最简单的 UE 4 C++ 教程 —— 绕轴旋转【二十六】

柔光的暖阳◎ 2022-09-02 00:52 440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，我们将学习如何使用 **RotateAngleAxis** 函数。首先创建一个新的C++ Actor 类，并将其命名为 **RotateAngleAxis** 。在头文件中，我们将创建两个浮点变量和两个**FVector** 变量，并将它们设置为 **EditAnywhere**，**以便稍后在编辑器中编辑它们**。

下面是最终的头文件代码。

### RotateAngleAxis.h ###

#pragma once
    
    #include "CoreMinimal.h"
    #include "GameFramework/Actor.h"
    #include "RotatingAngleAxis.generated.h"
    
    UCLASS()
    class UNREALCPP_API ARotatingAngleAxis : public AActor
    {
    	GENERATED_BODY()
    	
    public:	
    	// Sets default values for this actor's properties
    	ARotatingAngleAxis();
    
    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 AngleAxis;
    
    	UPROPERTY(EditAnywhere, Category = Movement)
    	FVector Dimensions;
    
    	UPROPERTY(EditAnywhere, Category = Movement)
    	FVector AxisVector;
    
    	UPROPERTY(EditAnywhere, Category = Movement)
    	float Multiplier;
    };

在 .cpp 中，让我们首先为 actor 设置一些默认值。

// Sets default values
    ARotatingAngleAxis::ARotatingAngleAxis()
    {
     	// 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;
    
    	Dimensions = FVector (300, 0, 0); ///< 旋转半径
    	AxisVector = FVector (0, 0, 1);
    	Multiplier = 50.f;
    
    }

我们所有的逻辑都在 Tick 函数中。在这个例子中，我们将使用一个固定的矢量点，所以每一帧我们都想通过将 **NewLocation** 设为固定的 **FVector** 来初始化我们的固定位置。

接下来，我们想要添加到 **AngleAxis** 变量中，该变量将指示 actor 应该旋转的角度。我们添加了 **DeltaTime** 乘以我们的 **Multiplier** 来平滑移动。如果 **AngleAxis** 大于或等于 360，我们将 **AngleAxis** 重置为 0。

接下来，我们将通过使用 **RotateAngleAxis** 函数从 **Dimensions** 位置（以它为半径旋转）来设置 **RotateValue**。  
这会返回将 actor 移动到下一个位置所需的单位数量。  
将 **RotateValue** 的 X、Y 和 Z 值相应地添加到 **NewLocation** 变量中。  
我们将把 **`RotateValue`** 和 `AngleAxis`变量打印到屏幕上，以便实时查看这些值。

最后，用 **SetActorLocation** 将角色的位置设置为 **NewLocation** 。

FVector RotateAngleAxis
    (
        const float AngleDeg, ///< 旋转的角度
        const FVector & Axis  ///< 围绕的旋转轴
    ) con

Tick 函数的定义

// Called every frame
    void ARotatingAngleAxis::Tick(float DeltaTime)
    {
    	Super::Tick(DeltaTime);
    
    	FVector NewLocation = FVector (0,0,800);
    
    	AngleAxis += DeltaTime * Multiplier;
    
    	if(AngleAxis >= 360.0f) 
    	{
    		AngleAxis = 0;
    	}
    
    	FVector RotateValue = Dimensions.RotateAngleAxis(AngleAxis, AxisVector);
    
    	GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, FString::Printf(TEXT("RotateValue: %s"), *RotateValue.ToString()));	
    	GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("AngleAxis: %f"), AngleAxis));
    
    	NewLocation.X += RotateValue.X;
    	NewLocation.Y += RotateValue.Y;
    	NewLocation.Z += RotateValue.Z;
    
    	SetActorLocation(NewLocation, false, 0, ETeleportType::None);
    	
    }

完整的 cpp 代码如下

#include "RotatingAngleAxis.h"
    
    // Sets default values
    ARotatingAngleAxis::ARotatingAngleAxis()
    {
     	// 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;
    
    	Dimensions = FVector (300, 0, 0);
    	AxisVector = FVector (0, 0, 1);
    	Multiplier = 50.f;
    
    }
    
    // Called when the game starts or when spawned
    void ARotatingAngleAxis::BeginPlay()
    {
    	Super::BeginPlay();	
    	
    }
    
    // Called every frame
    void ARotatingAngleAxis::Tick(float DeltaTime)
    {
    	Super::Tick(DeltaTime);
    
    	FVector NewLocation = FVector (0,0,800);
    
    	AngleAxis += DeltaTime * Multiplier;
    
    	if(AngleAxis >= 360.0f) 
    	{
    		AngleAxis = 0;
    	}
    
    
    	FVector myCharacter = GetWorld()->GetFirstPlayerController()->GetPawn()->GetActorLocation();
    
    	FVector RotateValue = Dimensions.RotateAngleAxis(AngleAxis, AxisVector);
    
    	GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, FString::Printf(TEXT("RotateValue: %s"), *RotateValue.ToString()));	
    	GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("AngleAxis: %f"), AngleAxis));
    
    	NewLocation.X += RotateValue.X;
    	NewLocation.Y += RotateValue.Y;
    	NewLocation.Z += RotateValue.Z;
        
        /// @note 仅公转
    	///SetActorLocation(NewLocation, false, 0, ETeleportType::None);
    
    
        /// @note 公转的同时还会绕自转
    	FRotator NewRotation = FRotator(0, AngleAxis, 0); ///< pitch, yaw, roll
    	FQuat QuatRotation = FQuat(NewRotation);
    	SetActorLocationAndRotation(NewLocation, QuatRotation, false, 0, ETeleportType::None); ///< 立即移动 actor 到指定的位置并旋转。
    	
    }

编译代码。将新 actor 拖放到游戏世界中。向 actor 添加一个静态网格组件（比如立方体）。当你按下 play 时，actor 会找到并绕着给定的矢量点旋转。。

运行效果如下

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3BhbmRhMTIzNGxlZQ_size_16_color_FFFFFF_t_70][]

[Link 1]: https://unrealcpp.com/rotate-angle-axis/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3BhbmRhMTIzNGxlZQ_size_16_color_FFFFFF_t_70]: /images/20220829/3181d40b75eb4f1da90bcf8b1e6e326f.png