Fix off-center window under TTF, add "Video/Center window" menu item

CHANGELOG

@@ -1,4 +1,6 @@
-Next
+  - fix off-center and off-screen window after entering the
+    configuration tool while using TTF output mode (aybe).
+  - add menu item for centering window "Video/Center window" (aybe).
   - Fixed update-version-number script to patch all *.iss files, not 
     just the specific one it did before, to ensure future releases have
     correct version numbers. (joncampbell123).

src/gui/menu.cpp

@@ -525,6 +525,9 @@ static const char *def_menu_video[] =
 #endif
     "VideoRatioMenu",
     "mapper_aspratio",
+#if defined(C_SDL2)
+    "center_window",
+#endif
 #if !defined(C_SDL2) && defined(MACOSX)
     "highdpienable",
 #endif

src/gui/menu_callback.cpp

@@ -2071,6 +2071,15 @@ bool vsync_set_syncrate_menu_callback(DOSBoxMenu * const menu,DOSBoxMenu::item *
     return true;
 }
 
+bool center_window_menu_callback(DOSBoxMenu * const menu,DOSBoxMenu::item * const menuitem) {
+    (void)menu;//UNUSED
+    (void)menuitem;//UNUSED
+#if defined(C_SDL2)
+    SDL_SetWindowPosition(sdl.window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
+#endif
+    return true;
+}
+
 bool set_titletext_menu_callback(DOSBoxMenu * const menu,DOSBoxMenu::item * const menuitem) {
     (void)menu;//UNUSED
     (void)menuitem;//UNUSED
@@ -3198,6 +3207,11 @@ void AllocCallback1() {
                         set_callback_function(scaler_set_menu_callback);
                 }
 
+#if defined(C_SDL2)
+                mainMenu.alloc_item(DOSBoxMenu::item_type_id,"center_window").set_text("Center window").
+                    set_callback_function(center_window_menu_callback);
+#endif
+
                 mainMenu.alloc_item(DOSBoxMenu::item_type_id,"set_titletext").set_text("Set title bar text...").
                     set_callback_function(set_titletext_menu_callback);
 

src/output/output_ttf.cpp

@@ -1455,6 +1455,7 @@ void ttf_switch_on(bool ss=true) {
 #ifdef C_SDL2
         transparency = 0;
         SetWindowTransparency(static_cast<Section_prop *>(control->GetSection("sdl"))->Get_int("transparency"));
+        SDL_SetWindowPosition(sdl.window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
 #endif
         if (!IS_PC98_ARCH && vga.draw.address_add != ttf.cols * 2) checkcol = ss?2:1;
     }