Run window change functions during redisplay

* doc/lispref/windows.texi (Window Sizes): Move (and rename)
descriptions of 'window-pixel-height-before-size-change' and
'window-pixel-width-before-size-change' to Window Hooks
section.
(Window Configurations): Remove warning against use of
'save-window-excursion' in 'window-size-change-functions'.
(Window Hooks): Rewrite section according to redesign of
window change functions.
* lisp/erc/erc-track.el (erc-window-configuration-change)
(erc-modified-channels-update): Call latter directly from
'window-configuration-change-hook' instead via
'post-command-hook'.
* lisp/frame.el (frame-size-changed-p): Change nomenclature
in let bindings.
* lisp/net/rcirc.el (rcirc-window-configuration-change)
(rcirc-window-configuration-change-1): Call latter directly
from 'window-configuration-change-hook' instead via
'post-command-hook'.
* lisp/window.el (window-pixel-width-before-size-change)
(window-pixel-height-before-size-change): Defalias.
(window--resize-mini-window, window-resize)
(adjust-window-trailing-edge, delete-window)
(delete-other-windows, balance-windows): Don't run
'window-configuration-change-hook' any more from here.
(split-window): Don't run 'window-configuration-change-hook'
from here.  'run-window-scroll-functions' from here.
(window--adjust-process-windows): Run from
'window-configuration-change-hook' only.
* src/frame.c (old_selected_frame): New Lisp variable.
(make_frame): Initialize frame's change_stamp slot.
(Fold_selected_frame): New function.
* src/frame.h (struct frame): New slots old_selected_window,
window_change, change_stamp and number_of_windows.
(fset_old_selected_window): New inlined function.
(FRAME_WINDOW_CHANGE, FRAME_OLD_SELECTED_WINDOW): New macros.
* src/window.c (old_selected_window): New Lisp variable.
(wset_old_buffer): New inlined function.
(Fframe_old_selected_window, Fold_selected_window)
(Fwindow_old_buffer): New functions.
(Fwindow_old_pixel_width, Fwindow_old_pixel_height): Rename
from Fwindow_pixel_width_before_size_change and
Fwindow_pixel_height_before_size_change.  Update doc-strings.
(Fwindow_old_body_pixel_width, Fwindow_old_body_pixel_height):
New functions.
(Fdelete_other_windows_internal): Set frame's window_change
slot instead of running 'window-configuration-change-hook'.
(Frun_window_configuration_change_hook): In doc-string tell
that this function is no more needed.
(Frun_window_scroll_functions): Amend doc-string.  Run with
window's buffer current.
(window_sub_list, window_change_record_windows)
(window_change_record_frame, window_change_record)
(run_window_change_functions_1, run_window_change_functions):
New functions.
(set_window_buffer): Set frame's window_change slot instead of
running 'window-configuration-change-hook'.
(make_window): Don't initialize pixel_width_before_size_change
and pixel_height_before_size_change slots.
(window_resize_apply, Fdelete_window_internal): Set frame's
window_change slot.
(Fsplit_window_internal): Set frame's window_change slot.
Don't run 'window-scroll-functions' from here.
* src/window.h (struct window): New slots old_buffer,
change_stamp, old_pixel_width (renamed from
pixel_width_before_size_change), old_pixel_height (renamed
from pixel_height_before_size_change), old_body_pixel_width
and old_body_pixel_height.
* src/xdisp.c (init_iterator): Set frame's window_change slot
when the body height or width changes.
(prepare_menu_bars): Don't run_window_size_change_functions.
(redisplay_internal): Don't run_window_size_change_functions,
run_window_change_functions instead.

5 files changed, 680 insertions, 257 deletions

diff --git a/src/frame.c b/src/frame.c
index ca6704a44c0..6d93abd09bf 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -55,9 +55,11 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #endif
 
 /* The currently selected frame.  */
-
 Lisp_Object selected_frame;
 
+/* The selected frame the last time window change functions were run.  */
+Lisp_Object old_selected_frame;
+
 /* A frame which is not just a mini-buffer, or NULL if there are no such
    frames.  This is usually the most recent such frame that was selected.  */
 
@@ -855,7 +857,8 @@ make_frame (bool mini_p)
   f->ns_transparent_titlebar = false;
 #endif
 #endif
-
+  /* This one should never be zero.  */
+  f->change_stamp = 1;
   root_window = make_window ();
   rw = XWINDOW (root_window);
   if (mini_p)
@@ -1451,7 +1454,8 @@ This function returns FRAME, or nil if FRAME has been deleted.  */)
   return do_switch_frame (frame, 1, 0, norecord);
 }
 
-DEFUN ("handle-switch-frame", Fhandle_switch_frame, Shandle_switch_frame, 1, 1, "^e",
+DEFUN ("handle-switch-frame", Fhandle_switch_frame,
+       Shandle_switch_frame, 1, 1, "^e",
        doc: /* Handle a switch-frame event EVENT.
 Switch-frame events are usually bound to this function.
 A switch-frame event is an event Emacs sends itself to
@@ -1471,6 +1475,18 @@ DEFUN ("selected-frame", Fselected_frame, Sselected_frame, 0, 0, 0,
 {
   return selected_frame;
 }
+
+DEFUN ("old-selected-frame", Fold_selected_frame,
+       Sold_selected_frame, 0, 0, 0,
+       doc: /* Return the old selected FRAME.
+FRAME must be a live frame and defaults to the selected one.
+
+The return value is the frame selected the last time window change
+functions were run.  */)
+  (void)
+{
+  return old_selected_frame;
+}
 
 DEFUN ("frame-list", Fframe_list, Sframe_list,
        0, 0, 0,
@@ -6098,9 +6114,10 @@ iconify the top level frame instead.  */);
   defsubr (&Swindow_system);
   defsubr (&Sframe_windows_min_size);
   defsubr (&Smake_terminal_frame);
-  defsubr (&Shandle_switch_frame);
   defsubr (&Sselect_frame);
+  defsubr (&Shandle_switch_frame);
   defsubr (&Sselected_frame);
+  defsubr (&Sold_selected_frame);
   defsubr (&Sframe_list);
   defsubr (&Sframe_parent);
   defsubr (&Sframe_ancestor_p);
diff --git a/src/frame.h b/src/frame.h
index b7059027fbe..ab3efdfa926 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -125,6 +125,10 @@ struct frame
      The selected window of the selected frame is Emacs's selected window.  */
   Lisp_Object selected_window;
 
+  /* This frame's selected window when run_window_change_functions was
+     called the last time on this frame.  */
+  Lisp_Object old_selected_window;
+
   /* This frame's minibuffer window.
      Most frames have their own minibuffer windows,
      but only the selected frame's minibuffer window
@@ -321,9 +325,14 @@ struct frame
      cleared.  */
   bool_bf explicit_name : 1;
 
-  /* True if configuration of windows on this frame has changed since
-     last call of run_window_size_change_functions.  */
-  bool_bf window_configuration_changed : 1;
+  /* True if at least one window on this frame changed since the last
+     call of run_window_change_functions.  Changes are either "state
+     changes" (a window has been created, deleted or got assigned
+     another buffer) or "size changes" (the total or body size of a
+     window changed).  run_window_change_functions exits early unless
+     either this flag is true or a window selection happened on this
+     frame.  */
+  bool_bf window_change : 1;
 
   /* True if the mouse has moved on this display device
      since the last time we checked.  */
@@ -406,6 +415,20 @@ struct frame
 
   /* Bitfield area ends here.  */
 
+  /* This frame's change stamp, set the last time window change
+     functions were run for this frame.  Should never be 0 because
+     that's the change stamp of a new window.  A window was not on a
+     frame the last run_window_change_functions was called on it if
+     it's change stamp differs from that of its frame.  */
+  int change_stamp;
+
+  /* This frame's number of windows, set the last time window change
+     functions were run for this frame.  Should never be 0 even for
+     minibuffer-only frames.  If no window has been added, this allows
+     to detect whether a window was deleted on this frame since the
+     last time run_window_change_functions was called on it.  */
+  ptrdiff_t number_of_windows;
+
   /* Number of lines (rounded up) of tool bar.  REMOVE THIS  */
   int tool_bar_lines;
 
