The size of a voxel in the Pyro simulation. Cutting your voxel size in half will require eight times the memory and time, so a careful trade off between detail and pragmatism is required.

This multiplier is applied on top of Voxel Size to determine size of velocity voxels. Larger values of this parameter thus correspond to lower- resolution velocity fields, which will simulate faster but produce less detail from the motion.

A scaling factor for time inside this solver. 1 is normal speed, greater than 1 speeds up the simulation, while less than 1 slows it down.

By default, this solver operates in sparse mode; that is, the needed calculations are performed only in the areas of interest, as governed by the active field. Dense on the other hand performs a full global solve everywhere within the domain. Change this to Minimal OpenCL to enable a fast, dense solve using your graphics card.

Use the OpenCL device to accelerate computations. This option is only available when Simulation Type is set to Dense.

Controls global substeps at the simulation level, as opposed to the pyro-specific substeps.

Global substeps are best used when you need to export the substepped geometry. They will use more memory per frame, however, all the substeps will be kept rather than just the final values each frame.

The solver will take at least this many substeps per frame. If you have unusual forces, you may want to increase this parameter for better stability. Increasing this parameter usually makes the simulation run noticeably slower.

The solver will take at most this many substeps per frame.

When Max Substeps is greater than 1, the solver uses this parameter to determine the number of substeps. The condition is that no substep can allow objects to interpenetrate by more than this many voxels. Higher values let the solver take larger substeps, possibly letting smoke pass through colliders.

Advection-Reflection attempts to inject energy lost due to pressure projection back into the simulation. Enabling this option may exhibit better vortex retainment in the flow.

Fraction of the projected velocities to re-inject when Advection-Reflection is not set to Disabled. Values near 1 will do a better job of conserving energy, but may result in instabilities.

The following video shows Single-Project mode.

The following video shows Double-Project mode.

Controls if the simulation is cached to memory.

Maximum size of the memory cache.

Limits the simulation domain size based on Size and Center.

The maximum size the pyro sim can reach. This is measured relative to the center. This can be useful to avoid unexpectedly running out of memory from bad inputs.

The origin of the pyro simulation. This is used as the center of the maximum size.

Amount of padding to add to the simulation region around the Reference Fields. Padding should be as small as possible, but large enough to ensure that moving smoke does not leave the container within a timestep.

List of fields that determine size of the simulation container. Resizing is done by first computing the bounding box around all voxels of Reference Fields that have a positive value, then expanding this intermediate region by Padding on all sides. This list of fields is also used to build the active region in sparse mode.

By default, the smoke solver will resize density, temperature, divergence, active, vel, collisionvel, and flame (for pyro only). Additional fields may be resized by specifying them here.

When enabled, size changes to the fields will be done in increments of 16 voxels. This is marginally more efficient, but the resultant fields will be larger than necessary.

When this parameter is enabled, newly-activated areas inherit their velocities from nearby active regions. This can help reduce tile artifacts that may appear on the smoke surface if the Padding is not large enough.

Falloff and Blendwidth parameters determine how new velocities are blended with the background field value (as set by Wind Tunnel Direction on the Smoke Object (Sparse) node). You should set Blendwidth to reflect the interpolation band around the active region: valid boundary velocities will be blended with the background value in a band of this thickness. If the Blendwidth is set too small, then extrapolation will not be effective at removing tile artifacts; however, if this value is set too large, then smoke will be accelerated outwards. If this happens, decreasing the Blendwidth or increasing Falloff (to a value on the order of simulation speeds) can help mitigate the problem.

When Extrapolate Velocity into New Tiles is enabled, valid velocity values are extrapolated into newly-activated nearby tiles. This parameter sets a minimum blending rate towards the background field value (as set by the Wind Tunnel Direction on the Smoke Object (Sparse) node). Increase this parameter if the smoke gets pulled outwards at the desired Blendwidth.

Controls the size of the interpolation band around the active region when Extrapolate Velocity into New Active Tiles is enabled. Newly-activated velocities in a band of this size will interpolate valid values towards the background value (as set by Wind Tunnel Direction). Increasing this parameter can help reduce tile artifacts that can appear when Padding is small.

When enabled, the active simulation region will take the motion of the gas into account. This will result in adaptive padding that is larger where the fluid is exiting at a faster rate. If this is disabled, the active region is expanded uniformly in all directions.

The minimum padding around the smoke when Expand by Velocity is turned on.

The maximum padding around the smoke when Expand by Velocity is turned on. You can enable this to limit the amount of internal expansion when using Expand by Velocity.

