Niagara Fluids Reference Guide (2023)

Grid3D_Gas_Emitter

This is the core simulation.

Grid3D_Gas_Controls_Base_Emitter

This emitter adds a centralized controller, debug slice functionality, and better render support. These controls are exposed in the Emitter Summary.

Grid3D_Gas_CONTROLS_Emitter

This emitter adds particle source support. Density, temperature, and velocity are injected into the simulation from a second emitter.

Grid3D_Gas_CONTROLS_CINE_Emitter

This is an alternative controls emitter that uses a slower, deterministic form for the particle source algorithm. It includes advanced texture coordinates and is designed for cinematic use.

Grid Bounds Overlay

Adds a toggle to the Override Parameters when you click the simulation in the Level Editor. From there, you can toggle the visibility of the red box around the simulation.

Cell Size Guides

Adds a toggle to the Override Parameters when you click the simulation in the Level Editor. From there, you can toggle the visibility of the guide cells on each major axis.

World Space Size

Adds a set of fields for the user to set in the Override Parameters when you click the simulation in the Level Editor. From there, you can change the size of the container box for the simulation.

Local Pivot

Change the offset for where the simulation origin should be.

Resolution Max Axis

Adds a toggle to the Override Parameters when you click on the simulation in the Level Editor. From there, you can set the resolution of the simulation, based on its longest side. A higher resolution will result in a more accurate look, but it will decrease performance.

Open Boundary +/- X/Y/Z

Toggle these options to adjust whether the edges of the simulation should be treated as a solid wall that particles can't travel through.

Override Delta Time

Set this value to override the engine's delta time with a fixed delta time.

Delta Time Scale

If Override Delta Time is not enabled, then the system uses the engine delta time. Enter a value in Delta Time Scale to modify the engine delta time by this amount.

Vorticity Confinement

Vorticity defines the spin of the simulation. Enter a value to amplify the vorticity in the simulation by this amount.

Pressure Relaxation

This value defines the pressure solver convergence. Enter a value between 0 and 1. We recommend keeping this value close to 1.

Pressure Solve Iterations

The more iterations you perform in the solver, the more accurate, however the slower it will be. Enter a value here that provides enough accuracy without a compromise in performance.

Density Dissipation

This value defines how quickly the density will dissipate to zero. The higher the number, the more quickly it will dissipate.

Temperature Dissipation

This value defines how quickly the temperature will dissipate to zero. The higher the number, the more quickly it will dissipate.

Velocity Dissipation

This value defines how quickly the velocity will dissipate to zero. The higher the number, the more quickly it will dissipate.

Density Buoyancy

This value defines the amount of downward velocity applied to the simulation based on its density. The higher this value, the more downward velocity.

Temperature Buoyancy

This value defines the amount of upward velocity applied to the simulation. The higher the number, the more upward velocity.

Gravity

Set the direction and magnitude of gravity in the simulation.

Seed Turbulence Gain

Set the strength of the turbulence. This is applied on the initialization frame only.

Seed Turbulence Frequency

This sets the size of the turbulence features. The smaller the number, the larger the features will look. This is applied on the initialization frame only.

Seed Turbulence Speed

Set how quickly the turbulence should move. This is applied on the initialization frame only.

Seed Turbulence Local Space

When enabled, the turbulence will follow the local space of the simulation. When disabled, turbulence will be fixed in world space. This is applied on the initialization frame only.

Turbulence Density Gain

Set the strength of the turbulence. This can be set as density and / or temperature.

Turbulence Density Band

Limit the turbulence between a defined range of densities.

Turbulence Temperature Gain

Set the strength of the turbulence. This can be set as density and / or temperature.

Turbulence Temperature Band

Limit the turbulence between a defined range of temperatures.

Turbulence Frequency

This sets the size of the turbulence features. The smaller the number, the larger the features will look.

Turbulence Speed

Set how quickly the turbulence should move.

Turbulence Bias

Bias the noise away from zero to give the turbulence direction.

Turbulence Local Space

When enabled, the turbulence will follow the local space of the simulation. When disabled, turbulence will be fixed in world space.

Render Step Size Mult

The simulation is calculated by breaking up the volume into cells, and then sampling the simulation in those cells. By default, the step size through the volume matches the size of the cells.

If you decrease the value in this multiplier, you will sample the simulation multiple times per cell. This is useful when a texture is modulating the simulation data, or if you are rendering detailed fire.

Render Density

This option controls whether to render the density or not. You can choose between None, Linear, or Curve. Linear mapping will map the data in the grid to the opacity of the gas. Or, you can set a curve for greater control.

Render Density Range

Set a density range to be rendered. The first value should be the density value that you want to be transparent, and the second should be the density value that gives the highest opacity.

Render Density Curve

If you set Render Density to Curve, then you can set the curve using this parameter. Expand the field to access the curve editor.

Render Density Gain

This value adds a multiplier on top of the final density being rendered.

Render Density Albedo

This value is a float which colors the smoke from black to white.

Shadow Quality

Baked shadows are calculated by breaking the volume up into cells, then stepping through the volume to sample the simulation in those cells. Adjust this value to sample the simulation multiple times per cell.

