vi: use alternate screen buffer

Implement the "ESC[?1049h" and "ESC[?1049l" ANSI escape sequences
to switch between the alternate and normal screen buffers.

This allows vi to restore the original screen contents on exit.

2 files changed, 68 insertions, 11 deletions

diff --git a/editors/vi.c b/editors/vi.c
index 91a3e0ac1..a8b4dc5a4 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -1020,12 +1020,7 @@ static void refresh(int full_screen)
 static void redraw(int full_screen)
 {
         // cursor to top,left; clear to the end of screen
-#if !ENABLE_PLATFORM_MINGW32
         write1(ESC_SET_CURSOR_TOPLEFT ESC_CLEAR2EOS);
-#else
-        write1(ESC_SET_CURSOR_TOPLEFT);
-        reset_screen();
-#endif
         screen_erase();         // erase the internal screen buffer
         last_status_cksum = 0;  // force status update
         refresh(full_screen);   // this will redraw the entire display
diff --git a/win32/winansi.c b/win32/winansi.c
index 38bd6824f..f5d836bd2 100644
--- a/win32/winansi.c
+++ b/win32/winansi.c
@@ -74,6 +74,67 @@ void set_title(const char *str)
                 SetConsoleTitle(str);
 }
 
+static HANDLE dup_handle(HANDLE h)
+{
+        HANDLE h2;
+
+        if (!DuplicateHandle(GetCurrentProcess(), h, GetCurrentProcess(),
+                                                        &h2, 0, TRUE, DUPLICATE_SAME_ACCESS))
+                return INVALID_HANDLE_VALUE;
+        return h2;
+}
+
+static void use_alt_buffer(int flag)
+{
+        static HANDLE console_orig = INVALID_HANDLE_VALUE;
+        static int initialised = FALSE;
+        CONSOLE_SCREEN_BUFFER_INFO sbi;
+        HANDLE h;
+
+        init();
+
+        if (console == INVALID_HANDLE_VALUE)
+                return;
+
+        if (!initialised) {
+                console_orig = dup_handle(console);
+                initialised = TRUE;
+        }
+
+        if (console_orig == INVALID_HANDLE_VALUE)
+                return;
+
+        if (flag) {
+                SECURITY_ATTRIBUTES sa;
+
+                // handle should be inheritable
+                memset(&sa, 0, sizeof(sa));
+                sa.nLength = sizeof(sa);
+                /* sa.lpSecurityDescriptor = NULL; - memset did it */
+                sa.bInheritHandle = TRUE;
+
+                // create new alternate buffer
+                h = CreateConsoleScreenBuffer(GENERIC_READ|GENERIC_WRITE,
+                                        FILE_SHARE_READ|FILE_SHARE_WRITE, &sa,
+                                        CONSOLE_TEXTMODE_BUFFER, NULL);
+                if (h == INVALID_HANDLE_VALUE)
+                        return;
+
+                if (GetConsoleScreenBufferInfo(console, &sbi))
+                        SetConsoleScreenBufferSize(h, sbi.dwSize);
+        }
+        else {
+                // revert to original buffer
+                h = dup_handle(console_orig);
+                if (h == INVALID_HANDLE_VALUE)
+                        return;
+        }
+
+        console = h;
+        SetConsoleActiveScreenBuffer(console);
+        close(STDOUT_FILENO);
+        _open_osfhandle((intptr_t)console, O_RDWR|O_BINARY);
+}
 
 #define FOREGROUND_ALL (FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE)
 #define BACKGROUND_ALL (BACKGROUND_RED | BACKGROUND_GREEN | BACKGROUND_BLUE)
@@ -371,12 +432,13 @@ static char *process_escape(char *pos)
                 erase_in_line();
                 break;
         case '?':
-                /* skip this to avoid ugliness when vi is shut down */
-                ++str;
-                while (isdigit(*str))
-                        ++str;
-                func = str;
-                break;
+                if (strncmp(str+1, "1049", 4) == 0 &&
+                                (str[5] == 'h' || str[5] == 'l') ) {
+                        use_alt_buffer(str[5] == 'h');
+                        func = str + 5;
+                        break;
+                }
+                /* fall through */
         default:
                 /* Unsupported code */
                 return pos;