@@ -662,6 +685,11 @@ fset_selected_window (struct frame *f, Lisp_Object val)
   f->selected_window = val;
 }
 INLINE void
+fset_old_selected_window (struct frame *f, Lisp_Object val)
+{
+  f->old_selected_window = val;
+}
+INLINE void
 fset_title (struct frame *f, Lisp_Object val)
 {
   f->title = val;
@@ -908,10 +936,9 @@ default_pixels_per_inch_y (void)
    are frozen on frame F.  */
 #define FRAME_WINDOWS_FROZEN(f) (f)->frozen_window_starts
 
-/* True if the frame's window configuration has changed since last call
-   of run_window_size_change_functions.  */
-#define FRAME_WINDOW_CONFIGURATION_CHANGED(f)   \
-  (f)->window_configuration_changed
+/* True if at least one window changed on frame F since the last time
+   window change functions were run on F.  */
+#define FRAME_WINDOW_CHANGE(f) (f)->window_change
 
 /* The minibuffer window of frame F, if it has one; otherwise nil.  */
 #define FRAME_MINIBUF_WINDOW(f) f->minibuffer_window
@@ -919,8 +946,10 @@ default_pixels_per_inch_y (void)
 /* The root window of the window tree of frame F.  */
 #define FRAME_ROOT_WINDOW(f) f->root_window
 
-/* The currently selected window of the window tree of frame F.  */
+/* The currently selected window of frame F.  */
 #define FRAME_SELECTED_WINDOW(f) f->selected_window
+/* The old selected window of frame F.  */
+#define FRAME_OLD_SELECTED_WINDOW(f) f->old_selected_window
 
 #define FRAME_INSERT_COST(f) (f)->insert_line_cost
 #define FRAME_DELETE_COST(f) (f)->delete_line_cost
@@ -1215,6 +1244,7 @@ SET_FRAME_VISIBLE (struct frame *f, int v)
   (f)->iconified = (eassert (0 <= (i) && (i) <= 1), (i))
 
 extern Lisp_Object selected_frame;
+extern Lisp_Object old_selected_frame;
 
 #if ! (defined USE_GTK || defined HAVE_NS)
 extern int frame_default_tool_bar_height;
diff --git a/src/window.c b/src/window.c
index 72185f9340a..0fc4f622995 100644
--- a/src/window.c
+++ b/src/window.c
@@ -77,6 +77,11 @@ static void apply_window_adjustment (struct window *);
    FRAME_SELECTED_WINDOW (selected_frame).  */
 Lisp_Object selected_window;
 
+/* The value of selected_window at the last time window change
+   functions were run.  This is always the same as
+   FRAME_OLD_SELECTED_WINDOW (old_selected_frame).  */
+Lisp_Object old_selected_window;
+
 /* A list of all windows for use by next_window and Fwindow_list.
    Functions creating or deleting windows should invalidate this cache
    by setting it to nil.  */
@@ -304,6 +309,12 @@ wset_buffer (struct window *w, Lisp_Object val)
   adjust_window_count (w, 1);
 }
 
+static void
+wset_old_buffer (struct window *w, Lisp_Object val)
+{
+  w->old_buffer = val;
+}
+
 DEFUN ("windowp", Fwindowp, Swindowp, 1, 1, 0,
        doc: /* Return t if OBJECT is a window and nil otherwise.  */)
   (Lisp_Object object)
@@ -428,6 +439,22 @@ return the selected window of that frame.  */)
   return window;
 }
 
+DEFUN ("frame-old-selected-window", Fframe_old_selected_window,
+       Sframe_old_selected_window, 0, 1, 0,
+       doc: /* Return old selected window of FRAME.
+FRAME must be a live frame and defaults to the selected one.
+
+The return value is the window selected on FRAME the last time window
+change functions were run for FRAME.  */)
+  (Lisp_Object frame)
+{
+  if (NILP (frame))
+    frame = selected_frame;
+  CHECK_LIVE_FRAME (frame);
+
+  return XFRAME (frame)->old_selected_window;
+}
+
 DEFUN ("set-frame-selected-window", Fset_frame_selected_window,
        Sset_frame_selected_window, 2, 3, 0,
        doc: /* Set selected window of FRAME to WINDOW.
@@ -465,6 +492,16 @@ selected windows appears and to which many commands apply.  */)
   return selected_window;
 }
 
+DEFUN ("old-selected-window", Fold_selected_window,
+       Sold_selected_window, 0, 0, 0,
+       doc: /* Return the old selected window.
+The return value is the window selected the last time window change
+functions were run.  */)
+  (void)
+{
+  return old_selected_window;
+}
+
 EMACS_INT window_select_count;
 
 /* If select_window is called with inhibit_point_swap true it will
@@ -597,9 +634,33 @@ Return nil for an internal window or a deleted window.  */)
   (Lisp_Object window)
 {
   struct window *w = decode_any_window (window);
+
   return WINDOW_LEAF_P (w) ? w->contents : Qnil;
 }
 
+DEFUN ("window-old-buffer", Fwindow_old_buffer, Swindow_old_buffer, 0, 1, 0,
+       doc: /* Return the old buffer displayed by WINDOW.
+WINDOW must be a live window and defaults to the selected one.
+
+The return value is the buffer shown in WINDOW at the last time window
+change functions were run.  It is nil if WINDOW was created after
+that.  It is t if WINDOW has been restored from a window configuration
+after that.  */)
+  (Lisp_Object window)
+{
+  struct window *w = decode_live_window (window);
+
+  return (NILP (w->old_buffer)
+          /* A new window.  */
+          ? Qnil
+          : (w->change_stamp != WINDOW_XFRAME (w)->change_stamp)
+          /* A window restored from a configuration.  */
+          ? Qt
+          /* A window that was live the last time seen by window
+             change functions.  */
+          : w->old_buffer);
+}
+
 DEFUN ("window-parent", Fwindow_parent, Swindow_parent, 0, 1, 0,
        doc: /* Return the parent window of window WINDOW.
 WINDOW must be a valid window and defaults to the selected one.
@@ -723,34 +784,32 @@ the height of the screen areas spanned by its children.  */)
   return make_fixnum (decode_valid_window (window)->pixel_height);
 }
 
-DEFUN ("window-pixel-width-before-size-change",
-       Fwindow_pixel_width_before_size_change,
-       Swindow_pixel_width_before_size_change, 0, 1, 0,
-       doc: /* Return pixel width of window WINDOW before last size changes.
+DEFUN ("window-old-pixel-width", Fwindow_old_pixel_width,
+       Swindow_old_pixel_width, 0, 1, 0,
+       doc: /* Return old total pixel width of WINDOW.
 WINDOW must be a valid window and defaults to the selected one.
 
-The return value is the pixel width of WINDOW at the last time
-`window-size-change-functions' was run.  It's zero if WINDOW was made
-after that.  */)
+The return value is the total pixel width of WINDOW after the last
+time window change functions found WINDOW live on its frame.  It is
+zero if WINDOW was created after that.  */)
   (Lisp_Object window)
 {
   return (make_fixnum
-          (decode_valid_window (window)->pixel_width_before_size_change));
+          (decode_valid_window (window)->old_pixel_width));
 }
 
-DEFUN ("window-pixel-height-before-size-change",
-       Fwindow_pixel_height_before_size_change,
-       Swindow_pixel_height_before_size_change, 0, 1, 0,
-       doc: /* Return pixel height of window WINDOW before last size changes.
+DEFUN ("window-old-pixel-height", Fwindow_old_pixel_height,
+       Swindow_old_pixel_height, 0, 1, 0,
+       doc: /* Return old total pixel height of WINDOW.
 WINDOW must be a valid window and defaults to the selected one.
 
