Replace refresh-from-pane in copy mode with a way to automatically

update as pane content changes. This is toggled by pressing r. GitHub
issue 5165 from Barrett Ruth.

usr.bin/tmux/grid.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: grid.c,v 1.148 2026/06/07 20:03:02 nicm Exp $ */
+/* $OpenBSD: grid.c,v 1.149 2026/06/10 14:29:08 nicm Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -292,7 +292,7 @@ grid_free_line(struct grid *gd, u_int py)
 }
 
 /* Free several lines. */
-static void
+void
 grid_free_lines(struct grid *gd, u_int py, u_int ny)
 {
 	u_int	yy;
@@ -320,6 +320,10 @@ grid_create(u_int sx, u_int sy, u_int hlimit)
 	gd->hsize = 0;
 	gd->hlimit = hlimit;
 
+	gd->scroll_added = 0;
+	gd->scroll_collected = 0;
+	gd->scroll_generation = 0;
+
 	if (gd->sy != 0)
 		gd->linedata = xcalloc(gd->sy, sizeof *gd->linedata);
 	else
@@ -405,6 +409,7 @@ grid_collect_history(struct grid *gd, int all)
 	grid_trim_history(gd, ny);
 
 	gd->hsize -= ny;
+	gd->scroll_collected += ny;
 	if (gd->hscrolled > gd->hsize)
 		gd->hscrolled = gd->hsize;
 }
@@ -442,6 +447,7 @@ grid_scroll_history(struct grid *gd, u_int bg)
 	grid_compact_line(&gd->linedata[gd->hsize]);
 	gd->linedata[gd->hsize].time = current_time;
 	gd->hsize++;
+	gd->scroll_added++;
 }
 
 /* Clear the history. */
@@ -452,6 +458,7 @@ grid_clear_history(struct grid *gd)
 
 	gd->hscrolled = 0;
 	gd->hsize = 0;
+	gd->scroll_generation++;
 
 	gd->linedata = xreallocarray(gd->linedata, gd->sy,
 	    sizeof *gd->linedata);
@@ -489,6 +496,7 @@ grid_scroll_history_region(struct grid *gd, u_int upper, u_int lower, u_int bg)
 	/* Move the history offset down over the line. */
 	gd->hscrolled++;
 	gd->hsize++;
+	gd->scroll_added++;
 }
 
 /* Expand line to fit to cell. */
@@ -1510,6 +1518,7 @@ grid_reflow(struct grid *gd, u_int sx)
 	free(gd->linedata);
 	gd->linedata = target->linedata;
 	free(target);
+	gd->scroll_generation++;
 }
 
 /* Convert to position based on wrapped lines. */

usr.bin/tmux/key-bindings.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: key-bindings.c,v 1.171 2026/06/07 08:25:59 nicm Exp $ */
+/* $OpenBSD: key-bindings.c,v 1.172 2026/06/10 14:29:08 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -530,7 +530,7 @@ key_bindings_init(void)
 		"bind -Tcopy-mode g { command-prompt -p'(goto line)' { send -X goto-line -- '%%' } }",
 		"bind -Tcopy-mode n { send -X search-again }",
 		"bind -Tcopy-mode q { send -X cancel }",
-		"bind -Tcopy-mode r { send -X refresh-from-pane }",
+		"bind -Tcopy-mode r { send -X refresh-toggle }",
 		"bind -Tcopy-mode t { command-prompt -1p'(jump to forward)' { send -X jump-to-forward -- '%%' } }",
 		"bind -Tcopy-mode Home { send -X start-of-line }",
 		"bind -Tcopy-mode End { send -X end-of-line }",
@@ -638,7 +638,7 @@ key_bindings_init(void)
 		"bind -Tcopy-mode-vi n { send -X search-again }",
 		"bind -Tcopy-mode-vi o { send -X other-end }",
 		"bind -Tcopy-mode-vi q { send -X cancel }",
-		"bind -Tcopy-mode-vi r { send -X refresh-from-pane }",
+		"bind -Tcopy-mode-vi r { send -X refresh-toggle }",
 		"bind -Tcopy-mode-vi t { command-prompt -1p'(jump to forward)' { send -X jump-to-forward -- '%%' } }",
 		"bind -Tcopy-mode-vi v { send -X rectangle-toggle }",
 		"bind -Tcopy-mode-vi w { send -X next-word }",

