame_window_p))
     {
-      if (!STRINGP (object))
-        cached_disp_pos = charpos;
       return charpos;
     }
 
   /* Look forward for the first character with a `display' property
      that will replace the underlying text when displayed.  */
+  limpos = make_number (lim);
   do {
-    pos = Fnext_single_char_property_change (pos, Qdisplay, object, Qnil);
+    pos = Fnext_single_char_property_change (pos, Qdisplay, object, limpos);
     CHARPOS (tpos) = XFASTINT (pos);
+    if (CHARPOS (tpos) >= lim)
+      {
+        *disp_prop_p = 0;
+        break;
+      }
     if (STRINGP (object))
       BYTEPOS (tpos) = string_char_to_byte (object, CHARPOS (tpos));
     else
       BYTEPOS (tpos) = CHAR_TO_BYTE (CHARPOS (tpos));
-    if (CHARPOS (tpos) >= eob)
-      break;
     spec = Fget_char_property (pos, Qdisplay, object);
     if (!STRINGP (object))
       bufpos = CHARPOS (tpos);
@@ -3244,8 +3219,6 @@ compute_display_string_pos (struct text_pos *position,
            || !handle_display_spec (NULL, spec, object, Qnil, &tpos, bufpos,
                                     frame_window_p));
 
-  if (!STRINGP (object))
-    cached_disp_pos = CHARPOS (tpos);
   return CHARPOS (tpos);
 }