How it works...

For us to reference Slate classes or functions in our code, our module must link with the Slate and SlateCore modules, so we add those to the module dependencies.

We need to instantiate our UI in one of the classes that loads when the game runs, so for this recipe, we use our custom PlayerController in the BeginPlay function as the place to create our UI.

Inside the BeginPlay implementation, we create a new SVerticalBox using the SNew function. We add a slot for a widget to our box, and set that slot to both horizontal and vertical centering.

Inside the slot, which we access using square brackets, we create a button that has Textblock inside it. In Textblock, we set the Text property to a string literal value.

With the UI now created, we call AddViewportWidgetForPlayer to display this widget on the local player's screen.

With our custom PlayerController ready, we now need to create a custom GameMode to specify that it should use our new PlayerController. With the custom PlayerController being loaded at the start of the game, when BeginPlay is called, our UI will be shown.

The UI is very small at this screen size. Refer to the following recipe for information on how to scale it appropriately for the resolution of the game window.