Controls size of the adaptive padding for the sparse active region, when Expand by Velocity is enabled. The active region will include more tiles (and the smoke will have a bugger buffer to move into) when this parameter is set to a larger value.

This parameter impacts the shape of the sparse active region when using Expand by Velocity. Smaller values of this parameter will permit sharper kinks in the active region. This can reduce the number of active simulation tiles, but may also negatively impact the motion of the fluid.

Limits the collision input to a single frame or to a sequence of frames.

Limits the collision input to a single frame or to a sequence of frames.

Sets the frame to which the collision input will be limited.

Controls animation range of the collider. Frames from the Collider Frame Range will be looped for simulation purposes. For example, if this is set to 1-6, then simulation frames 4, 5, 6, 7, 8, etc. will use the collider evaluated at frames 4, 5, 6, 1, 2, etc., respectively.

In case where the Simulation Type is set to Minimal OpenCL, the second input is expected to contain collision (signed distance field for the collider) and v (velocity field) volumes.

Length of a single collider cycle. If this value is larger than length of the Collision Frame Range, then some simulation frames will not have the collider present. Otherwise, the collider will loop and continuously affect the simulation.

In the end, collisions are always performed at the simulation resolution. However, often a lower fixed resolution can be used for the signed distance field of the object. This usually should be the same resolution that was used to generate the collision volume upstream.

Often if sourcing fire on the surface of an object, you don’t want the fire to get stuck in the surface, so it is useful to shrink the object a bit. This can provide that by offsetting the collision distances.

Positive values will dilate the collider, while negative values will shrink it.

Scales the incoming velocities for the collision. Increase the value to make the fluid more affected by the collision. When Collision Type is set to Collision Geometry, ensure you have point velocities set on the collision geometry, while when SDF + Volume Velocity is used a velocity volume is required as given by Velocity Volume.

The name of the volume representing your incoming collision signed distance field.

The name of the volume storing the volume velocities for the collision.

Controls if the collision geometry is rebuilt every frame or the first frame is used. Not rebuilding can result in faster simulations.

Allows you to create a solid wall at a certain coordinate along the X axis. The axis can be kept Open (no wall), be Closed Below (X coordinates less than the specified value are off-limits for the gas) or be Closed Above (X coordinates greater than the specified value are off-limits).

Allows you to create a solid wall at a certain coordinate along the Y axis. The axis can be kept Open (no wall), be Closed Below (Y coordinates less than the specified value are off-limits for the gas) or be Closed Above (Y coordinates greater than the specified value are off-limits).

Allows you to create a solid wall at a certain coordinate along the Z axis. The axis can be kept Open (no wall), be Closed Below (Z coordinates less than the specified value are off-limits for the gas) or be Closed Above (Z coordinates greater than the specified value are off-limits).

When enabled, height field at the specified SOP path will be used as a collider. This is currently not supported when Simulation Type is set to Minimal OpenCL.

Controls if the Height Field collider is rebuilt every frame or the first frame is used. Not rebuilding can result in faster simulations.

Limits the source input to a single frame or to a sequence of frames.

Limits the source input to a single frame or to a sequence of frames.

Sets the frame to which the source input will be limited.

Controls the input range of frames for sourcing. The first input will be evaluated at integer frames in this range for the purpose of sourcing.

Length of a single sourcing cycle. If this value is larger than length of the Source Frame Range, then some simulation frames will have no sourcing applied. Otherwise, the sources will loop and continuously inject into the simulation.

As an example, suppose Source Frame Range is set to 1-6 and Cycle Length is 120. Then source frames 1-6 will be applied to the same-numbered simulation frames, whereas simulation frames 7-120 will get no sourcing applied. As the cycle resets, source frames 1-6 will also be applied to simulation frames 121-126, etc.

These settings can be useful in tuning parameters for a simulation. An explosion, for instance, needs to be sourced only for the first few frames. A larger Cycle Length will let the smoke develop before the sourcing restarts and the explosion loops again. In the meantime, shaping and simulations can be manipulated to see their effect on the simulation.

When enabled, the sources are copied to the points of the given geometry at each frame. This enables you to place the same source volumes in several locations without explicitly merging them ahead of time. This is especially useful when performing a Minimal OpenCL solve, where you can use instancing to apply the same limited set of source frames in different places. P (position), orient (unit quaternion for orientation), and pivot (pivot location for rotations) point attributes on the instance geometry affect the placement of each instance.

The number of volume merging operations to perform.

Enables or disables the sourcing of this merging operation. Use this parameter to quickly test the simulation with or without this operation.

The merging operation.

Rank of the target field.

Name of the SOP volume or VDB to merge. For vector fields, this can be a single vector VDB or a space separated list of three scalar volumes or VBDs.

