[PATCH] Fix TUI text centering

[Tom Tromey <tom@tromey.com>]

In a couple of spots, the TUI tries to center some text in the window.
Andrew noticed that the calculation is done strangely and the text
ends up somewhat to the left of center.

This patch fixes the problem.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31355
---
 gdb/testsuite/gdb.tui/regs.exp |  5 ++++-
 gdb/tui/tui-data.c             | 20 +++++++++++++++-----
 gdb/tui/tui-data.h             |  6 +++---
 gdb/tui/tui-regs.c             | 12 +-----------
 gdb/tui/tui-winsource.c        | 20 +++-----------------
 5 files changed, 26 insertions(+), 37 deletions(-)

diff --git a/gdb/testsuite/gdb.tui/regs.exp b/gdb/testsuite/gdb.tui/regs.exp
index ea78b57d1a7..183c2ea0f03 100644
--- a/gdb/testsuite/gdb.tui/regs.exp
+++ b/gdb/testsuite/gdb.tui/regs.exp
@@ -46,7 +46,10 @@ Term::check_box "source box in regs layout" 0 7 80 8
 
 # The current frame is main, check that registers are available.
 set re_reg_vals_unavailable \
-    [string_to_regexp {[ Register Values Unavailable ]}]
+    [string_to_regexp \
+	 [string cat \
+	      [string repeat " " 23] \
+	      {[ Register Values Unavailable ]}]]
 gdb_assert \
     { ![Term::check_region_contents_p 0 0 80 8 $re_reg_vals_unavailable] } \
     "Register values available"
diff --git a/gdb/tui/tui-data.c b/gdb/tui/tui-data.c
index 38a87a2a6e9..03395d2df09 100644
--- a/gdb/tui/tui-data.c
+++ b/gdb/tui/tui-data.c
@@ -169,13 +169,23 @@ tui_win_info::set_title (std::string &&new_title)
 /* See tui-data.h.  */
 
 void
-tui_win_info::display_string (int y, int x, const char *str) const
+tui_win_info::center_string (const char *str)
 {
-  int n = width - box_width () - x;
-  if (n <= 0)
-    return;
+  werase (handle.get ());
+  check_and_display_highlight_if_needed ();
+
+  int avail_width = width - box_size ();
+  int len = strlen (str);
+
+  int x_pos = box_width ();
+  if (len < avail_width)
+    x_pos += (avail_width - len) / 2;
+
+  int n = avail_width - x_pos;
+  gdb_assert (n > 0);
 
-  mvwaddnstr (handle.get (), y, x, str, n);
+  mvwaddnstr (handle.get (), height / 2, x_pos, str, n);
+  refresh_window ();
 }
 
 /* See tui-data.h.  */
diff --git a/gdb/tui/tui-data.h b/gdb/tui/tui-data.h
index 1714f5ae455..4a44a0bc6e8 100644
--- a/gdb/tui/tui-data.h
+++ b/gdb/tui/tui-data.h
@@ -167,9 +167,9 @@ struct tui_win_info
   const std::string &title () const
   { return m_title; }
 
-  /* Display string STR in the window at position (Y,X), abbreviated if
-     necessary.  */
-  void display_string (int y, int x, const char *str) const;
+  /* Clear the window, maybe draw the boarder, and then display string
+     STR centered in the window, abbreviated if necessary.  */
+  void center_string (const char *str);
 
   /* Display string STR in the window at the current cursor position,
      abbreviated if necessary.  */
diff --git a/gdb/tui/tui-regs.c b/gdb/tui/tui-regs.c
index 504aed4b81f..f5c2ec1bb58 100644
--- a/gdb/tui/tui-regs.c
+++ b/gdb/tui/tui-regs.c
@@ -354,17 +354,7 @@ tui_data_window::first_data_item_displayed ()
 void
 tui_data_window::erase_data_content ()
 {
-  werase (handle.get ());
-  check_and_display_highlight_if_needed ();
-
-  const char *prompt = _("[ Register Values Unavailable ]");
-  int half_width = (width - box_size ()) / 2;
-  int x_pos;
-  if (strlen (prompt) >= half_width)
-    x_pos = 1;
-  else
-    x_pos = half_width - strlen (prompt);
-  display_string (height / 2, x_pos, prompt);
+  center_string (_("[ Register Values Unavailable ]"));
 }
 
 /* See tui-regs.h.  */
diff --git a/gdb/tui/tui-winsource.c b/gdb/tui/tui-winsource.c
index 2631714f248..6b8716cd27c 100644
--- a/gdb/tui/tui-winsource.c
+++ b/gdb/tui/tui-winsource.c
@@ -222,23 +222,9 @@ tui_update_source_windows_with_line (struct symtab_and_line sal)
 void
 tui_source_window_base::do_erase_source_content (const char *str)
 {
-  int x_pos;
-  int half_width = (width - box_size ()) / 2;
-
   m_content.clear ();
-  if (handle != NULL)
-    {
-      werase (handle.get ());
-      check_and_display_highlight_if_needed ();
-
-      if (strlen (str) >= half_width)
-	x_pos = 1;
-      else
-	x_pos = half_width - strlen (str);
-      display_string (height / 2, x_pos, str);
-
-      refresh_window ();
-    }
+  if (handle != nullptr)
+    center_string (str);
 }
 
 /* See tui-winsource.h.  */
@@ -714,7 +700,7 @@ tui_source_window_base::update_exec_info (bool refresh_p)
       if (src_element->is_exec_point)
 	element[TUI_EXEC_POS] = '>';
 
-      display_string (i + box_width (), box_width (), element);
+      mvwaddstr (handle.get (), i + box_width (), box_width (), element);
 
       show_line_number (i);
     }
-- 
2.43.0