From 97b5f22a7075e8a124b01309e7ba0e3ed7e910c1 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 15 Jun 2026 07:40:45 +0000
Subject: [PATCH] When redrawing a whole pane line, fall into tty_draw_line for
 any characters that are not plain ASCII. Fixes redraw issues with partial
 tabs and other wide characters when a pane is partly outside the window.

---
 screen-write.c | 62 +++++++++++++++++++++++++++++++++++++++-----------
 tmux.h         |  1 +
 tty.c          | 20 ++++++++++++++++
 3 files changed, 70 insertions(+), 13 deletions(-)

diff --git a/screen-write.c b/screen-write.c
index a5be7fe9..fbef8320 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -1127,6 +1127,25 @@ screen_write_backspace(struct screen_write_ctx *ctx)
 	screen_write_set_cursor(ctx, cx, cy);
 }
 
+/* Is this cell a single ASCII character? */
+static int
+screen_write_cell_is_single(const struct grid_cell *gc)
+{
+	if (gc->data.width != 1)
+		return (0);
+	if (gc->data.size != 1)
+		return (0);
+	if (*gc->data.data < 0x20 || *gc->data.data == 0x7f)
+		return (0);
+	if (gc->flags & GRID_FLAG_CLEARED)
+		return (0);
+	if (gc->flags & GRID_FLAG_PADDING)
+		return (0);
+	if (gc->flags & GRID_FLAG_TAB)
+		return (0);
+	return (1);
+}
+
 /* Redraw all visible cells on a line. */
 static void
 screen_write_redraw_line(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx,
@@ -1135,11 +1154,14 @@ screen_write_redraw_line(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx,
 	struct window_pane	*wp = ctx->wp;
 	struct screen		*s = ctx->s;
 	struct grid_cell	 gc, ngc;
-	u_int			 sx = screen_size_x(s), cx, i, n;
+	u_int			 sx = screen_size_x(s), cx, i;
 	int			 xoff = wp->xoff, yoff = wp->yoff;
 	struct visible_ranges	*r;
 	struct visible_range	*ri;
 
+	if (s->mode & MODE_SYNC)
+		return;
+
 	r = screen_redraw_get_visible_ranges(wp, xoff, yoff + yy, sx, NULL);
 	for (i = 0; i < r->used; i++) {
 		ri = &r->ranges[i];
@@ -1147,20 +1169,34 @@ screen_write_redraw_line(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx,
 			continue;
 
 		cx = ri->px - xoff;
-		for (n = 0; n < ri->nx && cx < sx; n++, cx++) {
-			grid_view_get_cell(s->grid, cx, yy, &gc);
-			if (~gc.flags & GRID_FLAG_SELECTED)
-				ttyctx->cell = &gc;
-			else {
-				screen_select_cell(s, &ngc, &gc);
-				ttyctx->cell = &ngc;
-			}
+		if (cx >= sx)
+			continue;
+		if (cx + ri->nx > sx)
+			ttyctx->n = sx - cx;
+		else
+			ttyctx->n = ri->nx;
+		if (ttyctx->n == 0)
+			continue;
+		ttyctx->ocx = cx;
+		ttyctx->ocy = yy;
 
-			ttyctx->ocx = cx;
-			ttyctx->ocy = yy;
-			if (~s->mode & MODE_SYNC)
-				tty_write(tty_cmd_cell, ttyctx);
+		if (ttyctx->n != 1) {
+			tty_write(tty_cmd_redrawline, ttyctx);
+			continue;
 		}
+
+		grid_view_get_cell(s->grid, cx, yy, &gc);
+		if (!screen_write_cell_is_single(&gc)) {
+			tty_write(tty_cmd_redrawline, ttyctx);
+			continue;
+		}
+		if (~gc.flags & GRID_FLAG_SELECTED)
+			ttyctx->cell = &gc;
+		else {
+			screen_select_cell(s, &ngc, &gc);
+			ttyctx->cell = &ngc;
+		}
+		tty_write(tty_cmd_cell, ttyctx);
 	}
 }
 
diff --git a/tmux.h b/tmux.h
index 20b3c228..5be1a809 100644
--- a/tmux.h
+++ b/tmux.h
@@ -2697,6 +2697,7 @@ void	tty_write(void (*)(struct tty *, const struct tty_ctx *),
 void	tty_cmd_alignmenttest(struct tty *, const struct tty_ctx *);
 void	tty_cmd_cell(struct tty *, const struct tty_ctx *);
 void	tty_cmd_cells(struct tty *, const struct tty_ctx *);
+void	tty_cmd_redrawline(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearendofline(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearendofscreen(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearline(struct tty *, const struct tty_ctx *);
diff --git a/tty.c b/tty.c
index ef4dcd25..bb7c0ae8 100644
--- a/tty.c
+++ b/tty.c
@@ -1430,6 +1430,26 @@ tty_draw_pane(struct tty *tty, const struct tty_ctx *ctx, u_int py)
 	}
 }
 
+void
+tty_cmd_redrawline(struct tty *tty, const struct tty_ctx *ctx)
+{
+	u_int			 i, x, rx, ry, j;
+	struct visible_ranges	*r;
+	struct visible_range	*rr;
+
+	if (tty_clamp_line(tty, ctx, ctx->ocx, ctx->ocy, ctx->n,
+	    &i, &x, &rx, &ry)) {
+		r = tty_check_overlay_range(tty, x, ry, rx);
+		for (j = 0; j < r->used; j++) {
+			rr = &r->ranges[j];
+			if (rr->nx == 0)
+				continue;
+			tty_draw_line(tty, ctx->s, i + rr->px - x,
+			    ctx->ocy, rr->nx, rr->px, ry, &ctx->style_ctx);
+		}
+	}
+}
+
 /* Check if character needs to be mapped for codeset. */
 const struct grid_cell *
 tty_check_codeset(struct tty *tty, const struct grid_cell *gc)