The DOP field that is to be modified.

Name of the SOP scalar volume or VDB containing the weights for Source Volume; applicable only when the Operation is set to Blend.

Name of the weight field for the destination; applicable only when the Operation is set to Blend.

A multiplier applied to the source values before merging.

Normalizes the Scale against the timestep and the canonical frame rate of 24. This ensures that sourcing is performed to the same real extent, regardless of the simulation timescale.

For example, with the default frame rate of 24, normalization causes the Scale to be used as is for every frame. If frame rate is increased to 48, effective scale will be halved per frame, resulting in the same amount of additive sourcing.

Controls how strongly the Target Field's values are pushed towards the Source Volume. Applies for the voxels in which the Source Volume has larger values than the Target Field.

Controls how strongly the Target Field's values are pushed towards the Source Volume. Applies for the voxels in which the Source Volume has smaller values than the Target Field.

When enabled, controls how strongly the Target Field's vectors are pushed to align with Source Volume's. This option can only be used with vector fields; when disabled for vector fields, guiding is performed independently for each component of the Target Field.

With vector fields, when Operation is set to Maximum or Minimum, this option can be enabled to signal that comparisons are to be done using lengths of the vectors, rather than component-wise.

When Operation is set to Subtract and this option is enabled, negative results will be changed to zero.

Provides a set of fields to viewport visualize next to the pyro simulation. Use this to get a better understanding of different field values in your simulation.

Sets the visualization type to 3 dimensional or 2D plane visualization.

The orientation of the cutting plane for visualization.

Where in space the center of the plane is. It is always set to encompass the scalar field’s bounds, so the only relevant axis is the one the plane’s normal matches.

The range controls how the field’s values are culled and mapped to the visualization color set by the Color Mapping ramp. Every field value below the given minimum guide range will be culled, which helps to isolate specific ranges, while the maximum guide value will me mapped to the right side of the Color Mapping ramp.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

The number of sampling divisions in x, y, and z for when the override divisions is enabled.

Dissipation reduces the density of smoke over time, so that it fades and eventually disappears. It is important to set an appropriate value for the Clamp Below parameter when performing a sparse simulation. Otherwise, tiny density values will linger and unnecessarily inflate the active simulation region.

Causes smoke to disappear over time. Low values cause smoke to disappear more slowly. A value of 0.1, for example, means that 10% of the smoke will disappear every twenty-fourth of a second, whereas a value of 1 will make all smoke disappear immediately.

When this option is turned on, density values that fall below the provided threshold are driven all the way down to 0. It is recommended to leave this enabled for sparse simulations, for otherwise tiny density values will keep the active region unnecessarily large.

When enabled, the amount of dissipation is scaled by the field specified.

The name of the pyro field to use to affect dissipation.

Remaps (normalizes) the Control Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. For example, if your Dissipation is set to 0.1, Control Field is temperature, and your minimum and maximum is 2 and 5 respectively, you will have dissipation equivalent of 0.1 where temperature values are 5 or higher, while it will linearly decrease to zero towards regions where your temperature values are 2. You will have no dissipation at all at regions with temperature values less then 2. Use the Remap Control Field to change how the scale value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Control Ramp to change how the control field should scale dissipation between the minimum and maximum values of Control Range.

The following video shows the effect of having the Remap Control Field disabled, remap with an increasing control ramp, and remap with a decreasing control ramp.

This ramp controls how the dissipation scale values are mapped between the minimum and maximum values of Control Range.

When enabled, density is added to the simulation using the flame field.

Controls how the output of the flame field is mixed with the density field.

Amount of density output from the flame field. This parameter acts as a multiplier for the remapped flame value.

Remaps (normalizes) the flame values based on the specified minimum and maximum. The output is always in a range of 0 to 1, which is then multiplied by Emission Scale to give the final output. For example, if your Emission Scale is set to 2, and your minimum and maximum is 0.2 and 0.5 respectively, you will have density output of 2 where flame values are 0.5 or higher, while it will linearly decrease to zero towards regions where your flame values are 0.2. You will have no density output at all at regions with flame values less then 0.2. Use the Remap Flame Range to change how the output density value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Flame Ramp to change how the flame field should scale density emission between the minimum and maximum values of Flame Range.

This ramp controls how the density emission scale values are mapped between the minimum and maximum values of Flame Range.

A blur factor on the temperature field. Higher values diffuse the temperature out further, emulating the spread of heat from hotter to colder areas.

How fast the temperature field cools to zero.

When enabled, temperature is added to the simulation using the flame field.

Controls how the output of the flame field is mixed with the temperature field.

