Rotating Actor

December 01, 2017

UE4 Version: 4.18.3

Github Link: https://github.com/Harrison1/unrealcpp/tree/master/RotatingActor

For this tutorial we are using the standard first person C++ template with starter content. If you don't know how to add a new actor class to your project, please visit the Add C++ Actor Class post.

In this tutorial we are going to change an actor's rotation every frame. Create a new C++ actor class and call it RotatingActor. In the header file we will create 3 float variables. We will set their UPROPERTY to EditAnywhere so we can change the values in the editor and we'll put all of the variables inside the Movement category to keep them together and separate from other attributes. Below is the final header script.

RotatingActor.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "RotatingActor.generated.h"

UCLASS()
class UNREALCPP_API ARotatingActor : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ARotatingActor();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	// declare our float variables 	
	UPROPERTY(EditAnywhere, Category = Movement)
	float PitchValue;

	UPROPERTY(EditAnywhere, Category = Movement)
	float YawValue;

	UPROPERTY(EditAnywhere, Category = Movement)
	float RollValue;
	
};

In the .cpp file set the default values to 0 for all the float variables.

set default values

// Sets default values
ARotatingActor::ARotatingActor()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	PitchValue = 0.f;
	YawValue = 0.f;
	RollValue = 0.f;

}

In the Tick function create a new FRotator variable titled NewRotation and set it equal to our float variables we created earlier. Next, create an FQuat variable and set it equal to NewRotatoin. Then, all we have to do is run AddActorLocalRotation to have our actor spin in place. Below is the final .cpp code.

Tick function

/ Called every frame
void ARotatingActor::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

	// on every frame change rotationg for a smooth rotating actor
	FRotator NewRotation = FRotator(PitchValue, YawValue, RollValue);
	
	FQuat QuatRotation = FQuat(NewRotation);
	
	AddActorLocalRotation(QuatRotation, false, 0, ETeleportType::None);


	// The below method causes a bug for the pitch value. The pitch value stops updating at 90 degrees
	// this is a known bug in the Unreal Engine. 
	// solution found by ue4 user nutellis https://answers.unrealengine.com/questions/591752/pitch-rotation-stucks-at-90-90-c.html

	// FRotator NewRotation = GetActorRotation();

	// NewRotation.Pitch += PitchValue;
	// NewRotation.Yaw += YawValue;
	// NewRotation.Roll += RollValue;
	
	// OR add values using the FRotator Add function
	// FRotator NewRotation = GetActorRotation().Add(PitchValue, YawValue, RollValue);


	// SetActorRotation(NewRotation);

}

Compile the code. Drag and drop your new actor into your game. Add a static mesh component to the actor. Set a value for the PitchValue and then when you push play the actor will spin in place.

Author

Harrison McGuire

Harrison McGuire