From 5be2c53d8c9e268d55ff1c63070ad2fcc343a8bb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Thu, 8 Apr 2021 12:58:47 +0200
Subject: [PATCH] =?UTF-8?q?term/vt:=20only=20do=20reverse-wrapping=20(?=
 =?UTF-8?q?=E2=80=98bw=E2=80=99)=20on=20cub1?=
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Foot currently does reverse-wrapping (‘auto_left_margin’, or ’bw’) on
everything that calls ‘term_cursor_left()’. This is wrong; it should
only be done for cub1. From man terminfo:

    auto_left_margin | bw | bw | cub1 wraps from column 0 to last
    column

This patch moves the reverse-wrapping logic from term_cursor_left() to
the handling of BS (backspace).

Closes #441
---
 terminal.c | 41 +++--------------------------------------
 vt.c       | 17 +++++++++++++++--
 2 files changed, 18 insertions(+), 40 deletions(-)

diff --git a/terminal.c b/terminal.c
index c05eb84e..e55230b4 100644
--- a/terminal.c
+++ b/terminal.c
@@ -1988,44 +1988,9 @@ term_cursor_home(struct terminal *term)
 void
 term_cursor_left(struct terminal *term, int count)
 {
-    xassert(count >= 0);
-    int new_col = term->grid->cursor.point.col - count;
-
-    /* Reverse wrap */
-    if (unlikely(new_col < 0)) {
-        if (likely(term->reverse_wrap && term->auto_margin)) {
-
-            /* Number of rows to reverse wrap through */
-            int row_count = (abs(new_col) - 1) / term->cols + 1;
-
-            /* Row number cursor will end up on */
-            int new_row_no = term->grid->cursor.point.row - row_count;
-
-            /* New column number */
-            new_col = term->cols - ((abs(new_col) - 1) % term->cols + 1);
-            xassert(new_col >= 0 && new_col < term->cols);
-
-            /* Don't back up past the scroll region */
-            /* TODO: should this be allowed? */
-            if (new_row_no < term->scroll_region.start) {
-                new_row_no = term->scroll_region.start;
-                new_col = 0;
-            }
-
-            struct row *new_row = grid_row(term->grid, new_row_no);
-            term->grid->cursor.point.col = new_col;
-            term->grid->cursor.point.row = new_row_no;
-            term->grid->cursor.lcf = false;
-            term->grid->cur_row = new_row;
-            return;
-        }
-
-        /* Reverse wrap disabled - don't let cursor move past first column */
-        new_col = 0;
-    }
-
-    xassert(new_col >= 0);
-    term->grid->cursor.point.col = new_col;
+    int move_amount = min(term->grid->cursor.point.col, count);
+    term->grid->cursor.point.col -= move_amount;
+    xassert(term->grid->cursor.point.col >= 0);
     term->grid->cursor.lcf = false;
 }
 
diff --git a/vt.c b/vt.c
index af4691ea..d3523efd 100644
--- a/vt.c
+++ b/vt.c
@@ -142,8 +142,21 @@ action_execute(struct terminal *term, uint8_t c)
 #else
         if (term->grid->cursor.lcf)
             term->grid->cursor.lcf = false;
-        else
-            term_cursor_left(term, 1);
+        else {
+            /* Reverse wrap */
+            if (unlikely(term->grid->cursor.point.col == 0) &&
+                likely(term->reverse_wrap && term->auto_margin))
+            {
+                if (term->grid->cursor.point.row <= term->scroll_region.start) {
+                    /* Don’t wrap past, or inside, the scrolling region(?) */
+                } else
+                    term_cursor_to(
+                        term,
+                        term->grid->cursor.point.row - 1,
+                        term->cols - 1);
+            } else
+                term_cursor_left(term, 1);
+        }
 #endif
         break;