How strongly the temperature field values are pushed towards the hotter flame output when Operation is set to Pull.

Amount of temperature output from the flame field. This parameter acts as a multiplier for the remapped flame value.

Remaps (normalizes) the flame values based on the specified minimum and maximum. The output is always in a range of 0 to 1, which is then multiplied by Emission Scale to give the final output. For example, if your Emission Scale is set to 2, and your minimum and maximum is 0.2 and 0.5 respectively, you will have temperature output of 2 where flame values are 0.5 or higher, while it will linearly decrease to zero towards regions where your flame values are 0.2. You will have no temperature output at all at regions with flame values less then 0.2. Use the Remap Flame Range to change how the output temperature value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Flame Ramp to change how the flame field should scale temperature emission between the minimum and maximum values of Flame Range.

This ramp controls how the temperature emission scale values are mapped between the minimum and maximum values of Flame Range.

When this option is enabled, flame field will be added to the smoke object, containing the remaining lifetime of reactants. You can turn off this toggle as a very minor optimization if the simulation does not require the flame field.

The number of seconds it takes to use up a value of 1 in the flame field.

When this option is enabled, Cd and Alpha fields will be added to the smoke object, containing the smoke color and color amount, respectively.

This parameter specifies the default color of smoke and initial state of the Cd field.

Controls the initial (and minimum) value of the Alpha field. Intuitively, the fluid will contain Default Alpha amount of dye of Default Color at the beginning of the simulation.

Causes the amount of color to reduce over time. By default, only the Alpha channel is dissipated; this does not directly affect smoke’s color, but makes it easier to mix in new color via sourcing. When Only Dissipate Alpha is disabled (under the Dissipation subtab), Cd values will also decay toward the smoke’s Default Color (as set on the Smoke Object (Sparse) node).

When this option is enabled, only the Alpha values are affected by dissipation: this makes it easier to color “older” smoke through sourcing. Disabling this parameter will cause dissipation to also drive Cd values toward the smoke’s default color. That is, when Only Dissipate Alpha is turned off, the smoke will gradually change its color back to the default value.

When enabled, the force exerted is scaled by the content of this field.

Map from this range of values in the control field.

Enables or disables the control field ramp.

The ramp’s vertical axis is strength of the effect and the horizontal axis is the value in the control field.

Blurs the smoke’s color field by mixing its values in neighborhoods of the given size.

Controls how far out the colors will blur per second.

Sharpens the smoke’s color field, effectively discouraging mixing of different colors.

Sharpening boosts the deviation of colors from averaged (blurred) values. This parameter controls the distance to which blurring is performed.

Sharpening boosts the deviation of colors from averaged (blurred) values. If the deviation falls below this threshold at a voxel, no sharpening is done to it. Increasing this value can help reduce the amount of introduced sharpening noise.

When enabled, the speed field is computed at each time step. This field stores lengths of the velocity vectors and can be used as the control field to attenuate the strength of attached microsolvers and shape operators. For example, you can weaken the effect of turbulence in areas with less motion by using speed as its control field.

Provides a set of forces to viewport visualize next to the pyro simulation. Use this to get a better understanding the affect of different forces in your simulation.

Sets the visualization type to 3 dimensional or 2D plane visualization.

The orientation of the cutting plane for visualization.

Where in space the center of the plane is. It is always set to encompass the scalar field’s bounds, so the only relevant axis is the one the plane’s normal matches.

The range controls how the force values are culled and mapped to the visualization color set by the Color Mapping ramp. Every force value below the given minimum guide range will be culled, which helps to isolate specific ranges, while the maximum guide value will me mapped to the right side of the Color Mapping ramp.

Computes the minimum and maximum range values of the selected force on the current frame. Use this to get an idea your maximum force value.

The number of sampling divisions in x, y, and z for when the override divisions is enabled.

Hot gas expands, causing it to rise due to lowered density. Acceleration due to buoyancy is calculated using values of the ambient and reference temperatures, as well as the Gravity settings. Value of this parameter is used as a multiplier for the buoyancy force.

Temperature corresponding to value of 0 in the temperature field (in Kelvin). This represents the ambient temperature of the environment.

Temperature corresponding to value of 1 in the temperature field (in Kelvin). The temperature range is used to calculate strength of the buoyancy force.

Acceleration due to gravity. Stronger gravity results in stronger buoyancy forces.

The direction in which gravity pulls. Hotter gas will tend to rise in the opposite direction.

Enable this to apply the gravity force on the fluid, scaled based on the density (or some other specified simulation field). With default settings of the parameters in this tab, it has the effect of making denser regions of the fluid fall faster.

