fluidShape

 
 
 

Container Properties

The attributes in this section define the basic characteristics of the fluid container.

Keep Voxels Square

When on, Keep Voxels Square sets the container's original resolution based on the container's Resolution and Size values while maintaining square voxels in the local space of the fluid. When Keep Voxels Square is on, you can use the Base Resolution attribute to adjust the fluid X, Y, and Z resolution simultaneously.

Square voxels can provide better simulation and rendering results for your fluid object.

You can still have a final non-proportional placement for the fluid while using Keep Voxels Square if you transform the fluid rather than modifying its size and offset. See Size. If the fluid's Transform node has Scale X, Y, and Z values that are not proportional, the container's voxels will only be kept square in the local space of the fluid, but not in world space. See Change fluid resolution.

If Auto Resize is on, Keep Voxels Square is on by default. If you open a fluid effect from a previous version of Maya, Keep Voxels Square is off.

Base Resolution

When Keep Voxels Square is on, setting Base Resolution simultaneously sets the X, Y, and Z Resolution values of your fluid container. Base Resolution defines the container's resolution along the largest axis of the fluid. The resolution along the smaller dimensions is reduced to maintain square voxels. When you change the fluid's Size values, the fluid size will be in a non-proportional state until you have finished setting the size along each axis. This also means that as you set Size, the individual Resolution values will also be affected, and you need to reset them to the desired values. See Change fluid resolution.

Resolution

Defines the resolution of the fluid container in voxels.

The default resolution is for 3D fluids is 10 10 10.

The default for 2D fluids is 40 40.

Higher resolutions produce finer detail, but increases simulation and rendering time.

Tip

Even if none of the fluid properties are defined as grids, increasing the resolution increases the quality of the rendered fluid.

Size

Defines the size of the fluid container in centimeters.

Tip
  • Make the size proportional to the grid resolution, even if you do not use any grids to define property values (you use all gradient style values). For example, if the size is 10.0 5.0 2.0, then a valid resolution would be 40 20 8. If the size is not proportional to the resolution, then the quality will be higher looking down one axis than another.
Note

A 2D fluid with a depth (Z Size) of 0 will not render properly as a volume.

Boundary X, Y, Z

The boundary attributes control the way the solver treats property values at the boundaries of the fluid container.

For each boundary select one of the following boundary definitions:

None

Makes all boundaries of the fluid container open so that fluid behaves as though the boundary isn’t there.

Both Sides

Closes both boundaries of the fluid container so they act like walls.

-X, -Y, or -ZSide

Closes the -X, -Y, or -Z boundary, respectively, so it acts like a wall.

X, Y, or Z Side

Closes the X, Y, or Z boundary, respectively, so it acts like a wall.

Wrapping

Causes the fluid flowing off one side of the fluid container to enter at the opposite side. This can be useful if you want to have a windy fog, but you do not want to continually replenish the Density at the in-flowing regions.

Note

The fluid does not actually leave the container where there are no boundaries. It just appears to. Fluid can only exist inside a container.

Use Height Field

(For 2D containers only.) Turn this option on to draw a 2D surface as a height field rather than a flat plane. This is useful for generating effects such as foam on a cappuccino or boat wakes.

This option affects both surface shaded renders as well as normal volume renders. (Remember that 2D fluids are really 3D fluids. The dynamic grid and textures are defined in 2D and projected onto the 3D volume.)

When Use Height Field is on, Opacity is reinterpreted to mean the height of a uniform opacity. This offset is in the Z axis coming out of the fluid. An Opacity value of 0.0 means a height of 0 and an Opacity value of 1 means the fluids fills up to the maximum Z boundary. The Z size of the 2D fluid is defined by the Size attribute.

The playback speed for Surface Render of 2D fluids is much faster if Use Height Field is on.

Contents Method

For each of the fluid properties, select which method to use to populate the fluid container with property values. For each property, you can scale the values in the container to uniformly increase or decrease them. See Contents Details.

Density/Velocity/Temperature/Fuel

Select one of the following options:

Off (zero)

Sets the property value to 0 throughout the fluid. When set to Off, the property has no effect on dynamic simulations.

Static Grid

Creates a grid for the property that lets you populate each voxel with specific property values (using fluid emitters, the Paint Fluids Tool, or initial state caches). While these values can be used in dynamic simulations, they cannot change due to any dynamic simulation.

Dynamic Grid

Creates a grid for the property that lets you populate each voxel with specific property values (using fluid emitters, the Paint Fluids Tool, or initial state caches) for use in any dynamic simulation.

Gradient

Uses the selected gradient to populate the fluid container with property values. Gradient values are predefined in Maya without the use of a grid. Gradient values are used in calculations for dynamic simulations but the values cannot change because of the simulation. They render more quickly than grid values because no calculations are required for simulation.

Density/Velocity/Temperature/Fuel Gradient

(Available when the previous method is set to Gradient.)

Select which predefined set of values you want to place in the container:

Constant

Sets the value to 1 throughout the fluid.

X Gradient

Sets a ramp of values from 1 to 0 along the X axis.

Y Gradient

Sets a ramp of values from 1 to 0 along the Y axis.

Z Gradient

Sets a ramp of values from 1 to 0 along the Z axis.

-X Gradient

Sets a ramp of values from 0 to 1 along the X axis.

-Y Gradient

Sets a ramp of values from 0 to 1 along the Y axis.

-Z Gradient

Sets a ramp of values from 0 to 1 along the Z axis.

Center Gradient

Sets a ramp of values from 1 at the center, to 0 along the edges.

Color Method

Color displays and renders only where Density is defined. Select which method to use to define color.

Use Shading Color

Defines color using the Color ramp attribute in the Shading section of the Attribute Editor.

Static Grid

Creates a color grid which you can populate with specific color values (using fluid emitters, the Paint Fluids Tool, or initial state caches). While these values can be used in dynamic simulations, they cannot change due to any dynamic simulation.

Dynamic Grid

Creates a color grid which you can populate with specific color values (using fluid emitters, the Paint Fluids Tool, or initial state caches) for use in a dynamic simulation.

For Static and Dynamic Grids, the default grid color is green/brown (close to RGB 0.4 0.4 0.3) to minimize fringing where any colored Density you add meets voxels with no Density values. If this is not an acceptable grid color, flood the color grid with the color you want and set it as your initial state, see Flood a container with values and Fluids initial state.

Falloff Method

Adds falloff edges to the display of fluids, so that you can prevent the fluid from appearing in part of the volume.

Off (zero)

No falloff occurs.

Static Grid

Adds a static grid to define falloff.

Display

The Display options affect how the fluid displays in the scene view. They do not affect the final rendered image.

Shaded Display

Defines which fluid properties display in the fluid container when Maya is in shaded display mode. If Maya is in wireframe mode, the Wireframe Display options apply to the selected property.

Select Off to display nothing in the fluid container when in shaded display mode.

Select As Render to display the fluid as close as possible to the final software render.

Isolating the display of a specific property of the fluid (for example, Fuel) is particularly useful when painting the property with the Paint Fluids Tool or adjusting settings for it. Tweak the Opacity Preview Gain to map the selected property to a useful range of opacity in the grid.

For display options combining Density with another property (for example, Density And Temp), color differentiates the two properties. If the second attribute is not color, then you get a built-in ramp (with blue, red and yellow) that maps the interval 0-1; where there is no density, there is no information about the second attribute.

Select Falloff to display a falloff for Fluid Effects.

Opacity Preview Gain

Adjusts the Opacity of the hardware display when the Shaded Display is not As Render. This is useful when painting values into the grid to help differentiate values that are very close together.

Slices per Voxel

Defines the number of slices displayed per voxel when Maya is in shaded display mode. A slice is a display of values on a single plane. Higher values produce more detail but reduce the speed of the screen draw. The default is 2. The maximum value is 12.