-The return value is the pixel height of WINDOW at the last time
-`window-size-change-functions' was run.  It's zero if WINDOW was made
-after that.  */)
+The return value is the total pixel height of WINDOW after the last
+time window change functions found WINDOW live on its frame.  It is
+zero if WINDOW was created after that.  */)
   (Lisp_Object window)
 {
   return (make_fixnum
-          (decode_valid_window (window)->pixel_height_before_size_change));
+          (decode_valid_window (window)->old_pixel_height));
 }
 
 DEFUN ("window-total-height", Fwindow_total_height, Swindow_total_height, 0, 2, 0,
@@ -984,6 +1043,26 @@ window_body_width (struct window *w, bool pixelwise)
               0);
 }
 
+DEFUN ("window-body-width", Fwindow_body_width, Swindow_body_width, 0, 2, 0,
+       doc: /* Return the width of WINDOW's text area.
+WINDOW must be a live window and defaults to the selected one.  Optional
+argument PIXELWISE non-nil means return the width in pixels.  The return
+value does not include any vertical dividers, fringes or marginal areas,
+or scroll bars.
+
+If PIXELWISE is nil, return the largest integer smaller than WINDOW's
+pixel width divided by the character width of WINDOW's frame.  This
+means that if a column at the right of the text area is only partially
+visible, that column is not counted.
+
+Note that the returned value includes the column reserved for the
+continuation glyph.  */)
+  (Lisp_Object window, Lisp_Object pixelwise)
+{
+  return make_fixnum (window_body_width (decode_live_window (window),
+                                         !NILP (pixelwise)));
+}
+
 DEFUN ("window-body-height", Fwindow_body_height, Swindow_body_height, 0, 2, 0,
        doc: /* Return the height of WINDOW's text area.
 WINDOW must be a live window and defaults to the selected one.  Optional
@@ -1001,24 +1080,34 @@ visible, that line is not counted.  */)
                                           !NILP (pixelwise)));
 }
 
-DEFUN ("window-body-width", Fwindow_body_width, Swindow_body_width, 0, 2, 0,
-       doc: /* Return the width of WINDOW's text area.
-WINDOW must be a live window and defaults to the selected one.  Optional
-argument PIXELWISE non-nil means return the width in pixels.  The return
-value does not include any vertical dividers, fringes or marginal areas,
-or scroll bars.
+DEFUN ("window-old-body-pixel-width",
+       Fwindow_old_body_pixel_width,
+       Swindow_old_body_pixel_width, 0, 1, 0,
+       doc: /* Return old width of WINDOW's text area in pixels.
+WINDOW must be a live window and defaults to the selected one.
 
-If PIXELWISE is nil, return the largest integer smaller than WINDOW's
-pixel width divided by the character width of WINDOW's frame.  This
-means that if a column at the right of the text area is only partially
-visible, that column is not counted.
+The return value is the pixel width of WINDOW's text area after the
+last time window change functions found WINDOW live on its frame.  It
+is zero if WINDOW was created after that.  */)
+  (Lisp_Object window)
+{
+  return (make_fixnum
+          (decode_live_window (window)->old_body_pixel_width));
+}
 
-Note that the returned value includes the column reserved for the
-continuation glyph.  */)
-  (Lisp_Object window, Lisp_Object pixelwise)
+DEFUN ("window-old-body-pixel-height",
+       Fwindow_old_body_pixel_height,
+       Swindow_old_body_pixel_height, 0, 1, 0,
+       doc: /* Return old height of WINDOW's text area in pixels.
+WINDOW must be a live window and defaults to the selected one.
+
+The return value is the pixel height of WINDOW's text area after the
+last time window change functions found WINDOW live on its frame.  It
+is zero if WINDOW was created after that.  */)
+  (Lisp_Object window)
 {
-  return make_fixnum (window_body_width (decode_live_window (window),
-                                         !NILP (pixelwise)));
+  return (make_fixnum
+          (decode_live_window (window)->old_body_pixel_height));
 }
 
 DEFUN ("window-mode-line-height", Fwindow_mode_line_height,
@@ -3264,7 +3353,7 @@ window-start value is reasonable when this function is called.  */)
   adjust_frame_glyphs (f);
   unblock_input ();
 
-  run_window_configuration_change_hook (f);
+  FRAME_WINDOW_CHANGE (f) = true;
 
   return Qnil;
 }
@@ -3318,6 +3407,15 @@ select_frame_norecord (Lisp_Object frame)
     Fselect_frame (frame, Qt);
 }
 
+/**
+ * run_window_configuration_change_hook:
+ *
+ * Run any functions on 'window-configuration-change-hook' for the
+ * frame specified by F.  The buffer-local values are run with the
+ * window showing the buffer selected.  The default value is run with
+ * the frame specified by F selected.  All functions are called with
+ * the selected window's buffer current.
+ */
 static void
 run_window_configuration_change_hook (struct frame *f)
 {
@@ -3371,7 +3469,10 @@ run_window_configuration_change_hook (struct frame *f)
 DEFUN ("run-window-configuration-change-hook", Frun_window_configuration_change_hook,
        Srun_window_configuration_change_hook, 0, 1, 0,
        doc: /* Run `window-configuration-change-hook' for FRAME.
-If FRAME is omitted or nil, it defaults to the selected frame.  */)
+If FRAME is omitted or nil, it defaults to the selected frame.
+
+This function should not be needed any more and will be therefore
+considered obsolete.  */)
   (Lisp_Object frame)
 {
   run_window_configuration_change_hook (decode_live_frame (frame));
@@ -3381,130 +3482,381 @@ If FRAME is omitted or nil, it defaults to the selected frame.  */)
 DEFUN ("run-window-scroll-functions", Frun_window_scroll_functions,
        Srun_window_scroll_functions, 0, 1, 0,
        doc: /* Run `window-scroll-functions' for WINDOW.
-If WINDOW is omitted or nil, it defaults to the selected window.  */)
+If WINDOW is omitted or nil, it defaults to the selected window.
+
+This function is curently only called by 'split-window' for the new
+window after it has established the size of the new window.  */)
   (Lisp_Object window)
 {
-  if (! NILP (Vwindow_scroll_functions))
+  struct window *w = decode_live_window (window);
+  ptrdiff_t count = SPECPDL_INDEX ();
+
+  record_unwind_current_buffer ();
+  Fset_buffer (w->contents);
+  if (!NILP (Vwindow_scroll_functions))
     run_hook_with_args_2 (Qwindow_scroll_functions, window,
-                          Fmarker_position (decode_live_window (window)->start));
+                          Fmarker_position (w->start));
+  unbind_to (count, Qnil);
+
   return Qnil;
 }
 
 
-/* Compare old and present pixel sizes of windows in tree rooted at W.
-   Return true iff any of these windows differs in size.  */
-
-static bool
-window_size_changed (struct window *w)
+/**
+ * window_sub_list:
+ *
+ * Return list of live windows constructed by traversing any window
+ * sub-tree rooted at WINDOW in preorder followed by right siblings of
+ * WINDOW.  Called from outside with second argument WINDOWS nil.  The
+ * returned list is in reverse order.
+ */
+static Lisp_Object
+window_sub_list (Lisp_Object window, Lisp_Object windows)
 {
-  if (w->pixel_width != w->pixel_width_before_size_change
-      || w->pixel_height != w->pixel_height_before_size_change)
-    return true;
 
-  if (WINDOW_INTERNAL_P (w))
+  struct window *w = XWINDOW (window);
+
+  while (w)
     {
-      w = XWINDOW (w->contents);
-      while (w)
-        {
-          if (window_size_changed (w))
-            return true;
+      if (WINDOW_INTERNAL_P (w))
+        windows = window_sub_list (w->contents, windows);
+      else
+        windows = Fcons (window, windows);
 