Scales the overall gravity force applied to the fluid.

Specifies the fluid simulation field that will be used to scale the gravity force.

The range of values of the Density Field that get mapped to 0-1.

Computes the minimum and maximum range values of the selected Density Field on the current frame. Use this to get an idea of your maximum field value.

Ramp that controls the strength of gravity to be applied, based on the remapped Density Field.

Parts of the fluid with a velocity in the direction of gravity greater than or equal to this value will not have any gravity force applied to it. Enable this if you find that the fluid is accelerating due to gravity more than desired. Increase this value if you find that the gravity force deactivates too early.

Sets the speed of the wind.

Which direction the wind is blowing in. The actual wind velocity is the product of Wind Direction and Wind Speed.

Introduces random forces to the simulation to add higher frequency details without changing the general motion or the overall shape. This operator is useful for breaking up undesirable smooth features in the smoke.

Controls the nature of the generated random vectors.

Variance of the aggregated noise field over a region of this size will be equal to Strength when Mode is set to Continuous. Provides a scale for normalizing the force against voxel size. A larger value for this parameter will increase magnitude of the applied force.

Controls size of the biggest blocks in the generated noise pattern when Mode is set to Block-Based.

The ratio of amplitudes between successive noise layers. Value of 0.5, for instance, means that the second layer will have half the amplitude of the first one. This parameter is only applicable in Block-Based mode.

Length of time (in seconds) that the noise pattern is held fixed; only applies when Mode is set to Block-Based.

The maximum number of noise levels to compose in Block-Based mode.

The ratio of block sizes between successive noise layers. Value of 2, for example, means that the first layer has blocks that are twice the size of the second layer; the second layer will in turn have blocks that are twice as large as the next layer. This parameter is only applicable in Block-Based mode.

The name of the pyro field to use to affect disturbance.

Remaps (normalizes) the Threshold Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. The default density Threshold Field with 0.05 to 0 range means that disturbance will be scaled by 1 at regions where density is zero, while regions with density bigger or equal to 0.05 will have no disturbance applied at all.

When enabled, the amount of disturbance is scaled by the field specified.

The name of the pyro field to use to affect disturbance.

Remaps (normalizes) the Control Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. For example, if your Disturbance is set to 0.5, Control Field is speed, and your minimum and maximum is 1 and 2 respectively, you will have disturbance equivalent of 0.5 where speed values are 2 or higher, while it will linearly decrease to zero towards regions where your speed values are 1. You will have no disturbance at all at regions with speed values less then 1. Use the Remap Control Field to change how the scale value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Control Ramp to change how the control field should scale disturbance between the minimum and maximum values of Control Range.

Adds “churning” noise to the velocity field. You should generally use this operator to add powerful large-scale noise, and rely on disturbance and shredding for smaller features.

Base swirl size in world units. Lower values produce smaller, more localized vortices, while larger values give rise to coherent long-range forces.

Controls the ratio of amplitudes between successive noise bands. Higher values increase the prevalence of higher-frequency vortices (smaller than the base Swirl Size).

Governs how fast the noise evolves. Higher values of this parameter result in slower evolution.

Number of turbulence levels to apply. Each successive layer has half the swirl size, and amplitude of the previous layer scaled by Grain.

Acts as an offset into the noise field. Change this value to modify the resultant forces.

The name of the pyro field to use to affect turbulence.

Remaps (normalizes) the Threshold Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. The default temperature Threshold Field with 0.01 to 0 range means that turbulence will be scaled by 1 at regions where temperature is zero, while regions with density bigger or equal to 0.01 will have no turbulence applied at all.

When enabled, the amount of turbulence is scaled by the field specified.

The name of the pyro field to use to affect turbulence.

Remaps (normalizes) the Control Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. For example, if your Turbulence is set to 0.1, Control Field is density, and your minimum and maximum is 1 and 2 respectively, you will have turbulence equivalent of 0.1 where density values are 2 or higher, while it will linearly decrease to zero towards regions where your density values are 1. You will have no turbulence at all at regions with density values less then 1. Use the Remap Control Field to change how the scale value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Control Ramp to change how the control field should scale turbulence between the minimum and maximum values of Control Range.

Introduces random forces to the simulation to add higher frequency details without changing the general motion or the overall shape. This operator is useful for breaking up undesirable smooth features in the smoke. Shredding will cause the values in the velocity field to only rotate towards the randomly generated directions without changing their length.

Controls the nature of the generated random vectors.

Controls size of the biggest blocks in the generated noise pattern when Mode is set to Block-Based.

