Add a new argument to 'recenter' to allow finer control of redisplay

* window.c (recenter): Add a new REDISPLAY argument to allow the
caller to control the redisplay behavior.  'recenter' will only
redisplay the frame if this new arg and 'recenter-redisplay' are
both non-nil.
(recenter-top-bottom): Pass an extra non-nil argument to
'recenter' to force a redisplay.  (Bug#31325)

4 files changed, 28 insertions, 19 deletions

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index 54977595956..9740bbebf2c 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -4138,7 +4138,7 @@ beginning or end of the buffer (depending on scrolling direction);
 only if point is already on that position do they signal an error.
 @end defopt
 
-@deffn Command recenter &optional count
+@deffn Command recenter &optional count redisplay
 @cindex centering point
 This function scrolls the text in the selected window so that point is
 displayed at a specified vertical position within the window.  It does
@@ -4152,8 +4152,9 @@ line in the window.
 
 If @var{count} is @code{nil} (or a non-@code{nil} list),
 @code{recenter} puts the line containing point in the middle of the
-window.  If @var{count} is @code{nil}, this function may redraw the
-frame, according to the value of @code{recenter-redisplay}.
+window.  If @var{count} is @code{nil} and @var{redisplay} is
+non-@code{nil}, this function may redraw the frame, according to the
+value of @code{recenter-redisplay}.
 
 When @code{recenter} is called interactively, @var{count} is the raw
 prefix argument.  Thus, typing @kbd{C-u} as the prefix sets the
@@ -4181,8 +4182,9 @@ respect to the entire window group.
 
 @defopt recenter-redisplay
 If this variable is non-@code{nil}, calling @code{recenter} with a
-@code{nil} argument redraws the frame.  The default value is
-@code{tty}, which means only redraw the frame if it is a tty frame.
+@code{nil} @var{count} argument and non-@code{nil} @var{redisplay}
+argument redraws the frame.  The default value is @code{tty}, which
+means only redraw the frame if it is a tty frame.
 @end defopt
 
 @deffn Command recenter-top-bottom &optional count
diff --git a/etc/NEWS b/etc/NEWS
index 63c59ae9218..d5f1abb5feb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -690,6 +690,11 @@ manual for more details.
 * Lisp Changes in Emacs 27.1
 
 +++
+** The function 'recenter' accepts an additional optional argument.
+If the optional second argument is nil, recenter will not redisplay
+the frame regardless of the value of 'recenter-redisplay'.
+
++++
 ** New functions 'major-mode-suspend' and 'major-mode-restore'.
 Use them when switching temporarily to another major mode, e.g. for
 'hexl-mode', or to switch between 'c-mode' and 'image-mode' in XPM.
diff --git a/lisp/window.el b/lisp/window.el
index fdd510401da..6d9d8bdcd2e 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -8778,15 +8778,15 @@ A prefix argument is handled like `recenter':
            (min (max 0 scroll-margin)
                 (truncate (/ (window-body-height) 4.0)))))
       (cond ((eq recenter-last-op 'middle)
-             (recenter))
+             (recenter nil t))
             ((eq recenter-last-op 'top)
-             (recenter this-scroll-margin))
+             (recenter this-scroll-margin t))
             ((eq recenter-last-op 'bottom)
-             (recenter (- -1 this-scroll-margin)))
+             (recenter (- -1 this-scroll-margin) t))
             ((integerp recenter-last-op)
-             (recenter recenter-last-op))
+             (recenter recenter-last-op t))
             ((floatp recenter-last-op)
-             (recenter (round (* recenter-last-op (window-height))))))))))
+             (recenter (round (* recenter-last-op (window-height))) t)))))))
 
 (define-key global-map [?\C-l] 'recenter-top-bottom)
 
diff --git a/src/window.c b/src/window.c
index a97f1dd3efb..20f6862e3b4 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5896,22 +5896,23 @@ displayed_window_lines (struct window *w)
 }
 
 
-DEFUN ("recenter", Frecenter, Srecenter, 0, 1, "P",
+DEFUN ("recenter", Frecenter, Srecenter, 0, 2, "P",
        doc: /* Center point in selected window and maybe redisplay frame.
 With a numeric prefix argument ARG, recenter putting point on screen line ARG
 relative to the selected window.  If ARG is negative, it counts up from the
 bottom of the window.  (ARG should be less than the height of the window.)
 
-If ARG is omitted or nil, then recenter with point on the middle line of
-the selected window; if the variable `recenter-redisplay' is non-nil,
-also erase the entire frame and redraw it (when `auto-resize-tool-bars'
-is set to `grow-only', this resets the tool-bar's height to the minimum
-height needed); if `recenter-redisplay' has the special value `tty',
-then only tty frames are redrawn.
+If ARG is omitted or nil, then recenter with point on the middle line
+of the selected window; if REDISPLAY & `recenter-redisplay' are
+non-nil, also erase the entire frame and redraw it (when
+`auto-resize-tool-bars' is set to `grow-only', this resets the
+tool-bar's height to the minimum height needed); if
+`recenter-redisplay' has the special value `tty', then only tty frames
+are redrawn.
 
 Just C-u as prefix means put point in the center of the window
 and redisplay normally--don't erase and redraw the frame.  */)
-  (register Lisp_Object arg)
+  (Lisp_Object arg, Lisp_Object redisplay)
 {
   struct window *w = XWINDOW (selected_window);
   struct buffer *buf = XBUFFER (w->contents);
@@ -5931,7 +5932,8 @@ and redisplay normally--don't erase and redraw the frame.  */)
 
   if (NILP (arg))
     {
-      if (!NILP (Vrecenter_redisplay)
+      if (!NILP (redisplay)
+          && !NILP (Vrecenter_redisplay)
           && (!EQ (Vrecenter_redisplay, Qtty)
               || !NILP (Ftty_type (selected_frame))))
         {