-          w = NILP (w->next) ? 0 : XWINDOW (w->next);
-        }
+      window = w->next;
+      w = NILP (window) ? 0 : XWINDOW (window);
     }
 
-  return false;
+  return windows;
 }
 
-/* Set before size change pixel sizes of windows in tree rooted at W to
-   their present pixel sizes.  */
 
-static void
-window_set_before_size_change_sizes (struct window *w)
+/**
+ * window_change_record_windows:
+ *
+ * Record changes for all live windows found by traversing any window
+ * sub-tree rooted at WINDOW in preorder followed by any right
+ * siblings of WINDOW.  This sets the old buffer, old pixel and old
+ * body pixel sizes of each live window found to the respective
+ * current values.  It also sets the change stamp of each window found
+ * to STAMP.  Return the number of live windows found.
+ *
+ * When not called by itself recursively, WINDOW is its frame's root
+ * window, STAMP is the current change stamp of WINDOW's frame and
+ * NUMBER is 0.
+ */
+static ptrdiff_t
+window_change_record_windows (Lisp_Object window, int stamp, ptrdiff_t number)
 {
-  w->pixel_width_before_size_change = w->pixel_width;
-  w->pixel_height_before_size_change = w->pixel_height;
+  struct window *w = XWINDOW (window);
 
-  if (WINDOW_INTERNAL_P (w))
+  while (w)
     {
-      w = XWINDOW (w->contents);
-      while (w)
+      if (WINDOW_INTERNAL_P (w))
+        number = window_change_record_windows (w->contents, stamp, number);
+      else
         {
-          window_set_before_size_change_sizes (w);
-          w = NILP (w->next) ? 0 : XWINDOW (w->next);
+          number += 1;
+          w->change_stamp = stamp;
+          wset_old_buffer (w, w->contents);
+          w->old_pixel_width = w->pixel_width;
+          w->old_pixel_height = w->pixel_height;
+          w->old_body_pixel_width = window_body_width (w, true);
+          w->old_body_pixel_height = window_body_height (w, true);
         }
+
+      w = NILP (w->next) ? 0 : XWINDOW (w->next);
     }
+
+  return number;
 }
 
 
-void
-run_window_size_change_functions (Lisp_Object frame)
+/**
+ * window_change_record_frame:
+ *
+ * Record changes for FRAME.  This records FRAME's selected window,
+ * updates FRAME's change stamp, records the states of all live
+ * windows of FRAME via window_change_record_windows and resets
+ * FRAME's window_change flag.
+ */
+static void
+window_change_record_frame (Lisp_Object frame)
 {
   struct frame *f = XFRAME (frame);
-  struct window *r = XWINDOW (FRAME_ROOT_WINDOW (f));
 
-  if (NILP (Vrun_hooks)
-      || !(f->can_x_set_window_size)
-      || !(f->after_make_frame))
-    return;
+  /* Record selected window.  */
+  fset_old_selected_window (f, FRAME_SELECTED_WINDOW (f));
 
-  if (FRAME_WINDOW_CONFIGURATION_CHANGED (f)
-      /* Here we implicitly exclude the possibility that the height of
-         FRAME and its minibuffer window both change leaving the height
-         of FRAME's root window alone.  */
-      || window_size_changed (r))
-    {
-      Lisp_Object globals = Fdefault_value (Qwindow_size_change_functions);
-      Lisp_Object windows = Fwindow_list (frame, Qlambda, Qnil);
-      /* The buffers for which the local hook was already run.  */
-      Lisp_Object buffers = Qnil;
+  /* Bump up FRAME's change stamp.  If this wraps, make it 1 to avoid
+     that a new window (whose change stamp is always set to 0) gets
+     reported as "existing before".  */
+  f->change_stamp += 1;
+  if (f->change_stamp == 0)
+    f->change_stamp = 1;
 
-      for (; CONSP (windows); windows = XCDR (windows))
-        {
-          Lisp_Object window = XCAR (windows);
-          Lisp_Object buffer = Fwindow_buffer (window);
-
-          /* Run a buffer-local value only once for that buffer and
-             only if at least one window showing that buffer on FRAME
-             actually changed its size.  Note that the function is run
-             with FRAME as its argument and as such oblivious to the
-             window checked below.  */
-          if (window_size_changed (XWINDOW (window))
-              && !NILP (Flocal_variable_p (Qwindow_size_change_functions, buffer))
-              && NILP (Fmemq (buffer, buffers)))
-            {
-              Lisp_Object locals
-                = Fbuffer_local_value (Qwindow_size_change_functions, buffer);
+  /* Bump up the change stamps of all live windows on this frame so
+     the next call of this function can tell whether any of them
+     "existed before" and record state for each of these windows.  */
+  f->number_of_windows
+    = window_change_record_windows (f->root_window, f->change_stamp, 0);
 
-              while (CONSP (locals))
-                {
-                  if (!EQ (XCAR (locals), Qt))
-                    safe_call1 (XCAR (locals), frame);
-                  locals = XCDR (locals);
-                }
+  /* Reset our flag.  */
+  FRAME_WINDOW_CHANGE (f) = false;
+}
 
