Add support for scroll up escape sequence (CSI S) and use it when

possible instead of sending individual line feeds.

input.c

@@ -222,6 +222,7 @@ enum input_csi_type {
 	INPUT_CSI_SGR,
 	INPUT_CSI_SM,
 	INPUT_CSI_SM_PRIVATE,
+	INPUT_CSI_SU,
 	INPUT_CSI_TBC,
 	INPUT_CSI_VPA,
 	INPUT_CSI_WINOPS,
@@ -243,6 +244,7 @@ static const struct input_table_entry input_csi_table[] = {
 	{ 'L', "",  INPUT_CSI_IL },
 	{ 'M', "",  INPUT_CSI_DL },
 	{ 'P', "",  INPUT_CSI_DCH },
+	{ 'S', "",  INPUT_CSI_SU },
 	{ 'X', "",  INPUT_CSI_ECH },
 	{ 'Z', "",  INPUT_CSI_CBT },
 	{ 'c', "",  INPUT_CSI_DA },
@@ -1413,6 +1415,9 @@ input_csi_dispatch(struct input_ctx *ictx)
 	case INPUT_CSI_SM_PRIVATE:
 		input_csi_dispatch_sm_private(ictx);
 		break;
+	case INPUT_CSI_SU:
+		screen_write_scrollup(sctx, input_get(ictx, 0, 1, 1));
+		break;
 	case INPUT_CSI_TBC:
 		switch (input_get(ictx, 0, 0, 0)) {
 		case 0:

screen-write.c

@@ -839,6 +839,8 @@ screen_write_scrollregion(struct screen_write_ctx *ctx, u_int rupper,
 	if (rupper >= rlower)	/* cannot be one line */
 		return;
 
+	screen_write_collect_flush(ctx);
+
 	/* Cursor moves to top-left. */
 	s->cx = 0;
 	s->cy = 0;
@@ -854,7 +856,6 @@ screen_write_linefeed(struct screen_write_ctx *ctx, int wrapped)
 	struct screen		*s = ctx->s;
 	struct grid		*gd = s->grid;
 	struct grid_line	*gl;
-	struct tty_ctx		 ttyctx;
 
 	gl = &gd->linedata[gd->hsize + s->cy];
 	if (wrapped)
@@ -864,14 +865,32 @@ screen_write_linefeed(struct screen_write_ctx *ctx, int wrapped)
 
 	if (s->cy == s->rlower) {
 		grid_view_scroll_region_up(gd, s->rupper, s->rlower);
-
 		screen_write_collect_scroll(ctx);
-		screen_write_initctx(ctx, &ttyctx);
-		tty_write(tty_cmd_linefeed, &ttyctx);
+		ctx->scrolled++;
 	} else if (s->cy < screen_size_y(s) - 1)
 		s->cy++;
 }
 
+/* Scroll up. */
+void
+screen_write_scrollup(struct screen_write_ctx *ctx, u_int lines)
+{
+	struct screen	*s = ctx->s;
+	struct grid	*gd = s->grid;
+	u_int		 i;
+
+	if (lines == 0)
+		lines = 1;
+	else if (lines > s->rlower - s->rupper + 1)
+		lines = s->rlower - s->rupper + 1;
+
+	for (i = 0; i < lines; i++) {
+		grid_view_scroll_region_up(gd, s->rupper, s->rlower);
+		screen_write_collect_scroll(ctx);
+	}
+	ctx->scrolled += lines;
+}
+
 /* Carriage return (cursor to start of line). */
 void
 screen_write_carriagereturn(struct screen_write_ctx *ctx)
@@ -1009,6 +1028,18 @@ screen_write_collect_flush(struct screen_write_ctx *ctx)
 	u_int					 y, cx, cy;
 	struct tty_ctx				 ttyctx;
 
