Emitter Update Group

This document provides reference information for Emitter Update modules in a Niagara emitter.

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Emitter Update modules occur every time the emitter ticks on the CPU. Modules in this group should compute values for Particle Spawn or Update parameters in this frame. Modules are executed in order from the top to the bottom of the stack.

Each of the module types in the Emitter Update group has its own section in this document, with tables that list and describe the default options available for that type of module. Keep in mind that you can create custom modules for any part of the Niagara emitter. The ones listed here are just the ones that are automatically included with Unreal Engine 4.

Beam Modules

Module

Description

Beam Emitter Setup

This module sets up and manages start points, endpoints and tangents for a beam emitter.

Chaos Modules

Module

Description

Spawn from Chaos

This module causes particles to spawn in response to a Chaos event.

Emitter State

Parameter

Description

Life Cycle Mode

This setting determines whether life cycle (looping, age and death) is managed by the emitter itself, or by the system that owns the emitter. Settings are:

  • System: When you select this option, the owning system will calculate all life cycle functions. In most cases, having systems calculate life cycle increases optimization. Selecting this option hides the other fields.

  • Self: When you select this option, the emitter itself will calculate life cycle functions. Selecting this option makes the other settings below available.

Inactive Response

This setting determines what happens when the emitter enters the Inactive state. Inactive means the emitter is dormant and no longer able to spawn or manage particles. Options are:

  • Complete: Particles will finish, then the emitter is killed.

  • Kill: Emitter and particles are both killed immediately.

  • Continue: Emitter is deactivated, but does not die until the system does.

Loop Behavior

This determines the behavior of the emitter. You can select from the following:

  • Once: the emitter plays the animation once.

  • Multiple: the emitter plays the animation a fixed number of times.

  • Infinite: the emitter plays the animation infinitely.

Loop Duration

This determines how long the loop lasts.

Loop Duration Mode

This determines whether the loop is finite or infinite.

Loop Delay

This setting delays the next loop by a given amount.

Scalability

Scalability Mode

This determines whether the emitter will take scalability settings from the system, or if it will have its own unique scalability settings. You can choose from the following:

  • System: When you select this option, the owning system will calculate all life cycle functions. In most cases, having systems calculate life cycle increases optimization. Selecting this option hides the other fields.

  • Self: When you select this option, the emitter itself will calculate life cycle functions. Selecting this option makes the other settings below available.

Enable Distance Culling

Check this box to enable. This enables the culling of emitters based on the emitter's distance from the camera. Emitters can go to sleep, reawaken, be killed, and so on when they are a certain distance from the camera.

Enable Visibility Culling

Check this box to enable. This enables the culling of emitters based on whether they are visible to the camera. Emitters can go to sleep, reawaken, be killed, and so on based on whether they are onscreen or offscreen.

Reset Age on Awaken

Check this box to enable. When this emitter reawakens after being put to sleep by a scalability setting, this setting will reset the emitter's age. This means spawn bursts will refire, and the emitter's life cycle will restart.

Location Module

Module

Description

Spawn Particles in Grid

This spawns particles based on user-defined grid resolution settings.

MAX Scripts Module

Module

Description

Spawn MS Vertex Animation Tools Morph Target

This spawns and samples Morph Target textures that were created with the Vertex Animation Tool. The Vertex Animation Tool generates textures that represent Morph Target blend shapes. This module spawns one particle for every vertex that was captured by the tool. This module is meant to be used with the Update MS Vertex Animation Tools Morph Target module.

Spawning Modules

Module

Description

Spawn Burst Instantaneous

This module spawns a burst of particles spontaneously.

Spawn Per Frame

This module spawns a burst of particles in each frame.

Spawn Per Unit

This module spawns particles based on distance traveled in Unreal units.

Spawn Rate

This module spawns particles continuously at a particular rate.

Utility Module

Module

Description

Emitter Frame Counter

Enabling Increment Counter in this module sets up a counter which increments with each frame in the emitter's animation.

New Scratch Pad Module

Selecting this item in the Add (Plus sign) menu opens the Scratch Pad panel (by default this docks next to the System Overview) and places a Scratch Pad module in the Selection panel. You can also open the Scratch Pad panel by using Windows > Scratch Pad. However, by placing a Scratch Pad module in the stack, any modules or dynamic inputs you create in the Scratch Pad are automatically connected to your script. If you open the Scratch Pad panel using the Windows menu, any items you create there will have to be added to your script manually.

Set New or Existing Value Directly

Selecting this item from the Add menu places a Set Parameter module in the Selection panel. Click the Plus sign (+) icon to select Add Parameter or Create New Parameter.

