vte: implement backspace control

Add new helper to console subsystem which performs a backspace
operation. We must take care of auto-wrap mode so we cannot simply use
the *_move_left() function.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>

src/console.c

@@ -289,6 +289,21 @@ void kmscon_console_newline(struct kmscon_console *con)
 	}
 }
 
+void kmscon_console_backspace(struct kmscon_console *con)
+{
+	if (!con)
+		return;
+
+	if (con->cursor_x >= con->cells_x) {
+		con->cursor_x = con->cells_x - 2;
+	} else if (con->cursor_x > 0) {
+		con->cursor_x--;
+	} else if (con->auto_wrap) {
+		con->cursor_x = con->cells_x - 1;
+		kmscon_console_move_up(con, 1, true);
+	}
+}
+
 void kmscon_console_move_to(struct kmscon_console *con, unsigned int x,
 							unsigned int y)
 {

src/console.h

@@ -91,6 +91,7 @@ void kmscon_console_map(struct kmscon_console *con);
 
 void kmscon_console_write(struct kmscon_console *con, kmscon_symbol_t ch);
 void kmscon_console_newline(struct kmscon_console *con);
+void kmscon_console_backspace(struct kmscon_console *con);
 void kmscon_console_move_to(struct kmscon_console *con, unsigned int x,
 							unsigned int y);
 void kmscon_console_move_up(struct kmscon_console *con, unsigned int num,

src/vte.c

@@ -152,6 +152,7 @@ static void parse_control(struct kmscon_vte *vte, uint32_t ctrl)
 			break;
 		case 0x08: /* BS */
 			/* Move cursor one position left */
+			kmscon_console_backspace(vte->con);
 			break;
 		case 0x09: /* HT */
 			/* Move to next tab stop or end of line */