The orientation of the slices is determined by the voxel most aligned with the view plane.

Voxel Quality

If Voxel Quality is set to Better, the display quality is higher in hardware display. If it is set to Faster, the display quality is lower, but the draw is faster.

Boundary Draw

Defines how the fluid container displays in 3D views. The grid corresponds with the Resolution settings.

Bottom

The fluid container displays as a bounding box with a detailed grid on the bottom side. For 2D fluids, this setting displays a detailed grid.

Reduced

The fluid container displays as a bounding box, with a detailed grid on the sides furthest away from the camera. For 2D fluids, this setting displays a detailed grid.

Outline

The fluid container displays as a bounding box, with a detailed grid on all six sides. For 2D fluids, a dotted line displayed around the container indicates the potential volume of the 2D fluid. Note that 2D fluids have thickness, and render as a volume, not as a flat planar surface. To render a fluid as a flat surface, you must map a 2D fluid texture to a plane.

Full

The fluid container displays as a bounding box, with full grid lines representing each voxel. For 2D fluids, this setting displays a detailed grid.

Bounding box

The fluid container displays as a bounding box only.

None

The fluid container does not display, however, any visible properties do display.

Numeric Display

Displays numeric values for the selected property (Density, Temperature, or Fuel) in each voxel of a Static or Dynamic Grid. The numbers that display represent the values before the Scale is applied. For example, if the Density value in a voxel is 0.2 and the DensityScale is 0.5, the number that displays in the voxel is 0.2, not 0.1. No numeric values display when this option is set to Off or when the Contents Method for the selected property is set to Gradient.

Numeric Display can be used in both shaded and wireframe display modes.

Wireframe Display

If the Contents Method is set to Gradient for the property selected for Shaded Display, this option defines how to represent the opacity of the property when Maya is in wireframe display mode.

If Contents Method is set to Static or Dynamic Grid for the property selected for Shaded Display, this option defines how to represent the values of the property when Maya is in wireframe display mode.

Off

Displays nothing in the fluid container.

Rectangles

Displays rectangles on the grid lines of the fluid container. Larger rectangles represent areas with higher values or opacity.

Particles

Displays particles to represent values or opacity. Areas with denser particles represent areas with higher values or opacity.

Velocity Draw

Turn this option on to display velocity vectors for the fluid. Velocity vectors represent the magnitude and direction of the Velocity in the container. Velocity vectors help you visualize the motion path of the fluid.

Draw Arrowheads

Turn this option on to display arrow heads on the velocity vectors. Turn this option off to speed drawing and reduce visual clutter.

Velocity Draw Skip

Increase this value to reduce the number of velocity arrows that are drawn. If the value is 1 then every other arrow is omitted (or skipped). If it is zero then all arrows are drawn. Increase this number on grids with a high resolutions to reduce visual clutter.

Draw Length

Defines the length of the velocity vectors (a factor applied to the magnitude of the velocity). The larger the value, the longer the velocity segments or arrows. For simulations with very low force, the velocity field might be very small in magnitude. In this case, increasing the value will help to visualize the velocity flow.

Dynamic Simulation

To simulate flow for a fluid property, the Contents Method for that property must be set to Dynamic Grid and Velocity cannot be Off. During simulation, the values in the container are solved using the Navier-Stokes fluid dynamics equations (solvers) and replaced with the new values to create the fluid motion. Use the attributes in this section to define the information used by the solvers.

Gravity

The Gravity setting is a built-in gravitational constant that simulates the gravitational attraction of the mass of the world in which the simulation is occurring. Negative values cause a downward pull (relative to the world coordinate system).

If Gravity is zero, DensityBuoyancy and TemperatureBuoyancy have no effect

Viscosity

Viscosity represents the resistance of the fluid to flow, or how thick, and non-liquid the material is. When this value is high, the fluid flows like tar. When this value is small, the fluid flows more like water.

(When Viscosity is 1, the material Reynolds Number is 0; when it is 0, the Reynolds Number is 10000. The Reynolds Number is a parameter used in solving the fluid dynamics equations that is proportional to the viscosity of the fluid.)

Friction

Defines internal friction used in Velocity solving.

Damp

Defines the amount the Velocity solution is damped towards zero at each time step. At a value of 1, the flow is totally suppressed. Small amounts of damping can be useful when boundaries are open to keep strong winds from building up and leading to instability.

Solver

Select one of the following options:

None

No solver is used.

Navier-Stokes

A Navier-Stokes solver is used (best for fluids, air, and other situations where flow swirls around but doesn’t expand outward or compress inward)

Spring Mesh

A wave propagation simulator is used (best for up-and-down, back-and-forth motion found in waves).

High Detail Solve

This option may reduce diffusion of density, velocity and other attributes during a simulation. For example, it may make fluid simulations appear much more detailed without increasing resolution, and allow the simulation of rolling vortices. Using High Detail Solve is ideal for creating effects such as explosions, rolling clouds and billowing smoke.

Off

Simulations run faster, but there is a lot of diffusion of both density and velocity as the simulation progresses.

Some artifacts that appear when using High Detail Solve can be removed using Density or TemperatureTension.

All Grids Except Velocity

Applies the additional solve steps to all grids except for velocity, requiring simulation computation time that is not much more than when High Detail Solve is Off.

Velocity Only

Only velocity grid values have the additional solve steps applied. This option may avoid some artifacts that can result from high detail on the density grid. (Use the HermiteGrid Interpolation option—while it is slower, it can yield high-quality results.)

All grids

Applies the additional solve steps first when computing the velocity, and also when applying the velocity to the rest of the grids. There is much more detail in the flow, resulting in a simulation that is significantly more realistic. Since propagating velocity is much more computationally intensive than propagating scalar grid values like density, using this option doubles the simulation computation time.

Substeps

Specifies the number of times the solver performs calculations per frame. Substeps are useful for improving the stability and simulation results of fast-moving fluids, fluids with high density grids, and when the High Detail Solve is used.

Solver Quality

Increasing the Solver Quality increases the number of steps used by the solver to compute the incompressibility of the fluid flow. This calculation, called the Poisson solve, is generally the most computation intensive part of the solve.

Lowering Solver Quality results in less detailed simulations with more diffusion. However, you can allow for some compression of the fluid by lowering Solver Quality, particularly when High Detail Solve is off and Forward Advection is on. Adding compression to a fluid is useful when using Self Attraction and Gradient Force in your effects. See Self Attraction and Repulsion.

Grid Interpolator

Select which interpolation algorithm to use to retrieve values from points within a voxel grid.

linear

Interpolate the values linearly. This is the faster of the two methods.

hermite

Use a hermite curve to interpolate the fluid. This method causes less diffusion than linear, but makes the simulation run several times more slowly, especially when the fluid is colliding with geometry. Use hermite if you want Friction to be computed by the solver at the boundaries. (Use this option with the Velocity OnlyHigh Detail Solve method—while it is slower, it can yield high-quality results. Do not use this option with the All Grids Except Velocity or All Grids options.)

Forward Advection

When Forward Advection is on, Density, Temperature, and Fuel grids are solved using a mass conserving forward propagation technique that pushes density forward through the grid. Velocity grids are not calculated using Forward Advection.

The default solve method uses a backwards propagation technique that pulls density into voxels from surrounding voxels.

Fluid effects solved using Forward Advection can produce fewer artifacts when High Detail Solve is used and results in less density diffusion than the default solve method. Forward Advection can also resolve instances where density remains static in voxels.

Note

The default solve method (Forward Advection turned off) relies on the incompressibility of the fluid flow and diffuses if Solver Quality is set to a low value. When Forward Advection is on, the fluid does not have this issue, making it useful for simulations that have compression effects.