usr.bin/tmux/tmux.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1077 2026/06/09 12:51:57 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1078 2026/06/10 14:29:08 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: June 9 2026 $
+.Dd $Mdocdate: June 10 2026 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -2293,11 +2293,22 @@ Toggle rectangle selection mode.
 .Xc
 Cycles the current line between centre, top, and bottom.
 .It Xo
-.Ic refresh\-from\-pane
+.Ic refresh\-on
+.Xc
+Turn on automatic refresh of the content from the pane, so that new output
+appears while in copy mode.
+Automatic refresh is off by default; it will scroll only while the cursor is at
+the bottom and is paused while a selection is in progress.
+.It Xo
+.Ic refresh\-off
+.Xc
+Turn off automatic refresh of the content from the pane.
+.It Xo
+.Ic refresh\-toggle
 (vi: r)
 (emacs: r)
 .Xc
-Refresh the content from the pane.
+Toggle automatic refresh of the content from the pane.
 .It Xo
 .Ic scroll\-bottom
 .Xc

usr.bin/tmux/tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1341 2026/06/09 21:22:22 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1342 2026/06/10 14:29:08 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -862,6 +862,10 @@ struct grid {
 	u_int			 hsize;
 	u_int			 hlimit;
 
+	u_int			 scroll_added;
+	u_int			 scroll_collected;
+	u_int			 scroll_generation;
+
 	struct grid_line	*linedata;
 };
 
@@ -3168,6 +3172,7 @@ int	 grid_cells_look_equal(const struct grid_cell *,
 	     const struct grid_cell *);
 struct grid *grid_create(u_int, u_int, u_int);
 void	 grid_destroy(struct grid *);
+void	 grid_free_lines(struct grid *, u_int, u_int);
 int	 grid_compare(struct grid *, struct grid *);
 void	 grid_collect_history(struct grid *, int);
 void	 grid_remove_history(struct grid *, u_int );

usr.bin/tmux/window-copy.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: window-copy.c,v 1.403 2026/06/09 21:22:22 nicm Exp $ */
+/* $OpenBSD: window-copy.c,v 1.404 2026/06/10 14:29:08 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -51,6 +51,11 @@ static void	window_copy_redraw_selection(struct window_mode_entry *, u_int);
 static void	window_copy_redraw_lines(struct window_mode_entry *, u_int,
 		    u_int);
 static void	window_copy_redraw_screen(struct window_mode_entry *);
+static void	window_copy_do_refresh(struct window_mode_entry *, int);
+static void	window_copy_refresh_timer(int, short, void *);
+static void	window_copy_refresh_arm(struct window_mode_entry *);
+static void	window_copy_refresh_start(struct window_mode_entry *);
+static void	window_copy_refresh_stop(struct window_mode_entry *);
 static void	window_copy_style_changed(struct window_mode_entry *);
 static int	window_copy_line_number_mode(struct window_mode_entry *);
 static int	window_copy_line_number_is_absolute(struct window_mode_entry *);
@@ -255,6 +260,10 @@ struct window_copy_mode_data {
 	int		 backing_written; /* backing display started */
 	struct input_ctx *ictx;
 
+	u_int		 sync_added;	/* snapshot of backing grid counters */
+	u_int		 sync_collected;
+	u_int		 sync_generation;
+
 	int		 viewmode;	/* view mode entered */
 
 	u_int		 oy;		/* number of lines scrolled up */
@@ -338,6 +347,10 @@ struct window_copy_mode_data {
 
 	struct event	 dragtimer;
 #define WINDOW_COPY_DRAG_REPEAT_TIME 50000
+
+	struct event	 refresh_timer;
+#define WINDOW_COPY_REFRESH_INTERVAL 50000
+	int		 refresh_active;
 };
 
 static void
@@ -424,6 +437,116 @@ window_copy_clone_screen(struct screen *src, struct screen *hint, u_int *cx,
 	return (dst);
 }
 