Add Parameter

When you select Add Parameter, you select from the parameters listed. This adds that parameter to the Set Parameter module in the Emitter Update group.

Some of these parameters can be set or modified in other modules. Some are only set using a Set Parameter module.

Parameter

Description

Emitter.Age

This parameter defines the age of this emitter.

Emitter.CurrentLoopDelay

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

Emitter.CurrentLoopDuration

This parameter defines the duration of the current emitter loop.

Emitter.ExecutionState

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

  • Active

  • Inactive

  • InactiveClear

  • Complete

Emitter.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.

Emitter.LocalSpace

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

  • 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.

Emitter.LoopCount

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

Emitter.LoopedAge

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

Emitter.NormalizedLoopAge

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

System.ExecutionState

This affects the state of the system. Valid value choices are Active, Inactive, InactiveClear, Complete, Disabled, and Num.

System.ExecutionStateSource

This 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.

Create New Parameter

When you select Create New Parameter, you select from the parameters listed. This adds a Set Parameter module to the Emitter Update group.

Parameter

Type

Description

Audio Oscilloscope

Data interface

This adds a new Audio Oscilloscope data interface module to the emitter. The Audio Oscilloscope module can directly access the waveform data of the audio signal.

Audio Spectrum

Data interface

This adds a new Audio Spectrum data interface module to the emitter. The Audio Spectrum module can drive a visualization based on how loud the audio is at specific frequencies.

Bool

Primitive

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

Camera Query

Data Interface

This adds a new Camera Query data interface module to the emitter. This data interface can be used to retrieve camera information (camera position, rotation, FOV, etc) for the specified controller index.

Collision Query

Data Interface

This adds a collision data interface to the emitter stack. This is usually used in conjunction with Collision modules.

Curl Noise

Data Interface

This adds a curl noise data interface to the emitter stack. If you use this in conjunction with Curl Noise Force modules, this data interface injects different types of noise into your simulation.

Curve for Colors

Data Interface

This adds a four-channel color curve data interface for the simulation. This curve can be sampled by dynamic inputs or other modules to create a time-varying color.

Curve for Floats

Data Interface

This adds a single-channel curve data interface for the simulation. This curve can be sampled by dynamic inputs or other modules to create a time-varying float value.

Curve for Vector 2Ds

Data Interface

This adds a two-channel curve data interface for the simulation. This curve can be sampled by dynamic inputs or other modules to create a time-varying pair of floats.

Curve for Vector 3s

Data Interface

This adds a three-channel curve data interface for the simulation. This curve can be sampled by dynamic inputs or other modules to create a time-varying set of floats.

Curve for Vector 4s

Data Interface

This adds a four-channel curve data interface for the simulation. This curve can be sampled by dynamic inputs or other modules to create a time-varying set of floats.

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.

ENiagara ExpansionMode

Enum

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

  • Inside

  • Centered

  • Outside

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.

Grid2D Collection

Data Interface

This is used with simulation stages. It enables the user to read or write to a 2D array of data, and then iterate over each pixel in the grid during a simulation stage.

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.

Neighbor Grid 3D

Data Interface

This is used with simulation stages. It enables the user to read or write to a 3D array of data, and then iterate over each pixel in the volume during a simulation stage.

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.

Occlusion Query

Data Interface

This adds a new Occlusion Query data interface module to the emitter. The data interface is used to read depth buffer occlusion information.

This can only be used with GPU emitters.

Particle Attribute Reader

Data Interface

This adds a new Particle Attribute Reader data interface to the emitter. The data interface can be used to query particle payload values from other emitters, and can sometimes be easier to use than Events.

Quat

Primitive

This creates a quaternion variable, used to represent rotations.

Simple Counter

Data Interface

This adds a new Simple Counter data interface module to the emitter. This data interface enables you to increment a thread-safe counter.

This can only be used with CPU emitter.

Skeletal Mesh

Data Interface

This is a data interface with functions to interact with a skeletal mesh's bones or sockets and skinned geometry.

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.

Spline

Data Interface

This is a data interface that interacts with a Spline Asset.

Static Mesh

Data Interface

This is a data interface with functions to interact with a static mesh's surface.

Texture Sample

Data Interface

This is a data interface with functions to interact with a texture on the GPU.

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.

Vector Field

Data Interface

This is a DataInterface with functions to query a vector field.

Volume Texture Sample

Data Interface

This adds a new Volume Texture data interface module to the emitter. You can use this to sample a volume texture.

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