Start Frame

Sets the frame after which the fluid simulation will start. The default is 1.0. Nothing will play back for this object prior to this frame. You could use this attribute to delay the effect of a field on a fluid until the frame of your choice.

Note

If you change the Time units setting (Window > Settings/Preferences > Preferences), you must set the Start Frame to the correct initial value so that Maya computes the start time again.

Simulation Rate Scale

Scales the time step used in emission and solving.

Disable Evaluation

Turn this option on to turn off solving during interactive playback. If there is a fluids cache present, Maya plays back the simulation from the cache.

Conserve Mass

Turn this option on to conserve mass when updating the Density values during solving.

Use Collisions

Turn this option off to disable the collision of fluid with collision geometry in the container.

Use Emission

Turn this option to off to ignore all connected fluid emitters during simulation.

Use Fields

Turn this option to off to ignore all connected external fields during simulation.

Emit In Substeps

When on, fluid emission is computed each substep rather than once per step. Turning on Emit In Substeps is useful for effects that have high emission speeds such as in an explosion.

Liquids

Enable Liquid Simulation

When on, you can use the Liquids attributes to create fluid effects simulations that look and behave like real liquids.

For more information about liquid simulations, see also Liquid simulation setup.

Liquid Method

Specifies the liquid simulation method used for liquid effects.

Liquid and Air

The fluid uses a solving method that differentiates the density of air and water in the fluid. The fluid solver treats the liquid density as an incompressible fluid, while the air is fully compressible.

A Liquid Min Density attribute lets you specify the density value at which the solver considers the fluid a liquid. For example, at the default value of 0.5, areas of the fluid with density values of 0.5 or greater simulate as an incompressible liquid, while areas that have density of less than 0.5 simulate as air. When Liquid Min Density is set to 0, there is no differentiation between air and water, causing the fluid to behave as a fully incompressible fluid. See Liquid Min Density.

This simulation method works best when the Solver Quality is set to a high value and Forward Advection is on. Use Replace emission type to maintain a single, continuous volume of fluid. You can use Density Tension to generate realistic surface tension in the fluid.

Density Based Mass

The fluid uses a solving method that varies mass according to fluid density. Areas of low density remain incompressible and apply an outward force to denser regions.

Using the Mass Range attribute, you can specify the relationship between mass and fluid density. For example, setting Mass Range to a high value makes the dense regions of the fluid heavier than areas with no density. See Mass Range.

You can use this method to simulate the interaction of two substances with different densities, such as oil and water, as well as simulate gas bubbles moving through a liquid.

This simulation method works best when the Forward Advection is on. Use Replace emission type to maintain a single, continuous volume of fluid.

Liquid Min Density

Specifies the density value at which the solver differentiates between liquid and air when the Liquid and Air simulation method is used. Liquid densities are calculated as incompressible fluids while air is fully compressible. At a value of 0 the solver does not differentiate between liquid and air and treats all fluid as incompressible, making it behaves as a single fluid.

Liquid Mist Fall

Applies a downward force to areas in the fluid that have density lower than the value specified by the Liquid Min Density value. At a value of 0, no force is applied. Increasing Liquid Mist Fall increases the strength of the downward force.

The force applied by Liquid Mist Fall is not the same as the Gravity force that is applied to the density grid. Liquid Mist Fall is useful for generating spray and mist effects for liquids or ensuring that there is no mist in your liquid effect.

Mass Range

Defines the relationship between mass and fluid density when the Density Based Mass simulation method is used. At higher Mass Range values, dense regions in the fluid are much heavier than low density regions, simulating a relationship similar to air and water.

Density Tension

Density Tension pushes density into round shapes, making the density boundaries more defined in the fluid. When set to high values, Density Tension can force fluid density into individual clusters on the grid. The effect of Density Tension in a fluid effect is similar to the effect of surface tension in liquids. Density Tension does not affect the velocity in voxels.

In some cases, Density Tension can be used to remove artifacts that appear when using High Detail Solve.

Density Tension is the same attribute as the Tension attribute and can be used with the default fluid solver when Enable Liquid Simulation is off. It has been added to the Liquids attribute section for user convenience.

Tension Force

Applies a force that simulates surface tension based on the density in the grid. Tension Force is similar to Density Tension, but rather than modifying density values, Tension Force modifies momentum by adding small amounts of velocity in the fluid.

You can use Tension Force with Density Tension to create realistic surface tension in your liquid effect. Tension Force can be used with the default fluid solver when Enable Liquid Simulation is off.

Density Pressure

Applies an outward force to counter the compression affect that Forward Advection can apply to fluid density, particularly along container boundaries. In this way, the attribute attempts to conserve the overall fluid volume ensuring no density loss. For example, in a water tank simulation, fluid may appear to collapse or drain without sufficient Density Pressure.

Density Pressure is the same attribute as the Pressure attribute that is located in the Density section of the Contents Details attributes. Density Pressure can be used with the default fluid solver when Enable Liquid Simulation is off. It has been added to the Liquids attribute section for user convenience.

Density Pressure Threshold

Specifies the density value at which Density Pressure is applied on a per voxel-basis. For voxels that have density lower than Density Pressure Threshold, no Density Pressure in applied.

Density Pressure Threshold has the same effect as the Pressure Threshold attribute that is located in the Density section of the Contents Details attributes. Density Pressure Threshold can be used with the default fluid solver method when Enable Liquid Simulation is off.

Auto Resize

Auto Resize

When on, Auto Resize dynamically resizes 2D and 3D fluid containers when the voxels near outer boundaries of the container have positive density. For example, 2D and 3D fluid containers expand or contract according to the current density of the fluid. As the fluid density dissipates in the simulation, the fluid boundary resizes to accommodate only positive fluid Density.

The smaller simulation area increases simulation speed, reduces rendered times, uses less memory, and results in smaller fluid cache files. See Dynamically resize a fluid container.

Resize Closed Boundaries

When on, fluid containers resize along the axis that have their respective Boundary attribute set to None, Both Sides, - Side, or Side. When off, fluid containers only resize along the axis that have their respective Boundary attribute set to None. Fluid containers do not resize along axis that have their Boundary attribute set to Wrap. See Boundary X, Y, Z and Change fluid behavior at the container boundaries.

Resize Closed Boundaries is on by default and only affects fluid containers when Auto Resize is on.

Resize To Emitter

When on, the fluid container uses the fluid emitter's position to set it's its offset and resolution in the scene. Turning on Resize To Emitter is useful in fluid effects with animated emitters as it ensures that the container moves and resizes to include the moving emitter. This means the emitter can be outside the fluid container at the start frame.

A Max Resolution attribute sets the outer resize boundaries. If the fluid has already expanded to the Max Resolution value, it will no longer expand to follow an emitter that moves outside of the fluid volume.

When Resize To Emitter is on, the fluid container jumps and contracts to emission regions in a single step. When Resize To Emitter is off, the container resizes one voxel per frame.

NoteYou can turn on Resize in Substeps to resize the container each Substep.
Resize In Substeps

When on, auto resized fluid containers resize each substep. When Resize In Substeps is off, fluids only resize one voxel per simulation step.

NoteCollision boundaries are evaluated per substep only when Auto Resize and Resize In Substeps are on.

Max Resolution

Specifies the average maximum resolution per side that a fluid container resizes when Resize to Emitter is on.

For example, if Max Resolution is set to 10, then the total resolution of the fluid cannot be greater than that of a 10×10×10 fluid. This means that you can have a 3D fluid with a Resolution of 5×20×10, but not 6×20×10, or you can have a 2D fluid with a Resolution of 20×50, but not 21×50.

Dynamic Offset

Displays the local space translation of the fluid that is computed when Auto Resize is on. Maya either sets the values during fluid auto resizing, or reads them from fluid nCache files.

