Extend fill-character to allow inside and outside to be separate and use

a different default (filled characters rather than dots) for inside.

cmd-break-pane.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-break-pane.c,v 1.74 2026/07/15 13:02:33 nicm Exp $ */
+/* $OpenBSD: cmd-break-pane.c,v 1.75 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -172,6 +172,7 @@ cmd_break_pane_exec(struct cmd *self, struct cmdq_item *item)
 		w->name = clean_name(name, 0);
 		options_set_number(w->options, "automatic-rename", 0);
 	}
+	window_set_fill_cells(w);
 
 	layout_init(w, wp);
 	wp->flags |= PANE_CHANGED;

options-table.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: options-table.c,v 1.240 2026/07/21 11:52:13 nicm Exp $ */
+/* $OpenBSD: options-table.c,v 1.241 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2011 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1460,8 +1460,8 @@ const struct options_table_entry options_table[] = {
 	{ .name = "fill-character",
 	  .type = OPTIONS_TABLE_STRING,
 	  .scope = OPTIONS_TABLE_WINDOW,
-	  .default_str = "",
+	  .default_str = "#{?is_inside,#[bg=themedarkgrey] ,#[fg=themelightgrey]#[acs]~}",
-	  .text = "Character used to fill unused parts of window."
+	  .text = "Format used to fill unused parts of window."
 	},
 
 	{ .name = "main-pane-height",

options.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: options.c,v 1.90 2026/07/10 13:38:45 nicm Exp $ */
+/* $OpenBSD: options.c,v 1.91 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1372,7 +1372,7 @@ options_push_changes(const char *name)
 	}
 	if (strcmp(name, "fill-character") == 0) {
 		RB_FOREACH(w, windows, &windows)
-			window_set_fill_character(w);
+			window_set_fill_cells(w);
 	}
 	if (strcmp(name, "key-table") == 0) {
 		TAILQ_FOREACH(loop, &clients, entry)

screen-redraw.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: screen-redraw.c,v 1.155 2026/07/21 13:27:41 nicm Exp $ */
+/* $OpenBSD: screen-redraw.c,v 1.156 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2026 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -320,7 +320,7 @@ redraw_reset_cell(struct redraw_build_ctx *bctx, u_int x, u_int y)
 	struct window			*w = bctx->w;
 
 	memset(bc, 0, sizeof *bc);
-	if (bctx->ox + x <= w->sx && bctx->oy + y <= w->sy)
+	if (bctx->ox + x < w->sx && bctx->oy + y < w->sy)
 		bc->data.type = REDRAW_SPAN_EMPTY;
 	else
 		bc->data.type = REDRAW_SPAN_OUTSIDE;
@@ -1232,9 +1232,15 @@ redraw_draw_border_span(struct redraw_draw_ctx *dctx,
 
 	if (wp == NULL) {
 		redraw_get_default_border_style(dctx, &gc, &pane_lines);
-		if (span->data.type != REDRAW_SPAN_BORDER)
+		if (span->data.type == REDRAW_SPAN_OUTSIDE)
-			pane_lines = PANE_LINES_SINGLE;
+			window_get_fill_cell(w, 0, &gc);
-		window_get_border_cell(w, NULL, pane_lines, cell_type, &gc);
+		else if (span->data.type == REDRAW_SPAN_EMPTY)
+			window_get_fill_cell(w, 1, &gc);
+		else {
+			if (span->data.type != REDRAW_SPAN_BORDER)
+				pane_lines = PANE_LINES_SINGLE;
+			window_get_border_cell(NULL, pane_lines, cell_type, &gc);
+		}
 	} else {
 		window_pane_get_border_style(wp, c, &gc);
 		window_pane_get_border_cell(wp, cell_type, &gc);

spawn.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: spawn.c,v 1.49 2026/07/15 13:02:33 nicm Exp $ */
+/* $OpenBSD: spawn.c,v 1.50 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2019 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -224,6 +224,7 @@ spawn_window(struct spawn_context *sc, char **cause)
 			w->name = xstrdup(sc->name);
 			options_set_number(w->options, "automatic-rename", 0);
 		}
+		window_set_fill_cells(w);
 	}
 