The ratio of amplitudes between successive noise layers. Value of 0.5, for instance, means that the second layer will have half the amplitude of the first one. This parameter is only applicable in Block-Based mode.

Length of time (in seconds) that the noise pattern is held fixed; only applies when Mode is set to Block-Based.

The maximum number of noise levels to compose in Block-Based mode.

The ratio of block sizes between successive noise layers. Value of 2, for example, means that the first layer has blocks that are twice the size of the second layer; the second layer will in turn have blocks that are twice as large as the next layer. This parameter is only applicable in Block-Based mode.

The name of the pyro field to use to affect shredding.

Remaps (normalizes) the Threshold Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. The default flame Threshold Field with 0.1 to 1 range means that shredding will be scaled by 1 at regions where flame is 1, while regions with flame less or equal to 0.1 will have no shredding applied at all.

When enabled, the amount of shredding is scaled by the field specified.

The name of the pyro field to use to affect shredding.

Remaps (normalizes) the Control Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1. For example, if your Shredding is set to 0.5, Control Field is density, and your minimum and maximum is 1 and 2 respectively, you will have shredding equivalent of 0.5 where density values are 2 or higher, while it will linearly decrease to zero towards regions where your density values are 1. You will have no shredding at all at regions with density values less then 1. Use the Remap Control Field to change how the scale value should change between minimum and maximum.

Computes the minimum and maximum range values of the selected field on the current frame. Use this to get an idea of your maximum field value.

Enables the Control Ramp to change how the control field should scale shredding between the minimum and maximum values of Control Range.

When enabled, goal divergence is added to the simulation in the specified Flame Range, causing expansion.

Amount of divergence from the flame field. Larger values result in a more violent expansion. Negative values cause the gas to be sucked inwards (instead of blown outwards).

Remaps (normalizes) the flame values based on the specified minimum and maximum. The output is always in a range of 0 to 1, which is then multiplied by Expansion Rate to give the final output. For example, if your Expansion Rate is set to 0.7, and your minimum and maximum is 0.2 and 0.5 respectively, you will have an expansion rate of 0.7 where flame values are 0.5 or higher, while it will linearly decrease to zero towards regions where your flame values are 0.2. You will have no expansion at all at regions with flame values less then 0.2. Use the Remap Flame Range to change how the output density value should change between minimum and maximum.

Enables the Flame Ramp to change how the flame field should scale expansion between the minimum and maximum values of Flame Range.

This ramp controls how the expansion scale values are mapped between the minimum and maximum values of Flame Range.

A blur factor on the velocity field. A value of 0 allows adjacent voxels to move in different directions without resistance, creating a more chaotic, turbulent look. Higher values of this parameter result in a more coherent velocity field, creating a more flowing look.

Enables the smoke aspect of the volume. Smoke absorbs and attenuates light traveling through it. Use Smoke Volume to identify the volume storing the smoke’s density.

Controls the overall density of the smoke. Increasing this value will give the smoke a thicker appearance. Reducing it will make the smoke less opaque.

Controls the overall color of the smoke. To get more natural looking smoke, change the menu on the right side of this parameter from Constant to Use Ramp. This will allow you to vary the smoke’s color with its density.

The minimum and maximum density values to map to the left and right endpoints of the Smoke Color Ramp.

Computes the minimum and maximum range values of the field binded using Smoke Volume on the current frame. Use this to get an idea of your maximum field value.

This ramp controls how the smoke’s density values are mapped to its color. The horizontal axis of the Smoke Color Ramp spans the Density Range. For example, you can use this ramp to make the smoke have a darker color where it is more dense.

Controls the color of shadows cast by the smoke. The complements of these values act like additional density multipliers for light of each color (red, green, or blue).

This multiplier applies on top of Density Scale when the volumes are lit. Increasing this value will result in less light penetrating the volume, without affecting the smoke’s opacity to the viewer. Decreasing this value reduces the light’s absorption, without changing how opaque the smoke appears.

Determines the intensity of self shadows from ambient light sources. The final amount of self-shadowing from these lights is controlled by the product of Density Scale, Shadow Scale, and Ambient Shadow Scale. The video demonstrates the value increasing from 0 to 1.

Enables the emission component used for fire and flame type simulations based on flame and temperature fields. Use the Bindings tab to set the field for fire intensity and for fire color. Use the Scatter tab on the Pyro Bake Volume following this node to enable emission based on scatter.

Fire simulation viewed with and without fire enabled.

Sets the emission intensity for the fire. Increase this value to make the fire brighter.

The minimum and maximum source values to map to the left and right endpoints of the Fire Intensity Ramp. Increase the minimum source value to reduce the emissive parts of the volume.