Auto Resize Threshold

When Auto Resize is on, Auto Resize Threshold sets the density threshold value that causes the fluid container to resize. Auto Resize Threshold uses the current Density value in the second row of voxels from the containers edge to determine the outer boundaries of the fluid, then resizes the fluid container accordingly. As you increase the threshold value, the fluid Density at the container boundaries increases.

See Dynamically resize a fluid container.

Auto Resize Margin

Specifies the number of empty voxels added between the fluid container boundary and regions of positive density in the fluid. Auto Resize Margin lets fluids flow more naturally near auto- resized boundaries and is useful for fast-moving and low density fluids. Auto Resize Margin does not affect the way Auto Resize Threshold resizes the fluid container.

When using Auto Resize Margin with fast flowing fluids, use low Substep values.

Self Attraction and Repulsion

Self Attraction and Repulsion attributes generate attractive and repulsive forces between Voxels in 2D or 3D fluid containers. Using the Self Force attribute, you can set whether the forces depend on the container’s density or temperature grid values.

The Equilibrium Value attribute set the target value which determines whether a voxel generates an attractive or repulsive force. Voxels with density or temperature values less than the Equilibrium Value generate an attractive force. Voxels with density or temperature values greater than the Equilibrium Value generate a repulsive force. See Equilibrium Value.

See also Using self attraction and repulsion forces.

Self Attraction and Repulsion can be applied to dynamic and static grids.

Self Force

Turns on the self attraction and repulsion forces and sets whether the force is based on the container’s Density or Temperature grid values.

Off(zero)

No self force is applied to the voxels in the fluid container.

Density

Sets the Self Force to be based on the Density grid values.

Temperature

Sets the Self Force to be based on the Temperature grid values.

Self Attract

Sets the strength of the attractive force. Self Attract does not effect voxels that have density or temperature values greater than the Equilibrium Value.

Self Repel

Sets the strength of the repulsive force. Self Repel does not effect voxels that have density or temperature values less than the Equilibrium Value.

Equilibrium Value

Sets the target value that determines whether voxels generate an attractive or repulsive force. Voxels that have density or temperature values that are less than the set Equilibrium Value generate an attractive force. Voxels with density or temperature values greater than the Equilibrium Value generate a repulsive force.

Self Force Distance

Sets the maximum distance, in voxels, that the self force is applied. For example, when set to 1, voxels are only affected by the self forces generated by the voxels next to them. If the Self Force Distance value is greater than the resolution of the fluid, each voxel in the container is attracted or repelled by every other voxel in the fluid. The default value for Self Force Distance is 16.

Large Self Force Distance values can increase simulation time. If you increase the Resolution of a fluid container, increase the Self Force Distance value to obtain the same effect. The effect of Self Force drops off with local space distance in a way that is similar to gravitational self attraction.

Contents Details

The attributes in this section are specific to each fluid property.

Density

Density represents the material property of the fluid in the real world. You could think of it as the geometry of the fluid. If you compare it to a normal sphere, the volume equivalent of the sphere’s surface is the distribution of the Density inside the container.

TipIn general, avoid Density values that are greater than 0.5 on the grid. If your Opacity is defined such that a Density of 0.9 still has visible transparency to it, then the transition to a Density of 1.0 or greater (totally opaque) will be quite sudden and unnatural.

A 1-1 correspondence with Density and Opacity is not typically desirable. An Opacity of 1.0 corresponds with an infinite density in nature (even materials like gold let a little light through). If the Density Scale is 1.0, the Transparency is 0.5, and the OpacityInput Bias is 0, you have a 1-1 correspondence. Lowering the Transparency and/or increasing the OpacityInput Bias helps create a more natural correspondence.

Density Scale

Multiplies the Density values in the fluid container (whether they are defined in grids, or defined by preset gradients) by the scale value. Using a Density Scale of less than 1 makes the Density appear more transparent. Using a Density Scale greater than 1 makes the Density appear more opaque.

In the following example, Density is set to Constant, which means it has a value of 1 throughout the fluid container. As you scale the Density values with a Density Scale less than 1, notice that the Density becomes less opaque and you can see the red ball contained in the fluid.

In the next example, Density is set to Dynamic Grid and the Density values are less than 1. As you scale the Density values with a Density Scale value greater than 1, notice that the Density becomes more opaque and the red ball contained in the fluid becomes more and more obscured by it.

Buoyancy

Dynamic Grid only. Simulates a difference in mass density between the regions with Density values and the regions without. If the Buoyancy value is positive the Density represents a substance that is lighter than the surrounding medium, like bubbles in water, and will thus rise. Negative values cause the Density to fall.

Dissipation

Defines the rate at which the Density gradually vanishes in a grid. At each time step Density is removed from each voxel (the Density value becomes smaller). In the following example, the Dissipation value is set to 1.

Note

Dissipation in Fluid Effects is not the same as Lifespan with particles. Lifespan describes an on/off state (you are either alive or dead). Dissipation is a gradual fading out—it’s not absolute. The effective lifespan of Density in a grid is relative to the emission Density, motion within the grid, Diffusion, and the Transparency of the fluid.

Diffusion

Defines the rate at which Density spreads into adjacent voxels in a Dynamic Grid. In the following example, the Diffusion value is set to 2.

Pressure

Applies an outward force to counter the compression effect that Forward Advection can apply to fluid density, particularly along container boundaries. In this way, the attribute attempts to conserve the overall fluid volume ensuring no density loss.

Pressure is the same attribute as the Density Pressure attribute that is located in the Liquids attributes.

Pressure Threshold

Specifies the density value at which Density Pressure is applied on a per voxel-basis. For voxels that have density lower than Density Pressure Threshold, no Density Pressure in applied.

Pressure Threshold is the attribute as the Density Pressure Threshold attribute that is located in the Liquids attributes.

Noise

Randomizes Density values each simulated step based on changes in voxel’s velocity. You can use Noise to add turbulence and detail to flowing fluids. Be aware that high Noise values can add unwanted jitter to the fluid.

Tension

Tension pushes density into rounder shapes, making the density boundaries more defined in the fluid. When set to high values, Tension can force fluid density into individual areas of in the grid. The effect of Tension in a fluid effect is similar to the effect of surface tension in liquids. Tension does not affect the velocity in voxels.

You can use Tension to smooth out detail and add puffiness to cloud and smoke effects. Tension can also be used to remove artifacts that appear when using High Detail Solve.

Tension Force

Applies a force that simulates surface tension based on the density in the grid. Tension Force is similar to Density Tension, but rather than modifying density values, Tension Force modifies momentum by adding small amounts of velocity in the fluid.

You can use Tension Force with Density Tension to create realistic surface tension in your liquid effect. Tension Force can be used with the default fluid solver when Enable Liquid Simulation is off.

Gradient Force

Applies a force along the direction of the density gradient or normal. Positive Gradient Force values push in the direction of increasing density, producing an attractive force. Negative values push density away from itself, producing a repelling force.

Gradient Force produces similar effects as the Self Attraction and Repulsion, but the effect is localized to the adjacent voxels, while Self Attraction and Repulsion generates forces between voxels on a per-voxel basis. Gradient Force takes less time to calculate than Self Attraction and Repulsion, reducing simulation time. See also Self Attraction and Repulsion.

Velocity

Velocity Scale X, Y, Z

Scales the velocity relative to the fluid.

Multiplies the Velocity values within the fluid container by the Scale value. Scaling does not affect the direction.

Swirl

Swirl generates small scale vortices and eddies in the fluid. It is useful for adding detail to simulations that are not using the High Detail Solve method. In some cases, high Swirl values can cause artifacts as well as instability in the fluid.

