Ch4 Actors and Components

• AActor() base

  A default Actor Class look like this

in header file MyFirstActor.h

#pragma once

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

UCLASS()
class CHAPTER_04_API AMyFirstActor : public AActor
{
    GENERATED_BODY()
    public:
        //Set default values for this actor's properities
        AMyFirstActor();
    protected:
        //Called when the game started or when spawned
        virtual void BeginPlay() override;
    public: 
        //Called every frame
        virtual void tick(float DeltaTime) override;
}

in cpp file MyFirstActor.cpp

#include "AMyFirstActor.h"
AMyFirstActor::AMyfirstActor()
{
    // set this actor to call Tick() every frame, can be turned off
    PrimaryActorTick.bCanEverTick = true;
}

//Called when game start or spawned
void AMyFirstActor::BeginPlay()
{
    Super::BeginPlay();
}

void AMyFirstActor::Tick(float DeltaTime)
{
    super::Tick(DeltaTime);
}

---

• Destroy AActor

Destroy by time setting timer at BeginPlay() function

FTimerHandle Timer;
GetWorldTimeManager.SetTimer(Timer, this, 
&ACustomGameModeBase::DestroyActorFunction, 10)

implement DestroyActorFunction()

void ACustomGameModeBase::DestroyActorFunction()
{
    if(SpawnedActor != nullptr)
    {
        //Display message on screen
        GEngine->AddOnScreenDebugMessage(-1, 10, FColor::Red, TEXT("Actor Destroyed"));

        SpawnedActor->Destroy();

    }
}

---

• Actor components

Mesh of Actor

//in header file
UPROPERTY()
UStaticMeshComponent *Mesh;

//in cpp file
AMyFirstActor::AMyFirstActor()
{
    //add this line
    Mesh = CreateDefaultSubobject<UStaticMeshComponent>("BaseMeshComponent");
}

Assets loading

after mesh is created, we can load assets from content directory

auto MeshAsset = ConstructoHelpers::FObjectFinder<UStaticMesh>(TEXT("StaticMesh'/Engine/BasicShapes/Cube.Cube'"));
// Check if the MeshAsset is valid before setting it 
if(MeshAsset.Object != nullptr)
{
    Mesh->SetStaticMesh(MeshAsset.Object);
}

Components attaching

let’s say that we have multiple mesh and assets need to bind together in header file HierachyActorh.

UPROPERTY(VisibleAnywhere)
USceneComponent *Root;

UPROPERTY(VisibleAnyWhere)
USceneComponent *ChildSceneComponent;

UPROPERTY(VisibleAnywhere)
UStaticMeshComponent *BoxOne;
UPROPERTY(VisibleAnywhere)
UStaticMeshComponent *BoxTwo;

in cpp file

// create subobject
Root = CreateDefaultSubobject<USceneComponent>("Root");

ChildSceneComponent = CreateDefaultSubobject<USceneComponent>("ChildSceneComponent");

BoxOne = CreateDefaultSubobject<UStaticMeshComponent>("BoxOne");
BoxTwo = CreateDefaultSubobject<UStaticMeshComponent>("BoxTwo");

// get a reference to the cube mesh
auto MeshAsset = ConstructHelpers::FObjectFinder<UStaticMesh>(TEXT("StaticMesh'/Engine/BasicShapes/Cube.cube'"));
//Give both boxes a mesh
if(MeshAsset.Object != nullptr)
{
    BoxOne->SetStaticMesh(MeshAsset.Object);
    BoxTwo->SetStaticMesh(MeshAsset.Object);
}

RootComponent = Root;

//set up the object's hierarchy
BoxOne->AttachTo(Root);
BoxTwo->AttachTo(ChildSceneComponent);

ChildSceneComponent->AttachTo(Root);

// offset and scale the child from the root
ChildSceneComponent->SetRelativeTransform(
    FTransform(FRotator(0,0,0),
            FVector(250,0,0),
            FVector(0.1f))
);