+/*
+ * Snapshot the source grid's monotonic scroll counters so the next incremental
+ * sync can tell how much history was added or collected since this point.
+ */
+static void
+window_copy_sync_snapshot(struct window_copy_mode_data *data, struct grid *src)
+{
+	data->sync_added = src->scroll_added;
+	data->sync_collected = src->scroll_collected;
+	data->sync_generation = src->scroll_generation;
+}
+
+/*
+ * Reconcile the backing screen with the live pane grid in place, copying only
+ * the history that scrolled in or was collected since the last snapshot rather
+ * than cloning the whole scrollback. The result is identical to a fresh
+ * window_copy_clone_screen, so the caller repositions and redraws the same way
+ * for both paths. Returns 1 on success, or 0 if the caller must fall back to a
+ * full clone (different source pane, geometry or generation change, or counter
+ * deltas that do not add up).
+ */
+static int
+window_copy_sync_backing(struct window_mode_entry *wme)
+{
+	struct window_copy_mode_data	*data = wme->data;
+	struct window_pane		*wp = wme->swp;
+	struct screen			*src = &wp->base;
+	struct screen			*dst = data->backing;
+	struct grid			*sg = src->grid;
+	struct grid			*dg = dst->grid;
+	u_int				 sy = sg->sy;
+	u_int				 old_hsize = dg->hsize;
+	u_int				 new_hsize = sg->hsize;
+	u_int				 added, collected, kept;
+
+	/*
+	 * Only a pane's own live grid is tracked incrementally. A different
+	 * source pane (copy-mode -s) goes through clone_screen, which also
+	 * trims trailing blank lines that this path does not.
+	 */
+	if (data->viewmode || wme->swp != wme->wp)
+		return (0);
+
+	/* Indices only line up at the same size and generation. */
+	if (sg->sx != dg->sx || sg->sy != dg->sy ||
+	    sg->scroll_generation != data->sync_generation)
+		return (0);
+
+	added = sg->scroll_added - data->sync_added;
+	collected = sg->scroll_collected - data->sync_collected;
+
+	/*
+	 * Reject anything that does not balance: counter wrap, a history-limit
+	 * change that collected past the snapshot, or arithmetic that does not
+	 * reproduce the new history size.
+	 */
+	if (added > (u_int)INT_MAX || collected > (u_int)INT_MAX ||
+	    collected > old_hsize || old_hsize + added < collected ||
+	    old_hsize + added - collected != new_hsize)
+		return (0);
+
+	kept = old_hsize - collected;
+
+	if (added == 0 && collected == 0) {
+		/* History is unchanged; only the viewport can have mutated. */
+		grid_duplicate_lines(dg, dg->hsize, sg, sg->hsize, sy);
+	} else {
+		/* Drop the oldest lines and shift the rest down. */
+		if (collected > 0) {
+			grid_free_lines(dg, 0, collected);
+			memmove(&dg->linedata[0], &dg->linedata[collected],
+			    (old_hsize + sy - collected) * sizeof *dg->linedata);
+			memset(&dg->linedata[old_hsize + sy - collected], 0,
+			    collected * sizeof *dg->linedata);
+		}
+
+		/* Resize linedata to the new history plus viewport. */
+		if (new_hsize + sy != old_hsize + sy - collected) {
+			dg->linedata = xreallocarray(dg->linedata,
+			    new_hsize + sy, sizeof *dg->linedata);
+			memset(&dg->linedata[old_hsize + sy - collected], 0,
+			    (new_hsize - kept) * sizeof *dg->linedata);
+		}
+
+		/*
+		 * Set hsize before copying so grid_duplicate_lines does not
+		 * clamp the count to the old, smaller grid size.
+		 */
+		dg->hsize = new_hsize;
+
+		/* Copy the newly scrolled history, then refresh the viewport. */
+		if (added > 0)
+			grid_duplicate_lines(dg, kept, sg, kept, added);
+		grid_duplicate_lines(dg, new_hsize, sg, new_hsize, sy);
+	}
+
+	dg->hscrolled = sg->hscrolled;
+
+	/* Match clone_screen's backing cursor placement. */
+	if (src->cy > dg->sy - 1) {
+		dst->cx = 0;
+		dst->cy = dg->sy - 1;
+	} else {
+		dst->cx = src->cx;
+		dst->cy = src->cy;
+	}
+
+	return (1);
+}
+
 static struct window_copy_mode_data *
 window_copy_common_init(struct window_mode_entry *wme)
 {
@@ -458,6 +581,7 @@ window_copy_common_init(struct window_mode_entry *wme)
 	data->modekeys = options_get_number(wp->window->options, "mode-keys");
 
