Third person and LineTracing C++

Question

Problem

I have a crosshair in the middle of the screen.

I need to create a lineTrace that passes straight through this crosshair.

As this is a third person game, I need the line trace to cast through the crosshair

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Question

How do I do this

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Code sample

    #include "GameFramework/PlayerController.h"
    #include "Engine/World.h"
    #include "DrawDebugHelpers.h"
    #include "Camera/PlayerCameraManager.h"
    #include "GrabObjects.h"
    #include "CollisionQueryParams.h"

    #define OUT

    //...

    // Called every frame
    void UGrabObjects::TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction)
    {
        //...

        FVector PlayerViewPointLocation;
        FRotator PlayerViewPointRotation;

        // Get player viewport 
        GetWorld()->GetFirstPlayerController()->GetPlayerViewPoint(
            OUT PlayerViewPointLocation, 
            OUT PlayerViewPointRotation
            );

        // Draw a line from player showing reach
        // PlayerViewPointRotation.Vector() is the unit vector
        FVector LineTraceEnd = PlayerViewPointLocation + PlayerViewPointRotation.Vector() * Reach;

        DrawDebugLine(
            GetWorld(),
            PlayerViewPointLocation,
            LineTraceEnd,
            FColor(0, 255, 0),
            0.f,
            0,
            5.f
        );

        //...
    }

```

Answer 1

You can try doing what you are now, but take the distance from the camera to the player, multiplied by the Camera forward vector to make it begin at the player. This should achieve what you want.

Example, may not be correct or work but hopefully conveys the idea:

float dist = FVector::Distance(PlayerViewPointLocation , GetWorld()->GetFirstPlayerController()->GetPawn()->GetActorLocation());
FVector StartPos = PlayerViewPointLocation + (GetWorld()->GetFirstPlayerController()->PlayerCameraManager->GetForwardVector() * dist);

Note: If you are familiar with Matrix transformations you can just use the Cameras Transform (inverse as you want to go from World to Local) to transform the players world space location into the cameras local. Then you can just use the X of the new vector.

Answer 2

Instead of using the predefined GetPlayerViewPoint() to set your location and rotation, you'll need to use this:

PlayerViewportLocation = GetWorld()->GetFirstPlayerController()->GetPawn()->GetActorLocation();
PlayerViewportRotation = GetWorld()->GetFirstPlayerController()->GetPawn()->GetActorRotation();

This will set your parameters from the location of the pawn itself and not the camera.