MiddleCodeCommonNot answered yet

How do you find the object under the mouse cursor or at screen center?

On a APlayerController, find the actor under the mouse cursor in the world. Convert the cursor's screen position into a world-space ray, trace along it, and report the actor that was hit.

Constraints:

Do not treat screen pixel coordinates as world points — deproject first.
Trace on ECC_Visibility; return nullptr when nothing is hit.
Read the hit actor only after confirming the trace actually hit.

AActor* AMyPlayerController::ActorUnderCursor()
{
    // your code here
}

Write the implementation.

Convert the screen point to a world ray with APlayerController::DeprojectScreenPositionToWorld, then line trace along it. For the cursor, GetHitResultUnderCursor does both steps in one call and fills an FHitResult.

✗Treating screen pixel coordinates as world-space points without deprojecting first
✗Forgetting that bShowMouseCursor must be enabled for GetHitResultUnderCursor to work
✗Confusing deproject (screen → world ray) with project (world → screen)

→How would you trace from the exact center of the screen instead of the cursor?
→Why does a deprojected ray need both an origin and a direction, not just a point?

Contents

Object under the cursor

The shortest path is GetHitResultUnderCursor, which deprojects and traces for you:

void AMyPlayerController::TraceUnderCursor()
{
    FHitResult Hit;
    const bool bHit = GetHitResultUnderCursor(ECC_Visibility, false, Hit);

    if (bHit && Hit.GetActor())
    {
        UE_LOG(LogTemp, Log, TEXT("Under cursor: %s"),
            *GetNameSafe(Hit.GetActor()));
    }
}

Object at screen center

Here you deproject manually: a screen point → a ray origin and direction.

void AMyPlayerController::TraceFromScreenCenter()
{
    int32 ViewportX, ViewportY;
    GetViewportSize(ViewportX, ViewportY);
    const FVector2D ScreenCenter(ViewportX * 0.5f, ViewportY * 0.5f);

    FVector WorldOrigin, WorldDirection;
    if (!DeprojectScreenPositionToWorld(
            ScreenCenter.X, ScreenCenter.Y, WorldOrigin, WorldDirection))
        return;

    const FVector End = WorldOrigin + WorldDirection * 10000.0f;

    FHitResult Hit;
    FCollisionQueryParams Params;
    Params.AddIgnoredActor(GetPawn());

    if (GetWorld()->LineTraceSingleByChannel(
            Hit, WorldOrigin, End, ECC_Visibility, Params))
    {
        UE_LOG(LogTemp, Log, TEXT("At screen center: %s"),
            *GetNameSafe(Hit.GetActor()));
    }
}

DeprojectScreenPositionToWorld returns the ray's world-space origin and its direction — screen pixels alone are not world coordinates.