Noise

Applies randomization to the velocity values on the Velocity Dynamic Grid to create turbulence in the fluid. Increasing Noise increases the randomization on a per-voxel basis and increases turbulence in the fluid.

Turbulence

Strength

Increase this value to increase the amount of force applied by the turbulence.

Frequency

Lowering Frequency makes the turbulence vortices larger. This is a spatial scale factor on the turbulence function and has no effect if the turbulence strength is zero.

Speed

Defines the rate at which the turbulence pattern changes over time.

Temperature

Temperature Scale

Multiplies the Temperature values defined in the container.

Buoyancy

Defines built-in buoyancy strength for Temperature solving.

Pressure

Pressure simulates the increase in pressure that results from the increasing temperature of a gas, which causes the fluid to expand quickly.

To see the full effects of Pressure in the fluid, turn on Forward Advection. Pressure is useful for explosion effects as it can cause a small amount of emitted fluid to quickly expand with turbulent motion.

Dissipation

Defines the rate at which the Temperature gradually dissipates in a grid. At each time step, Temperature is removed from each voxel (the Temperature value becomes smaller).

Pressure Threshold

Specifies the temperature value at which Pressure is applied on a per voxel-basis. For voxels that have temperature lower than Pressure Threshold, no Pressure in applied.

Diffusion

Defines the rate at which the Temperature diffuses between voxels in a Dynamic Grid.

Turbulence

Multiplier on the turbulence applied to the Temperature.

Noise

Randomizes the temperature values of voxels each simulated step. Noise is applied to temperature in constant amounts that are not affected by changes in velocity. You can use Noise to add detail to smooth flowing effects and to the texture grids.

Noise can creates effects similar to Turbulence, but differs in the way it creates randomization. Noise randomizes temperature values each step, while Turbulence randomizes the velocity based on the Temperature grid.

Tension

Tension pushes temperature into rounded shapes, making the temperature boundaries more defined in the fluid. When set to high values, Tension can force fluid temperature into individual areas of in the grid. The effect of Tension in a fluid effect is similar to the effect of surface tension in liquids. Tension does not affect velocity in voxels.

You can use Tension to add puffiness to cloud and smoke effects. Tension can also be used to remove artifacts that appear when using High Detail Solve.

Fuel

Fuel combined with Density defines a situation in which a reaction can take place. Density values represent the substance being reacted, and Fuel values describe the state of the reaction. Temperature can “ignite” Fuel to start a reaction (for example, an explosion effect). As the reaction progresses, the value of the fuel changes from unreacted (value 1) to fully reacted (value 0).

Fuel burns at temperatures greater than the Ignition Temperature.

Fuel Scale

Multiplies the Fuel values defined in the container.

Reaction Speed

Reaction Speed defines how quickly the reaction converts from a value of 1 to zero when the temperature is at or above the Max Temperature value. A value of 1.0 results in an instantaneous reaction.

Air/Fuel Ratio

Sets the amount of density required to completely burn a set volume of fuel. For example, to burn a volume of gasoline requires 15 times more air than fuel. To simulate a gasoline fire, set Air/Fuel Ratio to 15.

When Air/Fuel Ratio is used, fuel only burns in the areas of the fluid where density and fuel are mixed (areas of diffusion), resulting in a better looking flame with realistic boundaries and shape. When Air/Fuel Ratio is set to 0, the flame burns uniformly as if contained in it's own oxygen.

Ignition Temperature

Ignition Temperature defines the lowest temperature at which a reaction will occur. The reaction rate is zero at this temperature, increasing to the value defined by the Reaction Speed at the Max Temperature.

Max Temperature

Max Temperature defines the temperature beyond which a reaction occurs at the fastest speed.

Heat Released

Heat Released defines how much heat is released into the Temperature grid by a total reaction. This is how many reactions sustain themselves after an initial spark of ignition. The amount of heat added in a given step is proportional to the percentage of reacted material. You need to have the Temperature Method set to Dynamic Grid to use this option.

Light Released

Light Released defines how much light is released by the reaction. This is directly added into the final incandescent intensity of the shading and does not input into any grids.

Light Color

Light Color defines the color of the light released by the reaction. The Light Released attribute along with the amount of Density reacted in a given time step scales the overall brightness of this light.

Color

Color Dissipation

Defines the rate at which the Color dissipates in a grid.

Color Diffusion

Defines the rate at which Color diffuses into adjacent voxels in a Dynamic Grid.

Grids Cache

Select which grid caches to read when playing a dynamic simulation.

Read Density

If the cache contains a Density grid, read the Density values from the cache.

Read Velocity

If the cache contains a Velocity grid, read the Velocity values from the cache.

Read Temperature

If the cache contains a Temperature grid, read the Temperature values from the cache.

Read Fuel

If the cache contains a Fuel grid, read the Fuel values from the cache.

Read Color

If the cache contains a Color grid, read the Color values from the cache.

Read Texture Coordinates

If the cache contains texture coordinates, read them from the cache.

Read falloff

If the cache contains a falloff grid, read them from the cache.

Surface

Select how you want the surface of the fluid to render.

Volume Render

Software render the fluid as a volumetric cloud.

Surface Render

Software render the fluid as a surface. The surface is formed by thresholding the Density values in the fluid container. Where the Density is greater than the Surface Threshold you are inside the medium, where it is less than this value you are outside the medium. (Surface Render combines blobby style surface rendering with normal soft volume style rendering.)

To see the surface in hardware display, Shaded Display must be set to As Render or the outMesh must have a connection. The surface location is determined by the current Opacity setting combined with the Surface Threshold.

Hard Surface

Turn Hard Surface on to make the transparency of the material constant inside the material (like glass or water). This transparency is determined solely by the Transparency attribute and the distance travelled through the substance.

Soft Surface

Turn Soft Surface on to evaluate the changing Density based on the Transparency and Opacity attributes. The shadows tend to be softer and thin areas appear fuzzy.

For the light/normal shading Maya relaxes the angle of cutoff similar to the way Ambient Shade works in ambient lights.

For thick clouds like nuclear bombs, using Soft Surface can result in faster render times for a self shadowed effect, and unlike the Hard Surface render, you can have soft fuzzy areas.

Tip

For a better rendered look, set Render Interpolator to Smooth in the Shading Quality section of the Attribute Editor.

Surface Threshold

Threshold value used to create the implicit surface.

Surface Tolerance

Determines how close points sampled for a surface lie to the exact Surface ThresholdDensity. The tolerance value is defined relative to the Quality setting. The Quality determines the uniform step size, so that the actual distance this defines is equal to the step size Surface Tolerance.

Make the Quality setting just high enough so that you do not miss regions containing the surface. The render then further refines the surface using this tolerance.

If the Surface Tolerance is high then the surface will look dotty and of poor quality. Very low values result in longer render times and better quality.

In practical terms, Surface Tolerance helps better define the surface normal, because the local gradient used for the normal can vary quite a bit if the samples are not all close to the surface.

If your surfaces look grainy try lowering this value a bit (this is more critical when your Density is not smooth but very sharply defined, like with a thresholded texture, however a better solution is to make your Density smoother). If the graininess is due to missing the surface (that is, little holes) rather than noisy normals, then increasing the Quality is better.

Specular Color

Controls the amount of light emitted from regions of Density due to self illumination.

Cosine Power

Control the size of the specular highlights (also called “hot spots”) on the surface. The minimum value is 2. The higher the value, the more tightly focussed (smaller) is the highlight.

Environment

The Environment ramp defines a simple sky to ground environmental reflection on a surface. The left of the ramp represents the top of the sky and the right represents the bottom.

You define the reflection colors between the top and bottom of the sky by adding position markers to the ramp and changing the color at the markers. See Set fluid attribute ramps.

