Remove flickering from the TUI

In some cases, the TUI flickers when redrawing.  This can be seen
mostly easily when switching layouts.

This patch fixes the problem by exploiting the double buffering that
curses already does.  In some spots, the TUI will now disable flushing
the curses buffers to the screen; and then flush them all at once when
the rendering is complete.

gdb/ChangeLog
2020-01-19  Tom Tromey  <tom@tromey.com>

	* tui/tui.c (tui_show_assembly): Use tui_suppress_output.
	* tui/tui-wingeneral.h (class tui_suppress_output): New.
	(tui_wrefresh): Declare.
	* tui/tui-wingeneral.c (suppress_output): New global.
	(tui_suppress_output, ~tui_suppress_output): New constructor and
	destructor.
	(tui_wrefresh): New function.
	(tui_gen_win_info::refresh_window): Use tui_wrefresh.
	(tui_gen_win_info::make_window): Call wnoutrefresh when needed.
	* tui/tui-regs.h (struct tui_data_window) <no_refresh>: Declare
	method.
	* tui/tui-regs.c (tui_data_window::erase_data_content): Call
	tui_wrefresh.
	(tui_data_window::no_refresh): New method.
	(tui_data_item_window::refresh_window): Call tui_wrefresh.
	(tui_reg_command): Use tui_suppress_output
	* tui/tui-layout.c (tui_set_layout): Use tui_suppress_output.
	* tui/tui-data.h (struct tui_gen_win_info) <no_refresh>: New
	method.
	* tui/tui-command.c (tui_refresh_cmd_win): Call tui_wrefresh.

Change-Id: Icb832ae100b861de3af3307488e636fa928d5c9f

gdb/ChangeLog

@@ -1,3 +1,26 @@
+2020-01-19  Tom Tromey  <tom@tromey.com>
+
+	* tui/tui.c (tui_show_assembly): Use tui_suppress_output.
+	* tui/tui-wingeneral.h (class tui_suppress_output): New.
+	(tui_wrefresh): Declare.
+	* tui/tui-wingeneral.c (suppress_output): New global.
+	(tui_suppress_output, ~tui_suppress_output): New constructor and
+	destructor.
+	(tui_wrefresh): New function.
+	(tui_gen_win_info::refresh_window): Use tui_wrefresh.
+	(tui_gen_win_info::make_window): Call wnoutrefresh when needed.
+	* tui/tui-regs.h (struct tui_data_window) <no_refresh>: Declare
+	method.
+	* tui/tui-regs.c (tui_data_window::erase_data_content): Call
+	tui_wrefresh.
+	(tui_data_window::no_refresh): New method.
+	(tui_data_item_window::refresh_window): Call tui_wrefresh.
+	(tui_reg_command): Use tui_suppress_output
+	* tui/tui-layout.c (tui_set_layout): Use tui_suppress_output.
+	* tui/tui-data.h (struct tui_gen_win_info) <no_refresh>: New
+	method.
+	* tui/tui-command.c (tui_refresh_cmd_win): Call tui_wrefresh.
+
 2020-01-19  Tom Tromey  <tom@tromey.com>
 
 	* tui/tui-winsource.c (tui_update_source_windows_with_line):

gdb/tui/tui-command.c

@@ -70,7 +70,7 @@ tui_refresh_cmd_win (void)
 {
   WINDOW *w = TUI_CMD_WIN->handle.get ();
 
-  wrefresh (w);
+  tui_wrefresh (w);
 
   /* FIXME: It's not clear why this is here.
      It was present in the original tui_puts code and is kept in order to

gdb/tui/tui-data.h

@@ -99,6 +99,13 @@ public:
     return handle != nullptr;
   }
 
+  /* Disable output until the next call to doupdate.  */
+  virtual void no_refresh ()
+  {
+    if (handle != nullptr)
+      wnoutrefresh (handle.get ());
+  }
+
   /* Window handle.  */
   std::unique_ptr<WINDOW, curses_deleter> handle;
   /* Type of window.  */

gdb/tui/tui-layout.c

@@ -113,6 +113,8 @@ tui_set_layout (enum tui_layout_type layout_type)
 
   if (new_layout != cur_layout)
     {
+      tui_suppress_output suppress;
+
       show_layout (new_layout);
 
       /* Now determine where focus should be.  */

gdb/tui/tui-regs.c

@@ -381,7 +381,7 @@ tui_data_window::erase_data_content (const char *prompt)
 	x_pos = half_width - strlen (prompt);
       mvwaddstr (handle.get (), (height / 2), x_pos, (char *) prompt);
     }
-  wrefresh (handle.get ());
+  tui_wrefresh (handle.get ());
 }
 