Shadow Max Steps

Limit the number of steps to take when sampling for shadows.

Render Temperature

Choose how to render the Temperature component. You can choose from None, Black Body, or Curve.

None will not render the Temperature values.

Black Body will render an environmentally realistic fire, from black, to red, orange, yellow, then white.

Curve will let you set your own custom color values.

Render Temperature Range

Set a range of temperature values to map to the Render Temperature. This only applies when Render Temperature is set to Black Body or Curve.

Render Temperature Curve

If Render Temperature is set to Black Body, the alpha component of this curve defines the opacity of the fire.

If Render Temperature is set to Curve, this curve defines both the color and the opacity of the gas.

Render Temp Color Gain

Add an additional multiplier to the gas color.

Render Temp Opacity Gain

Add an additional multiplier to the opacity of the gas.

Light1/2

This data interface reads the attributes from a light you have connected to the Override Parameters of the Niagara system in the Level Editor.

Lgt1/2 Shadow Density

Set how much light the density component should occlude.

Lgt1/2 Default Intensity

Set the intensity of the default light.

Lgt1/2 Default Color

Set the color of the default light.

Lgt1/2 Default Direction

Set the direction of the default light. This direction is a vector that is set in world space.

Debug Sources

Enable this option to overwrite grid data on every frame with the source data. By doing this, you will see what the sources are introducing to the simulation.

Render Debug Slice

Enable this option to render a 2D slice inside the grid. Density is rendered in the red channel. Temperature is rendered in the green channel. Combined light intensity is rendered in the blue channel.

Render Debug Slice Axis

Choose which axis to orient the slice to.

Render Debug Slice Offset

Set how far along the axis to render the slice. This value should be between 0 and 1, with 0.5 being the center point.

Render Debug Slice Lights

Enable this option to render the light intensity in the blue channel.

Particle Attribute Reader

This data interface reads from another emitter in the system.

Scale Emission by dt

Enable this to ensure that the source data remains consistent, even if the engine tick rate varies.

Use Falloff

Enable this to anti-alias data at the edges of particles. This keeps sourcing consistent, even if the resolution changes.

Scatter Density

Enable this to look for the density attribute on the incoming particle source, fluids_source_density.

Scatter Temperature

Enable this to look for the temperature attribute on the incoming particle source, fluids_source_temperature.

Scatter Velocity

Enable this to look for the velocity attribute on the incoming particle source, fluids_source_velocity.

Use Radius

Enable this to overlap all cells in the simulation based on the particle radius, fluids_source_radius. This keeps the sourcing consistent, even if the resolution changes.

Density Mult

Enter a value to multiply the incoming particle density attribute by.

Splat Size Density

If Use Radius is disabled, enter a value to set how many cells should be stamped with the particle density data. Enter 1 to indicate the closest cell, or 2 to indicate the closest cell and the cells touching the closest cell. As you increase this number, the number of cells being written to increases significantly.

Temperature Mult

Enter a value to multiply the incoming particle temperature attribute by.

Splat Size Temperature

If Use Radius is disabled, enter a value to set how many cells should be stamped with the particle temperature data. Enter 1 to indicate the closest cell, or 2 to indicate the closest cell and the cells touching the closest cell. As you increase this number, the number of cells being written to increases significantly.

Local Space Particles

Enable this value to set the particles to be local to this simulation.

Velocity Mult

Enter a value to multiply the incoming particle velocity attribute by.

Splat Size Velocity

If Use Radius is disabled, enter a value to set how many cells should be stamped with the particle velocity data. Enter 1 to indicate the closest cell, or 2 to indicate the closest cell and the cells touching the closest cell. As you increase this number, the number of cells being written to increases significantly.

Texture Smoke Density Gain

Enter a value to modulate the density with noise.

Texture Smoke Color Gain

Enter a value to modulate the smoke albedo with noise.

Texture Fire Density Gain

Enter a value to modulate the opacity of the fire contribution with noise.

Texture Fire Color Gain

Enter a value to modulate the fire color intensity with noise.

Texture Scale

Enter a value to adjust the size of the noise pattern.

Texture Remap To 0

This parameter performs a fit operation. Enter a value that will be remapped to 0, adding contrast and bias to the effect.

Texture Remap To 1

This parameter performs a fit operation. Enter a value that will be remapped to 1, adding contrast and bias to the effect.

Value Data

Choose whether to limit the influence of the texture to Density or Temperature. The option you choose here will determine how to apply the following parameters: Value Band Min, Value Band Max, and Value Band Sharpness.

Value Band Min

Set the lower value of the simulation data to which the texture will be applied.

Value Band Max

Set the upper value of the simulation data to which the texture will be applied.

Value Band Sharpness

Set how the texture will transition within the band. Enter a sharpness value of 0 to have the transition happen slowly within the band, reaching full influence at the midpoint of Value Band Min and Value Band Max. Enter a sharpness value of 1 to have it influence immediately as soon as the data falls anywhere within the band.

Loop Duration

The coordinates reset and transition back and forth to avoid stretching. Enter a value to adjust the loop duration. The higher the loop duration, the more stretching you will see.

Debug Texture

Enable this option to override the material and only show the texturing value.