From 907f58cc3c2c76184dfd06129902b2147a2e4c5b Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Fri, 10 Feb 2023 14:01:43 +0000
Subject: Fix cursor position after zero width space, GitHub issue 3469.

---
 screen-write.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

(limited to 'screen-write.c')

diff --git a/screen-write.c b/screen-write.c
index 59d289ec..b82a43dc 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -34,7 +34,7 @@ static void	screen_write_collect_flush(struct screen_write_ctx *, int,
 static int	screen_write_overwrite(struct screen_write_ctx *,
 		    struct grid_cell *, u_int);
 static const struct grid_cell *screen_write_combine(struct screen_write_ctx *,
-		    const struct utf8_data *, u_int *);
+		    const struct utf8_data *, u_int *, u_int *);
 
 struct screen_write_citem {
 	u_int				x;
@@ -1820,7 +1820,7 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 	struct grid_cell 	 tmp_gc, now_gc;
 	struct tty_ctx		 ttyctx;
 	u_int			 sx = screen_size_x(s), sy = screen_size_y(s);
-	u_int		 	 width = gc->data.width, xx, last, cy;
+	u_int		 	 width = gc->data.width, xx, last, cx, cy;
 	int			 selected, skip = 1;
 
 	/* Ignore padding cells. */
@@ -1847,18 +1847,18 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 	 */
 	if (ctx->flags & SCREEN_WRITE_ZWJ) {
 		screen_write_collect_flush(ctx, 0, __func__);
-		screen_write_combine(ctx, &zwj, &xx);
+		screen_write_combine(ctx, &zwj, &xx, &cx);
 	}
 	if (width == 0 || (ctx->flags & SCREEN_WRITE_ZWJ)) {
 		ctx->flags &= ~SCREEN_WRITE_ZWJ;
 		screen_write_collect_flush(ctx, 0, __func__);
-		if ((gc = screen_write_combine(ctx, ud, &xx)) != NULL) {
+		if ((gc = screen_write_combine(ctx, ud, &xx, &cx)) != NULL) {
 			cy = s->cy;
 			screen_write_set_cursor(ctx, xx, s->cy);
 			screen_write_initctx(ctx, &ttyctx, 0);
 			ttyctx.cell = gc;
 			tty_write(tty_cmd_cell, &ttyctx);
-			s->cx = xx + 1 + gc->data.width; s->cy = cy;
+			s->cx = cx; s->cy = cy;
 		}
 		return;
 	}
@@ -1980,16 +1980,19 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 /* Combine a UTF-8 zero-width character onto the previous. */
 static const struct grid_cell *
 screen_write_combine(struct screen_write_ctx *ctx, const struct utf8_data *ud,
-    u_int *xx)
+    u_int *xx, u_int *cx)
 {
 	struct screen		*s = ctx->s;
 	struct grid		*gd = s->grid;
 	static struct grid_cell	 gc;
-	u_int			 n;
+	u_int			 n, width;
 
 	/* Can't combine if at 0. */
-	if (s->cx == 0)
+	if (s->cx == 0) {
+		*xx = 0;
 		return (NULL);
+	}
+	*xx = s->cx;
 
 	/* Empty data is out. */
 	if (ud->size == 0)
@@ -2003,30 +2006,35 @@ screen_write_combine(struct screen_write_ctx *ctx, const struct utf8_data *ud,
 	}
 	if (n > s->cx)
 		return (NULL);
-	*xx = s->cx - n;
 
 	/* Check there is enough space. */
 	if (gc.data.size + ud->size > sizeof gc.data.data)
 		return (NULL);
+	(*xx) -= n;
 
-	log_debug("%s: %.*s onto %.*s at %u,%u", __func__, (int)ud->size,
-	    ud->data, (int)gc.data.size, gc.data.data, *xx, s->cy);
+	log_debug("%s: %.*s onto %.*s at %u,%u (width %u)", __func__,
+	    (int)ud->size, ud->data, (int)gc.data.size, gc.data.data, *xx,
+	    s->cy, gc.data.width);
 
 	/* Append the data. */
 	memcpy(gc.data.data + gc.data.size, ud->data, ud->size);
 	gc.data.size += ud->size;
+	width = gc.data.width;
 
 	/* If this is U+FE0F VARIATION SELECTOR-16, force the width to 2. */
 	if (gc.data.width == 1 &&
-		ud->size == 3 &&
-		memcmp(ud->data, "\357\270\217", 3) == 0) {
+	    ud->size == 3 &&
+	    memcmp(ud->data, "\357\270\217", 3) == 0) {
 		grid_view_set_padding(gd, (*xx) + 1, s->cy);
 		gc.data.width = 2;
+		width += 2;
 	}
 
 	/* Set the new cell. */
 	grid_view_set_cell(gd, *xx, s->cy, &gc);
 
+	*cx = (*xx) + width;
+	log_debug("%s: character at %u; cursor at %u", __func__, *xx, *cx);
 	return (&gc);
 }
 
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