 /* See tui-regs.h.  */
@@ -434,6 +434,14 @@ tui_data_window::refresh_window ()
     win.refresh_window ();
 }
 
+void
+tui_data_window::no_refresh ()
+{
+  tui_gen_win_info::no_refresh ();
+  for (auto &&win : m_regs_content)
+    win.no_refresh ();
+}
+
 /* This function check all displayed registers for changes in values,
    given a particular frame.  If the values have changed, they are
    updated with the new value and highlighted.  */
@@ -502,7 +510,7 @@ tui_data_item_window::refresh_window ()
 	 windows, which according to the ncurses man pages aren't well
 	 supported.  */
       touchwin (handle.get ());
-      wrefresh (handle.get ());
+      tui_wrefresh (handle.get ());
     }
 }
 
@@ -574,6 +582,8 @@ tui_reg_command (const char *args, int from_tty)
       /* Make sure the curses mode is enabled.  */
       tui_enable ();
 
+      tui_suppress_output suppress;
+
       /* Make sure the register window is visible.  If not, select an
 	 appropriate layout.  We need to do this before trying to run the
 	 'next' or 'prev' commands.  */

gdb/tui/tui-regs.h

@@ -70,6 +70,8 @@ struct tui_data_window : public tui_win_info
 
   void refresh_window () override;
 
+  void no_refresh () override;
+
   const char *name () const override
   {
     return DATA_NAME;

gdb/tui/tui-wingeneral.c

@@ -30,13 +30,51 @@
 
 #include "gdb_curses.h"
 
+/* This is true if we're currently suppressing output, via
+   wnoutrefresh.  This is needed in case we create a new window while
+   in this mode.  */
+
+static bool suppress_output;
+
+/* See tui-data.h.  */
+
+tui_suppress_output::tui_suppress_output ()
+  : m_saved_suppress (suppress_output)
+{
+  suppress_output = true;
+
+  for (const auto &win : all_tui_windows ())
+    win->no_refresh ();
+}
+
+/* See tui-data.h.  */
+
+tui_suppress_output::~tui_suppress_output ()
+{
+  suppress_output = m_saved_suppress;
+  if (!suppress_output)
+    doupdate ();
+
+  for (const auto &win : all_tui_windows ())
+    win->refresh_window ();
+}
+
+/* See tui-data.h.  */
+
+void
+tui_wrefresh (WINDOW *win)
+{
+  if (!suppress_output)
+    wrefresh (win);
+}
+
 /* See tui-data.h.  */
 
 void
 tui_gen_win_info::refresh_window ()
 {
   if (handle != NULL)
-    wrefresh (handle.get ());
+    tui_wrefresh (handle.get ());
 }
 
 /* Draw a border arround the window.  */
@@ -134,7 +172,11 @@ tui_gen_win_info::make_window ()
 {
   handle.reset (newwin (height, width, y, x));
   if (handle != NULL)
-    scrollok (handle.get (), TRUE);
+    {
+      if (suppress_output)
+	wnoutrefresh (handle.get ());
+      scrollok (handle.get (), TRUE);
+    }
 }
 
 void

gdb/tui/tui-wingeneral.h

@@ -33,4 +33,27 @@ extern void tui_unhighlight_win (struct tui_win_info *);
 extern void tui_highlight_win (struct tui_win_info *);
 extern void tui_refresh_all ();
 
+/* An RAII class that suppresses output on construction (calling
+   wnoutrefresh on the existing windows), and then flushes the output
+   (via doupdate) when destroyed.  */
+
+class tui_suppress_output
+{
+public:
+
+  tui_suppress_output ();
+  ~tui_suppress_output ();
+
+  DISABLE_COPY_AND_ASSIGN (tui_suppress_output);
+
+private:
+
+  /* Save the state of the suppression global.  */
+  bool m_saved_suppress;
+};
+
+/* Call wrefresh on the given window.  However, if output is being
+   suppressed via tui_suppress_output, do not call wrefresh.  */
+extern void tui_wrefresh (WINDOW *win);
+
 #endif /* TUI_TUI_WINGENERAL_H */

gdb/tui/tui.c

@@ -30,6 +30,7 @@
 #include "tui/tui-regs.h"
 #include "tui/tui-stack.h"
 #include "tui/tui-win.h"
+#include "tui/tui-wingeneral.h"
 #include "tui/tui-winsource.h"
 #include "tui/tui-source.h"
 #include "target.h"
@@ -577,6 +578,7 @@ tui_disable_command (const char *args, int from_tty)
 void
 tui_show_assembly (struct gdbarch *gdbarch, CORE_ADDR addr)
 {
+  tui_suppress_output suppress;
   tui_add_win_to_layout (DISASSEM_WIN);
   tui_update_source_windows_with_addr (gdbarch, addr);
 }