Add Engine.FocusGameViewport to implement game menu with camera focus gather

Source/Engine/Engine/Engine.cpp

@@ -409,6 +409,19 @@ JsonAsset* Engine::GetCustomSettings(const StringView& key)
     return Content::LoadAsync<JsonAsset>(assetId);
 }
 
+void Engine::FocusGameViewport()
+{
+#if USE_EDITOR
+    Editor::Managed->FocusGameViewport();
+#else
+    if (MainWindow)
+    {
+        MainWindow->BringToFront();
+        MainWindow->Focus();
+    }
+#endif
+}
+
 bool Engine::HasGameViewportFocus()
 {
 #if USE_EDITOR

Source/Engine/Engine/Engine.h

@@ -153,6 +153,11 @@ public:
 
     static Window* MainWindow;
 
+    /// <summary>
+    /// Brings focused to the game viewport (game can receive input).
+    /// </summary>
+    API_FUNCTION() static void FocusGameViewport();
+
     /// <summary>
     /// Checks whenever the game viewport is focused by the user (eg. can receive input).
     /// </summary>