给 Actor 添加径向推力

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。

// 当游戏开始或生成时调用
void AAddRadialForce::BeginPlay()
{
    Super::BeginPlay();

    // 为撞击结果创建 tarray 数组
    TArray<FHitResult> OutHits;

    // 获得 actor 的位置
    FVector MyLocation = GetActorLocation();

    // 开始和结束位置。该球体会创建镜像扫描
    FVector Start = MyLocation;
    FVector End = MyLocation;

    // 创建碰撞球体
    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);

    // 绘制碰撞球体
    DrawDebugSphere(GetWorld(), GetActorLocation(), MyColSphere.GetSphereRadius(), 50, FColor::Cyan, true);
}

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：

参考