System Spawn Group

This document provides reference information for modules in the System Spawn group.

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System Spawn modules occur once per created system. Modules in this section set up initial values for each system. Modules are executed in order from the top to the bottom of the stack.

Each of these module types has its own section, with tables describe how that module functions. Keep in mind, you can create custom modules for any part of a Niagara system or emitter. The ones listed here are just the ones that are automatically included with Unreal Engine.

Create New Parameter

When you select Create New Parameter, you select from the variables listed. This adds a Set Variable module to the Emitter Update section, which allows you to interact with Niagara variables outside of the usual module graph.

Parameter

Type

Description

Bool

Primitive

This adds a Set Variable module that has a true/false checkbox.

ENiagaraBooleanLogicOps

Enum

This is an enumeration used by various modules and dynamic inputs that want to test using boolean logic:

  • Greater Than

  • Greater Than Or Equal To

  • Equal To

  • Not Equal To

ENiagaraCoordinateSpace

Enum

This is an enumeration used by various modules and dynamic inputs to distinguish between coordinate spaces:

  • Simulation: If the emitter is set to local, use local. Otherwise, use World.

  • World: In the world space of the game.

  • Local: In the coordinate space of the owning component.

ENiagaraExecutionState

Enum

This enumeration type is used by parameters that manage system or emitter execution states, such as Emitter.ExecutionState or System.ExecutionState.

ENiagaraExecutionStateSource

Enum

This indicates the source of an execution state setting. It is used to allow scalability to change the state, but only if the state has not been defined by something with higher precedence.

ENiagaraExpansionMode

Enum

This enumeration is used by location modules to determine where the origin point of expansion is:

  • Inside

  • Centered

  • Outside

ENiagaraLegacyTrailMode

Enum

This enum controls the way that the width scale property affects animation trails. This is only used for Legacy Anim Trail support when converting from Cascade to Niagara.

ENiagaraOrientationAxis

Enum

This is an enumeration used by several modules to determine which axis to do calculations with:

  • X Axis

  • Y Axis

  • Z Axis

ENiagaraRandomnessMode

Enum

This sets the type of random number generation used by this emitter. Valid choices are:

  • Simulation Defaults

  • Deterministic

  • Non-Deterministic

Float

Primitive

This creates a float value variable.

Int32

Primitive

This creates an integer variable.

Linear Color

Primitive

This creates an RGBA color variable, represented as a color picker.

Matrix

Primitive

This creates a 4x4 matrix variable.

Mesh Tri Coordinate

Struct

This is a simple struct containing a triangle index along with a barycentric coordinate on the face of that triangle.

Niagara ID

Struct

This is a two-part struct used to track particles. Index in the indirection table for this particle. It allows fast access to this particle's data. It is always unique among currently living particles, but will be reused after the particle dies. AcquireTag is a unique tag for when this ID was acquired. It allows us to differentiate between particles when one dies and another particle reuses the dead particle's Index.

Quat

Primitive

This creates a quaternion variable, used to represent rotations.

Spawn Info

Struct

This is a structure used in spawning to specify the Count of particles to create, InterpStartDt or offset from the current frame begin time to start spawning, IntervalDt defining the time gap between particles being spawned, and SpawnGroup allowing spawned particles to belong to different categories.

Vector

Primitive

This creates a three-channel set of floats.

Vector 2D

Primitive

This creates a two-channel set of floats.

Vector 4

Primitive

This creates a four-channel set of floats.

Set Specific Parameters

When you select Set Specific Parameter, you select from the parameters listed. This adds a Set Variable module to the System Spawn group. Note: some of these parameters can be set or modified in other modules. Some are only set using a Set Variable module.

Parameter

Description

System Name.Age

This parameter defines the age of the named system.

System Name.CurrentLoopDelay

This parameter defines the current amount of delay before the named system's current loop repeats.

System Name.CurrentLoopDuration

This parameter defines the duration of the named system's loop.

System Name.ExecutionState

This affects the state of the system. Valid value choices are:

  • Active

  • Inactive

  • InactiveClear

  • Complete

System Name.ExecutionStateSource

This indicates the source of an execution state setting. It is used to allow scalability to change the state, but only if the state has not been defined by something with higher precedence.

System Name.LocalSpace

This parameter defines whether the position of particles is respective to the world origin or the owning Niagara Component's location.Settings are:

  • False: Particle position is in WorldSpace and will be relative to the World origin. A particle with position 0,0,0 will render at the World origin.

  • True: Particle position is in LocalSpace and will be relative to the owning Niagara Component's location. A particle with position 0,0,0 will render at the owning Niagara Component's location.

System Name.LoopCount

This parameter defines how many times the system's loop repeats.

System Name.LoopedAge

This parameter calculates the age of the system relative to its current loop. For example, if a system has been active for 8 seconds and it loops every 5 seconds, the system's LoopedAge will be 3 seconds. LoopedAge returns to 0 every time a system loops.

System Name.NormalizedLoopAge

This parameter calculates the age of the system relative to its current loop, normalized from 0 to 1. NormalizedLoopAge is expressed as LoopedAge divided by CurrentLoopDuration. If a system has been active for 8 seconds and it loops every 5 seconds, the system's LoopedAge will be 3. The system's NormalizedLoopAge will be 0.6.

System.ExecutionState

This affects the state of the system. Valid value choices are:

  • Active

  • Inactive

  • InactiveClear

  • Complete

System.ExecutionStateSource

This variable is linked to the ENiagaraExecutionStateSource parameter, which indicates the source of a system execution state setting. It is used to allow scalability to change the state, but only if the state has not been defined by something with higher precedence.

Shapes Modules

Parameter

Description

Sphere Plane Intersection System

This module finds any position in which a plane intersects a sphere.

Output.Module.CircleCentertoPosition can be used to add an outward force to the particle on the intersection plane.

Vector Field Modules

Parameter

Description

Construct Bounding Box for Vector Field

Transforms twelve instances of the Bounding Box Edge Mesh in such a way that they form a cube representing the bounding box of some vector field. Optionally, this applies a local translation, rotation and scale transformation.

Distribute Arrows for Vector Field

Distributes points in a grid based on a vector field. Optionally, this applies a local translation, rotation and scale transformation.

Get Vector Field Properties

Extracts relevant properties from a vector field object, and calculates some additional useful properties. Optionally, this applies a local translation, rotation and scale transformation.

Sample Vector Field

Samples a vector field, applying a per-particle intensity factor and an optional falloff factor that fades the influence of the vector field towards the edges of the bounding box. Optionally, this applies a local translation, rotation and scale transformation.

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