Grabber.cpp

#include "Grabber.h"
#include "Engine/World.h"
#include "GameFramework/PlayerController.h"
#include "DrawDebugHelpers.h"

#define OUT

// Sets default values for this component's properties
UGrabber::UGrabber()
{
	// Set this component to be initialized when the game starts, and to be ticked every frame.  You can turn these features
	// off to improve performance if you don't need them.
	bWantsBeginPlay = true;
	PrimaryComponentTick.bCanEverTick = true;
}


// Called when the game starts
void UGrabber::BeginPlay()
{
	Super::BeginPlay();
	FindPhysicsHandleComponent();
	SetupInputComponent();
}

/// Look for attached Physics Handle
void UGrabber::FindPhysicsHandleComponent()
{
	/// Look for attached Input Component (only appears at run time)
	PhysicsHandle = GetOwner()->FindComponentByClass<UPhysicsHandleComponent>();
	if (PhysicsHandle == nullptr)
	{
		UE_LOG(LogTemp, Error, TEXT("%s missing physics handle component"), *GetOwner()->GetName())
	}
}

/// Look for attached Input Component (only appears at run time)
void UGrabber::SetupInputComponent()
{
	InputComponent = GetOwner()->FindComponentByClass<UInputComponent>();
	if (InputComponent)
	{
		InputComponent->BindAction("Grab", IE_Pressed, this, &UGrabber::Grab);
		InputComponent->BindAction("Grab", IE_Released, this, &UGrabber::Release);
	}
	else
	{
		UE_LOG(LogTemp, Error, TEXT("%s missing input component"), *GetOwner()->GetName())
	}
}

// Called every frame
void UGrabber::TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction)
{
	Super::TickComponent(DeltaTime, TickType, ThisTickFunction);

	// if the phyiscs handle is attached
	if (PhysicsHandle->GrabbedComponent)
	{
		// move the object that we're holding
		PhysicsHandle->SetTargetLocation(GetReachLineEnd());
	}
}

void UGrabber::Grab() {
	/// LINE TRACE and see if we reach any actors with physics body collision channel set
	auto HitResult = GetFirstPhysicsBodyInReach();
	auto ComponentToGrab = HitResult.GetComponent(); //gets the mesh in our case
	auto ActorHit = HitResult.GetActor();
	
	/// If we hit something then attach a physics handle
	if (ActorHit)
	{
		if (!PhysicsHandle) { return; }
		PhysicsHandle->GrabComponentAtLocationWithRotation(
			ComponentToGrab, 
			NAME_None, // no bones needed
			ActorHit->GetActorLocation(),
			ActorHit->GetActorRotation()
		);
	}
}

void UGrabber::Release()
{
	UE_LOG(LogTemp, Warning, TEXT("Grab released"))
}

const FHitResult UGrabber::GetFirstPhysicsBodyInReach()
{
	/// Line-trace (AKA ray-cast) out to reach distance
	FHitResult HitResult;
	FCollisionQueryParams TraceParameters(FName(TEXT("")), false, GetOwner());
	GetWorld()->LineTraceSingleByObjectType(
		OUT HitResult,
		GetReachLineStart(),
		GetReachLineEnd(),
		FCollisionObjectQueryParams(ECollisionChannel::ECC_PhysicsBody),
		TraceParameters
	);
	return HitResult;
}

FVector UGrabber::GetReachLineStart()
{
	FVector PlayerViewPointLocation;
	FRotator PlayerViewPointRotation;
	GetWorld()->GetFirstPlayerController()->GetPlayerViewPoint(
		OUT PlayerViewPointLocation,
		OUT PlayerViewPointRotation
	);
	return PlayerViewPointLocation;
}

FVector UGrabber::GetReachLineEnd()
{
	FVector PlayerViewPointLocation;
	FRotator PlayerViewPointRotation;
	GetWorld()->GetFirstPlayerController()->GetPlayerViewPoint(
	OUT PlayerViewPointLocation,
	OUT PlayerViewPointRotation
);

	return PlayerViewPointLocation + PlayerViewPointRotation.Vector() * Reach;
}