From 7f626c89595abd5dae6716d6b6e21ea96e22a856 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Fri, 12 May 2017 11:13:43 +0000
Subject: [PATCH] Can use INDN to clear regions with default background colour
 if margins are supported.

---
 tty.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/tty.c b/tty.c
index e182be22..720eb417 100644
--- a/tty.c
+++ b/tty.c
@@ -808,6 +808,7 @@ tty_clear_area(struct tty *tty, const struct window_pane *wp, u_int py,
 
 	/* If genuine BCE is available, can try escape sequences. */
 	if (!tty_fake_bce(tty, wp, bg)) {
+		/* Use ED if clearing off the bottom of the terminal. */
 		if (px == 0 &&
 		    px + nx >= tty->sx &&
 		    py + ny >= tty->sy &&
@@ -818,8 +819,9 @@ tty_clear_area(struct tty *tty, const struct window_pane *wp, u_int py,
 		}
 
 		/*
-		 * If we're setting a background colour (so it is not default),
-		 * we can use DECFRA.
+		 * On VT420 compatible terminals we can use DECFRA if the
+		 * background colour isn't default (because it doesn't work
+		 * after SGR 0).
 		 */
 		if (tty->term_type == TTY_VT420 && bg != 8) {
 			xsnprintf(tmp, sizeof tmp, "\033[32;%u;%u;%u;%u$x",
@@ -827,6 +829,17 @@ tty_clear_area(struct tty *tty, const struct window_pane *wp, u_int py,
 			tty_puts(tty, tmp);
 			return;
 		}
+
+		/*
+		 * If margins are supported, can just scroll the area off to
+		 * clear it.
+		 */
+		if (tty_use_margin(tty) && tty_term_has(tty->term, TTYC_INDN)) {
+			tty_region(tty, py, py + ny - 1);
+			tty_margin(tty, px, px + nx - 1);
+			tty_putcode1(tty, TTYC_INDN, ny);
+			return;
+		}
 	}
 
 	/* Couldn't use an escape sequence, loop over the lines. */