-              buffers = Fcons (buffer, buffers);
-            }
-        }
 
-      while (CONSP (globals))
+/**
+ * window_change_record:
+ *
+ * Record selected window in old_selected_window and selected frame in
+ * old_selected_frame.
+ */
+static void
+window_change_record (void)
+{
+  /* Strictly spoken we don't need old_selected_window at all - its
+     value is the old selected window of old_selected_frame.  */
+  old_selected_window = selected_window;
+  old_selected_frame = selected_frame;
+}
+
+
+/**
+ * run_window_change_functions_1:
+ *
+ * Run window change functions specified by SYMBOL with argument
+ * WINDOW_OR_FRAME.  If BUFFER is nil, WINDOW_OR_FRAME specifies a
+ * frame.  In this case, run the default value of SYMBOL.  Otherwise,
+ * WINDOW_OR_FRAME denotes a window showing BUFFER.  In this case, run
+ * the buffer local value of SYMBOL in BUFFER, if any.
+ */
+static void
+run_window_change_functions_1 (Lisp_Object symbol, Lisp_Object buffer,
+                               Lisp_Object window_or_frame)
+{
+  Lisp_Object funs = Qnil;
+
+  if (NILP (buffer))
+    funs = Fdefault_value (symbol);
+  else if (!NILP (Fassoc (symbol, BVAR (XBUFFER (buffer), local_var_alist),
+                          Qnil)))
+    /* Don't run global value buffer-locally.  */
+    funs = buffer_local_value (symbol, buffer);
+
+  while (CONSP (funs))
+    {
+      if (!EQ (XCAR (funs), Qt))
+        safe_call1 (XCAR (funs), window_or_frame);
+      funs = XCDR (funs);
+    }
+}
+
+
+/**
+ * run_window_change_functions:
+ *
+ * Run window change functions for each live frame.  This function
+ * must be called from a "safe" position in redisplay_internal.
+ *
+ * Do not run any functions for a frame whose window_change flag is
+ * nil and where no window selection happened since the last time this
+ * function was called.  Also, skip any tooltip frame.
+ *
+ * The change functions run are, in this order:
+ *
+ * 'window-buffer-change-functions' which are run for a window that
+ * changed its buffer or that was not shown the last time window
+ * change functions were run.  The default value is also run when a
+ * window was deleted since the last time window change functions were
+ * run.
+ *
+ * `window-size-change-functions' run for a window that changed its
+ * body or total size, a window that changed its buffer or a window
+ * that was not shown the last time window change functions were run.
+ *
+ * `window-selected-change-functions' run for a window that was
+ * (de-)selected since the last time window change functions were run.
+ *
+ * A buffer-local value of these functions is run if and only if the
+ * window for which the functions are run, currently shows the buffer.
+ * Each call gets one argument - the window showing the buffer.  This
+ * means that the buffer-local value of these functions may be called
+ * as many times at the buffer is shown on the frame.
+ *
+ * The default value of these functions is called only after all
+ * buffer-local values for all of these functions have been run.  Each
+ * such call receives one argument - the frame for which this function
+ * is run.
+ *
+ * After the three change functions cited above have been run in the
+ * indicated way, functions on 'window-configuration-change-hook' are
+ * run.  A buffer-local value is run if a window shows that buffer and
+ * has either changed its buffer or its body or total size or did not
+ * appear on this frame since the last time window change functions
+ * were run.  The functions are called without argument and the
+ * buffer's window selected.  The default value is run without
+ * argument and the frame for which the function is run selected.
+ *
+ * This function does not save and restore match data.  Any functions
+ * it calls are responsible for doing that themselves.
+ */
+void
+run_window_change_functions (void)
+{
+  Lisp_Object tail, frame;
+  bool selected_frame_change = !EQ (selected_frame, old_selected_frame);
+  ptrdiff_t count_outer = SPECPDL_INDEX ();
+
+  record_unwind_protect_void (window_change_record);
+
+  FOR_EACH_FRAME (tail, frame)
+    {
+      struct frame *f = XFRAME (frame);
+      Lisp_Object root = FRAME_ROOT_WINDOW (f);
+      bool frame_window_change = FRAME_WINDOW_CHANGE (f);
+      bool window_buffer_change, window_size_change;
+      bool frame_buffer_change = false, frame_size_change = false;
+      bool frame_selected_change
+        = (selected_frame_change
+           && (EQ (frame, old_selected_frame)
+               || EQ (frame, selected_frame)));
+      bool frame_selected_window_change
+        = !EQ (FRAME_OLD_SELECTED_WINDOW (f), FRAME_SELECTED_WINDOW (f));
+      bool window_deleted = false;
+      Lisp_Object windows;
+      ptrdiff_t number_of_windows;
+      ptrdiff_t count_inner = SPECPDL_INDEX ();
+
+      if (!f->can_x_set_window_size
+          || !f->after_make_frame
+          || FRAME_TOOLTIP_P (f)
+          || !(frame_window_change
+               || frame_selected_change
+               || frame_selected_window_change))
+        /* Either we cannot run hooks for this frame yet or no window
+           change has been reported for this frame since the last time
+           we ran window change functions on it.  */
+        continue;
+
+      /* Analyze windows and run buffer locals hooks in pre-order.  */
+      windows = Fnreverse (window_sub_list (root, Qnil));
+      number_of_windows = 0;
+
+      record_unwind_protect (window_change_record_frame, frame);
+
+      /* The following loop collects all data needed to tell whether
+         the default value of a hook shall be run and runs any buffer
+         local hooks right away.  */
+      for (; CONSP (windows); windows = XCDR (windows))
         {
-          if (!EQ (XCAR (globals), Qt))
-            safe_call1 (XCAR (globals), frame);
-          globals = XCDR (globals);
+          Lisp_Object window = XCAR (windows);
+          struct window *w = XWINDOW (window);
+          Lisp_Object buffer = WINDOW_BUFFER (w);
+
+          /* Count this window even if it has been deleted while
+             running a hook.  */
+          number_of_windows += 1;
+
+          if (!WINDOW_LIVE_P (window))
+            continue;
+
+          /* A "buffer change" means either the window's buffer
+             changed or the window was not part of this frame the last
+             time window change functions were run for it.  */
+          window_buffer_change =
+            (frame_window_change
+             && (!EQ (buffer, w->old_buffer)
+                 || w->change_stamp != f->change_stamp));
+          /* A "size change" means either a buffer change or that the
+             total or body size of the window has changed.
+
+             Note: A buffer change implies a size change because either
+             this window didn't show the buffer before or this window
+             didn't show the buffer the last time the window change
+             functions were run.  In either case, an application
+             tracing size changes in a buffer-locally fashion might
+             want to be informed about that change.  */
+          window_size_change =
+            (frame_window_change
+             && (window_buffer_change
+                 || w->pixel_width != w->old_pixel_width
+                 || w->pixel_height != w->old_pixel_height
+                 || window_body_width (w, true) != w->old_body_pixel_width
+                 || window_body_height (w, true) != w->old_body_pixel_height));
+
+          /* The following two are needed when running the default
+             values for this frame below.  */
+          frame_buffer_change = frame_buffer_change || window_buffer_change;
+          frame_size_change = frame_size_change || window_size_change;
+
+          if (window_buffer_change)
+            run_window_change_functions_1
+              (Qwindow_buffer_change_functions, buffer, window);
+
+          if (window_size_change && WINDOW_LIVE_P (window))
+            run_window_change_functions_1
+              (Qwindow_size_change_functions, buffer, window);
+
+          /* This window's selection has changed when it it was
+             (de-)selected as its frame's or the globally selected
+             window.  */
+          if (((frame_selected_change
+                && (EQ (window, old_selected_window)
+                    || EQ (window, selected_window)))
+               || (frame_selected_window_change
+                   && (EQ (window, FRAME_OLD_SELECTED_WINDOW (f))
+                       || EQ (window, FRAME_SELECTED_WINDOW (f)))))
+              && WINDOW_LIVE_P (window))
+            run_window_change_functions_1
+              (Qwindow_selection_change_functions, buffer, window);
         }
 
-      window_set_before_size_change_sizes (r);
+      /* When the number of windows on a frame has decreased, at least
+         one window of that frame was deleted.  In that case, we want
+         to run the default buffer and configuration change hooks.  The
+         default size change hook is not necessarily run in that case,
+         but usually will be unless the deletion was "compensated" by
+         a reduction of the frame size or an increase of a minibuffer
+         window size.  */
+      window_deleted = number_of_windows < f->number_of_windows;
+      /* A frame changed buffers when one of its windows has changed
+         its buffer or at least one window was deleted.  */
+      if ((frame_buffer_change || window_deleted) && FRAME_LIVE_P (f))
+        run_window_change_functions_1
+          (Qwindow_buffer_change_functions, Qnil, frame);
+
+      /* A size change occurred when at least one of the frame's
+         windows has changed size.  */
+      if (frame_size_change && FRAME_LIVE_P (f))
+        run_window_change_functions_1
+          (Qwindow_size_change_functions, Qnil, frame);
+
+      /* A frame has changed its window selection when its selected
+         window has changed or when it was (de-)selected.  */
+      if ((frame_selected_change || frame_selected_window_change)
+          && FRAME_LIVE_P (f))
+        run_window_change_functions_1
+          (Qwindow_selection_change_functions, Qnil, frame);
+
+      /* A frame's configuration changed when one of its windows has
+         changed buffer or size or at least one window was deleted.  */
+      if ((frame_size_change || window_deleted) && FRAME_LIVE_P (f))
+        /* This will run any buffer local window configuration change
+           hook as well.  */
+        run_window_configuration_change_hook (f);
 
-      if (FRAME_HAS_MINIBUF_P (f) && !FRAME_MINIBUF_ONLY_P (f))
-        /* Record size of FRAME's minibuffer window too.  */
-        window_set_before_size_change_sizes
-          (XWINDOW (FRAME_MINIBUF_WINDOW (f)));
+      if (!FRAME_LIVE_P (f))
+        continue;
 
-      FRAME_WINDOW_CONFIGURATION_CHANGED (f) = false;
+      /* Record changes (via window_change_record_frame) for this
+         frame, even when an unhandled error occurred.  */
+      unbind_to (count_inner, Qnil);
     }
-}
 
+  /* Record selected window and frame.  */
+  unbind_to (count_outer, Qnil);
+}
 
 /* Make WINDOW display BUFFER.  RUN_HOOKS_P means it's allowed
    to run hooks.  See make_frame for a case where it's not allowed.
@@ -3581,14 +3933,18 @@ set_window_buffer (Lisp_Object window, Lisp_Object buffer,
       apply_window_adjustment (w);
     }
 
