/ue-niagara-effects

name: ue-niagara-effects
description: "Use this skill when working with Niagara particle systems, VFX, effects, emitter, Niagara component, or Niagara parameter in Unreal Engine C++. Covers spawning systems, setting parameters, data interfaces (SkeletalMesh, StaticMesh, Curve, Array), OnSystemFinished delegate, and performance tuning. See references/niagara-parameter-types.md for type mapping and references/niagara-data-interfaces.md for data interface catalogue. For particle materials, see ue-materials-rendering."
metadata:
  version: 1.0.0

UE Niagara Effects

You are an expert in controlling Unreal Engine's Niagara VFX system from C++.

Context Check

Read `.agents/ue-project-context.md` before proceeding. Confirm:

• The `Niagara` plugin is listed under enabled plugins (`Plugins/FX/Niagara`).
• The target module's `Build.cs` has `"Niagara"` (and optionally `"NiagaraCore"`) in `PublicDependencyModuleNames`.
• Platform targets: note whether mobile or dedicated-server builds are in scope, because Niagara is

typically suppressed on dedicated servers and may need LOD simplification on mobile.

Information Gathering

Before writing Niagara C++ code, clarify:

1. **Effect lifecycle** — one-shot (fire and forget) or persistent / looping? 2. **Parameter needs** — which Niagara User Parameters must be set from gameplay (positions, colors, scalars)? 3. **Data interfaces required** — SkeletalMesh, StaticMesh, Curve, Array, or custom? 4. **Simulation target** — CPU or GPU sim? (affects which DI features are available) 5. **Performance budget** — pooling required? Mobile scalability tier? 6. **Completion handling** — does gameplay need a callback when the effect finishes?

---

System Structure (UE Concept Map)

UNiagaraSystem  (asset: UNiagaraSystem)
  └── UNiagaraEmitter[]         (per-emitter asset, referenced via FNiagaraEmitterHandle)
        └── UNiagaraScript[]   (Spawn / Update / Event scripts; authored in Niagara editor)
              └── Modules       (stack of NiagaraScript nodes; not C++ classes)

Runtime instances:
  UNiagaraComponent             (scene component that drives one UNiagaraSystem instance)
    └── FNiagaraSystemInstance  (internal runtime state; access via GetSystemInstanceController())

**Key rule**: authors expose parameters to C++ by setting their namespace to `User.` in the Niagara editor. Only `User.*` parameters can be overridden at runtime from C++.

---

Spawning Niagara Systems

Fire-and-Forget (One-Shot) at World Location

#include "NiagaraFunctionLibrary.h"
#include "NiagaraComponent.h"

// Minimal one-shot spawn — component auto-destroys when the system completes.
UNiagaraComponent* NiagaraComp = UNiagaraFunctionLibrary::SpawnSystemAtLocation(
    this,                           // WorldContextObject
    ImpactVFXSystem,                // UPROPERTY(EditAnywhere) UNiagaraSystem*
    HitLocation,                    // FVector Location
    FRotator::ZeroRotator,          // FRotator Rotation
    FVector(1.f),                   // FVector Scale
    /*bAutoDestroy=*/ true,
    /*bAutoActivate=*/ true,
    /*PoolingMethod=*/ ENCPoolMethod::AutoRelease,   // use pool when available
    /*bPreCullCheck=*/ true
);

// Set parameters before the first tick if needed.
if (NiagaraComp)
{
    NiagaraComp->SetVariableVec3(FName("User.HitNormal"), HitNormal);
    NiagaraComp->SetVariableLinearColor(FName("User.HitColor"), DamageColor);
}

Attached to a Component (Persistent / Looping)

// Attaches to a socket and stays active until manually deactivated.
UNiagaraComponent* TrailComp = UNiagaraFunctionLibrary::SpawnSystemAttached(
    TrailVFXSystem,
    WeaponMesh,                             // USceneComponent* AttachToComponent
    FName("MuzzleSocket"),                  // FName AttachPointName
    FVector::ZeroVector,
    FRotator::ZeroRotator,
    EAttachLocation::SnapToTarget,
    /*bAutoDestroy=*/ false,
    /*bAutoActivate=*/ true,
    ENCPoolMethod::ManualRelease,
    /*bPreCullCheck=*/ true
);

Persistent Component on an Actor (Preferred for Repeated Use)

// In header:
UPROPERTY(VisibleAnywhere)
TObjectPtr<UNiagaraComponent> EngineTrailVFX;

// In constructor:
EngineTrailVFX = CreateDefaultSubobject<UNiagaraComponent>(TEXT("EngineTrailVFX"));
EngineTrailVFX->SetupAttachment(GetRootComponent());
EngineTrailVFX->SetAutoActivate(false);   // start inactive; activate via gameplay

// In gameplay code:
EngineTrailVFX->SetAsset(EngineTrailSystem);    // swap asset without destroying component
EngineTrailVFX->Activate(/*bReset=*/ true);

Lifecycle Control

NiagaraComp->Activate(/*bReset=*/ false);       // activate; resume if paused
NiagaraComp->Activate(/*bReset=*/ true);        // activate with full reset
NiagaraComp->Deactivate();                      // stop spawning, let particles drain
NiagaraComp->DeactivateImmediate();             // kill all particles immediately
NiagaraComp->ResetSystem();                     // restart from time 0
NiagaraComp->ReinitializeSystem();              // full re-init + restart (expensive; prefer ResetSystem)
NiagaraComp->SetPaused(true);                   // pause simulation
NiagaraComp->SetAutoDestroy(true);              // destroy component when system finishes

---

Setting Parameters from C++

All setter variants accept the parameter name as `FName` prefixed with its namespace. User-exposed parameters use the `User.` prefix.

// Scalar types
NiagaraComp->SetVariableFloat(FName("User.DamageAmount"), 150.f);
NiagaraComp->SetVariableInt(FName("User.ProjectileCount"), 12);
NiagaraComp->SetVariableBool(FName("User.bIsCritical"), bIsCriticalHit);

// Vector types
NiagaraComp->SetVariableVec2(FName("User.UVOffset"), FVector2D(0.5, 0.25));
NiagaraComp->SetVariableVec3(FName("User.TargetPosition"), TargetLocation);
NiagaraComp->SetVariableVec4(FName("User.CustomData"), FVector4(1, 0.5, 0, 1));
NiagaraComp->SetVariableLinearColor(FName("Use