11.实时旋转 Actor

接上一节教程，在本教程中，我们将每帧都对一个 actor 进行旋转。创建一个新的 C++ Actor 类并将其命名为 RotatingActor。在头文件中，我们将创建 3 个浮点变量。我们将把它们的 UPROPERTY 设置为 EditAnywhere，这样我们就可以在编辑器中更改值，我们将把所有变量放在 Movement 类别中，以使它们在一起，并与其他属性分开。

下面是最终的头文件。

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;

};

在 .cpp 文件中将所有浮点变量的默认值设置为 0。

// 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;

}

在 Tick 函数中创建一个名为 NewRotation 的 FRotator 变量，并将其设置为前面创建的浮点变量。接下来，创建一个 FQuat 变量（四元数），并将其设置为 NewRotatoin 。然后，我们要做的就是运行 AddActorLocalRotation，让 actor 旋转到位。

下面是最终的.cpp 代码。

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);

}

效果图

为该 actor 添加 cube 组件，并设置 pitch 后，它就绕着 Y 轴旋转（UE4 是左手坐标系）

参考

实时旋转 Actor【十一】