-  if (run_hooks_p)
-    {
-      if (!NILP (Vwindow_scroll_functions))
-        run_hook_with_args_2 (Qwindow_scroll_functions, window,
-                              Fmarker_position (w->start));
-      if (!samebuf)
-        run_window_configuration_change_hook (XFRAME (WINDOW_FRAME (w)));
-    }
+  if (run_hooks_p && !NILP (Vwindow_scroll_functions))
+    run_hook_with_args_2 (Qwindow_scroll_functions, window,
+                          Fmarker_position (w->start));
+
+  /* Ensure that window change functions are run later if the buffer
+     differs and the window is neither a mini nor a pseudo window.
+
+     Note: Running window change functions for the minibuffer is noisy
+     and was generally suppressed in the past.  Is there any reason we
+     should run them?  */
+  if (!samebuf && !MINI_WINDOW_P (w) && !WINDOW_PSEUDO_P (w))
+    FRAME_WINDOW_CHANGE (XFRAME (w->frame)) = true;
 
   unbind_to (count, Qnil);
 }
@@ -3828,8 +4184,6 @@ make_window (void)
   w->phys_cursor_width = -1;
 #endif
   w->sequence_number = ++sequence_number;
-  w->pixel_width_before_size_change = 0;
-  w->pixel_height_before_size_change = 0;
   w->scroll_bar_width = -1;
   w->scroll_bar_height = -1;
   w->column_number_displayed = -1;
@@ -4095,6 +4449,9 @@ window_resize_apply (struct window *w, bool horflag)
   else
     /* Bug#15957.  */
     w->window_end_valid = false;
+
+  if (!WINDOW_PSEUDO_P (w))
+    FRAME_WINDOW_CHANGE (WINDOW_XFRAME (w)) = true;
 }
 
 
@@ -4559,17 +4916,11 @@ set correctly.  See the code of `split-window' for how this is done.  */)
   block_input ();
   window_resize_apply (p, horflag);
   adjust_frame_glyphs (f);
-  /* Set buffer of NEW to buffer of reference window.  Don't run
-     any hooks.  */
-  set_window_buffer (new, r->contents, false, true);
+  /* Set buffer of NEW to buffer of reference window.  */
+  set_window_buffer (new, r->contents, true, true);
+  FRAME_WINDOW_CHANGE (f) = true;
   unblock_input ();
 
-  /* Maybe we should run the scroll functions in Elisp (which already
-     runs the configuration change hook).  */
-  if (! NILP (Vwindow_scroll_functions))
-    run_hook_with_args_2 (Qwindow_scroll_functions, new,
-                          Fmarker_position (n->start));
-  /* Return NEW.  */
   return new;
 }
 
@@ -4720,6 +5071,8 @@ Signal an error when WINDOW is the only window on its frame.  */)
         }
       else
         unblock_input ();
+
+      FRAME_WINDOW_CHANGE (f) = true;
     }
   else
     /* We failed: Relink WINDOW into window tree.  */
@@ -6310,7 +6663,6 @@ struct saved_window
 
   Lisp_Object window, buffer, start, pointm, old_pointm;
   Lisp_Object pixel_left, pixel_top, pixel_height, pixel_width;
-  Lisp_Object pixel_height_before_size_change, pixel_width_before_size_change;
   Lisp_Object left_col, top_line, total_cols, total_lines;
   Lisp_Object normal_cols, normal_lines;
   Lisp_Object hscroll, min_hscroll, hscroll_whole, suspend_auto_hscroll;
@@ -6426,12 +6778,6 @@ the return value is nil.  Otherwise the value is t.  */)
       struct window *root_window;
       struct window **leaf_windows;
       ptrdiff_t i, k, n_leaf_windows;
-      /* Records whether a window has been added or removed wrt the
-         original configuration.  */
-      bool window_changed = false;
-      /* Records whether a window has changed its buffer wrt the
-         original configuration.  */
-      bool buffer_changed = false;
 
       /* Don't do this within the main loop below: This may call Lisp
          code and is thus potentially unsafe while input is blocked.  */
@@ -6441,11 +6787,6 @@ the return value is nil.  Otherwise the value is t.  */)
           window = p->window;
           w = XWINDOW (window);
 
-          if (NILP (w->contents))
-            /* A dead window that will be resurrected, the window
-               configuration will change.  */
-            window_changed = true;
-
           if (BUFFERP (w->contents)
               && !EQ (w->contents, p->buffer)
               && BUFFER_LIVE_P (XBUFFER (p->buffer)))
@@ -6530,10 +6871,6 @@ the return value is nil.  Otherwise the value is t.  */)
           w->pixel_top = XFIXNAT (p->pixel_top);
           w->pixel_width = XFIXNAT (p->pixel_width);
           w->pixel_height = XFIXNAT (p->pixel_height);
-          w->pixel_width_before_size_change
-            = XFIXNAT (p->pixel_width_before_size_change);
-          w->pixel_height_before_size_change
-            = XFIXNAT (p->pixel_height_before_size_change);
           w->left_col = XFIXNAT (p->left_col);
           w->top_line = XFIXNAT (p->top_line);
           w->total_cols = XFIXNAT (p->total_cols);
@@ -6581,9 +6918,6 @@ the return value is nil.  Otherwise the value is t.  */)
           if (BUFFERP (p->buffer) && BUFFER_LIVE_P (XBUFFER (p->buffer)))
             /* If saved buffer is alive, install it.  */
             {
-              if (!EQ (w->contents, p->buffer))
-                /* Record buffer configuration change.  */
-                buffer_changed = true;
               wset_buffer (w, p->buffer);
               w->start_at_line_beg = !NILP (p->start_at_line_beg);
               set_marker_restricted (w->start, p->start, w->contents);
@@ -6617,8 +6951,6 @@ the return value is nil.  Otherwise the value is t.  */)
           else if (!NILP (w->start))
             /* Leaf window has no live buffer, get one.  */
             {
-              /* Record buffer configuration change.  */
-              buffer_changed = true;
               /* Get the buffer via other_buffer_safely in order to
                  avoid showing an unimportant buffer and, if necessary, to
                  recreate *scratch* in the course (part of Juanma's bs-show
@@ -6666,10 +6998,7 @@ the return value is nil.  Otherwise the value is t.  */)
       /* Now, free glyph matrices in windows that were not reused.  */
       for (i = 0; i < n_leaf_windows; i++)
         if (NILP (leaf_windows[i]->contents))
-          {
-            free_window_matrices (leaf_windows[i]);
-            window_changed = true;
-          }
+          free_window_matrices (leaf_windows[i]);
 
       /* Allow x_set_window_size again and apply frame size changes if
          needed.  */
@@ -6699,35 +7028,10 @@ the return value is nil.  Otherwise the value is t.  */)
          selected window.  */
       if (FRAME_LIVE_P (XFRAME (data->selected_frame)))
         do_switch_frame (data->selected_frame, 0, 0, Qnil);
-
-      if (window_changed)
-        /* At least one window has been added or removed.  Run
-           `window-configuration-change-hook' and make sure
-           `window-size-change-functions' get run later.
-
-           We have to do this in order to capture the following
-           scenario: Suppose our frame contains two live windows W1 and
-           W2 and 'set-window-configuration' replaces them by two
-           windows W3 and W4 that were dead the last time
-           run_window_size_change_functions was run.  If W3 and W4 have
-           the same values for their old and new pixel sizes but these
-           values differ from those of W1 and W2, the sizes of our
-           frame's two live windows changed but window_size_changed has
-           no means to detect that fact.
-
-           Obviously, this will get us false positives, for example,
-           when we restore the original configuration with W1 and W2
-           before run_window_size_change_functions gets called.  */
-        {
-          run_window_configuration_change_hook (f);
-          FRAME_WINDOW_CONFIGURATION_CHANGED (f) = true;
-        }
-      else if (buffer_changed)
-        /* At least one window has changed its buffer.  Run
-           `window-configuration-change-hook' only.  */
-        run_window_configuration_change_hook (f);
     }
 
