UE4_20 Scripting with C++ 03

在继续学习新的内容时仅针对学过的章节做一点总结，最好是比较一下Unity3D。不对这两种引擎本身做褒贬。相对的，U3D的一些知识却能帮助去理解UE4的Actor和Componet。Unity3D一开始就要接触到GameObject以及Component，然后会通过代码来获取和设置GameObject的属性，或者是获取与设置Component的属性。

U3D的脚本是CS文件，对于U3D而言，同样也是组件，需要与物体绑定以执行功能；
而UE4的C++类中实现U3D组件功能的却是ComponentActor,SceneActor等等的类。

U3D的脚本文件具有生命周期，Awake()  Start()  Update() OnDistory() 等；
UE4的类也具有生命周期：BeginPlay() Tick() 并且对于UObject与OnDestroyCondition()，
对于Actor有Destroy方法

U3D的GameObject类是所有对象的基类，
UE4的基类是UObject和AActor，其中AActor又继承自UObject

U3D提供了游戏对象的常用操作：
查找：Find()、FindGameObjectWithTAg、FindGameObjectsWithTag()等
创建：New GameObject ,或者是Instantiate
获取组件信息：GetComponent<ComponentName>()
Transform为固定组件，
gameObject为脚本所绑定的物体

UE4中Actor的操作呢？
对于Actor类可以在类中直接操作，需查看Actor相关文档
关注了如何创建和销毁一个Actor，GetWolrd()->SpawnActor，
而且明确规定了Object或者Actor不能够通过new的方式来创建
在代码中为Actor添加组件。
对于ActorComponent或者是SceneCompont,可以通过GetOwner获取当前所绑定的Actor

接下来继续Chapter4剩下的内容，偏重于实操：

单词本：
Inventory：库存，清单，财产目录
An InventoryComponent enables its containing Actor to store InventoryActors in its inventory, and place them back into the game world.

Creating an InventoryComponent for an RPG

说明：这个实例用到了本书后两章讲解的内容Handling Events and Delegates,以及Input and Collision。不要求立即照着做

自定义一个清单组件，用于使得一个Actor把一些资源类目放到清单中，并且从清单中再把资源放到游戏世界中。第一版的这里是看不了的，比较的乱。第二版提供了详细的插图作为参考。这一部分的代码过于硬核。故先简述逻辑。

粘一段移动的代码，自行体会下有多硬核

现在主推的比较合理的做法：

创建InventoryCompont清单组件，这是一个ActorComponent,里面含有一个Tarray<InVentoryActor* >
用于存储放到清单中的物体
创建InVentoryActor，这个为要拾取的物体，该物体具有PickUp和PutDown操作
创建一个Character，包含清单组件，在Character的碰撞事件中判断是是否是InVentoryActor
，是的话，就调用InVentoryActor的PickUp操作，
另外自定义DropDown按键事件，按下时会调用InVentoryActor的PutDown操作

注意事项：为了使能碰撞事件，需要StaticMesh具有碰撞体

//InventoryActor.h
#pragma once
#include "CoreMinimal.h"
#include "Engine/StaticMeshActor.h"
#include "InventoryActor.generated.h"
UCLASS()
class CHAPTER_04_API AInventoryActor : public AStaticMeshActor
{
	GENERATED_BODY()
	AInventoryActor();	
public:
	virtual void PickUp();
	virtual void PutDown(FTransform TargetLocation);
	
};

//InventoryActor.cpp
AInventoryActor::AInventoryActor()
:Super(){
	PrimaryActorTick.bCanEverTick = true;
	auto MeshAsset=ConstructorHelpers::FObjectFinder<UStaticMesh>(
		TEXT("StaticMesh'/Game/SM_Cube.SM_Cube'"));
	if(MeshAsset.Object!=nullptr){
		GetStaticMeshComponent()->SetStaticMesh(MeshAsset.Object);
		GetStaticMeshComponent()->SetCollisionProfileName(UCollisionProfile::Pawn_ProfileName);	
	}
	GetStaticMeshComponent()->SetMobility(EComponentMobility::Movable);
	SetActorEnableCollision(true);
}

void AInventoryActor::PickUp()
{
	SetActorTickEnabled(false);
	SetActorHiddenInGame(true);
	SetActorEnableCollision(false);
}
void AInventoryActor::PutDown(FTransform TargetLocation)
{
	SetActorTickEnabled(true);
	SetActorHiddenInGame(false);
	SetActorEnableCollision(true);
	SetActorLocation(TargetLocation.GetLocation());
}

//InventoryComponent.h
#pragma once
#include "CoreMinimal.h"
#include "InventoryActor.h"
#include "Components/ActorComponent.h"
#include "InventoryComponent.generated.h"
UCLASS( ClassGroup=(Custom), meta=(BlueprintSpawnableComponent) )
class CHAPTER_04_API UInventoryComponent : public UActorComponent
{
	GENERATED_BODY()
public:	
	UInventoryComponent();
protected:
	virtual void BeginPlay() override;
public:	
	virtual void TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction) override;
	UPROPERTY()
	TArray<AInventoryActor*>CurrentInventory;
	UFUNCTION()
		int32 AddToInventory(AInventoryActor* ActorToAdd);
	UFUNCTION()
		void RemoveFromInventory(AInventoryActor* ActorToRemove);	
};

