Recompute prev_stop and base_level_stop when the iterator is

repositioned to a different location.

 xdisp.c (handle_stop_backwards): Add a prototype.
 (reseat): call handle_stop_backwards to recompute prev_stop and
 base_level_stop for the new position.  Solves the crash when
 scrolling backwards.

2 files changed, 33 insertions, 2 deletions

diff --git a/src/ChangeLog.bidi b/src/ChangeLog.bidi
index 11ed09b6d54..08c51d2ee98 100644
--- a/src/ChangeLog.bidi
+++ b/src/ChangeLog.bidi
@@ -1,3 +1,10 @@
+2010-01-09  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (handle_stop_backwards): Add a prototype.
+        (reseat): call handle_stop_backwards to recompute prev_stop and
+        base_level_stop for the new position.  Solves the crash when
+        scrolling backwards.
+
 2010-01-02  Eli Zaretskii  <eliz@gnu.org>
 
         * .gdbinit (pitx): Display some bidi information about the
diff --git a/src/xdisp.c b/src/xdisp.c
index 7a6d634aa39..339df654dae 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -905,6 +905,7 @@ static void store_mode_line_noprop_char P_ ((char));
 static int store_mode_line_noprop P_ ((const unsigned char *, int, int));
 static void x_consider_frame_title P_ ((Lisp_Object));
 static void handle_stop P_ ((struct it *));
+static void handle_stop_backwards P_ ((struct it *, EMACS_INT));
 static int tool_bar_lines_needed P_ ((struct frame *, int *));
 static int single_display_spec_intangible_p P_ ((Lisp_Object));
 static void ensure_echo_area_buffers P_ ((void));
@@ -5527,7 +5528,30 @@ reseat (it, pos, force_p)
   if (force_p
       || CHARPOS (pos) > it->stop_charpos
       || CHARPOS (pos) < original_pos)
-    handle_stop (it);
+    {
+      if (it->bidi_p)
+        {
+          /* For bidi iteration, we need to prime prev_stop and
+             base_level_stop with our best estimations.  */
+          if (CHARPOS (pos) < it->prev_stop)
+            {
+              handle_stop_backwards (it, BEGV);
+              if (CHARPOS (pos) < it->base_level_stop)
+                it->base_level_stop = 0;
+            }
+          else if (CHARPOS (pos) > it->stop_charpos
+                   && it->stop_charpos >= BEGV)
+            handle_stop_backwards (it, it->stop_charpos);
+          else  /* force_p */
+            handle_stop (it);
+        }
+      else
+        {
+          handle_stop (it);
+          it->prev_stop = it->base_level_stop = 0;
+        }
+
+    }
 
   CHECK_IT (it);
 }
@@ -6711,7 +6735,7 @@ next_element_from_buffer (it)
            && IT_CHARPOS (*it) < it->prev_stop)
     {
       if (it->base_level_stop <= 0)
-        it->base_level_stop = 1;
+        it->base_level_stop = BEGV;
       if (IT_CHARPOS (*it) < it->base_level_stop)
         abort ();
       handle_stop_backwards (it, it->base_level_stop);