Selected Position
Selected Color

Interpolation

Controls the way colors blend between positions on the ramp. The default setting is Linear.

None

See None.

Linear

See Linear.

Smooth

See Smooth.

Spline

See Spline.

Refractive Index

Index of refraction. This attribute affects how reflectivity changes with viewing angle. It makes use of Fresnel’s law. Materials with a low refractive index are generally only reflective at glancing angles. This is useful for a wet look or for water, because water has a lower refractive index than most solids. At a refractive index of 1.0 the material is considered to be the same as the medium, and theoretically there should be no specularity in this case (as with a cloud). However, for convenience, there is full specularity in this case (no view angle modulation).

Output Mesh

The Output Mesh attributes allow you to control the resolution, smoothness, and speed of fluid to polygon mesh conversions.

Mesh Method

Specifies the type of polygon mesh used to generate the output mesh iso-surface. By default, Mesh Method is set to Triangle Mesh.

Triangle Mesh
Converts the fluid to a cube polygon mesh using the marching cubes method.
Tetrahedra
Converts the fluid to a triangle polygon mesh using the marching tetrahedra method.
Acute Tetrahedra
Converts the fluid to a triangle polygon mesh using the marching tetrahedra method, and produces a slightly higher resolution mesh than the Tetrahedra Mesh Method.
Quad Mesh
Converts the fluid to a quad polygon mesh.
Mesh Resolution

Use this attribute to adjust the resolution of your fluid output mesh. Setting the Mesh Resolution to a low value allows you to quickly render fluid effects for partial previews. Higher output resolutions produce finer detail in the fluid, but increase rendering time. This attribute affects both the interactive display of surface style fluids, as well as the quality of the fluid to polygon mesh conversion.

Mesh Resolution does not affect the quality of the native fluid node render. Higher resolution values better resolve effects such as opacity texturing of the fluid. In addition, the higher resolution sampling takes advantage of the smooth render interpolation method when the method is enabled.

Mesh Smoothing Iterations

Specifies the amount of smoothing applied to the output mesh. Smooth iterations change the length of the triangle edges, making the topology more uniform and generating a smoother iso-surface. The smoothness of your output mesh increases with increased Mesh Smoothing Iterations values, however, calculation time also increases.

Color Per Vertex

When on, color per-vertex data is generated when you convert a fluid object to a polygon mesh.

To generate color per-vertex data for your fluid output mesh, either set a color grid or map color using a Color ramp. See Color.

Opacity Per Vertex

When on, opacity per-vertex data is generated when you convert a fluid object to a polygon mesh. The per-vertex data is stored in a color set and can be visualized by making it the current color set of the mesh, or used with the mental ray Vertex Colors texture. See Opacity.

Incandescence Per Vertex

When on, incandescence per-vertex data is generated when you convert a fluid objects to a polygon mesh. The per-vertex data is stored as a color set and can be visualized by making it the current color set of the mesh, or used with the mental ray Vertex Colors texture.

To generate incandescence per-vertex data for your fluid output mesh, make sure you must have valid inputs to an Incandescence ramp. For example, if Incandescence is mapped to Temperature, and there is no temperature grid for the fluid, you will not get incandescence values. See Incandescence.

Velocity Per Vertex

When on, velocity per-vertex data is generated when you convert a fluid object to a output mesh. Velocity per vertex is derived from the internal mapping of fluid velocity values to R, G, and B color values. You can use velocity per-vertex data to create motion blur in the rendered fluid output mesh.

Velocity per-vertex data is passed to the output mesh by way of the polySurfaceShape node's color set named Motion Vector Color Set. By default, this color set is set to the velocityPV data generated from the fluid object.

Uvw Per Vertex

When on, UVs and a UVW color set are generated when you convert a fluid object to a polygon mesh. The texture coordinates let you map a texture to the surface of your output mesh. See Converting fluids to polygons.

You may need modify the meshes' UV topology to get the desired placement of the texture on the mesh. You can view and edit UVs using the UV Texture Editor. For more information about UVs, see Introduction to UV mapping and UV Texture Editor reference.

Note

If the Coordinate Method is set to Grid (Textures section of the FluidShape node), the UVW values move with the flow of the fluid. Otherwise, are like a fixed project based on the fluid bounds.

Use Gradient Normals

Turn this attribute on to make the normals on a fluid output mesh smoother. When on, user normals are created for the output mesh. The normals are based on the direction of the opacity gradient within the fluid volume at the vertex.

This setting does not affect the interactive display of surface fluids, which uses the gradient normals. When turned off, the output mesh normals used for rendering are derived from the angles between triangles, which can result in relatively sharp edges where thin triangles are present.

Advanced ramp features

Advanced ramp features exist. For more information, see the following topics:

Shading

Use the attributes in this section to apply built-in shading effects to the fluid.

Note

In most cases, it’s better to use the built-in texturing (in the Textures section), however normal texturing works and should have good results in the case of 2D fluids. For 3D fluids, the textures will map to the entry points of the volume samples. To make a solid texture better represented within the volume, you can increase the volume samples using Volume Samples Override in the Render Stats section of the Attribute Editor.

Transparency

Transparency combined with Opacity determines how much light can penetrate the defined Density. Transparency scales the single channel Opacity value. Using Transparency you can adjust the Opacity and also set its color.

You could adjust the Opacity of a fluid by moving the Transparency slider, ignoring all the other controls.

Note

A transparency of 0.5 0.5 0.5 may render slightly faster than other values.

Glow Intensity

Controls the brightness of the glow (the faint halo of light around the fluid). Glow Intensity is 0 by default, so no glow is added to the fluid. As you increase the Glow Intensity, the apparent size of the glow effect increases.

Glow Intensity is different from the Incandescence attribute in two important ways:

Color

The Color ramp defines a range of color values used to render the fluid. The particular colors selected from this range correspond with the values for the selected Color Input. Color Input values of 0 map to the color at the left of the ramp, Color Input values of 1 map to the color at the right of the ramp, and values between 0 and 1 map to the color corresponding with the position on the ramp (relative to the Input Bias). The color represents how much incoming light is absorbed or scattered. If it is black, all light is absorbed, while white fluids scatter all incoming light.

You define the colors on the ramp by adding position markers to the ramp and changing the color at the markers. See Set fluid attribute ramps.

Advanced ramp features exist. See Advanced ramp features for more information.

Selected Position

This value indicates the position of the selected color on the ramp (between 0 on the left to 1 on the right).

Selected Color

Indicates the color on the ramp at the selected position. To change the color, click the Selected Color box and select a new color from Color Chooser.

Interpolation

Controls the way colors blend between positions on the ramp. The default setting is Linear.

None

There is no interpolation between colors. Each color is distinct.

Linear

The values are interpolated with a linear curve in RGB color space.

Smooth

The values are interpolated along a bell curve so that each color on the ramp dominates the region around it, then blends quickly to the next color.

Spline

The values are interpolated with a spline curve, taking the colors at neighboring position markers into account for a smoother transition.

Color Input

Defines the attribute used to map the color value.

Constant

Sets the color in the entire container to the color at the end of the ramp (1.0).

X, Y, Z, and Center Gradient

Sets the color in the entire container to a gradient corresponding with the ramp colors (from 1 to 0).

The other options all set the Color Input to the color corresponding with the value from the grid. For example if Density is the Color Input, the color at the start of the color ramp is used for Density values of 0 and the color at the end of the ramp for Density values of 1.0. Midrange values map according to the Input Bias.

Input Bias

Color Input Bias adjusts the sensitivity of the selected Color Input. Input values of 0 and 1 always map to the start and end of the ramp, while the bias determines where in the ramp a value of 0.5 maps. If the Input Bias is 0.0 then a Color Input value of 0.5 maps to the exact middle of the color ramp. Instead of values that are very close using the color at one part of the ramp, you can use the full range of colors to represent the values.

