Inheriting from AChaosSolverActor with a custom class - why can't I link to the external symbols of the pure virtual functions?

[dankrusi]

I must be too tired or something, but for the life of me I can’t figure out how to link a simple inheriting class AMyChaosSolverActor?

I always get linking errors such as when I call the base class functions:

error LNK2019: unresolved external symbol "public: virtual void __cdecl AChaosSolverActor::BuildSimulationProxy(void)" (?BuildSimulationProxy@AChaosSolverActor@@UEAAXXZ) referenced in function "public: virtual void __cdecl AMyChaosSolverActor::BuildSimulationProxy(void)" (?BuildSimulationProxy@AMyChaosSolverActor@@UEAAXXZ)

MyChaosSolverActor.h:

#pragma once

#include "CoreMinimal.h"
#include "Chaos/ChaosSolverActor.h"
#include "MyChaosSolverActor.generated.h"

/**
 * 
 */
UCLASS()
class CHAOSCPPTESTS_API AMyChaosSolverActor : public AChaosSolverActor
{
	GENERATED_BODY()
	
public:
    // Required virtual function implementations
    virtual void BuildSimulationProxy() override;
    virtual void ResetSimulationProxy() override;
    virtual void WriteToSimulation(float DeltaTime, bool bAsyncTask) override;
    virtual void ReadFromSimulation(float DeltaTime, bool bAsyncTask) override;

    // Required by IDataflowSimulationInterface
    virtual void PreProcessSimulation(float DeltaTime) override;
    virtual void PostProcessSimulation(float DeltaTime) override;

    // Required by IDataflowPhysicsSolverInterface
    virtual FString GetSimulationType() const override;
};

MyChaosSolverActor.cpp:

#include "MyChaosSolverActor.h"

#include "Chaos/ChaosSolverActor.h"

void AMyChaosSolverActor::BuildSimulationProxy()
{
    Super::BuildSimulationProxy(); // <-- Super call causing link error
}

void AMyChaosSolverActor::ResetSimulationProxy()
{
}

void AMyChaosSolverActor::WriteToSimulation(float DeltaTime, bool bAsyncTask)
{
}

void AMyChaosSolverActor::ReadFromSimulation(float DeltaTime, bool bAsyncTask)
{
}

void AMyChaosSolverActor::PreProcessSimulation(float DeltaTime)
{
}

void AMyChaosSolverActor::PostProcessSimulation(float DeltaTime)
{
}

FString AMyChaosSolverActor::GetSimulationType() const
{
    return FString(TEXT("CustomChaosSolver"));
}

Build.cs:

using UnrealBuildTool;

public class ChaosCPPTests : ModuleRules
{
	public ChaosCPPTests(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
	
		PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "EnhancedInput", "ChaosSolverEngine" });

		PrivateDependencyModuleNames.AddRange(new string[] {  });
	}
}

Thanks a lot for you help, and sorry if I missed something basic.

[dankrusi]

To save you some time:

ChaosSolverActor.h:

~~~~
	//~ Begin IDataflowPhysicsSolverInterface interface
	virtual FString GetSimulationName() const override {return GetName();};
	virtual FDataflowSimulationAsset& GetSimulationAsset() override {return SimulationAsset;};
	virtual const FDataflowSimulationAsset& GetSimulationAsset() const override {return SimulationAsset;};
	virtual FDataflowSimulationProxy* GetSimulationProxy() override {return &RigidSolverProxy;}
	virtual const FDataflowSimulationProxy* GetSimulationProxy() const  override {return &RigidSolverProxy;}
	virtual void BuildSimulationProxy() override;
	virtual void ResetSimulationProxy() override;
	virtual void WriteToSimulation(const float DeltaTime, const bool bAsyncTask) override;
	virtual void ReadFromSimulation(const float DeltaTime, const bool bAsyncTask) override;
	//~ End IDataflowPhysicsSolverInterface interface
~~~~

The method BuildSimulationProxy() is implemented by ChaosSolverActor.

[3dRaven]

Not sure if you copied over the rest of the overrides from your last message.

