ItemGrabber.cpp

#include "GameFramework/PlayerController.h"
#include "DrawDebugHelpers.h"
#include "ItemGrabber.h"
// To give myself a heads up that something is an out parameter.
#define OUT


// ----------------------------------------------------------------------
/// Sets default values for this component's properties.
UItemGrabber::UItemGrabber()
{
    // 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.
    PrimaryComponentTick.bCanEverTick = true;

    // ...
}


// ----------------------------------------------------------------------
/// Called when the game starts.
void UItemGrabber::BeginPlay()
{
    Super::BeginPlay();
    NotifyLoading();
    Player = GetWorld()->GetFirstPlayerController();

    // Get the PhysicsHandle component we added to the DefaultPawnBP.
    // UItemGrabber is also attached to DefaultPawnBP, so GetOwner will work for this too.
    // Since FindComponentByClass is a function template, we construct by <type>.
    // This will return the first UPhysicsHandleComponent found in the Owner (DefaultPawnBP).
    PhysicsHandle = GetOwner()->FindComponentByClass<UPhysicsHandleComponent>();

    if (!PhysicsHandle) {
        UE_LOG(LogTemp, Error,
            TEXT("%s has no Physics Handle Component (needed by ItemGrabber)!"),
            *GetOwner()->GetName()
        );
    }
    // ...
}


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

    // Get player's viewpoint and set it to our PlayerView data structure.
    Player->GetPlayerViewPoint(
        OUT PlayerView.Location,
        OUT PlayerView.Rotation);

    GetGrabbableObject();
    DebugLineStuff();
    // If key is pressed, grab object and move to set short distance in front of player.
    // If key is released, release object.
    // ...
}


// ----------------------------------------------------------------------
/// Do a line trace and see what object we can grab. Update GrabbableHit.
void UItemGrabber::GetGrabbableObject()
{
    // The max length point of the ray cast we want.
    // Player location + rotation * the length of grab.
    LineTraceEnd = PlayerView.Location + PlayerView.Rotation.Vector() * Reach;

    // Define what should be considered a collision for what can be grabbed.
    const FCollisionQueryParams TraceParameters(
        FName(TEXT("")),    // The tag name.
        false,              // Use complex collisions?
        GetOwner()          // Which objects to ignore (make sure the ray hitting ourselves doesn't count).
    );

    // LineTrace (raycast) from view to certain distance, see what the cast hits.
    GetWorld()->LineTraceSingleByObjectType(
        OUT GrabbableHit,
        PlayerView.Location,
        LineTraceEnd,
        FCollisionObjectQueryParams(ECC_PhysicsBody),
        TraceParameters
    );
}

// --------------------------------------------------------------------
// Debug helper functions.
// --------------------------------------------------------------------

/// Draw debug line for grabby hands, log grabbable object hit.
void UItemGrabber::DebugLineStuff()
{
    FColor Color;

    DrawDebugLine(
        GetWorld(),              // InWorld.
        PlayerView.Location,     // LineStart.
        LineTraceEnd,            // LineEnd.
        Color.FromHex("00FF15"), // Color.
        false,                   // PersistentLines.
        1,                       // LifeTime.
        0,                       // DepthPriority
        2                        // Thickness.
    );

    // Checking if GrabbableHit has an actor yet,
    // should stop us from referencing a null pointer and crashing.
    if (GrabbableHit.GetActor()) {
        UE_LOG(LogTemp, Warning,
            TEXT("Grabbable object: %s"),
            *GrabbableHit.GetActor()->GetName()
        );
    }
}

/// Notify this component was loaded successfully.
void UItemGrabber::NotifyLoading()
{
    UE_LOG(LogTemp, Warning,
    TEXT("UItemGrabber loaded successfully on %s."),
    *GetOwner()->GetName()
);
}