A slightly different approach
Disclaimer: I'm not an UE4 developer. Guilty as charged for seeing an unanswered bounty too big to ignore. So I started thinking and looking - and I've found something that could be bent to your needs. Enters pixelstreaming.
Pixelstreaming is a beta feature that is primarily designed to allow for embedding the game into a browser. This opens a two way communication between a server where the GPU heavy computations happen and a browser where the player can interact with the content - the mouseclick & other events are sent back to the server. Apparently it allows some additional neat stuff, however that is not relevant for the question at hand.
Since you want to embedd the Unreal application into your NativeScript tool(menu of some kind if I understood correctly), you could make your application a from two separate parts:
- One part would run the server.
- The second part would handle the overlay via the pixelstreaming.
This reduces the issue of embedding the UE4 into an application to the(possibly easier) issue of embedding a browser into your application. (Or if your application is browser based - voila, problem solved.)
If you don't want to handle the remote communication, just have the server-side run on the localhost.(With the nice sideeffect of saving bandwidth.)
Alternatively, if you are feeling adventurous, you could go and write your own WebRTC support on the application side to bypass the need for the browser alltogether. It might not be worth the effort though.
Side note: The first of the links you provided is a feature request which hints at the unfortunate fact that UE4 doesn't support embedding. This is further enforced by the fact that one of the people there says somethig along the lines "Unity can to this, it would be nice if UE4 could as well."
Yet a different approach:
You could embedd and use a virtual display to insert the UE4 part into your controller - you would be basically tricking UE4 into thinking that the desired display device is a canvas inside your application.
This thread suggests a similar approach:
In general, the way to connect two libraries like this would be through a platform dependent window handle, e.g. a HWND under Windows. Check the UE api if you find any way to bind the render target to a HWND. Then you could create a wxWindow in wxWidgets and tell UE to render into that window. That would be a first step.
I'm not sure if anything I've listed will be of much help but hey, at least I tried :-). Good luck with your game.
At the same time, the author suggests to:
Reverse the problem:
Using the UE4 slate framework and online subsystem. You would use the former to create the menus you need directly in the UE4 and then use the latter to link to the logic you want to have outside of the UE4. However that is not what you asked for so I'm listing it only for the completeness sake.
