Moving from UDK to UE4(pointers)

Development Programming & Scripting C++
1

Hi guys…

I started learning Unreal Script 3 months back and was kind of ok with it. When UE4 got released I decided to switch engines. But now I am feeling as if I hit a wall. I need little help in understanding pointers. Generally the documentation and the wiki didn’t help me a lot. I know what c++ pointers are though.

Here is a small code from 3rd person which I want to start learning from.


UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category=Camera)
	TSubobjectPtr<class USpringArmComponent> CameraBoom;

From what I understood, this creates a pointer of the class SpringArmComponent which


 * This component tried to maintain its children at a fixed distance from the parent,
 * but will retract the children if there is a collision, and spring back when there is no collision.

I need help to understand what this do. And how does “->” work…


	// Create a camera boom (pulls in towards the player if there is a collision)
	CameraBoom = PCIP.CreateDefaultSubobject<USpringArmComponent>(this, TEXT("CameraBoom"));
	CameraBoom->AttachTo(RootComponent);
	CameraBoom->TargetArmLength = 300.0f; // The camera follows at this distance behind the character	
	CameraBoom->bUseControllerViewRotation = true; // Rotate the arm based on the controller

And this part



	// Create a follow camera
	FollowCamera = PCIP.CreateDefaultSubobject<UCameraComponent>(this, TEXT("FollowCamera"));
	FollowCamera->AttachTo(CameraBoom, USpringArmComponent::SocketName); // Attach the camera to the end of the boom and let the boom adjust to match the controller orientation
2

See this Wiki thread. explained pointers extremely well including why we should use it and the advantages.

He also explains about those signs like “->” and “::” etc.

3

I had read it I still had doubts.

Like what is


CameraBoom = PCIP.CreateDefaultSubobject<USpringArmComponent>(this, TEXT("CameraBoom"));

Mostly from what I understand, it creatures a instance of the class SpringArmComponent

And here,


CameraBoom->TargetArmLength = 300.0f;

CameraBoom-> points to the data location of TargetArmLength in the instance class that was created. Am I correct?

4

Pointerb it self is just addrress to instance on varable by using “.” You diracly refereing to pointer or object instance direcly (if its not pointer), when you use -> you refering to what pointer point to. Either way intelisence in VS2013 should red out if you use wrong symbol

5

Hmm didn’t understand properly what you said.

6 

UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category=Camera)
	TSubobjectPtr<class USpringArmComponent> CameraBoom;

This basically creates a variable CameraBoom , this is done in header (.h) file.


// Create a camera boom (pulls in towards the player if there is a collision)
	CameraBoom = PCIP.CreateDefaultSubobject<USpringArmComponent>(this, TEXT("CameraBoom"));
        CameraBoom->AttachTo(RootComponent);
	CameraBoom->TargetArmLength = 300.0f; // The camera follows at this distance behind the character	
	CameraBoom->bUseControllerViewRotation = true; // Rotate the arm based on the controller

This creates a subobject and attaches to the root component of your actor.
Last two lines are simply settings for the ArmComponent.


// Create a follow camera
	FollowCamera = PCIP.CreateDefaultSubobject<UCameraComponent>(this, TEXT("FollowCamera"));
	FollowCamera->AttachTo(CameraBoom, USpringArmComponent::SocketName); // Attach the camera to the end of the boom and let the boom adjust to match the controller orientation

Obviously these lines create a camera and attach it to the ArmComponent.

Now what happens here is you’re simply adding a camera to your character,
if you open the editor, open the blueprint for the default template character,
switch to “Components” tab, and there you shall see a camera above the character,
and a red line pointing from camera to the character.
Well this is same thing, and the red line is TargetArmLength , it defines the distance and angle from ArmComponent to the camera.


->

This sign means it points to a variable of created object(s).