If you want to program your UI completely in C++ I suggest you to use Slate. It’s the UI framework that powers Unreal Engine 4 editor and the UMG widgets are just UObjects that wrap Slate native widgets.
Slate has a declarative syntax which I think it makes it cool considering it’s C++.
You should take a look at these links:
https://docs.unrealengine.com/en-US/…ate/index.html
If you use Slate of course you’ll have better performance, but I prefer UMG because there is an WYSIWYG designer and you don’t have to recompile your game module everytime you want to see changes in your UI, so keep in mind you’ll have slower iteration times if you go with Slate.