最简单的 UE 4 C++ 教程 —— 实时旋转 Actor【十一】

喜欢ヅ旅行 2022-09-01 07:38 468阅读 0赞

**【原教程是基于 UE 4.18，我是基于 UE 4.25】**

[英文原地址][Link 1]

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）

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[Link 1]: https://unrealcpp.com/rotating-actor/
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3BhbmRhMTIzNGxlZQ_size_16_color_FFFFFF_t_70 1]: /images/20220829/34422a0dc5784f4c88caf2325bbcc980.png