By increasing the minimum value from zero, the area of the fire will shrink (Enable Mask is turned off).

Computes the minimum and maximum range values of the field binded using Fire Intensity Volume on the current frame. Use this to get an idea of your maximum field value.

Controls how the raw Intensity Volume values are mapped to effective intensity. The horizontal axis of this ramp spans Source Range.

Sets how the color is calculated for the fire. Color Ramp will map the colors using Fire Color Ramp from the given Source Range. Choose Physical Blackbody or Planck Backbody to compute color based on the temperature of an incandescent blackbody.

The minimum and maximum source values to map to the left and right endpoints of the Fire Color Ramp.

Computes the minimum and maximum range values of the field binded using Fire Color Volume on the current frame. Use this to get an idea of your maximum field value.

Controls how the Color Volume values are mapped to emission color. The horizontal axis of this ramp spans Source Range.

Scale applied to the Color Volume values before they are mapped to blackbody color.

When turned on, the computed Physical Blackbody curves are remapped using Adaptation and Burn.

Squashes or stretches the low end of the generated intensity, similar to exposing a photograph for shadows.

Manipulates the high end of the generated intensity.

The path to the shader that is assigned to the volumes. The shop_materialpath primitive attribute will point to the specified material, ensuring that it is used for renders. This will take precedence over any assigned material at the object level. Turn this off if you do not want to assign a material at the SOP level.

The name of the volume to be used as smoke. Usually you should leave this as density.

The name of the volume used to color the smoke. You have to set the menu next to Smoke Color to Constant for the Diffuse Volume to be used. When this menu is set to Use Ramp instead, smoke will be colored using the Smoke Volume (density by default).

The name of the volume to be used for the intensity of the fire emission.

The name of the volume to be used for the color of the fire emission.

Turns off certain parts of the evaluation network to facilitate fast OpenCL solving that avoids data copying between main and video memory. This parameter is locked by default, instead change the Simulation Type on the Setup tab to Minimal OpenCL.

Puts the solver in sparse mode, allowing it to perform its computations only in relevant areas. This parameter is locked by default, instead change the Simulation Type on the Setup tab to Sparse.

When enabled, all substeps will divide the frame by Max Substeps. For example, if Max Substeps is set to 4, but the CFL Condition only requires 3 substeps, the solver will take frame steps 0.25, 0.5, and 0.25. This option can be useful for re-using input geometry that has been cached to file at increments of 1/Max Substeps.

Delays the actual simulation this many frames after the object creation. Nodes attached to the Sourcing input will still be executed. This may be needed if some solve nodes can’t be processed before certain initial conditions have been met.

When enabled, pressure projection will be done using a much cheaper (but less accurate) method.

Rule that determines where the fields specified in Fields to Reset are modified.

List of fields to reset, based on the Reset Rule. In the regions where they are modified, these fields are set to their initial value.

A list of forces to scale by the value of the density field at each voxel.

A list of forces to apply uniformly to all voxels (ignoring their density value).

The algorithm used to perform advection. Semi-Lagrangian is the most basic: it simply traces trajectories through the Velocity Field once to update the Field values. Modified MacCormack carries out an extra tracing step to approximate and compensate for the introduced error; as a result, sharp features of the original field can be better preserved. BFECC performs yet another trace to predict the motion of the estimated error, producing the best results at the highest computational cost.

The error correction steps of Modified MacCormack and BFECC advection may introduce final voxel values that lie outside the range of the original field: this can create negative densities or large velocities, for example. When such values are detected, the final field value depends on the setting of this parameter.

Apply a smooth blend between non-clamped and clamped values as the advected field approaches the clamping limit. Particularly with the Revert option, applying a small amount of Blend (0.05-0.1) can reduce grid artifacts in the advected field.

Controls how trajectories are traced through the velocity field. Options in this menu are listed in the order of increasing accuracy and computational cost.

When enabled, trajectory tracing will be done in steps to ensure that the calculated path reflects variations in the velocity field. The step size is governed by the value of this parameter. Particularly, the number of field voxels traveled in each step is equal to the CFL Condition.

Provides a safety limit on the number of steps that can be taken to trace trajectories.

To minimize the cost of tracing paths through the Velocity Field, the target fields are organized into batches (based on their voxel sampling settings), and each batch is advected simultaneously. Enabling this option allows you to limit the number of fields that can be processed in each batch. This is useful for reducing peak memory usage of the advection step.

By default, the solver will advect density, temperature, vel, and flame (for pyro only). Additional fields may be advected by specifying them here.

When enabled, Field Advection settings will also be used to advect the velocity field. Turning this option off allows you to change advection settings for velocity.

