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

原教程是基于 UE 4.18，我是基于 UE 4.25

英文原地址

核心 API

FCollisionShape

AddRadialImpulse

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;
	
};

AddRadialForce.cpp

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 。

// 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);
}

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。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 ，并向每个成功转换的 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

#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