 	evtimer_set(&data->dragtimer, window_copy_scroll_timer, wme);
+	evtimer_set(&data->refresh_timer, window_copy_refresh_timer, wme);
 
 	return (data);
 }
@@ -475,6 +599,7 @@ window_copy_init(struct window_mode_entry *wme,
 	data = window_copy_common_init(wme);
 	data->backing = window_copy_clone_screen(base, &data->screen, &cx, &cy,
 	    wme->swp != wme->wp);
+	window_copy_sync_snapshot(data, base->grid);
 
 	data->cx = cx;
 	if (cy < screen_hsize(data->backing)) {
@@ -541,6 +666,7 @@ window_copy_free(struct window_mode_entry *wme)
 	struct window_copy_mode_data	*data = wme->data;
 
 	evtimer_del(&data->dragtimer);
+	evtimer_del(&data->refresh_timer);
 
 	free(data->searchmark);
 	free(data->searchstr);
@@ -2781,34 +2907,136 @@ window_copy_cmd_search_forward_incremental(struct window_copy_cmd_state *cs)
 	return (action);
 }
 
-static enum window_copy_cmd_action
-window_copy_cmd_refresh_from_pane(struct window_copy_cmd_state *cs)
+/*
+ * Reconcile the backing screen with the live pane, incrementally if possible
+ * and otherwise by recloning, then reposition the view. When following, jump
+ * to the bottom so new output stays visible; otherwise keep the same lines on
+ * screen. Driven by the automatic refresh timer.
+ */
+static void
+window_copy_do_refresh(struct window_mode_entry *wme, int follow)
 {
-	struct window_mode_entry	*wme = cs->wme;
 	struct window_pane		*wp = wme->swp;
 	struct window_copy_mode_data	*data = wme->data;
 	u_int				 oy_from_top;
 
-	if (data->viewmode)
-		return (WINDOW_COPY_CMD_NOTHING);
 	if (data->oy > screen_hsize(data->backing))
 		data->oy = screen_hsize(data->backing);
 	oy_from_top = screen_hsize(data->backing) - data->oy;
 
-	screen_free(data->backing);
-	free(data->backing);
-	data->backing = window_copy_clone_screen(&wp->base, &data->screen, NULL,
-	    NULL, wme->swp != wme->wp);
+	if (!window_copy_sync_backing(wme)) {
+		screen_free(data->backing);
+		free(data->backing);
+		data->backing = window_copy_clone_screen(&wp->base,
+		    &data->screen, NULL, NULL, wme->swp != wme->wp);
+	}
 
-	if (oy_from_top <= screen_hsize(data->backing))
+	if (follow) {
+		data->cy = screen_size_y(&data->screen) - 1;
+		data->cx = window_copy_cursor_limit(wme,
+		    screen_hsize(data->backing) + data->cy, 0);
+		data->oy = 0;
+	} else if (oy_from_top <= screen_hsize(data->backing))
 		data->oy = screen_hsize(data->backing) - oy_from_top;
 	else {
 		data->cy = 0;
 		data->oy = screen_hsize(data->backing);
 	}
 
