From 68e04907de6a13933805d3437872bd859f4ce6c1 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 6 Feb 2017 19:45:23 +0000
Subject: [PATCH] Do not go through the whole attributes setting process if the
 new cell is the same as the previous one.

---
 tmux.h |  3 +++
 tty.c  | 29 +++++++++++++++++++++++------
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/tmux.h b/tmux.h
index 4009a44f..f310a37a 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1054,6 +1054,9 @@ struct tty {
 
 	struct grid_cell cell;
 
+	int              last_wp;
+	struct grid_cell last_cell;
+
 #define TTY_NOCURSOR 0x1
 #define TTY_FREEZE 0x2
 #define TTY_TIMER 0x4
diff --git a/tty.c b/tty.c
index 7ecf2a2d..c1769d14 100644
--- a/tty.c
+++ b/tty.c
@@ -246,6 +246,9 @@ tty_start_tty(struct tty *tty)
 	tty_putcode(tty, TTYC_SGR0);
 	memcpy(&tty->cell, &grid_default_cell, sizeof tty->cell);
 
+	memcpy(&tty->last_cell, &grid_default_cell, sizeof tty->last_cell);
+	tty->last_wp = -1;
+
 	tty_putcode(tty, TTYC_RMKX);
 	if (tty_use_acs(tty))
 		tty_putcode(tty, TTYC_ENACS);
@@ -1250,13 +1253,15 @@ tty_reset(struct tty *tty)
 {
 	struct grid_cell	*gc = &tty->cell;
 
-	if (grid_cells_equal(gc, &grid_default_cell))
-		return;
+	if (!grid_cells_equal(gc, &grid_default_cell)) {
+		if ((gc->attr & GRID_ATTR_CHARSET) && tty_use_acs(tty))
+			tty_putcode(tty, TTYC_RMACS);
+		tty_putcode(tty, TTYC_SGR0);
+		memcpy(gc, &grid_default_cell, sizeof *gc);
+	}
 
-	if ((gc->attr & GRID_ATTR_CHARSET) && tty_use_acs(tty))
-		tty_putcode(tty, TTYC_RMACS);
-	tty_putcode(tty, TTYC_SGR0);
-	memcpy(gc, &grid_default_cell, sizeof *gc);
+	memcpy(&tty->last_cell, &grid_default_cell, sizeof tty->last_cell);
+	tty->last_wp = -1;
 }
 
 /* Turn off margin. */
@@ -1478,6 +1483,18 @@ tty_attributes(struct tty *tty, const struct grid_cell *gc,
 	struct grid_cell	*tc = &tty->cell, gc2;
 	u_char			 changed;
 
+	/* Ignore cell if it is the same as the last one. */
+	if (wp != NULL &&
+	    (int)wp->id == tty->last_wp &&
+	    ~(wp->window->flags & WINDOW_STYLECHANGED) &&
+	    gc->attr == tty->last_cell.attr &&
+	    gc->fg == tty->last_cell.fg &&
+	    gc->bg == tty->last_cell.bg)
+		return;
+	tty->last_wp = (wp != NULL ? (int)wp->id : -1);
+	memcpy(&tty->last_cell, gc, sizeof tty->last_cell);
+
+	/* Copy cell and update default colours. */
 	memcpy(&gc2, gc, sizeof gc2);
 	if (wp != NULL)
 		tty_default_colours(&gc2, wp);