Adding this to the header, copied over from AChaosSolverActor into AMyChaosSolverActor gives a successful compile

    virtual FString GetSimulationName() const override { return GetName(); };
    virtual FDataflowSimulationAsset& GetSimulationAsset() override { return SimulationAsset; };
    virtual const FDataflowSimulationAsset& GetSimulationAsset() const override { return SimulationAsset; };
    virtual FDataflowSimulationProxy* GetSimulationProxy() override { return &RigidSolverProxy; }
    virtual const FDataflowSimulationProxy* GetSimulationProxy() const  override { return &RigidSolverProxy; }

MyChaosSolverActor.h (1.4 KB)
MyChaosSolverActor.cpp (744 Bytes)

[dankrusi]

Many thanks for your help!

Yes sorry - I trimmed away a bit too much, ofcourse I also have those methods.

I’m not sure how you are able to compile - things like SimulationAsset are private to ChaosSolverActor (I am on UE 5.5).

If I change from Super to AChaosSolverActor, I can call those AChaosSolverActor methods which are inline in the header (like AChaosSolverActor::GetSimulationAsset()), however I still can’t link to other methods like AChaosSolverActor::BuildSimulationProxy():

error LNK2019: unresolved external symbol "public: virtual void __cdecl AChaosSolverActor::BuildSimulationProxy(void)" (?BuildSimulationProxy@AChaosSolverActor@@UEAAXXZ) referenced in function "public: virtual void __cdecl AMyChaosSolverActor::BuildSimulationProxy(void)" (?BuildSimulationProxy@AMyChaosSolverActor@@UEAAXXZ)

I don’t understand why the one works and the other doesn’t - the only difference being that
AChaosSolverActor::GetSimulationAsset() is inline in the header.

Is it because these are marked as CHAOSSOLVERENGINE_API (__declspec)?

Thanks for your help in understanding how to properly extend engine actors and components, without modifying engine source directly.

Here is a test class:

UCLASS()
class CHAOSTESTS_API AMyChaosSolverActor : public AChaosSolverActor
{
	GENERATED_BODY()

public:

	//~ Begin IDataflowPhysicsSolverInterface interface
	virtual FString GetSimulationName() const override { return GetName(); };
	virtual FDataflowSimulationAsset& GetSimulationAsset() override { return AChaosSolverActor::GetSimulationAsset(); };
	virtual const FDataflowSimulationAsset& GetSimulationAsset() const override { return AChaosSolverActor::GetSimulationAsset(); };
	virtual FDataflowSimulationProxy* GetSimulationProxy() override { return AChaosSolverActor::GetSimulationProxy(); }
	virtual const FDataflowSimulationProxy* GetSimulationProxy() const  override { return AChaosSolverActor::GetSimulationProxy(); }
	virtual void BuildSimulationProxy() override { AChaosSolverActor::BuildSimulationProxy(); }; // causes linker issue
	virtual void ResetSimulationProxy() override {};
	virtual void WriteToSimulation(const float DeltaTime, const bool bAsyncTask) override {};
	virtual void ReadFromSimulation(const float DeltaTime, const bool bAsyncTask) override {};
	//~ End IDataflowPhysicsSolverInterface interface


	// Required by IDataflowSimulationInterface
	virtual void PreProcessSimulation(float DeltaTime) override {  };
	virtual void PostProcessSimulation(float DeltaTime) override {};

	// Required by IDataflowPhysicsSolverInterface
	virtual FString GetSimulationType() const override { return GetName(); };
};

[sergio.gardeazabal]

Hi,

Yes, these method’s symbols are not exported as you noticed. That is the reason why you can’t call them from an external (your) module.

Sadly, I don’t think there is much you can do other than modifying the engine to export them by adding CHAOSSOLVERENGINE_API.

I also suggest checking that the module where you class lives, has ChaosSolverEngine as dependency on its build.cs file, otherwise exporting them will not fix the issue.

[dankrusi]

Thanks Sergio, yes indeed some of the methods are not marked as CHAOSSOLVERENGINE_API. I was distracted a bit by some of the interface being exposed, and others not.

I will try to duplicate the ChaosSolverActor functionality without inheriting. Gut feeling is that its probably easier to maintain changes in the engine source than go this route.

BTW: The Chaos Visual Tools / Live Debugger is amazing. Not sure if you are involved with that.

[sergio.gardeazabal]

Yes, I am the developer of the Chaos Visual Debugger.

So, Thank you!, I am glad you like it (and hopefully it has been useful).

It is still on Beta so expect some rough edges, but for anyone else if you want to give it a try, this is a doc I put together a while ago Chaos Visual Debugger - User Guide for UE 5.5 | Tutorial