If this option is enabled, the solver will build the collision and collisionvel fields, allowing automatic interaction between smoke and collision objects.

Controls how far from the collision objects the relevant fields are to be built. This value is measured in voxels. If disabled, the fields will be initialized everywhere.

The local velocity of an affector object is a combination of the angular and linear velocity. However, if the object is deforming and points match frame to frame, the local point velocity can be used as well to estimate the deformation effect.

If an affector object doesn’t have a stable point count, but does have a volume representation, the change in the volume representation can be used as an estimate of deformation velocity.

Normally, the collision relationship uses the signed distance field for each object. However, if the object is a different type you can use other ways of getting its effective signed distance field. If this option is enabled, the object is examined for a surface scalarfield, which is treated as a signed distance field. If a density field is present, it is treated as a fog volume with a 0.5 cutoff. If a Geometry geometry is attached, and it consists of a single volume, that volume will be treated as a fog volume (with cutoff of 0.5). However, if its boundary condition is set to SDF, it will be treated as an SDF.

When enabled, the specified fields will be reset inside the colliders.

These fields will be reset inside the colliders when Correct Collisions is turned on.

The degree to which the colliders are affected by smoke is controlled by the value of this parameter. Higher values will increase the effect of pressure forces on the colliders. A value of 0 will prevent any feedback.

Colliders are integrated into the system using a weak coupling approach. The number of projection iterations is controlled by this parameter. Larger values will slow down the simulation, but yield better interaction with collision objects.

Strength of hourglass filtering. Value of 0 disables the filtering altogether, while 1 performs full filtering.

Instead of performing the filtering everywhere, it can be selectively applied to voxels where divergence is still detected by turning this option on.

Similar to Scale by Divergence, this setting applies the filtering with different strength in different places. Instead of pure divergence, however, the quantity used to control filtering strength is the ratio of divergence to speed.

Controls how sensitive filter strength is to the remaining divergence (or divergence relative to speed if Use Relative Divergence is enabled). That is, the relevant quantity is multiplied by this amount before it is used to determine filter strength.

The number of fields to export from the simulation.

Toggles whether this specific field should be exported.

The scalar or vector field to extract from the simulation. It will be properly named, ie, the vel field will create vel.x, vel.y, and vel.z named volumes. It will also be in a group named after the DOP object.

While this is designed around exporting fields, any geometry can actually be exported here.

Controls how the volume will appear in the viewport. Ancillary data volumes like velocity and rest fields are often useful to mark as invisible so they are available to mantra but don’t get in the way of viewing.

When this option is enabled, the advection wind vector (specified under Wind subtab of the Shape tab) is added to the exported velocity field. This option is not available in Minimum OpenCL solve mode to avoid slowing down the simulation.

Computes the minimum and maximum values of each volume and stores it as a primitive attribute of the same name. If the volume is vector type and is converted to VDB, the maximum length is stored.

Convert these volumes into VDBs. Zero areas will be discarded as inactive. Volume sets, such as vel.x, vel.y, and vel.z, will be merged into a single vector VDB.

Marks the volume to use 16-bit float values. This requires half the memory of full 32-bit values, but can be slower to process. Houdini volumes will be 16-bit in memory and on disk. VDBs are only 16-bit when saved to disk.

NOTE: For Houdini volumes this will only convert volumes to 16-bit, not convert back to 32-bit. Use the Volume Compress to switch volumes back to 32-bit.

When enabled, the active region of the specified VDB will be restricted to the active region of the Cull Mask Volume. This can help reduce the memory footprint of the primitives while retaining the volume values in needed areas.

The names of volumes to resample. This is a space separated list of volume names and can contain wildcards. Note that volumes with suffixes (such as .x or .y) will match with and without the suffix. This way vel in this parameter will match with the volume named vel.x. Volumes whose names match this pattern will then be resampled by the voxel size scale.

A scale factor to change the size of the voxels in the resampled volume. 2 will double the voxel size, so result in half the resolution, and one eighth the total voxels.

Scales the flame volume by this and does a maximum of this with density. This is required for smokeless regions that otherwise may be skipped by the renderer. To get a truly zero alpha channel, the smoke density can be set to 0.

Names of VDBs to transform as vector volumes. All volumes that match the foo.x, foo.y and foo.z will be merged into single 3-tuple VDBs. If the name matches this list, they will also be flagged as vector-type so they will transform. This ensures velocity vectors transform but avoid having color transforming. This is a space-separated list and can include wildcards.

When Cull Volume is enabled, this volume specifies the active region to retain. That is, voxels that are outside the active region of Cull Mask Volume will be deactivated.