+	if (ctx->scrolled != 0) {
+		log_debug("%s: scrolled %u (region %u-%u)", __func__,
+		    ctx->scrolled, s->rupper, s->rlower);
+		if (ctx->scrolled > s->rlower - s->rupper + 1)
+			ctx->scrolled = s->rlower - s->rupper + 1;
+
+		screen_write_initctx(ctx, &ttyctx);
+		ttyctx.num = ctx->scrolled;
+		tty_write(tty_cmd_scrollup, &ttyctx);
+	}
+	ctx->scrolled = 0;
+
 	cx = s->cx; cy = s->cy;
 	for (y = 0; y < screen_size_y(s); y++) {
 		TAILQ_FOREACH_SAFE(ci, &ctx->list[y].items, entry, tmp) {

tmux.h

@@ -241,6 +241,7 @@ enum tty_code_code {
 	TTYC_ICH1,	/* insert_character, ic */
 	TTYC_IL,	/* parm_insert_line, IL */
 	TTYC_IL1,	/* insert_line, il */
+	TTYC_INDN,      /* parm_index, indn */
 	TTYC_INVIS,	/* enter_secure_mode, mk */
 	TTYC_IS1,	/* init_1string, i1 */
 	TTYC_IS2,	/* init_2string, i2 */
@@ -663,6 +664,7 @@ struct screen_write_ctx {
 
 	struct screen_write_collect_item *item;
 	struct screen_write_collect_line *list;
+	u_int			 scrolled;
 
 	u_int			 cells;
 	u_int			 written;
@@ -1658,6 +1660,7 @@ void	tty_cmd_erasecharacter(struct tty *, const struct tty_ctx *);
 void	tty_cmd_insertcharacter(struct tty *, const struct tty_ctx *);
 void	tty_cmd_insertline(struct tty *, const struct tty_ctx *);
 void	tty_cmd_linefeed(struct tty *, const struct tty_ctx *);
+void	tty_cmd_scrollup(struct tty *, const struct tty_ctx *);
 void	tty_cmd_reverseindex(struct tty *, const struct tty_ctx *);
 void	tty_cmd_setselection(struct tty *, const struct tty_ctx *);
 void	tty_cmd_rawstring(struct tty *, const struct tty_ctx *);
@@ -1984,6 +1987,7 @@ void	 screen_write_cursormove(struct screen_write_ctx *, u_int, u_int);
 void	 screen_write_reverseindex(struct screen_write_ctx *);
 void	 screen_write_scrollregion(struct screen_write_ctx *, u_int, u_int);
 void	 screen_write_linefeed(struct screen_write_ctx *, int);
+void	 screen_write_scrollup(struct screen_write_ctx *, u_int);
 void	 screen_write_carriagereturn(struct screen_write_ctx *);
 void	 screen_write_clearendofscreen(struct screen_write_ctx *, u_int);
 void	 screen_write_clearstartofscreen(struct screen_write_ctx *, u_int);

tty-term.c

@@ -95,6 +95,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_ICH1] = { TTYCODE_STRING, "ich1" },
 	[TTYC_IL] = { TTYCODE_STRING, "il" },
 	[TTYC_IL1] = { TTYCODE_STRING, "il1" },
+	[TTYC_INDN] = { TTYCODE_STRING, "indn" },
 	[TTYC_INVIS] = { TTYCODE_STRING, "invis" },
 	[TTYC_IS1] = { TTYCODE_STRING, "is1" },
 	[TTYC_IS2] = { TTYCODE_STRING, "is2" },

tty.c

@@ -1021,6 +1021,32 @@ tty_cmd_linefeed(struct tty *tty, const struct tty_ctx *ctx)
 	tty_putc(tty, '\n');
 }
 
+void
+tty_cmd_scrollup(struct tty *tty, const struct tty_ctx *ctx)
+{
+	struct window_pane	*wp = ctx->wp;
+	u_int			 i;
+
+	if ((!tty_pane_full_width(tty, ctx) && !tty_use_margin(tty)) ||
+	    tty_fake_bce(tty, wp, ctx->bg) ||
+	    !tty_term_has(tty->term, TTYC_CSR)) {
+		tty_redraw_region(tty, ctx);
+		return;
+	}
+
+	tty_attributes(tty, &grid_default_cell, wp);
+
+	tty_region_pane(tty, ctx, ctx->orupper, ctx->orlower);
+	tty_margin_pane(tty, ctx);
+
+	if (ctx->num == 1 || !tty_term_has(tty->term, TTYC_INDN)) {
+		tty_cursor(tty, tty->rright, ctx->yoff + tty->rlower);
+		for (i = 0; i < ctx->num; i++)
+			tty_putc(tty, '\n');
+	} else
+		tty_putcode1(tty, TTYC_INDN, ctx->num);
+}
+
 void
 tty_cmd_clearendofscreen(struct tty *tty, const struct tty_ctx *ctx)
 {