 	/* Switch to the new window if required. */

tmux.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1148 2026/07/22 20:12:58 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1149 2026/07/23 09:38:27 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: July 22 2026 $
+.Dd $Mdocdate: July 23 2026 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -5712,8 +5712,13 @@ Set the time in milliseconds for which the indicators shown by the
 .Ic display\-panes
 command appear.
 .Pp
-.It Ic fill\-character Ar character
+.It Ic fill\-character Ar format
-Set the character used to fill areas of the terminal unused by a window.
+Set the format used to fill areas of the terminal unused by a pane.
+The format is expanded once for areas inside the window with
+.Ql is_inside
+set, and once for areas outside the window with
+.Ql is_outside
+set.
 .Pp
 .It Ic main\-pane\-height Ar height
 .It Ic main\-pane\-width Ar width

tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1414 2026/07/22 20:12:58 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1415 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1438,7 +1438,8 @@ struct window {
 	int			 sb;
 	int			 sb_pos;
 
-	struct utf8_data	*fill_character;
+	struct grid_cell	 inside_cell;
+	struct grid_cell	 outside_cell;
 	int			 flags;
 #define WINDOW_BELL 0x1
 #define WINDOW_ACTIVITY 0x2
@@ -3732,7 +3733,6 @@ void		*window_pane_get_new_data(struct window_pane *,
 		     struct window_pane_offset *, size_t *);
 void		 window_pane_update_used_data(struct window_pane *,
 		     struct window_pane_offset *, size_t);
-void		 window_set_fill_character(struct window *);
 void		 window_pane_default_cursor(struct window_pane *);
 int		 window_pane_mode(struct window_pane *);
 int		 window_pane_show_scrollbar(struct window_pane *);
@@ -3760,8 +3760,10 @@ struct style_range *window_pane_status_get_range(struct window_pane *, u_int,
 int		 window_pane_is_floating(struct window_pane *);
 
 /* window-border.c */
-void		 window_get_border_cell(struct window *, struct window_pane *,
+void		 window_set_fill_cells(struct window *);
-		     enum pane_lines, int, struct grid_cell *);
+void		 window_get_border_cell(struct window_pane *, enum pane_lines,
+		     int, struct grid_cell *);
+void		 window_get_fill_cell(struct window *, int, struct grid_cell *);
 void		 window_pane_get_border_cell(struct window_pane *, int,
 		     struct grid_cell *);
 void		 window_pane_get_border_style(struct window_pane *,

window-border.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: window-border.c,v 1.2 2026/07/17 12:42:51 nicm Exp $ */
+/* $OpenBSD: window-border.c,v 1.3 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2026 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -23,18 +23,82 @@
 
 #include "tmux.h"
 
+/* Set window fill cell. */
+static void
+window_set_fill_cell(struct window *w, int inside, struct grid_cell *gc)
+{
+	struct format_tree	*ft;
+	struct screen		 s;
+	struct screen_write_ctx	 ctx;
+	struct grid_cell	 new_gc;
+	const char		*value;
+	char			*expanded;
+
+	memcpy(gc, &grid_default_cell, sizeof *gc);
+	gc->attr |= GRID_ATTR_CHARSET;
+	utf8_set(&gc->data, CELL_BORDERS[CELL_NONE]);
+
+	ft = format_create(NULL, NULL, FORMAT_WINDOW|w->id, FORMAT_NOJOBS);
+	format_defaults(ft, NULL, NULL, NULL, w->active);
+	format_add(ft, "is_inside", "%d", inside);
+	format_add(ft, "is_outside", "%d", !inside);
+
+	value = options_get_string(w->options, "fill-character");
+	expanded = format_expand(ft, value);
+	format_free(ft);
+
+	screen_init(&s, 1, 1, 0);
+	screen_write_start(&ctx, &s);
+	format_draw(&ctx, &grid_default_cell, 1, expanded, NULL, 0);
+	screen_write_stop(&ctx);
+	free(expanded);
+
+	grid_view_get_cell(s.grid, 0, 0, &new_gc);
+	if (new_gc.data.width == 1)
+		memcpy(gc, &new_gc, sizeof *gc);
+	screen_free(&s);
+}
+
+/* Set window fill cells. */
+void
+window_set_fill_cells(struct window *w)
+{
+	window_set_fill_cell(w, 1, &w->inside_cell);
+	window_set_fill_cell(w, 0, &w->outside_cell);
+}
+
+/* Merge a window fill cell over an existing style. */
+static void
+window_copy_fill_cell(struct grid_cell *gc, const struct grid_cell *fill)
+{
+	utf8_copy(&gc->data, &fill->data);
+	gc->attr |= fill->attr;
+	gc->flags |= fill->flags;
+	if (fill->fg != 8)
+		gc->fg = fill->fg;
+	if (fill->bg != 8)
+		gc->bg = fill->bg;
+	if (fill->us != 8)
+		gc->us = fill->us;
+}
+
+/* Get window fill cell. */
+void
+window_get_fill_cell(struct window *w, int inside, struct grid_cell *gc)
+{
+	if (inside)
+		window_copy_fill_cell(gc, &w->inside_cell);
+	else
+		window_copy_fill_cell(gc, &w->outside_cell);
+}
+
 /* Get border cell. */
 void
-window_get_border_cell(struct window *w, struct window_pane *wp,
+window_get_border_cell(struct window_pane *wp, enum pane_lines pane_lines,
-    enum pane_lines pane_lines, int cell_type, struct grid_cell *gc)
+    int cell_type, struct grid_cell *gc)
 {
 	u_int	idx;
 