//InventoryComponent.Cpp
int32 UInventoryComponent::AddToInventory(AInventoryActor * ActorToAdd)
{
	return CurrentInventory.Add(ActorToAdd);
}

void UInventoryComponent::RemoveFromInventory(AInventoryActor * ActorToRemove)
{
	CurrentInventory.Remove(ActorToRemove);
}

//InventoryCharacter.h
#pragma once
#include "CoreMinimal.h"
#include "InventoryComponent.h"
#include "InventoryActor.h"
#include "GameFramework/Character.h"
#include "InventoryCharacter.generated.h"
UCLASS()
class CHAPTER_04_API AInventoryCharacter : public ACharacter
{
        ...

	UPROPERTY()
		UInventoryComponent* MyInventory;
	UFUNCTION()
		void DropItem();
	UFUNCTION()
		void TakeItem(AInventoryActor* InventoryItem);
	UFUNCTION()
		virtual void NotifyHit(class UPrimitiveComponent* MyComp, AActor* Other, class UPrimitiveComponent* OtherComp, bool bSelfMoved, FVector HitLocation, FVector HitNormal, FVector NormalImpulse, const FHitResult& Hit)override;
	UFUNCTION()
		void MoveForward(float AxisValue);
	UFUNCTION()
		void MoveRight(float AxisValue);
        ...

};
//InventoryCharacter.cpp
#include "InventoryCharacter.h"
#include "GameFramework/CharacterMovementComponent.h"
#include "Components/InputComponent.h"
// Sets default values
AInventoryCharacter::AInventoryCharacter()
{
 	// Set this character to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;
	MyInventory = CreateDefaultSubobject<UInventoryComponent>("MyInventory");
}

// Called to bind functionality to input
void AInventoryCharacter::SetupPlayerInputComponent(UInputComponent* PlayerInputComponent)
{
	Super::SetupPlayerInputComponent(PlayerInputComponent);
	PlayerInputComponent->BindAction("DropItem", IE_Pressed, this, &AInventoryCharacter::DropItem);
	PlayerInputComponent->BindAxis("MoveForward", this, &AInventoryCharacter::MoveForward);
	PlayerInputComponent->BindAxis("MoveRight", this, &AInventoryCharacter::MoveRight);
	PlayerInputComponent->BindAxis("CameraPitch", this, &AInventoryCharacter::AddControllerPitchInput);
	PlayerInputComponent->BindAxis("CameraYaw", this, &AInventoryCharacter::AddControllerYawInput);
}
void AInventoryCharacter::DropItem()
{
	if (MyInventory->CurrentInventory.Num() == 0) { return; }
	AInventoryActor* Item = MyInventory->CurrentInventory.Last();
	MyInventory->RemoveFromInventory(Item);

	FVector ItemOrigin;
	FVector ItemBounds;
	Item->GetActorBounds(false, ItemOrigin, ItemBounds);
	FTransform PutDownLocation = GetTransform() + FTransform(RootComponent->GetForwardVector());
	Item->PutDown(PutDownLocation);
}

void AInventoryCharacter::NotifyHit(UPrimitiveComponent * MyComp, AActor * Other, UPrimitiveComponent * OtherComp, bool bSelfMoved, FVector HitLocation, FVector HitNormal, FVector NormalImpulse, const FHitResult & Hit)
{
	AInventoryActor* InventoryItem = Cast<AInventoryActor>(Other);
	if(InventoryItem!=nullptr){
		TakeItem(InventoryItem);
		GEngine->AddOnScreenDebugMessage(-1, 3.f, FColor::Red, TEXT("PickUp"));
	}
}
void AInventoryCharacter::TakeItem(AInventoryActor * InventoryItem)
{
	InventoryItem->PickUp();
	MyInventory->AddToInventory(InventoryItem);
}
void AInventoryCharacter::MoveForward(float AxisValue)
{
	FVector MoveDirection = GetActorForwardVector();
	AddMovementInput(MoveDirection,AxisValue);
}
void AInventoryCharacter::MoveRight(float AxisValue)
{
	FVector MoveDirection = GetActorRightVector();
	AddMovementInput(MoveDirection, AxisValue);
}

再来分析下代码：逻辑结构就像下图

TArray集合提供了add/remove用于增删元素，在PickUp操作中，主要是Disable Ticking、Hide Actor 、Disable collision，最后设PutDown操作中则是SetActorTickEnabled, SetActorHiddenInGame, 和 SetActorEnableCollision，最后是重新设置Actor的位置。

在Character中，主要是通过重写NotifyHit，当碰撞发生时，获取碰撞体的信息，如果是要拾取的物体，则调用该物体的PickUp，并且把该物体存储到清单中。

Creating an OrbitingMovement Component和Creating a building that spawns units

这两小节保留，书上讲的有点浅了，涉及3D数学，对于3D数学的玩法，日后需要专门的整理一遍。

UE4_20 Scripting with C++ 03

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