+  FRAME_WINDOW_CHANGE (f) = true;
+
   if (!NILP (new_current_buffer))
     {
       Fset_buffer (new_current_buffer);
@@ -6889,10 +7193,6 @@ save_window_save (Lisp_Object window, struct Lisp_Vector *vector, ptrdiff_t i)
       p->pixel_top = make_fixnum (w->pixel_top);
       p->pixel_width = make_fixnum (w->pixel_width);
       p->pixel_height = make_fixnum (w->pixel_height);
-      p->pixel_width_before_size_change
-        = make_fixnum (w->pixel_width_before_size_change);
-      p->pixel_height_before_size_change
-        = make_fixnum (w->pixel_height_before_size_change);
       p->left_col = make_fixnum (w->left_col);
       p->top_line = make_fixnum (w->top_line);
       p->total_cols = make_fixnum (w->total_cols);
@@ -7581,9 +7881,9 @@ init_window_once (void)
 {
   struct frame *f = make_initial_frame ();
   XSETFRAME (selected_frame, f);
-  Vterminal_frame = selected_frame;
+  old_selected_frame = Vterminal_frame = selected_frame;
   minibuf_window = f->minibuffer_window;
-  selected_window = f->selected_window;
+  old_selected_window = selected_window = f->selected_window;
 }
 
 void
@@ -7604,6 +7904,8 @@ syms_of_window (void)
 
   DEFSYM (Qwindow_configuration_change_hook, "window-configuration-change-hook");
   DEFSYM (Qwindow_size_change_functions, "window-size-change-functions");
+  DEFSYM (Qwindow_buffer_change_functions, "window-buffer-change-functions");
+  DEFSYM (Qwindow_selection_change_functions, "window-selection-change-functions");
   DEFSYM (Qwindowp, "windowp");
   DEFSYM (Qwindow_configuration_p, "window-configuration-p");
   DEFSYM (Qwindow_live_p, "window-live-p");
@@ -7688,24 +7990,66 @@ on their symbols to be controlled by this variable.  */);
   Vwindow_point_insertion_type = Qnil;
   DEFSYM (Qwindow_point_insertion_type, "window-point-insertion-type");
 
-  DEFVAR_LISP ("window-configuration-change-hook",
-               Vwindow_configuration_change_hook,
-               doc: /* Functions to call when window configuration changes.
-The buffer-local value is run once per window, with the relevant window
-selected; while the global value is run only once for the modified frame,
-with the relevant frame selected.  */);
-  Vwindow_configuration_change_hook = Qnil;
+  DEFVAR_LISP ("window-buffer-change-functions", Vwindow_buffer_change_functions,
+               doc: /* Functions called during redisplay when window buffers have changed.
+The value should be a list of functions that take one argument.
+
+Functions specified buffer-locally are called for each window showing
+the corresponding buffer if and only if that window has been added or
+changed its buffer since the last redisplay.  In this case the window
+is passed as argument.
+
+Functions specified by the default value are called for each frame if
+at least one window on that frame has been added, deleted or changed
+its buffer since the last redisplay.  In this case the frame is passed
+as argument.  */);
+  Vwindow_buffer_change_functions = Qnil;
 
   DEFVAR_LISP ("window-size-change-functions", Vwindow_size_change_functions,
-    doc: /* Functions called during redisplay, if window sizes have changed.
+               doc: /* Functions called during redisplay when window sizes have changed.
 The value should be a list of functions that take one argument.
-During the first part of redisplay, for each frame, if any of its windows
-have changed size since the last redisplay, or have been split or deleted,
-all the functions in the list are called, with the frame as argument.
-If redisplay decides to resize the minibuffer window, it calls these
-functions on behalf of that as well.  */);
+
+Functions specified buffer-locally are called for each window showing
+the corresponding buffer if and only if that window has been added or
+changed its buffer or its total or body size since the last redisplay.
+In this case the window is passed as argument.
+
+Functions specified by the default value are called for each frame if
+at least one window on that frame has been added or changed its buffer
+or its total or body size since the last redisplay.  In this case the
+frame is passed as argument.  */);
   Vwindow_size_change_functions = Qnil;
 
+  DEFVAR_LISP ("window-selection-change-functions", Vwindow_selection_change_functions,
+               doc: /* Functions called during redisplay when the selected window has changed.
+The value should be a list of functions that take one argument.
+
+Functions specified buffer-locally are called for each window showing
+the corresponding buffer if and only if that window has been selected
+or deselected since the last redisplay.  In this case the window is
+passed as argument.
+
+Functions specified by the default value are called for each frame if
+the frame's selected window has changed since the last redisplay.  In
+this case the frame is passed as argument.  */);
+  Vwindow_selection_change_functions = Qnil;
+
+  DEFVAR_LISP ("window-configuration-change-hook", Vwindow_configuration_change_hook,
+               doc: /* Functions called during redisplay when window configuration has changed.
+The value should be a list of functions that take no argument.
+
+Functions specified buffer-locally are called for each window showing
+the corresponding buffer if at least one window on that frame has been
+added, deleted or changed its buffer or its total or body size since
+the last redisplay.  Each call is performed with the window showing
+the buffer temporarily selected.
+
+Functions specified by the default value are called for each frame if
+at least one window on that frame has been added, deleted or changed
+its buffer or its total or body size since the last redisplay.  Each
+call is performed with the frame temporarily selected.  */);
+  Vwindow_configuration_change_hook = Qnil;
+
   DEFVAR_LISP ("recenter-redisplay", Vrecenter_redisplay,
                doc: /* Non-nil means `recenter' redraws entire frame.
 If this option is non-nil, then the `recenter' command with a nil
@@ -7817,6 +8161,7 @@ displayed after a scrolling operation to be somewhat inaccurate.  */);
   Vfast_but_imprecise_scrolling = false;
 
   defsubr (&Sselected_window);
+  defsubr (&Sold_selected_window);
   defsubr (&Sminibuffer_window);
   defsubr (&Swindow_minibuffer_p);
   defsubr (&Swindowp);
@@ -7826,10 +8171,12 @@ displayed after a scrolling operation to be somewhat inaccurate.  */);
   defsubr (&Sframe_root_window);
   defsubr (&Sframe_first_window);
   defsubr (&Sframe_selected_window);
+  defsubr (&Sframe_old_selected_window);
   defsubr (&Sset_frame_selected_window);
   defsubr (&Spos_visible_in_window_p);
   defsubr (&Swindow_line_height);
   defsubr (&Swindow_buffer);
+  defsubr (&Swindow_old_buffer);
   defsubr (&Swindow_parent);
   defsubr (&Swindow_top_child);
   defsubr (&Swindow_left_child);
@@ -7840,8 +8187,10 @@ displayed after a scrolling operation to be somewhat inaccurate.  */);
   defsubr (&Swindow_use_time);
   defsubr (&Swindow_pixel_width);
   defsubr (&Swindow_pixel_height);
-  defsubr (&Swindow_pixel_width_before_size_change);
-  defsubr (&Swindow_pixel_height_before_size_change);
+  defsubr (&Swindow_old_pixel_width);
+  defsubr (&Swindow_old_pixel_height);
+  defsubr (&Swindow_old_body_pixel_width);
+  defsubr (&Swindow_old_body_pixel_height);
   defsubr (&Swindow_total_width);
   defsubr (&Swindow_total_height);
   defsubr (&Swindow_normal_size);
diff --git a/src/window.h b/src/window.h
index ee6ec3bb19a..9c4aea85ea6 100644
--- a/src/window.h
+++ b/src/window.h
@@ -142,6 +142,11 @@ struct window
        as well.  */
     Lisp_Object contents;
 
+    /* The old buffer of this window, set to this window's buffer by
+       run_window_change_functions every time it sees this window.
+       Unused for internal windows.  */
+    Lisp_Object old_buffer;
+
     /* A marker pointing to where in the text to start displaying.
        BIDI Note: This is the _logical-order_ start, i.e. the smallest
        buffer position visible in the window, not necessarily the
@@ -229,6 +234,14 @@ struct window
     /* Unique number of window assigned when it was created.  */
     EMACS_INT sequence_number;
 
