Lerp Ticker

What is Lerp Ticker?

Lerp Ticker is the class that is responsible with handling global tick function calls for the Lerper and DynamicLerper objects.

Lerper ticker is a UActorComponent, attached to an actor, created in the main GameMode so that each level has Lerp Ticker instantiated.

#pragma once

#include "CoreMinimal.h"
#include "Components/ActorComponent.h"
#include "ACBGMLerpTicker.generated.h"

DECLARE_MULTICAST_DELEGATE_OneParam(FOnUniversalTick, float)

UCLASS( ClassGroup=(Custom), meta=(BlueprintSpawnableComponent) )
class REGRET_API UACBGMLerpTicker final : public UActorComponent
{
	GENERATED_BODY()

public:	
	UACBGMLerpTicker();
	virtual ~UACBGMLerpTicker() override;

	template <typename T>
	static FDelegateHandle BindTickFunction(T* ClassPtr, void(T::*Func)(float))
	{
		return Active->OnUniversalTick.AddRaw(ClassPtr, Func);
	}
	
	static void UnbindTickFunction(const FDelegateHandle& DelegateHandle);

protected:
	FOnUniversalTick OnUniversalTick;
	static UACBGMLerpTicker* Active;

private:
	virtual void OnComponentCreated() override;
	virtual void TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction) override;
};

FOnUniversalTick is declared using Unreal Engine’s DECLARE_MULTICAST_DELEGATE_OneParam macro. Based on that, OnUniversalTick will be declared and referenced by the class.

BindTickFunction is now implicitly inlined. Declaration and implementation of template types is only possible in the header file.

#include "ACBGMLerpTicker.h"

UACBGMLerpTicker* UACBGMLerpTicker::Active;

UACBGMLerpTicker::UACBGMLerpTicker()
{
	PrimaryComponentTick.bCanEverTick = true;
}

UACBGMLerpTicker::~UACBGMLerpTicker()
{
}

void UACBGMLerpTicker::OnComponentCreated()
{
	Active = this;
}

void UACBGMLerpTicker::TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction)
{
	Super::TickComponent(DeltaTime, TickType, ThisTickFunction);
	OnUniversalTick.Broadcast(DeltaTime);
}

void UACBGMLerpTicker::UnbindTickFunction(const FDelegateHandle& DelegateHandle)
{
	Active->SetComponentTickEnabled(false);
	Active->OnUniversalTick.Remove(DelegateHandle);
	Active->SetComponentTickEnabled(true);
}

We use OnComponentCreated to set our singleton Active to this.

In TickComponent, we broadcast our delegate to all the bound functions.

In UnbindTickFunction, we temporarily disable Active’s tick function. Then, we remove the bound function from UniversalTick. Finally, Active’s tick function gets re-enabled.

Why was OnComponentCreated used?

The question that might arise is that why OnComponentCreated has been used to assign the singleton, and not the constructor itself. The ticker class is a UObject and it’s instantiated is the engine’s responsibility. The behavior is not guaranteed and as a result, using OnComponentCreated will be the guaranteed solution to our singleton problem (While debugging, it seems that after the instantiation of any UObject, the object will not be in the same memory address as it used to be during its constructor. It’s possible that the move constructor gets called, as no reconstruction happens for us to assign Active to the proper object in memory.).