From 8608c6970d67d5dec37400bcb4fb6a0c46efc165 Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicm@openbsd.org>
Date: Mon, 12 Oct 2009 16:59:55 +0000
Subject: [PATCH] When backspace is received at the beginning of a line and the
 previous line was wrapped, move the cursor back up to the end of the previous
 line.

Another one of the forgotten persons requested this quite a while ago (I need
to start noting names on todo items...) when it was quite hard to
implement. Now it is easy and I don't see it can do any harm, so hey presto...
---
 input.c        |  2 +-
 screen-write.c | 20 ++++++++++++++++++++
 tmux.h         |  1 +
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/input.c b/input.c
index ba3d9223..d8737888 100644
--- a/input.c
+++ b/input.c
@@ -646,7 +646,7 @@ input_handle_c0_control(u_char ch, struct input_ctx *ictx)
 		ictx->wp->window->flags |= WINDOW_BELL;
 		break;
 	case '\010': 	/* BS */
-		screen_write_cursorleft(&ictx->ctx, 1);
+		screen_write_backspace(&ictx->ctx);
 		break;
 	case '\011': 	/* TAB */
 		/* Don't tab beyond the end of the line. */
diff --git a/screen-write.c b/screen-write.c
index 6b6aa400..2ce98dee 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -513,6 +513,25 @@ screen_write_cursorleft(struct screen_write_ctx *ctx, u_int nx)
 	s->cx -= nx;
 }
 
+/* Backspace; cursor left unless at start of wrapped line when can move up. */
+void
+screen_write_backspace(struct screen_write_ctx *ctx)
+{
+	struct screen		*s = ctx->s;
+	struct grid_line	*gl;
+
+	if (s->cx == 0) {
+		if (s->cy == 0)
+			return;
+		gl = &s->grid->linedata[s->grid->hsize + s->cy - 1];
+		if (gl->flags & GRID_LINE_WRAPPED) {
+			s->cy--;
+			s->cx = screen_size_x(s) - 1;
+		}
+	} else
+		s->cx--;
+}
+
 /* VT100 alignment test. */
 void
 screen_write_alignmenttest(struct screen_write_ctx *ctx)
@@ -536,6 +555,7 @@ screen_write_alignmenttest(struct screen_write_ctx *ctx)
 	s->cy = 0;
 
 	s->rupper = 0;
+
 	s->rlower = screen_size_y(s) - 1;
 
 	tty_write(tty_cmd_alignmenttest, &ttyctx);
diff --git a/tmux.h b/tmux.h
index 02f9bbd0..2d25c1de 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1646,6 +1646,7 @@ void	 screen_write_putc(
     	     struct screen_write_ctx *, struct grid_cell *, u_char);
 void	 screen_write_copy(struct screen_write_ctx *,
 	     struct screen *, u_int, u_int, u_int, u_int);
+void	 screen_write_backspace(struct screen_write_ctx *);
 void	 screen_write_cursorup(struct screen_write_ctx *, u_int);
 void	 screen_write_cursordown(struct screen_write_ctx *, u_int);
 void	 screen_write_cursorright(struct screen_write_ctx *, u_int);