Niagara and VFX

The five events

ESDFVFXEvent:

Event	Emitted when
LightImpact	A valid hit below the profile’s heavy VFX thresholds
HeavyImpact	A hit at or above HeavyImpactVFXMinimumPower or HeavyImpactVFXMinimumImpulse
Break	The object is destroyed
DebrisImpact	A debris piece collides fast enough
Custom	Requested explicitly by your own code, with a name

Custom is what makes the VFX layer extensible without touching the framework: your gameplay can request a named effect through the same deterministic, budgeted path as the built-in events.

Weighted variations

Each event reads an array of FSDFWeightedNiagaraSystem:

Property	Default	Meaning
System	none	Soft UNiagaraSystem reference
Weight	1.0	Relative selection weight
MinimumScale	0.9	Lower bound of the random scale
MaximumScale	1.1	Upper bound
bOrientToImpactNormal	true	Align the system’s local Z axis to the impact normal
RotationOffset	zero	Rotation applied after orientation

Soft references mean the Niagara assets are loaded on demand, not pinned by every profile that mentions them. Empty and zero-weight entries are ignored safely.

Orientation

With bOrientToImpactNormal enabled, the system’s local Z axis is aligned to ImpactNormal, then RotationOffset is applied. That is the behaviour you want for surface-hugging effects — dust puffs, splinter sprays, chips.

Disable it for effects authored in world space, such as a volumetric burst that should always rise vertically regardless of which face was hit.

Splinters that look like the object

The supplied wood break effect (NS_SDF_Impact_Wood, used by every wood preset) makes its splinters and chips belong to the object that broke:

• They start where you struck it and burst up and along the swing — never back into the object, where a tall prop’s back or openings would catch them.
• They never hang in the air. Splinters collide on the Camera trace channel, which every SDF debris body ignores: they fly through the broken pieces and land on the real floor. A splinter that still stalls above the floor the object stood on is removed, and every splinter shrinks away at the end of its life instead of popping.
• They take on the object’s look. Splinters show the object’s own base colour texture, each from a different spot; chips are tinted from it and keep their shapes. A light oak bench throws light oak splinters.

How the texture is found

1. When SDF generates, regenerates or modifies a destructible, it records the texture wired into the dominant material’s Base Color in the profile’s SourceAppearance (FSDFDebrisAppearance: BaseColorTexture, AverageColor, bValid).
2. Without a recorded texture, SDF inspects the material at runtime and keeps colour textures only — sRGB, not normal, roughness, AO or mask maps, not virtual — preferring names such as BaseColor, Albedo, Diffuse, _BC or _D.
3. When nothing qualifies, the splinters keep the supplied wood look.

The texture feeds SDF’s own particle materials, M_SDF_WoodSplinter_Source and M_SDF_WoodChip_Source. The object’s material is never put on particles: a material without the Niagara usage flags renders as the grey default checker in a cooked game.

User parameters written on every built-in spawn

SDF sets these on the spawned component before it activates. Systems that do not declare them ignore them.

Name	Type	Meaning
SDFImpactDirection	Vector3	Hit direction blended with the surface normal
SDFImpactStrength	Float	Destruction Power: VeryLight 0.6, Light 0.85, Medium 1.0, Heavy 1.4, Massive 1.8
SDFRandomSeed	Int32	Seed carried by the request
SDFSplinterOrigin	Position	The struck point (break location when the hit carried none)
SDFSplinterDirection	Vector3	Burst direction: up, along the swing, a little out of the struck face
SDFBoundsMin, SDFBoundsMax	Position	World bounds of the intact object; SDFBoundsMin.Z is the floor it stood on
SDFSourceBaseColor	Texture	The object’s base colour texture, or none
SDFUseSourceTexture	Float	1 when a texture was found, else 0
SDFSourceColor	Linear Color	Average colour of that texture, recorded at authoring

For a duplicated wood system, keep the emitter names NE_SDF_Splinters and NE_SDF_WoodChips and run the editor command SDF.Dev.SetupSplinterEffect /Game/Path/NS_YourWood.NS_YourWood. It wires the texture user parameter into the renderers’ material bindings and saves the system.

Deterministic selection

SelectWeightedVFXVariation(Variations, RandomSeed, OutScale, OutRotation, ImpactNormal, ImpactDirection) is a pure, static, Blueprint-callable function. The same seed yields the same system, scale and rotation.

Built-in spawning versus delegates

Property	Effect
bEnableVFXRequests	Master switch: emit VFX requests at all
bEnableBuiltInVFXSpawning	Also spawn the selected Niagara system directly

The request payload

FSDFDestructionVFXRequest:

Field	Meaning
Event	Which of the five events
CustomEventName	Semantic identifier, meaningful for Custom
SourceActor	The destructible
Location	World position
ImpactNormal	Surface normal used for orientation
ImpactDirection	Direction of the causing hit
Rotation	Resolved rotation
Scale	Resolved scale
ImpactSpeed	Speed associated with the event
DestructionPower	Power of the causing hit
SelectedSystem	The Niagara variation picked
RandomSeed	Seed used
SelectedVariationIndex	Index into the profile array
bBuiltInSpawnRequested	Built-in spawning was configured
bBuiltInSpawnAttempted	A spawn was actually attempted
bBuiltInSpawnSuppressedByBudget	The per-frame built-in VFX budget suppressed it
SplinterOrigin	Where splinters start: the struck point on a break
SplinterDirection	Burst direction for splinters
SourceBounds	World bounds of the intact object
Appearance	FSDFDebrisAppearance of the broken object (texture, average colour, valid flag)

Requesting a custom effect

RequestVFXEvent(Event, Location, ImpactNormal, ImpactDirection, ImpactSpeed, DestructionPower, RandomSeed, CustomName) on the destructible component resolves and emits one request. Pass Custom with a CustomName that your presentation system understands, and populate CustomEffects on the profile if you also want built-in spawning.

DestructibleComponent->RequestVFXEvent(
    ESDFVFXEvent::Custom,
    ImpactLocation,
    ImpactNormal,
    ImpactDirection,
    /* ImpactSpeed */ 0.f,
    ESDFDestructionPower::Medium,
    /* RandomSeed */ -1,
    TEXT("EmberBurst"));

Where to listen

Scope	Delegate
One object	USDFDestructibleComponent::OnDestructionVFXRequested
Whole world	USDFDestructionSubsystem::OnDestructionVFXRequested

The global delegate is the correct integration point for a pooled particle manager or a custom Niagara routing layer.

Debris impact VFX

Throttled by the same three-property pattern as audio:

• MinimumDebrisImpactVFXSpeed (default 200.0);
• DebrisImpactVFXCooldown (default 0.15 s);
• MaximumDebrisImpactVFXPerDebrisActor (default 1).

VFX budget

MaxBuiltInVFXEventsPerFrame (default 64) caps built-in spawning only. External listeners keep receiving every request.

GetVFXStats returns FSDFDestructionVFXStats with TotalRequests, TotalBuiltInSpawnAttempts, TotalBuiltInSpawnsSuppressed and BuiltInSpawnAttemptsThisFrame. GetLastVFXRequest returns the most recent payload; ResetVFXStatistics clears the counters.