UE4 C++ Line trace "Ignore Self" not working

[MihailoML]

Hello, I have a very simple line trace in my Actor Tick function:

FHitResult outHit;
FVector Start = PromptLocation->GetComponentLocation();
FVector End = DerrickCharacter->GetActorLocation();
TArray<AActor*> actorsToIgnore;

bool bHit = UKismetSystemLibrary::LineTraceSingle(GetWorld(), Start, End, UEngineTypes::ConvertToTraceType(ECC_Visibility), false, actorsToIgnore, EDrawDebugTrace::ForOneFrame, outHit, true);

And this is the function Syntax from the Unreal Docs:

static bool LineTraceSingle
(
const UObject * WorldContextObject,
const FVector Start,
const FVector End,
ETraceTypeQuery TraceChannel,
bool bTraceComplex,
const TArray< AActor * > & ActorsToIgnore,
EDrawDebugTrace::Type DrawDebugType,
FHitResult & OutHit,
bool bIgnoreSelf,
FLinearColor TraceColor,
FLinearColor TraceHitColor,
float DrawTime
)

Everything works well, except that the bIgnoreSelf argument which I set to “true” is not working. When the line trace goes through it’s own Static Mesh it detects a hit.

Keep in mind that the same exact code in Blueprint works perfectly. The line trace doesn’t detect a hit when going through the Static Mesh (when Ignore Self is ticked)

Here’s how it looks in game:

Does anyone have any idea?

[3dRaven]

you need to add the actor to the actorsToIgnore array

if it’s in the character

actorsToIgnore.Add(this);

[MihailoML]

This solves the issue. Thanks!

But do you know why doesn’t the same code work the same in blueprints and in c++?
I’m still wondering why I have to “add (this)” to actorsToIgnore in the c++ version, and I don’t have to do that in the Blueprint version. Why the IgnoreSelf doesn’t work in c++?

[3dRaven]

@MihailoML

IgnoreSelf

I’m guessing the bp version just does that command behind the scenes in the line trace.

C++ always has more direct control of functions but there is usually some extra work with passing in structs.

[youling112358]

I look into its code and find this parameter ‘bIgnoreSelf’ used in this function

If the WorldContextObject you passed by is the Actor you want to ignore, then it will be added into the Params and then it works as same as blueprint ones.

Sometimes blueprint function will hide this same parameter and pass the self automatically and I think the 'WorldContextObject‘ not just means GetWorld()

[MihailoML]

Oh. So when calling LineTraceSingle(), as the first parameter we should put this (get self) instead of GetWorld()?