[PATCH 4/5] tui: make updating of start_line in tui_puts more consistent

[Patrick Palka <patrick at parcs dot ath dot cx>]

The command window's start_line field is used by tui_redisplay_readline
to figure out on which window line to start redrawing the (possibly
multi-line) command line.  It differs from cur_line only when the length
of the line being outputted is longer than the width of the window.  In
this case, start_line will not equal to cur_line.  Instead, start_line
will be equal to cur_line - N where N is the number of times the current
line was wrapped around the width of the command window.  start_line
takes into consideration whether line wrapping has occurred, and
cur_line does not.

The function tui_puts however currently does not respect this property
of start_line.  After a call to tui_puts, start_line will always be
equal to cur_line even when the outputted line may have wrapped a few
times.  This patch makes tui_puts properly update start_line.  It must
only be updated if a newline is emitted, or if ncurses scrolls the
command window (thus shifting all the line numbers).

gdb/ChangeLog:

	* tui/tui-io.c (tui_puts): Fix the updating of start_line.
---
 gdb/tui/tui-io.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
index 5b9ca20..9302391 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -168,7 +168,12 @@ tui_puts (const char *string)
         }
       else if (tui_skip_line != 1)
         {
+	  int prev_line, prev_col;
+
           tui_skip_line = -1;
+
+	  getyx (w, prev_line, prev_col);
+
 	  /* Expand TABs, since ncurses on MS-Windows doesn't.  */
 	  if (c == '\t')
 	    {
@@ -183,14 +188,23 @@ tui_puts (const char *string)
 	    }
 	  else
 	    waddch (w, c);
+
+	  if (c == '\n')
+	    TUI_CMD_WIN->detail.command_info.start_line = getcury (w);
+	  else if (getcurx (w) <= prev_col && getcury (w) == prev_line)
+	    {
+	      /* If the cursor is on the last line of the command window and the
+		 added character caused the line to wrap, then we have to adjust
+		 start_line to compensate for the scrolling up of each line that
+		 the line wrapping caused.  */
+	      TUI_CMD_WIN->detail.command_info.start_line--;
+	    }
         }
       else if (c == '\n')
         tui_skip_line = -1;
     }
   getyx (w, TUI_CMD_WIN->detail.command_info.cur_line,
          TUI_CMD_WIN->detail.command_info.curch);
-  TUI_CMD_WIN->detail.command_info.start_line
-    = TUI_CMD_WIN->detail.command_info.cur_line;
 }
 
 /* Readline callback.
-- 
2.5.0.rc0.5.g91e10c5.dirty