Fix bug #6671 with point position in the window when scrolling far away.

 src/xdisp.c (redisplay_window): Don't check buffer's clip_changed
 flag as a prerequisite for invoking try_scrolling.
 (try_scrolling): Limit scrolling to 100 screen lines.
 (SCROLL_LIMIT): New macro.
 (try_scrolling): Use it when setting scroll_limit.
 (redisplay_window): Even when falling back on "recentering",
 position point in the window according to scroll-conservatively,
 scroll-margin, and scroll-*-aggressively variables.

2 files changed, 67 insertions, 7 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 83bcca1db65..ef3a1546913 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -3,6 +3,11 @@
         * xdisp.c (redisplay_window): Don't check buffer's clip_changed
         flag as a prerequisite for invoking try_scrolling.  (Bug#6671)
         (try_scrolling): Limit scrolling to 100 screen lines.
+        (SCROLL_LIMIT): New macro.
+        (try_scrolling): Use it when setting scroll_limit.
+        (redisplay_window): Even when falling back on "recentering",
+        position point in the window according to scroll-conservatively,
+        scroll-margin, and scroll-*-aggressively variables.  (Bug#6671)
 
 2011-03-26  Juanma Barranquero  <lekktu@gmail.com>
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 270d29d0213..263bedec4a2 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13003,6 +13003,9 @@ enum
   SCROLLING_NEED_LARGER_MATRICES
 };
 
+/* If scroll-conservatively is more than this, never recenter.  */
+#define SCROLL_LIMIT 100
+
 static int
 try_scrolling (Lisp_Object window, int just_this_one_p,
                EMACS_INT arg_scroll_conservatively, EMACS_INT scroll_step,
@@ -13017,7 +13020,7 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
   int extra_scroll_margin_lines = last_line_misfit ? 1 : 0;
   Lisp_Object aggressive;
   /* We will never try scrolling more than this number of lines.  */
-  int scroll_limit = 100;
+  int scroll_limit = SCROLL_LIMIT;
 
 #if GLYPH_DEBUG
   debug_method_add (w, "try_scrolling");
@@ -14202,11 +14205,10 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
         }
     }
 
-  /* Finally, just choose place to start which centers point */
+  /* Finally, just choose a place to start which positions point
+     according to user preferences.  */
 
  recenter:
-  if (centering_position < 0)
-    centering_position = window_box_height (w) / 2;
 
 #if GLYPH_DEBUG
   debug_method_add (w, "recenter");
@@ -14218,10 +14220,62 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
   if (!buffer_unchanged_p)
     w->base_line_number = Qnil;
 
-  /* Move backward half the height of the window.  */
+  /* Determine the window start relative to point.  */
   init_iterator (&it, w, PT, PT_BYTE, NULL, DEFAULT_FACE_ID);
   it.current_y = it.last_visible_y;
+  if (centering_position < 0)
+    {
+      int margin =
+        scroll_margin > 0
+        ? min (scroll_margin, WINDOW_TOTAL_LINES (w) / 4)
+        : 0;
+      int scrolling_up = PT > CHARPOS (startp) + margin;
+      Lisp_Object aggressive =
+        scrolling_up
+        ? BVAR (current_buffer, scroll_up_aggressively)
+        : BVAR (current_buffer, scroll_down_aggressively);
+
+      if (!MINI_WINDOW_P (w)
+          && scroll_conservatively > SCROLL_LIMIT || NUMBERP (aggressive))
+        {
+          int pt_offset = 0;
+
+          /* Setting scroll-conservatively overrides
+             scroll-*-aggressively.  */
+          if (!scroll_conservatively && NUMBERP (aggressive))
+            {
+              double float_amount = XFLOATINT (aggressive);
+
+              pt_offset = float_amount * WINDOW_BOX_TEXT_HEIGHT (w);
+              if (pt_offset == 0 && float_amount > 0)
+                pt_offset = 1;
+              if (pt_offset)
+                margin -= 1;
+            }
+          /* Compute how much to move the window start backward from
+             point so that point will be displayed where the user
+             wants it.  */
+          if (scrolling_up)
+            {
+              centering_position = it.last_visible_y;
+              if (pt_offset)
+                centering_position -= pt_offset;
+              centering_position -=
+                FRAME_LINE_HEIGHT (f) * (1 + margin + (last_line_misfit != 0));
+              /* Don't let point enter the scroll margin near top of
+                 the window.  */
+              if (centering_position < margin * FRAME_LINE_HEIGHT (f))
+                centering_position = margin * FRAME_LINE_HEIGHT (f);
+            }
+          else
+            centering_position = margin * FRAME_LINE_HEIGHT (f) + pt_offset;
+        }
+      else
+        /* Move backward from point half the height of the window.  */
+        centering_position = window_box_height (w) / 2;
+    }
   move_it_vertically_backward (&it, centering_position);
+
   xassert (IT_CHARPOS (it) >= BEGV);
 
   /* The function move_it_vertically_backward may move over more
@@ -14238,8 +14292,9 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
 
   it.current_x = it.hpos = 0;
 
-  /* Set startp here explicitly in case that helps avoid an infinite loop
-     in case the window-scroll-functions functions get errors.  */
+  /* Set the window start position here explicitly, to avoid an
+     infinite loop in case the functions in window-scroll-functions
+     get errors.  */
   set_marker_both (w->start, Qnil, IT_CHARPOS (it), IT_BYTEPOS (it));
 
   /* Run scroll hooks.  */