Overriding Not Exposed Functions

NimForUE generates bindings only to a subset of the Unreal Engine API that is exposed to Blueprints. But what if we really need to override a virtual function that is not exposed to Blueprints?

Let say that we want to override a vitual function in the native, non exposed UDefaultSizedThumbnailRenderer class. The first thing we need to do is to add UnrealEd to our bindings in the game.json file:

{
  "extraModuleNames": ["UnrealEd"],
  "extraNonBpModuleNames": ["UnrealEd"]
}

Afterwards, run the ./nue genbindingsall command to regenerate the bindings.

The bindings generated for UDefaultSizedThumbnailRenderer look like this:

type
  UDefaultSizedThumbnailRenderer* {.importcpp: "$1_", inheritable, pure,
                                    header: "UEGenBindings.h".} = object of UThumbnailRenderer
    defaultSizeX*: int32
    defaultSizeY*: int32

As you can see, bindings have a $1_ which means that it’s a type we are generating (you can see see that in the export version of the bindings).

Since we want to override a virtual (C++) function, we need to add the actual type to the PCH (Precompiled headers). Since we can’t load every single Unreal Engine type to the common PCH (UEDeps.h), we need to add the ones that we need game PCH.

In the game folder, just near the game.json we need to add a nuegame.h file and then a include to the header:

#include "Editor/UnrealEd/Classes/ThumbnailRendering/DefaultSizedThumbnailRenderer.h"

Since Unreal Engine doesn’t know that file exists yet, we need to trigger a change in the Unreal Build Tools (UBT) side of things. Just add an empty space or something to NimForUE.build.cs.

Note

A PR has been accepted that adds a way to trigger this without manually adding the change, i.e. a cmd that invalidates the UBT cache for the NimForUE plugin or the just the NimForUE module.

Then, delete the .headerdata file and run the ./nue genbindingsall command again. The bindings will be updated and look like this:

type
  UDefaultSizedThumbnailRenderer* {.importcpp, inheritable, pure.} = object of UThumbnailRenderer
    defaultSizeX* {.importcpp: "DefaultSizeX".}: int32
    defaultSizeY* {.importcpp: "DefaultSizeY".}: int32

They dont have the $1_, whic means we are using the actual C++ type and we can override it.

Using this method you can tweak the PCH includes even further.