From d78914317c0c6b55b655f49b55b445316670948f Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Wed, 14 Oct 2026 13:47:12 +0100
Subject: [PATCH] Track window scrolling for damage.

---
 screen-redraw.c | 34 ++++++++++++++++++++++++++++++++++
 tmux.h          |  8 ++++++++
 tty.c           |  8 ++++++++
 3 files changed, 50 insertions(+)

diff --git a/screen-redraw.c b/screen-redraw.c
index 77b81132a..122b14eb5 100644
--- a/screen-redraw.c
+++ b/screen-redraw.c
@@ -1111,6 +1111,7 @@ redraw_free_damage(struct window *w)
 		free(rd);
 	}
 	w->damage_count = 0;
+	w->scroll_pending = 0;
 }
 
 /* Collapse all pending damage for a window into one rectangle. */
@@ -1209,6 +1210,39 @@ redraw_damage_window(struct window *w, u_int x, u_int y, u_int sx, u_int sy)
 	redraw_apply_window_damage(w, x, y, sx, sy, 0);
 }
 
+/* Record damage caused by terminal scrolling. */
+void
+redraw_damage_scroll(struct window *w, u_int x, u_int y, u_int sx, u_int sy)
+{
+	if (!w->scroll_pending) {
+		w->scroll_generation++;
+		w->scroll_pending = 1;
+	}
+	redraw_apply_window_damage(w, x, y, sx, sy, REDRAW_DAMAGE_SCROLL);
+}
+
+/* Remember whether this client used terminal scrolling for the damage. */
+void
+redraw_scroll_result(struct tty *tty, const struct tty_ctx *ctx, int failed)
+{
+	struct window_pane	*wp = ctx->arg;
+	struct window		*w;
+
+	if (wp == NULL)
+		return;
+	w = wp->window;
+	if (!w->scroll_pending)
+		return;
+	if (tty->scroll_window != w ||
+	    tty->scroll_generation != w->scroll_generation) {
+		tty->scroll_window = w;
+		tty->scroll_generation = w->scroll_generation;
+		tty->scroll_failed = 0;
+	}
+	if (failed)
+		tty->scroll_failed = 1;
+}
+
 /* Mark all cached redraw scenes as out of date. */
 void
 redraw_invalidate_all_scenes(void)
diff --git a/tmux.h b/tmux.h
index 9962aef5f..0703af264 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1479,6 +1479,8 @@ struct window {
 
 	struct redraw_damages	 damage;
 	u_int			 damage_count;
+	uint64_t		 scroll_generation;
+	int			 scroll_pending;
 
 	struct menu_data	*menu;
 	u_int			 menu_last_px;
@@ -1854,6 +1856,10 @@ struct tty {
 	struct event	 key_timer;
 	struct tty_key	*key_tree;
 
+	struct window		*scroll_window;
+	uint64_t		 scroll_generation;
+	int			 scroll_failed;
+
 #ifdef ENABLE_IMAGES
 	struct image_backend	*image_backend;
 	void			*image_data;
@@ -3645,6 +3651,8 @@ int	 redraw_client_has_window(struct client *, struct window *);
 void	 redraw_invalidate_scene(struct window *);
 void	 redraw_invalidate_all_scenes(void);
 void	 redraw_damage_window(struct window *, u_int, u_int, u_int, u_int);
+void	 redraw_damage_scroll(struct window *, u_int, u_int, u_int, u_int);
+void	 redraw_scroll_result(struct tty *, const struct tty_ctx *, int);
 void	 redraw_free_damage(struct window *);
 void	 redraw_client_damage(struct client *);
 int	 redraw_get_status_border_cell_type(struct redraw_span **, u_int);
diff --git a/tty.c b/tty.c
index 233deb491..8f2566b04 100644
--- a/tty.c
+++ b/tty.c
@@ -1682,10 +1682,12 @@ tty_cmd_reverseindex(struct tty *tty, const struct tty_ctx *ctx)
 	    !tty_term_has(tty->term, TTYC_RIN)) ||
 	    ctx->sx == 1 ||
 	    ctx->sy == 1) {
+		redraw_scroll_result(tty, ctx, 1);
 		tty_redraw_region(tty, ctx);
 		return;
 	}
 
+	redraw_scroll_result(tty, ctx, 0);
 	tty_default_attributes(tty, ctx->bg, &ctx->style_ctx);
 
 	tty_region_pane(tty, ctx, ctx->orupper, ctx->orlower);
@@ -1710,10 +1712,12 @@ tty_cmd_linefeed(struct tty *tty, const struct tty_ctx *ctx)
 	    !tty_term_has(tty->term, TTYC_CSR) ||
 	    ctx->sx == 1 ||
 	    ctx->sy == 1) {
+		redraw_scroll_result(tty, ctx, 1);
 		tty_redraw_region(tty, ctx);
 		return;
 	}
 
+	redraw_scroll_result(tty, ctx, 0);
 	tty_default_attributes(tty, ctx->bg, &ctx->style_ctx);
 
 	tty_region_pane(tty, ctx, ctx->orupper, ctx->orlower);
@@ -1748,10 +1752,12 @@ tty_cmd_scrollup(struct tty *tty, const struct tty_ctx *ctx)
 	    !tty_term_has(tty->term, TTYC_CSR) ||
 	    ctx->sx == 1 ||
 	    ctx->sy == 1) {
+		redraw_scroll_result(tty, ctx, 1);
 		tty_redraw_region(tty, ctx);
 		return;
 	}
 
+	redraw_scroll_result(tty, ctx, 0);
 	tty_default_attributes(tty, ctx->bg, &ctx->style_ctx);
 
 	tty_region_pane(tty, ctx, ctx->orupper, ctx->orlower);
@@ -1786,10 +1792,12 @@ tty_cmd_scrolldown(struct tty *tty, const struct tty_ctx *ctx)
 	    !tty_term_has(tty->term, TTYC_RIN)) ||
 	    ctx->sx == 1 ||
 	    ctx->sy == 1) {
+		redraw_scroll_result(tty, ctx, 1);
 		tty_redraw_region(tty, ctx);
 		return;
 	}
 
+	redraw_scroll_result(tty, ctx, 0);
 	tty_default_attributes(tty, ctx->bg, &ctx->style_ctx);
 
 	tty_region_pane(tty, ctx, ctx->orupper, ctx->orlower);