Add an option to set the character used for unused areas of the

terminal, GitHub issue 3110.

options-table.c

@@ -882,6 +882,13 @@ const struct options_table_entry options_table[] = {
 	  .text = "Style of the marked line in copy mode."
 	},
 
+	{ .name = "fill-character",
+	  .type = OPTIONS_TABLE_STRING,
+	  .scope = OPTIONS_TABLE_WINDOW,
+	  .default_str = "",
+	  .text = "Character used to fill unused parts of window."
+	},
+
 	{ .name = "main-pane-height",
 	  .type = OPTIONS_TABLE_STRING,
 	  .scope = OPTIONS_TABLE_WINDOW,

options.c

@@ -1108,6 +1108,8 @@ options_push_changes(const char *name)
 	struct window_pane	*wp;
 	int			 c;
 
+	log_debug("%s: %s", __func__, name);
+
 	if (strcmp(name, "automatic-rename") == 0) {
 		RB_FOREACH(w, windows, &windows) {
 			if (w->active == NULL)
@@ -1130,6 +1132,10 @@ options_push_changes(const char *name)
 			    &wp->screen->default_mode);
 		}
 	}
+	if (strcmp(name, "fill-character") == 0) {
+		RB_FOREACH(w, windows, &windows)
+			window_set_fill_character(w);
+	}
 	if (strcmp(name, "key-table") == 0) {
 		TAILQ_FOREACH(loop, &clients, entry)
 			server_client_set_key_table(loop, NULL);

screen-redraw.c

@@ -47,11 +47,16 @@ enum screen_redraw_border_type {
 
 /* Get cell border character. */
 static void
-screen_redraw_border_set(struct window_pane *wp, enum pane_lines pane_lines,
-    int cell_type, struct grid_cell *gc)
+screen_redraw_border_set(struct window *w, struct window_pane *wp,
+    enum pane_lines pane_lines, int cell_type, struct grid_cell *gc)
 {
 	u_int	idx;
 
+	if (cell_type == CELL_OUTSIDE && w->fill_character != NULL) {
+		utf8_copy(&gc->data, &w->fill_character[0]);
+		return;
+	}
+
 	switch (pane_lines) {
 	case PANE_LINES_NUMBER:
 		if (cell_type == CELL_OUTSIDE) {
@@ -409,7 +414,7 @@ screen_redraw_make_pane_status(struct client *c, struct window_pane *wp,
 		else
 			py = wp->yoff + wp->sy;
 		cell_type = screen_redraw_type_of_cell(c, px, py, pane_status);
-		screen_redraw_border_set(wp, pane_lines, cell_type, &gc);
+		screen_redraw_border_set(w, wp, pane_lines, cell_type, &gc);
 		screen_write_cell(&ctx, &gc);
 	}
 	gc.attr &= ~GRID_ATTR_CHARSET;
@@ -690,7 +695,7 @@ screen_redraw_draw_borders_cell(struct screen_redraw_ctx *ctx, u_int i, u_int j)
 		    screen_redraw_check_is(x, y, pane_status, marked_pane.wp))
 			gc.attr ^= GRID_ATTR_REVERSE;
 	}
-	screen_redraw_border_set(wp, ctx->pane_lines, cell_type, &gc);
+	screen_redraw_border_set(w, wp, ctx->pane_lines, cell_type, &gc);
 
 	if (cell_type == CELL_TOPBOTTOM &&
 	    (c->flags & CLIENT_UTF8) &&

tmux.1

@@ -4114,6 +4114,9 @@ Set clock colour.
 .Xc
 Set clock hour format.
 .Pp
+.It Ic fill-character Ar character
+Set the character used to fill areas of the terminal unused by a window.
+.Pp
 .It Ic main-pane-height Ar height
 .It Ic main-pane-width Ar width
 Set the width or height of the main (left or top) pane in the

tmux.h

@@ -1102,6 +1102,7 @@ struct window {
 	u_int			 new_xpixel;
 	u_int			 new_ypixel;
 
+	struct utf8_data	*fill_character;
 	int			 flags;
 #define WINDOW_BELL 0x1
 #define WINDOW_ACTIVITY 0x2
@@ -2976,6 +2977,7 @@ 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 *);
 
 /* layout.c */
 u_int		 layout_count_cells(struct layout_cell *);

window.c

@@ -331,6 +331,7 @@ 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);
 	window_update_activity(w);
 
 	log_debug("%s: @%u create %ux%u (%ux%u)", __func__, w->id, sx, sy,
@@ -362,6 +363,7 @@ window_destroy(struct window *w)
 		event_del(&w->offset_timer);
 
 	options_free(w->options);
+	free(w->fill_character);
 
 	free(w->name);
 	free(w);
@@ -1589,3 +1591,20 @@ window_pane_update_used_data(struct window_pane *wp,
 		size = EVBUFFER_LENGTH(wp->event->input) - used;
 	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;
+	}
+}