+    /* The change stamp of this window.  Set to 0 when the window is
+       created, it is set to its frame's change stamp every time
+       run_window_change_functions is run on that frame with this
+       window live.  It is left alone when the window exists only
+       within a window configuration.  Not useful for internal
+       windows.  */
+    int change_stamp;
+
     /* The upper left corner pixel coordinates of this window, as
        integers relative to upper left corner of frame = 0, 0.  */
     int pixel_left;
@@ -243,10 +256,13 @@ struct window
     int pixel_width;
     int pixel_height;
 
-    /* The pixel sizes of the window at the last time
-       `window-size-change-functions' was run.  */
-    int pixel_width_before_size_change;
-    int pixel_height_before_size_change;
+    /* The pixel and pixel body sizes of the window at the last time
+       run_window_change_functions was run with this window live.  Not
+       useful for internal windows.  */
+    int old_pixel_width;
+    int old_pixel_height;
+    int old_body_pixel_width;
+    int old_body_pixel_height;
 
     /* The size of the window.  */
     int total_cols;
@@ -1023,6 +1039,7 @@ wset_next_buffers (struct window *w, Lisp_Object val)
    This value is always the same as FRAME_SELECTED_WINDOW (selected_frame).  */
 
 extern Lisp_Object selected_window;
+extern Lisp_Object old_selected_window;
 
 /* This is a time stamp for window selection, so we can find the least
    recently used window.  Its only users are Fselect_window,
@@ -1051,7 +1068,7 @@ extern void grow_mini_window (struct window *, int, bool);
 extern void shrink_mini_window (struct window *, bool);
 extern int window_relative_x_coord (struct window *, enum window_part, int);
 
-void run_window_size_change_functions (Lisp_Object);
+void run_window_change_functions (void);
 
 /* Make WINDOW display BUFFER.  RUN_HOOKS_P means it's allowed
    to run hooks.  See make_frame for a case where it's not allowed.  */
diff --git a/src/xdisp.c b/src/xdisp.c
index 7725570ced3..86495078fb6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2786,6 +2786,7 @@ init_iterator (struct it *it, struct window *w,
                struct glyph_row *row, enum face_id base_face_id)
 {
   enum face_id remapped_base_face_id = base_face_id;
+  int body_width = 0, body_height = 0;
 
   /* Some precondition checks.  */
   eassert (w != NULL && it != NULL);
@@ -2962,7 +2963,7 @@ init_iterator (struct it *it, struct window *w,
     {
       /* Mode lines, menu bar in terminal frames.  */
       it->first_visible_x = 0;
-      it->last_visible_x = WINDOW_PIXEL_WIDTH (w);
+      it->last_visible_x = body_width = WINDOW_PIXEL_WIDTH (w);
     }
   else
     {
@@ -2982,8 +2983,12 @@ init_iterator (struct it *it, struct window *w,
       else
         it->first_visible_x =
           window_hscroll_limited (w, it->f) * FRAME_COLUMN_WIDTH (it->f);
-      it->last_visible_x = (it->first_visible_x
-                            + window_box_width (w, TEXT_AREA));
+
+      body_width = window_box_width (w, TEXT_AREA);
+      if (!w->pseudo_window_p && !MINI_WINDOW_P (w)
+          && body_width != w->old_body_pixel_width)
+        FRAME_WINDOW_CHANGE (it->f) = true;
+      it->last_visible_x = it->first_visible_x + body_width;
 
       /* If we truncate lines, leave room for the truncation glyph(s) at
          the right margin.  Otherwise, leave room for the continuation
@@ -2997,7 +3002,8 @@ init_iterator (struct it *it, struct window *w,
         }
 
       it->header_line_p = window_wants_header_line (w);
-      it->current_y = WINDOW_HEADER_LINE_HEIGHT (w) + w->vscroll;
+      body_height = WINDOW_HEADER_LINE_HEIGHT (w);
+      it->current_y =  body_height + w->vscroll;
     }
 
   /* Leave room for a border glyph.  */
@@ -3006,6 +3012,10 @@ init_iterator (struct it *it, struct window *w,
     it->last_visible_x -= 1;
 
   it->last_visible_y = window_text_bottom_y (w);
+  body_height += it->last_visible_y;
+  if (!w->pseudo_window_p && !MINI_WINDOW_P (w)
+      && body_height != w->old_body_pixel_height)
+    FRAME_WINDOW_CHANGE (it->f) = true;
 
   /* For mode lines and alike, arrange for the first glyph having a
      left box line if the face specifies a box.  */
@@ -12200,8 +12210,6 @@ prepare_menu_bars (void)
               && !XBUFFER (w->contents)->text->redisplay)
             continue;
 
-          run_window_size_change_functions (frame);
-
           if (FRAME_PARENT_FRAME (f))
             continue;
 
@@ -14119,20 +14127,6 @@ redisplay_internal (void)
     {
       echo_area_display (false);
 
-      /* If echo_area_display resizes the mini-window, the redisplay and
-         window_sizes_changed flags of the selected frame are set, but
-         it's too late for the hooks in window-size-change-functions,
-         which have been examined already in prepare_menu_bars.  So in
-         that case we call the hooks here only for the selected frame.  */
-      if (sf->redisplay)
-        {
-          ptrdiff_t count1 = SPECPDL_INDEX ();
-
-          record_unwind_save_match_data ();
-          run_window_size_change_functions (selected_frame);
-          unbind_to (count1, Qnil);
-        }
-
       if (message_cleared_p)
         update_miniwindow_p = true;
 
@@ -14149,15 +14143,6 @@ redisplay_internal (void)
            && (current_buffer->clip_changed || window_outdated (w))
            && resize_mini_window (w, false))
     {
-      if (sf->redisplay)
-        {
-          ptrdiff_t count1 = SPECPDL_INDEX ();
-
-          record_unwind_save_match_data ();
-          run_window_size_change_functions (selected_frame);
-          unbind_to (count1, Qnil);
-        }
-
       /* Resized active mini-window to fit the size of what it is
          showing if its contents might have changed.  */
       must_finish = true;
@@ -14347,7 +14332,19 @@ redisplay_internal (void)
                   && (w = XWINDOW (selected_window)) != sw)
                 goto retry;
 
-              /* We used to always goto end_of_redisplay here, but this
+              if (!NILP (Vrun_hooks))
+                {
+                  run_window_change_functions ();
+
+                  /* If windows or buffers changed or selected_window
+                     changed, redisplay again.  */
+                  if ((windows_or_buffers_changed)
+                      || (WINDOWP (selected_window)
+                          && (w = XWINDOW (selected_window)) != sw))
+                    goto retry;
+                }
+
+                /* We used to always goto end_of_redisplay here, but this
                  isn't enough if we have a blinking cursor.  */
               if (w->cursor_off_p == w->last_cursor_off_p)
                 goto end_of_redisplay;
@@ -14706,9 +14703,22 @@ redisplay_internal (void)
   /* If we just did a pending size change, or have additional
      visible frames, or selected_window changed, redisplay again.  */
   if ((windows_or_buffers_changed && !pending)
-      || (WINDOWP (selected_window) && (w = XWINDOW (selected_window)) != sw))
+      || (WINDOWP (selected_window)
+          && (w = XWINDOW (selected_window)) != sw))
     goto retry;
 
+  if (!NILP (Vrun_hooks))
+    {
+      run_window_change_functions ();
+
+      /* If windows or buffers changed or selected_window changed,
+         redisplay again.  */
+      if ((windows_or_buffers_changed)
+          || (WINDOWP (selected_window)
+              && (w = XWINDOW (selected_window)) != sw))
+        goto retry;
+    }
+
   /* Clear the face and image caches.
 
      We used to do this only if consider_all_windows_p.  But the cache