Sweep Multi Line Trace

December 01, 2017

UE4 Version: 4.18.3

Github Link: https://github.com/Harrison1/unrealcpp/tree/master/MySweepActor

For this tutorial we are using the standard first person C++ template with starter content. If you don't know how to add a new actor class to your project, please visit the Add C++ Actor Class post.

This tutorial will illustrate how to use the SweepMultiByChannel to return the results hit inside a given radius.

Create a new C++ actor class and call it MySweepActor. We are not going to do anything to the header file. Below is the final header file script.

MySweepActor.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "MySweepActor.generated.h"

UCLASS()
class UNREALCPP_API AMySweepActor : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	AMySweepActor();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;
	
};

Before we get the logic of the code we have to first #include the DrawDebugHelpers.h file help us visualize our actor.

include helpers

#include "MySweepActor.h"
// include debug helpers
#include "DrawDebugHelpers.h"

For this example we are going to perform all of our logic in our BeginPlay() function. First we'll create a TArray of FHitResults and call it OutHits. We want the sphere to start and stop in the same location and will make it equal the actor's location by using GetActorLocation. The Collision sphere can be different shapes, in this example we will make it a sphere by using FCollisionShape::MakeSphere and we'll set it's radius set to 500 unreal units. Next, run the DrawDebugSphere to visualize the sweeping sphere. Then, we want to set a bool called isHit to check if our sweep hit anything. We run GetWorld()->SweepMultiByChannel to perform the sweep channel trace and return the hit to the OutHits array. You can learn more about the SweepMultiByChannel function here. If isHit is true we will loop through the TArray and print out the hit actor's name and other relevant information. You can learn more about TArrays here.

Below is the final .cpp file.

MySweepActor.cpp

#include "MySweepActor.h"
#include "DrawDebugHelpers.h"


// Sets default values
AMySweepActor::AMySweepActor()
{
 	// 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 AMySweepActor::BeginPlay()
{
	Super::BeginPlay();

	// create tarray for hit results
	TArray<FHitResult> OutHits;
	
	// start and end locations
	FVector SweepStart = GetActorLocation();
	FVector SweepEnd = GetActorLocation();

	// create a collision sphere
	FCollisionShape MyColSphere = FCollisionShape::MakeSphere(500.0f);

	// draw collision sphere
	DrawDebugSphere(GetWorld(), GetActorLocation(), MyColSphere.GetSphereRadius(), 50, FColor::Purple, true);
	
	// check if something got hit in the sweep
	bool isHit = GetWorld()->SweepMultiByChannel(OutHits, SweepStart, SweepEnd, FQuat::Identity, ECC_WorldStatic, MyColSphere);

	if (isHit)
	{
		// loop through TArray
		for (auto& Hit : OutHits)
		{
			if (GEngine) 
			{
				// screen log information on what was hit
				GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("Hit Result: %s"), *Hit.Actor->GetName()));
				// uncommnet to see more info on sweeped actor
				// GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, FString::Printf(TEXT("All Hit Information: %s"), *Hit.ToString()));
			}						
		}
	}
	
}

// Called every frame
void AMySweepActor::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

Compile the code. Drag and drop the actor into your game and the sweep will output the results.

Author

Harrison McGuire

Harrison McGuire