Performing Box Sweeps for Melee Combat Detection

Utilize shape-based sweeping to accurately detect collisions within a defined area, ideal for creating responsive melee hit registration.

In this lesson, you will learn how to transition from simple line traces to volume-based box sweeps to ensure your melee attacks feel fair and responsive.

Why Line Traces Aren't Enough

When implementing melee combat, a LineTraceByChannel is often too narrow. If your sword swings quickly, a single line might pass through an enemy between frames, causing the attack to "miss" entirely. A Box Sweep solves this by projecting a 3D box volume along a path, catching any collision that enters that space during the swing.

Implementing the Box Sweep

Instead of firing a ray, we use SweepSingleByChannel. Think of this as sliding an invisible box through the game world. If that box overlaps with an actor’s collision volume, the sweep registers a hit.

You define the box using a FCollisionShape and provide a start and end location for the swing arc. Here is how you initialize the shape and perform the check:

// 1. Define the box dimensions (Half-Extent)
FCollisionShape BoxShape = FCollisionShape::MakeBox(FVector(10.f, 20.f, 50.f));

// 2. Perform the sweep
FHitResult HitResult;
bool bHasHit = GetWorld()->SweepSingleByChannel(
    HitResult,
    StartLocation,
    EndLocation,
    FQuat::Identity, // Orientation of the box
    ECC_GameTraceChannel1, // Your custom Melee collision channel
    BoxShape
);

if (bHasHit) {
    // Apply damage to HitResult.GetActor()
}

Strategic Placement

The key to a professional melee system is matching the box to the weapon’s mesh. For a sword, your box should be long and thin. For a heavy club, make it wider. By using your previously defined Custom Collision Channels, you ensure the sweep ignores the player character itself while specifically targeting enemies.

Because sweeps are more computationally expensive than line traces, remember to trigger them only during the "active" frames of your animation using AnimNotify events. This keeps your game performing smoothly while providing that satisfying, "heavy" collision feedback players expect from melee combat.

Key Takeaway: Box Sweeps provide a reliable, volume-based collision detection method that prevents "ghost hits" by accounting for the physical width of your weapon during an attack animation.