-	if (cell_type == CELL_NONE && w->fill_character != NULL) {
-		utf8_copy(&gc->data, &w->fill_character[0]);
-		return;
-	}
-
 	switch (pane_lines) {
 	case PANE_LINES_NUMBER:
 		if (cell_type == CELL_NONE) {
@@ -79,7 +143,7 @@ window_pane_get_border_cell(struct window_pane *wp, int cell_type,
 {
 	enum pane_lines	pane_lines = window_pane_get_pane_lines(wp);
 
-	window_get_border_cell(wp->window, wp, pane_lines, cell_type, gc);
+	window_get_border_cell(wp, pane_lines, cell_type, gc);
 }
 
 /* Get pane border style. */
@@ -147,7 +211,7 @@ window_make_pane_status(struct window_pane *wp, struct client *c, u_int width,
 	pane_lines = window_pane_get_pane_lines(wp);
 	for (i = 0; i < width; i++) {
 		cell_type = redraw_get_status_border_cell_type(&span, i);
-		window_get_border_cell(wp->window, wp, pane_lines, cell_type, &gc);
+		window_get_border_cell(wp, pane_lines, cell_type, &gc);
 		screen_write_cell(&ctx, &gc);
 	}
 	gc.attr &= ~GRID_ATTR_CHARSET;

window.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: window.c,v 1.367 2026/07/21 13:04:01 nicm Exp $ */
+/* $OpenBSD: window.c,v 1.368 2026/07/23 09:38:27 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -439,8 +439,6 @@ window_create(u_int sx, u_int sy, u_int xpixel, u_int ypixel)
 	w->id = next_window_id++;
 	RB_INSERT(windows, &windows, w);
 
-	window_set_fill_character(w);
-
 	if (gettimeofday(&w->creation_time, NULL) != 0)
 		fatal("gettimeofday failed");
 	window_update_activity(w);
@@ -474,7 +472,6 @@ window_destroy(struct window *w)
 		event_del(&w->offset_timer);
 
 	options_free(w->options);
-	free(w->fill_character);
 
 	free(w->name);
 	free(w);
@@ -2431,25 +2428,6 @@ window_pane_update_used_data(struct window_pane *wp,
 	wpo->used += size;
 }
 
-void
-window_set_fill_character(struct window *w)
-{
-	const char		*value;
-	struct utf8_data	*ud;
-
-	free(w->fill_character);
-	w->fill_character = NULL;
-
-	value = options_get_string(w->options, "fill-character");
-	if (*value != '\0' && utf8_isvalid(value)) {
-		ud = utf8_fromcstr(value);
-		if (ud != NULL && ud[0].width == 1)
-			w->fill_character = ud;
-		else
-			free(ud);
-	}
-}
-
 void
 window_pane_default_cursor(struct window_pane *wp)
 {