For example, if Density is the Color Input and the Density values in the container are all close to 0.1, you can use the Input Bias to shift the ramp color range so the Density values around 0.1 can be differentiated using the full range of colors on the ramp. If you do not change the Input Bias, the differences in color for values close to 0.1 could be indistinguishable.

Incandescence

Incandescence controls the amount and color of light emitted from regions of Density due to self illumination. The particular colors selected from this range correspond with the values for the selected Incandescence Input. Incandescent emission is not affected by illumination or shadowing.

The Incandescence ramp defines a range of incandescent color values. The particular colors selected from this range correspond with the values for the selected Incandescence Input. Incandescence Input values of 0 map to the color at the left of the ramp, Incandescence Input values of 1 map to the color at the right of the ramp, and values between 0 and 1 map to the color corresponding with the position on the ramp (relative to the Input Bias).

You define the colors on the ramp by adding position markers to the ramp and changing the color at the markers. See Set fluid attribute ramps.

Advanced ramp features exist. See Advanced ramp features for more information.

Selected Position
Selected Color

Interpolation

See Interpolation.

None

See None.

Linear

See Linear.

Smooth

See Smooth.

Spline

See Spline.

Incandescence Input

Defines the attribute used to map the incandescence color value.

Constant

Sets the incandescence color in the entire container to the color at the end of the ramp (1.0).

X, Y, Z, and Center Gradient

Sets the incandescence color in the entire container to a gradient corresponding with the ramp colors (from 1 to 0).

The other options all set the Incandescence Input to the color corresponding with the value from the grid. For example if Temperature is the Incandescence Input, the color at the start of the incandescence ramp is used for Temperature values of 0 and the color at the end of the ramp for Temperature values of 1.0. Midrange values map according to the Input Bias.

Input Bias

Incandescence Input Bias adjusts the sensitivity of the selected Incandescence Input. Input values of 0 and 1 always map to the start and end of the ramp, while the bias determines where in the ramp a value of 0.5 maps. If the Input Bias is 0.0 then an Incandescence Input value of 0.5 maps to the exact middle of the color ramp. Instead of values that are very close using the color at one part of the ramp, you can use the full range of colors to represent the values.

For example, if Temperature is the Temperature Input and the Temperature values in the container are all close to 0.1, you can use the Input Bias to shift the ramp color range so the Temperature values around 0.1 can be differentiated using the full range of colors on the ramp. If you do not change the Input Bias, the differences in color for values close to 0.1 could be indistinguishable.

Opacity

Opacity represents how much the fluid blocks light. The Opacity curve defines a range of opacity values used to render the fluid. The particular opacity values selected from this range are determined by the selected Opacity Input.

The vertical component represents the Opacity values from 0 (totally transparent) to 1 (totally opaque), the horizontal component represents Opacity Input values from 0 to 1. By clicking on the graph and dragging the points, you make a curve that defines what the opacity is for any input value. The default is a linear 1-1 relationship—input values (for example, Density) of 0 have no opacity, values of 0.5 have an opacity of 0.5, values of 1 have an opacity of 1. See Set fluid attribute ramps.

Density is the default Opacity Input, and the default linear curve makes the Opacity exactly equal to the Density. Given that you cannot get more opaque than 1.0, Densities greater than 1.0 are totally opaque. This simulates the total saturation of a fluid (that is, so much smoke you have a block of solid carbon).

To give Density hard edges, like the edges on thick clouds, you can edit the Opacity curve to threshold out the thin Density (low Density values) and define a hard falloff. If you are dealing with very thin Density, positioning the markers on the curve for the desired falloff might involve the markers being very close together all the way to one edge of the curve. The Input Bias attribute allows you to define the general look of the function with an easy-to-read layout (that is, without crowding the values), and then affect the input range to map it to the desired part of the function.

Texturing is also applied to the inputs to opacity rather than the output. This allows you to use the Opacity curve to apply hard edges to the texture, rather than texturing a hard edged Density. The gain on the texture is simply how the texture affects opacity—small gain, small effect.

You could adjust the opacity of a fluid by moving the Transparency slider, ignoring all the other controls.

Selected Position

This value indicates the position of the selected Opacity Input marker on the ramp (between 0 on the left to 1 on the right).

Selected Value

Indicates the opacity value on the ramp at the selected position. To change the value, drag the marker dot up or down, or type the value in this box.

Interpolation

Controls the way values blend between position markers on the curve. The default setting is Linear.

None

There is no interpolation between values.

Linear

The values are interpolated with a linear curve.

Smooth

The values are interpolated along a bell curve so that each value on the graph dominates the region around it, then blends quickly to the next value.

Spline

The values are interpolated with a spline curve, taking the values at neighboring position markers into account for a smoother transition.

Opacity Input

Defines the property used to map the opacity value.

Constant

Sets the opacity in the entire container to the opacity at the far right of the curve (Opacity Input value 1).

X, Y, Z, and Center Gradient

Sets the opacity in the entire container to a gradient corresponding with the curve (from Opacity Input value 1 to 0).

The other options all set the Opacity Input value to the corresponding opacity value on the curve. For example if Density is the Opacity Input, the opacity value at the start of the curve is used for Density values of 0 and the opacity value at the end of the curve is used for Density values of 1.0. Midrange values map according to the Input Bias.

Input Bias

Opacity Input Bias adjusts the sensitivity of the selected Opacity Input used.

Input values of 0 and 1 always map to the start and end of the opacity curve, although the bias determines where in the curve a value of 0.5 maps. For example if you used Density as an input, and you want the fluid to become opaque at a Density of 0.001, then the Density bias can be used to shift most of the curve into this Density range. Instead of cramming several values at the beginning of the ramp you can use the full range. If the Input Bias is 0.0 then a value of 0.5 maps to the exact middle of the Opacity curve.

Matte Opacity

The attributes in this section control how this fluid shows up in the matte (alpha channel or mask) when you render with one. This is useful if you will be compositing your rendered images.

Matte Opacity Mode

Select how Maya uses the Matte Opacity value.

Black Hole

The Matte Opacity value is ignored, and all the matte for this fluid is set to be transparent. Use this option when you use substitute geometry in a scene to stand in for objects in a background image that you will be compositing with later. Your stand-in objects will ‘punch a hole’ in the matte. This allows other computer-generated geometry to pass behind your stand-in objects. Later, when foreground and background are composited, the results will be correct, with the background object showing through the ‘black hole’ areas.

Solid Matte

The entire matte for the fluid is set to the value of the Matte Opacity attribute. This option is like Opacity Gain, except that the normally-calculated matte values are ignored in favor of the Matte Opacity setting. If there are transparent areas on the object, the transparency in these areas is ignored in the matte. Use this setting to composite an object with transparent areas, when you don’t want the background to show through them.

Opacity Gain

Matte values are calculated based on the transparency of the object then multiplied by the Matte Opacity value. With Opacity Gain, you can animate the Matte Opacity value to change the overall transparency of the object when it is later composited.

Matte Opacity has a default value of one, so by default Solid Matte and Opacity Gain have no effect.

Matte Opacity

Matte Opacity is used with Matte Opacity Mode to affect how the matte (alpha channel or mask) for this fluid is calculated.

Shading Quality

Quality

(Not available on fluid texture.) Increase this value to increase the number of samples per ray used in the render, thereby increasing the shading quality of the render.

By mapping a texture to this attribute, you could define exactly which regions of a fluid got the highest shading quality (although the slowdown due to texturing might negate any benefits).

Contrast Tolerance

(Not available on fluid texture.) Defines the maximum contrast in the effective transparency of a volume span allowed by the Adaptive subdivisions sample method. When the contrast between two spans is greater than this value Maya subdivides the span. The contrast is defined as the effective difference in accumulated transparency from the viewpoint.

