Melee Trace

Frame-rate independent hit detection with swept traces and automatic damage application.

Frame-perfect hit detection that works at any frame rate. No more attacks passing through enemies.

When to Use This

• Any game with melee combat (works for both AI and player characters)
• Fast weapon swings that might miss at low framerates
• Multiple hit zones on a single weapon (blade tip vs. hilt)
• Configurable damage per weapon or attack

This system is completely standalone and works independently of the AI systems.

Core Concepts

The Problem

Traditional per-frame collision checks can miss:

Frame 1:  Sword ──→    [Enemy]
Frame 2:              [Enemy]   ←── Sword
                        ↑
          Sword passed through between frames!

At 30 FPS, a fast sword swing can teleport 50cm between frames, missing the target entirely.

The Solution: Swept Traces

The component remembers where the weapon was last frame and traces the entire path:

Frame 1 position ═══════════════► Frame 2 position
                   ↑
            Continuous trace catches the hit

This works identically at 30 FPS or 144 FPS.

Trace Sockets

Weapons define trace sockets, which are points along the weapon that are tracked:

                  ┌─────────────────┐
   Handle         │     BLADE       │         Tip
   [socket]───────┴─────────────────┴────────[socket]
     ↑                                          ↑
  blade_start                               blade_end

The component traces between these sockets, creating a swept volume that matches the weapon's swing.

Trace Shapes

For swords, use CapsuleTwoPoint with blade_start and blade_end sockets.

Quick Setup

1. Add Sockets to Weapon Mesh

In your weapon's skeletal/static mesh, add sockets:

• blade_start: Base of the hitbox
• blade_end: Tip of the hitbox

2. Create Weapon Blueprint

Inherit from ASECWeaponBase:

// In Class Defaults:
AttachSocket: "RightHandSocket"     // Socket on character skeleton
DefaultAttachOffset: (Transform)     // Offset after attachment
 
TraceSockets:
  - ID: "Blade"
    Shape: CapsuleTwoPoint
    SocketOrBoneName: "blade_start"
    EndSocketOrBoneName: "blade_end"
    Radius: 15.0
    TraceChannel: ECC_Pawn
 
DamageConfig: DA_SwordDamage        // Reference to damage data asset

3. Create Damage Config

Right-click → Data Asset → SECDamageConfig

BaseDamage: 25.0
DamageType: UDamageType_Physical
bCanBeBlocked: true
bCanBeParried: true
ImpulseStrength: 500.0

See Configuration Reference for all options.

4. Add Notify States to Animation

In your attack montage:

1. Right-click timeline at the start of the swing
2. Add Notify State → SECMeleeTraceWindow
3. Drag to cover the active swing frames
4. Configure: SocketIDs: ["Blade"]

Timing guide:

Frame:     0    10    20    30    40    50
Animation: [━━━━][━━━━][━━━━][━━━━][━━━━]
           Windup Strike  Follow Recovery
                  ↑
Trace Window:    [═══════════]
                Start        End

5. Done!

When the weapon is equipped and the montage plays:

1. Weapon auto-registers its trace sockets with the character's MeleeTraceComponent
2. Notify state triggers tracing during active frames
3. Hits apply damage automatically via ApplyDamage

Key Properties

On Weapon (ASECWeaponBase)

On Character (USECMeleeTraceComponent)

Key Functions

// Called automatically by weapon on equip
void RegisterWeaponTraceSockets(const TArray<FSECTraceSocket>& Sockets);
 
// Called by notify state
void StartTracing(const TArray<FName>& SocketIDs, UDamageConfig* Config, bool bDebug);
void StopTracing();
 
// Manual control (if not using notify states)
void BeginTrace(FName SocketID);
void EndTrace(FName SocketID);
 
// Events
FOnMeleeHit OnMeleeHit;  // Delegate when hit occurs

Advanced: Custom Damage Handling

If you don't want to use Unreal's built-in ApplyDamage, bind to the delegate:

MeleeTraceComponent->OnMeleeHit.AddDynamic(this, &AMyCharacter::HandleMeleeHit);
 
void AMyCharacter::HandleMeleeHit(const FHitResult& Hit, float Damage, UDamageConfig* Config)
{
    // Your custom damage logic
    IHealthInterface* Health = Cast<IHealthInterface>(Hit.GetActor());
    if (Health)
    {
        Health->TakeDamage(Damage, Config->bCanBeBlocked, Config->bCanBeParried);
    }
}

Debug Tools

Console Command:

SEC.Debug.Melee.DrawTracing 1   // Visualize swept traces

In Component:

MeleeTraceComponent->bDebugDraw = true;

This draws the trace volumes in real-time. Very useful for tuning socket positions and timing.

Common Issues

Integration Points

When used with the full plugin, the melee trace integrates automatically. Weapons register on equip and animation notifies trigger tracing.

For standalone use (player characters, destructibles), just add USECMeleeTraceComponent to your actor and call StartTracing()/StopTracing() manually.