最简单的 UE 4 C++ 教程 —— 给 Actor 添加径向推力【十八】

缺乏、安全感 2022-09-01 08:44 211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，本教程非常有趣，我们将通过在设定范围内的所有物体上添加径向推力来模拟爆炸。

创建一个名为 **AddRadialForce** 的新角色。我们不需要对头文件做任何操作。下面是由虚幻生成的默认头文件。

### AddRadialForce.h ###

#pragma once
    
    #include "CoreMinimal.h"
    #include "GameFramework/Actor.h"
    #include "AddRadialForce.generated.h"
    
    UCLASS()
    class UNREALCPP_API AAddRadialForce : public AActor
    {
    	GENERATED_BODY()
    	
    public:	
    	// Sets default values for this actor's properties
    	AAddRadialForce();
    
    protected:
    	// Called when the game starts or when spawned
    	virtual void BeginPlay() override;
    
    public:	
    	// Called every frame
    	virtual void Tick(float DeltaTime) override;
    	
    };

为了在调试过程中提供帮助，让我们将 **DrawDebugHelpers** 头文件添加到代码中。

#include "AddRadialForce.h"
    // add debug helpfers
    #include "DrawDebugHelpers.h"

在这个例子中，我们将在 **BeginPlay()** 函数中执行所有的逻辑。我们想要收集我们范围内的所有命中结果，并从范围的扫描中获得结果。为此，我们将使用 **TArray** 跟踪重叠的 actor。

void AAddRadialForce::BeginPlay()
    {
    	Super::BeginPlay();
    
    	// create tarray for hit results
    	TArray<FHitResult> OutHits;
    
    	// crate tarray for sweep actors
    	TArray<AActor*> SweepActors;
    	
    }

接下来我们要声明 **TArray** 数组 **OutHits** 。我们希望扫描范围从 actor 的位置开始同时也从该位置结束，并让 **CollisionShape** 是一个 500 单位的球体。您可以使用 **GetActorLocation()** 来获取 actor 的位置，它返回一个向量。我们使用 **FCollisionShape:: makephere (500.0f)** 来创建一个**CollisionShape**。

// Called when the game starts or when spawned
    void AAddRadialForce::BeginPlay()
    {
    	Super::BeginPlay();
    
    	// create tarray for hit results
    	TArray<FHitResult> OutHits;
    
    	// get actor locations
    	FVector MyLocation = GetActorLocation();
    	
    	// start and end locations. The sphere will create the radial sweep.
    	FVector Start = MyLocation;
    	FVector End = MyLocation;
    
    	// create a collision sphere
    	FCollisionShape MyColSphere = FCollisionShape::MakeSphere(500.0f);
    	
    }

为了可视化扫描的球体，我们将绘制一个调试球体。

接下来我们要检查我们的 actor 在我们 **BeginPlay()** 时是否击中了任何东西。每个 actor 都有**GetWorld** 功能。从 ，我们将使用从 **GetWorld()** 函数得到的 **SweepMultiByChannel()** 函数并对其设置上面刚创建的变量作为参数。这将返回一个 **bool**，指示是否有其他 actor 在该 actor 的范围内。

void AAddRadialForce::BeginPlay()
    {
    	Super::BeginPlay();
    
    	// create tarray for hit results
    	TArray<FHitResult> OutHits;
    
    	// get actor locations
    	FVector MyLocation = GetActorLocation();
    	
    	// start and end locations. The sphere will create the radial sweep.
    	FVector Start = MyLocation;
    	FVector End = MyLocation;
    
    	// create a collision sphere
    	FCollisionShape MyColSphere = FCollisionShape::MakeSphere(500.0f);
    
    	// draw collision sphere
    	DrawDebugSphere(GetWorld(), GetActorLocation(), MyColSphere.GetSphereRadius(), 50, FColor::Cyan, true);
    	
    	// check if something got hit in the sweep
    	bool isHit = GetWorld()->SweepMultiByChannel(OutHits, Start, End, FQuat::Identity, ECC_WorldStatic, MyColSphere);
    	
    }

如果 isHit 为真，我们将通过遍历数组 OutHits ，并向每个成功 cast 的 actor 的根组件添加径向推力。

if (isHit)
    	{
    		// loop through TArray
    		for (auto& Hit : OutHits)
    		{
    			UStaticMeshComponent* MeshComp = Cast<UStaticMeshComponent>((Hit.GetActor())->GetRootComponent());
    
    			if (MeshComp)
    			{
                    // alternivly you can use  ERadialImpulseFalloff::RIF_Linear for the impulse to get linearly weaker as it gets further from origin.
    				// set the float radius to 500 and the float strength to 2000.
    				MeshComp->AddRadialImpulse(GetActorLocation(), 500.f, 2000.f, ERadialImpulseFalloff::RIF_Constant, true);
    			}
    		}
    	}

最终完整 cpp 代码如下

#include "AddRadialForce.h"
    // add debug helpfers
    #include "DrawDebugHelpers.h"
    
    // Sets default values
    AAddRadialForce::AAddRadialForce()
    {
     	// 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;
    
    }
    
    // Called when the game starts or when spawned
    void AAddRadialForce::BeginPlay()
    {
    	Super::BeginPlay();
    
    	// create tarray for hit results
    	TArray<FHitResult> OutHits;
    
    	// get actor locations
    	FVector MyLocation = GetActorLocation();
    	
    	// start and end locations. The sphere will create the radial sweep.
    	FVector Start = MyLocation;
    	FVector End = MyLocation;
    
    	// create a collision sphere
    	FCollisionShape MyColSphere = FCollisionShape::MakeSphere(500.0f);
    
    	// draw collision sphere
    	DrawDebugSphere(GetWorld(), GetActorLocation(), MyColSphere.GetSphereRadius(), 50, FColor::Cyan, true);
    	
    	// check if something got hit in the sweep
    	bool isHit = GetWorld()->SweepMultiByChannel(OutHits, Start, End, FQuat::Identity, ECC_WorldStatic, MyColSphere);
    
    	if (isHit)
    	{
    		// loop through TArray
    		for (auto& Hit : OutHits)
    		{
    			UStaticMeshComponent* MeshComp = Cast<UStaticMeshComponent>((Hit.GetActor())->GetRootComponent());
    
    			if (MeshComp)
    			{
    				// alternivly you can use  ERadialImpulseFalloff::RIF_Linear for the impulse to get linearly weaker as it gets further from origin.
    				// set the float radius to 500 and the float strength to 2000.
    				MeshComp->AddRadialImpulse(GetActorLocation(), 500.f, 2000.f, ERadialImpulseFalloff::RIF_Constant, true);
    			}
    		}
    	}
    	
    }
    
    // Called every frame
    void AAddRadialForce::Tick(float DeltaTime)
    {
    	Super::Tick(DeltaTime);
    
    }

实际运行起来的效果图如下

![20210727132006459.gif][]

[Link 1]: https://unrealcpp.com/add-radial-impulse-to-actor/
[20210727132006459.gif]: /images/20220829/24251def53b146758622e823fa81427d.png