Trigger Box

December 01, 2017

UE4 Version: 4.18.3

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

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.

In this tutorial will trigger an event when the character overlaps a TriggerBox.

Create a new C++ TriggerBox class and call it MyTriggerBox. In the header file add OnOverlapBegin and OnOverlapEnd functions. Below is the final header file.

MyTriggerBox.h

#pragma once

#include "CoreMinimal.h"
#include "Engine/TriggerBox.h"
#include "MyTriggerBox.generated.h"

UCLASS()
class UNREALCPP_API AMyTriggerBox : public ATriggerBox
{
	GENERATED_BODY()

protected:

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

public:

	// constructor sets default values for this actor's properties
	AMyTriggerBox();

    // declare overlap begin function
	UFUNCTION()
	void OnOverlapBegin(class UPrimitiveComponent* OverlappedComp, class AActor* OtherActor, class UPrimitiveComponent* OtherComp, int32 OtherBodyIndex, bool bFromSweep, const FHitResult& SweepResult);

	// declare overlap end function
	UFUNCTION()
	void OnOverlapEnd(class UPrimitiveComponent* OverlappedComp, class AActor* OtherActor, class UPrimitiveComponent* OtherComp, int32 OtherBodyIndex);

In the .cpp file to help us visualize the trigger box, we will have to #include the DrawDebugHelpers.h file.

include files

#include "MyTriggerBox.h"
// include draw debu helpers header file
#include "DrawDebugHelpers.h"

We can also #define some shortcuts for debug logging.

shortcuts for debug logging

#define print(text) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 1.5, FColor::Green,text)
#define printFString(text, fstring) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT(text), fstring))

In the actor's init function we will register the overlap events with OnActorBeginOverlap.AddDynamic and OnActorEndOverlap.AddDynamic.

register overlap events
AMyTriggerBox::AMyTriggerBox()
{
    //Register Events
    OnActorBeginOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapBegin);
    OnActorEndOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapEnd);
}

On BeginPlay we will draw the debug box using DrawDebugBox.

DrawDebugBox

void AMyTriggerBox::BeginPlay()
{
	Super::BeginPlay();

    DrawDebugBox(GetWorld(), GetActorLocation(), GetComponentsBoundingBox().GetExtent(), FColor::Purple, true, -1, 0, 5);
	
}

Next, we will write our overlap functions that simply print a message to the screen indicating the actor that that entered and exited the TriggerBox.

overlap functions

void AMyTriggerBox::OnOverlapBegin(class AActor* OverlappedActor, class AActor* OtherActor)
{
    // check if Actors do not equal nullptr and that 
    if (OtherActor && (OtherActor != this)) {
        // print to screen using above defined method when actor enters trigger box
        print("Overlap Begin");
        printFString("Overlapped Actor = %s", *OverlappedActor->GetName());
    }
}

void AMyTriggerBox::OnOverlapEnd(class AActor* OverlappedActor, class AActor* OtherActor)
{
    if (OtherActor && (OtherActor != this)) {
        // print to screen using above defined method when actor leaves trigger box
        print("Overlap Ended");
        printFString("%s has left the Trigger Box", *OtherActor->GetName());
    }
}

Compile the code. Drag and drop your new actor into your game. Push play and walk in and out of the trigger box. Below is the final .cpp file.

MyTriggerBox.cpp

#define print(text) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 1.5, FColor::Green,text)
#define printFString(text, fstring) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT(text), fstring))

#include "MyTriggerBox.h"
// include draw debu helpers header file
#include "DrawDebugHelpers.h"

AMyTriggerBox::AMyTriggerBox()
{
    //Register Events
    OnActorBeginOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapBegin);
    OnActorEndOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapEnd);
}

// Called when the game starts or when spawned
void AMyTriggerBox::BeginPlay()
{
	Super::BeginPlay();

    DrawDebugBox(GetWorld(), GetActorLocation(), GetComponentsBoundingBox().GetExtent(), FColor::Purple, true, -1, 0, 5);
	
}

void AMyTriggerBox::OnOverlapBegin(class AActor* OverlappedActor, class AActor* OtherActor)
{
    // check if Actors do not equal nullptr and that 
    if (OtherActor && (OtherActor != this)) {
        // print to screen using above defined method when actor enters trigger box
        print("Overlap Begin");
        printFString("Overlapped Actor = %s", *OverlappedActor->GetName());
    }
}

void AMyTriggerBox::OnOverlapEnd(class AActor* OverlappedActor, class AActor* OtherActor)
{
    if (OtherActor && (OtherActor != this)) {
        // print to screen using above defined method when actor leaves trigger box
        print("Overlap Ended");
        printFString("%s has left the Trigger Box", *OtherActor->GetName());
    }
}

Author

Harrison McGuire

Harrison McGuire