When a redraw is deferred because the terminal hasn't finished reading

the data from the last one, other panes could update while waiting, so
we set the flag to redraw them all when the new redraw actually
happened. But this means a lot of redrawing panes unnecessarily if they
haven't changed - so instead set a flag to say "at least one pane needs
to be redrawed" then look at the invidual pane flags to see which ones
need it.

screen-redraw.c

@@ -438,17 +438,24 @@ screen_redraw_screen(struct client *c)
 	tty_sync_start(&c->tty);
 
 	if (flags & (CLIENT_REDRAWWINDOW|CLIENT_REDRAWBORDERS)) {
+		log_debug("%s: redrawing borders", c->name);
 		if (ctx.pane_status != PANE_STATUS_OFF)
 			screen_redraw_draw_pane_status(&ctx);
 		screen_redraw_draw_borders(&ctx);
 	}
-	if (flags & CLIENT_REDRAWWINDOW)
+	if (flags & CLIENT_REDRAWWINDOW) {
+		log_debug("%s: redrawing panes", c->name);
 		screen_redraw_draw_panes(&ctx);
+	}
 	if (ctx.statuslines != 0 &&
-	    (flags & (CLIENT_REDRAWSTATUS|CLIENT_REDRAWSTATUSALWAYS)))
+	    (flags & (CLIENT_REDRAWSTATUS|CLIENT_REDRAWSTATUSALWAYS))) {
+		log_debug("%s: redrawing status", c->name);
 		screen_redraw_draw_status(&ctx);
-	if (c->overlay_draw != NULL && (flags & CLIENT_REDRAWOVERLAY))
+	}
+	if (c->overlay_draw != NULL && (flags & CLIENT_REDRAWOVERLAY)) {
+		log_debug("%s: redrawing overlay", c->name);
 		c->overlay_draw(c, &ctx);
+	}
 
 	tty_reset(&c->tty);
 	tty_sync_end(&c->tty);

server-client.c

@@ -1681,7 +1681,7 @@ server_client_check_redraw(struct client *c)
 	struct session		*s = c->session;
 	struct tty		*tty = &c->tty;
 	struct window_pane	*wp;
-	int			 needed, flags, mode = tty->mode;
+	int			 needed, flags, mode = tty->mode, new_flags = 0;
 	struct timeval		 tv = { .tv_usec = 1000 };
 	static struct event	 ev;
 	size_t			 left;
@@ -1689,11 +1689,12 @@ server_client_check_redraw(struct client *c)
 	if (c->flags & (CLIENT_CONTROL|CLIENT_SUSPENDED))
 		return;
 	if (c->flags & CLIENT_ALLREDRAWFLAGS) {
-		log_debug("%s: redraw%s%s%s%s", c->name,
+		log_debug("%s: redraw%s%s%s%s%s", c->name,
 		    (c->flags & CLIENT_REDRAWWINDOW) ? " window" : "",
 		    (c->flags & CLIENT_REDRAWSTATUS) ? " status" : "",
 		    (c->flags & CLIENT_REDRAWBORDERS) ? " borders" : "",
-		    (c->flags & CLIENT_REDRAWOVERLAY) ? " overlay" : "");
+		    (c->flags & CLIENT_REDRAWOVERLAY) ? " overlay" : "",
+		    (c->flags & CLIENT_REDRAWPANES) ? " panes" : "");
 	}
 
 	/*
@@ -1711,6 +1712,8 @@ server_client_check_redraw(struct client *c)
 				break;
 			}
 		}
+		if (needed)
+			new_flags |= CLIENT_REDRAWPANES;
 	}
 	if (needed && (left = EVBUFFER_LENGTH(tty->out)) != 0) {
 		log_debug("%s: redraw deferred (%zu left)", c->name, left);
@@ -1720,12 +1723,7 @@ server_client_check_redraw(struct client *c)
 			log_debug("redraw timer started");
 			evtimer_add(&ev, &tv);
 		}
-
+		c->flags |= new_flags;
-		/*
-		 * We may have got here for a single pane redraw, but force a
-		 * full redraw next time in case other panes have been updated.
-		 */
-		c->flags |= CLIENT_ALLREDRAWFLAGS;
 		return;
 	} else if (needed)
 		log_debug("%s: redraw needed", c->name);
@@ -1741,10 +1739,12 @@ server_client_check_redraw(struct client *c)
 		 */
 		TAILQ_FOREACH(wp, &c->session->curw->window->panes, entry) {
 			if (wp->flags & PANE_REDRAW) {
+				log_debug("%s: redrawing pane %%%u", __func__, wp->id);
 				tty_update_mode(tty, tty->mode, NULL);
 				screen_redraw_pane(c, wp);
 			}
 		}
+		c->flags &= ~CLIENT_REDRAWPANES;
 	}
 
 	if (c->flags & CLIENT_ALLREDRAWFLAGS) {

tmux.h

@@ -1244,6 +1244,7 @@ struct tty {
 #define TTY_BLOCK 0x80
 #define TTY_HAVEDA 0x100
 #define TTY_HAVEDSR 0x200
+#define TTY_SYNCING 0x400
 	int		 flags;
 
 	struct tty_term	*term;
@@ -1538,12 +1539,14 @@ struct client {
 #define CLIENT_CONTROL_NOOUTPUT 0x4000000
 #define CLIENT_DEFAULTSOCKET 0x8000000
 #define CLIENT_STARTSERVER 0x10000000
+#define CLIENT_REDRAWPANES 0x20000000
 #define CLIENT_ALLREDRAWFLAGS		\
 	(CLIENT_REDRAWWINDOW|		\
 	 CLIENT_REDRAWSTATUS|		\
 	 CLIENT_REDRAWSTATUSALWAYS|	\
 	 CLIENT_REDRAWBORDERS|		\
-	 CLIENT_REDRAWOVERLAY)
+	 CLIENT_REDRAWOVERLAY|		\
+	 CLIENT_REDRAWPANES)
 #define CLIENT_UNATTACHEDFLAGS	\
 	(CLIENT_DEAD|		\
 	 CLIENT_SUSPENDED|	\

tty.c

@@ -1438,15 +1438,19 @@ tty_draw_line(struct tty *tty, struct window_pane *wp, struct screen *s,
 void
 tty_sync_start(struct tty *tty)
 {
-	if (tty_get_flags(tty) & TERM_SYNC)
+	if ((~tty->flags & TTY_SYNCING) && (tty_get_flags(tty) & TERM_SYNC)) {
 		tty_puts(tty, "\033P=1s\033\\");
+		tty->flags |= TTY_SYNCING;
+	}
 }
 
 void
 tty_sync_end(struct tty *tty)
 {
-	if (tty_get_flags(tty) & TERM_SYNC)
+	if (tty_get_flags(tty) & TERM_SYNC) {
 		tty_puts(tty, "\033P=2s\033\\");
+		tty->flags &= ~TTY_SYNCING;
+	}
 }
 
 static int
@@ -1480,6 +1484,14 @@ tty_write(void (*cmdfn)(struct tty *, const struct tty_ctx *),
 	TAILQ_FOREACH(c, &clients, entry) {
 		if (!tty_client_ready(c, wp))
 			continue;
+		if (c->flags & CLIENT_REDRAWPANES) {
+			/*
+			 * Redraw is already deferred to redraw another pane -
+			 * redraw this one also when that happens.
+			 */
+			wp->flags |= PANE_REDRAW;
+			break;
+		}
 
 		ctx->bigger = tty_window_offset(&c->tty, &ctx->ox, &ctx->oy,
 		    &ctx->sx, &ctx->sy);