Optimizing Multi-Hit Traces for Piercing Projectiles

In this lesson, you will learn how to configure MultiLineTraceByChannel to process multiple targets along a single projectile path, allowing your attacks to pierce through enemies.

Why Multi-Hit Traces?

When you use a standard LineTraceByChannel, the engine stops as soon as it hits the first object. This is perfect for a basic bullet, but for a piercing spell or a sniper rifle that over-penetrates, you need to collect an array of all objects hit along the trajectory. Instead of firing a new trace every time you hit an enemy, you can perform one "Multi" trace that returns every actor intersecting your path.

Implementing the Multi-Trace

The key difference between a standard trace and a multi-hit trace is the data structure returned. While a single trace returns a Hit Result struct, a multi-trace returns an Array of Hit Results.

Here is how you handle the logic:

// Define the trace start and end points
FVector Start = GetActorLocation();
FVector End = Start + (GetActorForwardVector() * 2000.0f);

// Create an array to store all results
TArray<FHitResult> OutHits;

// Execute the Multi-Line Trace
bool bHit = GetWorld()->MultiLineTraceByChannel(
    OutHits, 
    Start, 
    End, 
    ECC_GameTraceChannel1, // Your custom piercing channel
    FCollisionQueryParams::DefaultQueryParam
);

// Iterate through the array to process each hit
for (const FHitResult& Hit : OutHits)
{
    if (AActor* Target = Hit.GetActor())
    {
        // Apply damage or effects to each target in the path
        ApplyPiercingDamage(Target);
    }
}

Performance Considerations

Because multi-traces return every object along the path, it is vital to keep your collision logic clean. Always ensure your Collision Profile is set to "Ignore" for objects you don't care about (like small debris or invisible triggers). The more objects the trace overlaps, the more memory is used to populate that array. By using specific Trace Channels instead of the default visibility channel, you ensure the physics engine only considers relevant gameplay objects, keeping your piercing logic highly performant.

Key Takeaway: By utilizing Multi-Line Traces, you gain access to an array of all collision hits, allowing your projectiles to penetrate multiple targets efficiently in a single physics query.