JuniorCodeVery commonNot answered yet

How do you perform a line trace in C++ in Unreal Engine?

Implement a single-line trace from a weapon's muzzle straight forward and return the first blocking hit, or nullptr if the ray hits nothing.

Constraints:

End must be an absolute world-space point, not a direction vector.
Exclude the firing actor (and its owner) from the trace so it cannot hit itself.
Trace on ECC_Visibility; read the FHitResult only after the boolean result is true.

AActor* AWeapon::FireTrace()
{
    // your code here
}

Write the implementation.

Call GetWorld()->LineTraceSingleByChannel(Hit, Start, End, Channel, Params). It writes the first blocking hit into an FHitResult and returns true if something was hit. Start and End are world-space points.

✗Passing a direction vector instead of an absolute world-space End point
✗Forgetting to add the tracing actor to FCollisionQueryParams and hitting itself
✗Reading FHitResult fields without first checking the boolean return value

→How do you trace against multiple objects instead of stopping at the first blocker?
→What is the difference between tracing by channel and tracing by object type?

A simple line trace

void AWeapon::FireTrace()
{
    const FVector Start = GetActorLocation();
    const FVector End   = Start + GetActorForwardVector() * 5000.0f;

    FHitResult Hit;

    // Exclude the weapon's owner from the trace so it doesn't hit itself
    FCollisionQueryParams Params;
    Params.AddIgnoredActor(this);
    Params.AddIgnoredActor(GetOwner());

    const bool bHit = GetWorld()->LineTraceSingleByChannel(
        Hit, Start, End, ECC_Visibility, Params);

    if (bHit)
    {
        // Hit.GetActor()      — the actor that was hit
        // Hit.ImpactPoint     — the world-space point of impact
        // Hit.ImpactNormal    — the surface normal at the impact point
        UE_LOG(LogTemp, Log, TEXT("Hit: %s"), *GetNameSafe(Hit.GetActor()));
        DrawDebugLine(GetWorld(), Start, Hit.ImpactPoint, FColor::Red, false, 1.0f);
    }
    else
    {
        DrawDebugLine(GetWorld(), Start, End, FColor::Green, false, 1.0f);
    }
}