+	window_copy_sync_snapshot(data, wp->base.grid);
 	window_copy_size_changed(wme);
-	return (WINDOW_COPY_CMD_REDRAW);
+}
+
+static void
+window_copy_refresh_arm(struct window_mode_entry *wme)
+{
+	struct window_copy_mode_data	*data = wme->data;
+	struct timeval			 tv = {
+		.tv_sec = WINDOW_COPY_REFRESH_INTERVAL / 1000000,
+		.tv_usec = WINDOW_COPY_REFRESH_INTERVAL % 1000000
+	};
+
+	if (data->refresh_active)
+		evtimer_add(&data->refresh_timer, &tv);
+}
+
+static void
+window_copy_refresh_timer(__unused int fd, __unused short events, void *arg)
+{
+	struct window_mode_entry	*wme = arg;
+	struct window_pane		*wp = wme->wp;
+	struct window_copy_mode_data	*data = wme->data;
+	int				 follow;
+
+	if (TAILQ_FIRST(&wp->modes) != wme || !data->refresh_active)
+		return;
+
+	/*
+	 * Skip the refresh while a selection is being made, otherwise it would
+	 * move; only follow new output if the cursor is still at the bottom.
+	 */
+	if ((wp->flags & PANE_UNSEENCHANGES) && data->screen.sel == NULL &&
+	    data->cursordrag == CURSORDRAG_NONE) {
+		follow = (data->oy == 0 &&
+		    data->cy == screen_size_y(&data->screen) - 1);
+		window_copy_do_refresh(wme, follow);
+		window_copy_redraw_screen(wme);
+		/* The timer runs outside key handling, so force a repaint. */
+		wp->flags |= PANE_REDRAW;
+		wp->flags &= ~PANE_UNSEENCHANGES;
+	}
+
+	window_copy_refresh_arm(wme);
+}
+
+static void
+window_copy_refresh_start(struct window_mode_entry *wme)
+{
+	struct window_copy_mode_data	*data = wme->data;
+
+	/*
+	 * Do not refresh a view of another pane (copy-mode -s): the source may
+	 * disappear and changes are not tracked on this pane.
+	 */
+	if (data->viewmode || wme->swp != wme->wp || data->refresh_active)
+		return;
+	data->refresh_active = 1;
+	window_copy_refresh_arm(wme);
+}
+
+static void
+window_copy_refresh_stop(struct window_mode_entry *wme)
+{
+	struct window_copy_mode_data	*data = wme->data;
+
+	data->refresh_active = 0;
+	evtimer_del(&data->refresh_timer);
+}
+
+static enum window_copy_cmd_action
+window_copy_cmd_refresh_on(struct window_copy_cmd_state *cs)
+{
+	window_copy_refresh_start(cs->wme);
+	return (WINDOW_COPY_CMD_NOTHING);
+}
+
+static enum window_copy_cmd_action
+window_copy_cmd_refresh_off(struct window_copy_cmd_state *cs)
+{
+	window_copy_refresh_stop(cs->wme);
+	return (WINDOW_COPY_CMD_NOTHING);
+}
+
+static enum window_copy_cmd_action
+window_copy_cmd_refresh_toggle(struct window_copy_cmd_state *cs)
+{
+	struct window_copy_mode_data	*data = cs->wme->data;
+
+	if (data->refresh_active)
+		window_copy_refresh_stop(cs->wme);
+	else
+		window_copy_refresh_start(cs->wme);
+	return (WINDOW_COPY_CMD_NOTHING);
 }
 
 static enum window_copy_cmd_action
@@ -3275,11 +3503,23 @@ static const struct {
 	  .clear = WINDOW_COPY_CMD_CLEAR_ALWAYS,
 	  .f = window_copy_cmd_rectangle_toggle
 	},
-	{ .command = "refresh-from-pane",
+	{ .command = "refresh-on",
 	  .args = { "", 0, 0, NULL },
 	  .flags = WINDOW_COPY_CMD_FLAG_READONLY,
-	  .clear = WINDOW_COPY_CMD_CLEAR_ALWAYS,
-	  .f = window_copy_cmd_refresh_from_pane
+	  .clear = WINDOW_COPY_CMD_CLEAR_NEVER,
+	  .f = window_copy_cmd_refresh_on
+	},
+	{ .command = "refresh-off",
+	  .args = { "", 0, 0, NULL },
+	  .flags = WINDOW_COPY_CMD_FLAG_READONLY,
+	  .clear = WINDOW_COPY_CMD_CLEAR_NEVER,
+	  .f = window_copy_cmd_refresh_off
+	},
+	{ .command = "refresh-toggle",
+	  .args = { "", 0, 0, NULL },
+	  .flags = WINDOW_COPY_CMD_FLAG_READONLY,
+	  .clear = WINDOW_COPY_CMD_CLEAR_NEVER,
+	  .f = window_copy_cmd_refresh_toggle
 	},
 	{ .command = "scroll-bottom",
 	  .args = { "", 0, 0, NULL },