一.要将相机设置在Pawn类里

1.在MyPawn头文件里，加上摇臂和相机组件

#include "GameFramework/SpringArmComponent.h"
#include "Camera/CameraComponent.h"

2.在Pawm里声明SceneComponet，SpringArmComponent,CameraComponent组件指针

再声明一个移动缩放调用的函数

public:
	UPROPERTY(VisibleAnywhere,BlueprintReadOnly,Category = "MySceneComponent")
	USceneComponent* MyRoot;
	UPROPERTY(VisibleAnywhere,BlueprintReadOnly,Category = "MySceneComponent")
	USpringArmComponent* MySpringArm;
	UPROPERTY(VisibleAnywhere,BlueprintReadOnly,Category = "MySceneComponent")
	UCameraComponent* MyCamera;
	//鼠标划轮移动镜头缩放
	void Zoom(bool Direction,float ZoomSpeed);

在Pawn里将的组件通过CreateDefaultSubobject<T>（TEXT("Name")）创造命名。

根组件赋值为MyRoot的物体组件。SetupAttackment来连接子组件。将MySpringArm的bDoCollisionTest = false来停止碰撞。

AMyPawn::AMyPawn()
{
 	// Set this pawn to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;
	MyRoot = CreateDefaultSubobject<USceneComponent>(TEXT("MyRootComponent"));
	MySpringArm = CreateDefaultSubobject<USpringArmComponent>(TEXT("MySpringArmComponent"));
	MyCamera = CreateDefaultSubobject<UCameraComponent>(TEXT("MyCameraComponent"));
	RootComponent = MyRoot;
	MySpringArm->SetupAttachment(MyRoot);
	MyCamera->SetupAttachment(MySpringArm);
	MySpringArm->bDoCollisionTest = false;  //让它无碰撞

3.设置好Pawn的Transform信息。

	FVector MyLocation = FVector(0,0,0);
	FRotator MyRotation = FRotator(-50,0,0);
	FVector MyScale = FVector(1,1,1);
	SetActorLocation(MyLocation);
	SetActorRotation(MyRotation);
	SetActorScale3D(MyScale);

4.在滑动函数里，将相机的伸缩臂的伸缩方向和速度的逻辑写好

void AMyPawn::Zoom(bool Direction, float ZoomSpeed)
{
	if (Direction) //1
	{
		if (MySpringArm->TargetArmLength >= 300 && MySpringArm->TargetArmLength < 5000)  //如果摄像机摇臂在300 到 5000之间
		{
			MySpringArm->TargetArmLength += (ZoomSpeed * 2);
			GEngine->AddOnScreenDebugMessage(-1, 5.0f, FColor::Red, FString::Printf(TEXT("SpringArmLength is %f"), MySpringArm->TargetArmLength));
		}
	}
	else
	{
		if (MySpringArm->TargetArmLength > 300 && MySpringArm->TargetArmLength <= 5000)
		{
			MySpringArm->TargetArmLength -= (ZoomSpeed * 2);
			GEngine->AddOnScreenDebugMessage(-1,5.0f,FColor::Red,FString::Printf(TEXT("SpringArmLength is %f"),MySpringArm->TargetArmLength));
		}
	}
}

5.在PlayerController.cpp头文件里包含Pawn。注意顺序（MyPlayerController.h要放在第一个）

#include "MyPlayerController.h"
#include "MyPawn.h"

在PlayerController.h里声明 绑定输入 和 其他功能函数

	virtual void SetupInputComponent();
	void WheelUpFunction();
	void WheelDownFunction();

设置输入绑定事件，由于要重写SetupInputComponent虚函数，首先要继承父类的Super::SetupInputComponent()； 这个在UE里要写。再加上额外添加的代理绑定功能。

通过绑定输入代理，调用PlayerController的新定义的函数

void AMyPlayerController::SetupInputComponent()
{
	Super::SetupInputComponent();
	InputComponent->BindAction("WheelUp",IE_Pressed,this,&AMyPlayerController::WheelUpFunction);
	InputComponent->BindAction("WheelDown",IE_Pressed,this,&AMyPlayerController::WheelDownFunction);
}

新定义的函数中，通过GetPawn()拿到，GameMode里的Pawn,把它转换为AMyPawn。如果转换成功，在调用里面的MyPawn里的Zoom函数。

void AMyPlayerController::WheelUpFunction()
{
	if (GetPawn())
	{
		AMyPawn* MyCameraPawn = Cast<AMyPawn>(GetPawn());
		if (MyCameraPawn)
		{
			MyCameraPawn->Zoom(true, 10);
		}
	}
}

void AMyPlayerController::WheelDownFunction()
{
	if (GetPawn())
	{
		AMyPawn* MyCameraPawn = Cast<AMyPawn>(GetPawn());
		if (MyCameraPawn)
		{
			MyCameraPawn->Zoom(false, 10);
		}
	}
}

可以伸缩，并且打印SpringArm的长度