If this value is high, then the sampling will look like Uniform sampling.

If the Contrast Tolerance is low then the quality improves and the render time increases, although you will not require as many samples as uniform sampling for a given render quality.

The Quality setting should be just high enough that you do not miss dense regions altogether (this creates artifacts like dotty fringes around clouds).

Sample Method

(Not available on fluid texture.) Controls how the fluid is sampled during rendering. Jitter avoids banding artifacts, but adds noise to the final image unless the Quality is set high.

Render Interpolator

Select the interpolation algorithm to use when retrieving values from fractional points within a fluid voxel when shading a ray. Sharply contrasting densities may show grid artifacts (like a mesh with no normal smoothing) with Linear interpolation. Smooth interpolation renders slower, but eliminates these problems.

Textures

Using the textures that are built into the fluidShape node you can increase the sampling time for high quality rendering. The sampling for the built-in textures is adaptive.

Texture Color

Turn this option on to apply the current texture (defined by Texture Type) to the Color Input value for the color ramp.

Texture Incandescence

Turn this option on to apply the current texture (defined by Texture Type) to the Incandescence Input values.

Texture Opacity

Turn this option on to apply the current texture (defined by Texture Type) to the Opacity Input values.

Texture Type

Select how to texture the Density in the container. The texture center is the center of the fluid.

Perlin Noise

The standard 3D noise used in the solidFractal texture.

Billow

Has a puffy, cloud-like effect. Billow is computationally intensive and therefore slow.

Volume Wave

A sum of 3D waves in space.

Wispy

A Perlin Noise that uses a second noise as a smear map. This makes the noise stretch out in places, creating a streaky, wispy effect.

Space Time

A 4-dimensional version of Perlin Noise, where time is the 4th dimension.

Mandelbrot

Texture the opacity of your fluid using this built-in Mandelbrot texture.

The Mandelbrot set is a set of mathematical points in the complex plane, the boundary of which is an interesting fractal shape. Through this node, you can select the Mandelbrot Set, the Julia set, the Mandelbox set and other hybrid evaluations. Using this texture, you can add interesting effects to your Mandelbrot set fractal, such as circles, leaves, points, checker patterns, and Pickover stalks.

Choose among different shading methods and customize the range of the color values used to represent your Mandelbrot set points.

See Mandelbrot for more information about the Mandelbrot texture and its attributes.

Coordinate Method

Select how to define the texture coordinates.

Fixed

Sets the values to equal the object space coordinate system (0-1 for the container in X, Y and Z).

Grid

Uses a grid of points and interpolates to define in between values. The coordinate values move using the Density solver. This makes the texture to move with the movement of the Density, rather than appearing fixed in space.

Coordinate Speed

Scales how fast coordinates are moved by Velocity when the Coordinate Method is Grid.

When Coordinate Speed is 1.0 the coordinates move through the volume at the same speed as the other properties (for example, Density). However this tends to result in the texture smearing out after a few steps.

Lower values tend to preserve the character of the texture and can look more natural.

Animating this value can be useful in some situations, such as when you do not want the texture to deform before a certain point (keyframe it to zero until the desired start point).

Color Tex Gain

Determines how much the texture affects the Color Input value. If the color range is red to blue, then texturing causes red to blue variations. When Color Tex Gain is zero there is no color texturing.

Incand Tex Gain

Determines how much the texture affects the Incandescence Input value. If the incandescence range is red to blue, then texturing causes red to blue variations. When Incand Tex Gain is zero there is no incandescence texturing.

Opacity Tex Gain

Determines how much the texture affects the Opacity Input value. For example, if the opacity curve goes from 0.0 to 0.6, then texturing causes variations between these values. When Opacity Tex Gain is zero there is no opacity texturing.

Threshold

The number added to the whole fractal, making it uniformly brighter. If some parts of the fractal are pushed up out of range (greater than 1.0), they are clipped to 1.0.

Amplitude

A scaling factor applied to all the values in the texture, centered around the texture’s average value. When you increase Amplitude, the light areas get lighter and the dark areas get darker.

If you set Amplitude to a value greater than 1.0, then those parts of the texture that scale out of range are clipped.

Ratio

Controls the frequency of the fractal noise. Increase this value to increase the fineness of detail in the fractal.

Frequency Ratio

Determines the relative spacial scale of the noise frequencies.

Depth Max

Controls how much calculation is done by the texture. Since the Fractal texture process produces a more detailed fractal, it takes longer to perform. By default, the texture chooses an appropriate level for the volume being rendered. Use Depth Max to control the maximum amount of calculation for the texture.

Invert Texture

Turn Invert Texture on to reverse the range of the texture so that dense regions become thin and thin become dense. If it is on, then texture = 1 - texture.

Inflection

Turn Inflection on to apply a kink in the noise function. This is useful for creating puffy or bumpy effects.

Texture Time

Use this attribute to animate the texture. You can keyframe the Texture Time attribute to control the rate and amount of change of the texture.

Type the expression "= time" into the edit cell to cause the texture to billow when rendered in an animation. Type "= time * 2" to make it billow twice as fast.

Frequency

Determines the fundamental frequency for the noise. As this value increases the noise becomes more detailed. It has the inverse effect of the Texture Scale attribute.

Texture Scale

Determines the scale of the noise in the local X, Y and Z directions. The effect is similar to scaling the transform node for the texture.

When you increase Texture Scale in any direction, the fractal detail seems to smear out in that direction.

Texture Origin

The zero point for the noise. Changing this value moves the noise through space.

The origin is relative to the noise Frequency. So if the noise is really stretched out in Y (larger Y-scale) the same offset will move it more in Y than the other directions. An advantage to this is that the noise loops when you offset the origin by 1.0.

Texture Rotate

Sets the X, Y, and Z rotation values of the fluid’s built-in texture. The center of the fluid is the pivot point for rotation. The effect is similar to setting rotation on a texture placement node.

Implode

Warps the noise function in a concentric fashion about a point defined by the Implode Center. When the Implode value is zero there is no effect. When the value is 1.0 it is a spherical projection of the noise function, creating a starburst effect. Negative values can be used to skew the noise outward instead of inward.

Tip

Noise textures are too uniform for explosion and starburst animations. Adjust and keyframe this attribute for a starburst effect in an explosion. Adjust the Implode Center attribute to place the origin of the effect.

Implode Center X, Y, Z

Defines the center point about which the implode effect is defined.

Billow Density

Controls how many cells there are imbedded in the medium used by the Billow texture type. When Billow Density is 1.0, the medium is completely packed with cells. Reduce this value to make the cells more sparse.

Spottyness

Controls the randomization of the density of the individual cells used by the Billow texture type. When Spottyness is close to 0, all the cells have the same density. As you increase Spottyness, some cells become denser or thinner than others, in a random fashion.

Size Rand

Controls the randomization of the size of the individual blobs used by the Billow texture type. When Size Rand is close to 0, all the cells have the same size. As you increase Size Rand, some cells become smaller than others, in a random fashion.

Randomness

Controls how the cells for the Billow noise type are arranged relative to one another. Set Randomness to 1.0 to get a realistic random distribution of cells, as would be found in nature. If you set Randomness to 0, all the spots are laid out in a completely regular pattern. This can provide interesting effects when used as a bump map.

Falloff

Controls the way intensity falls off for individual blobs for the Billow noise type.

Linear

A uniform falloff from the center to a value of zero at the edges of the blobs.

Smooth

More natural looking, using a gaussian falloff.

Fast

Focuses the intensity more towards the center of the blobs.

Bubble

Uses a reverse falloff, fading to zero at the blob center.

Number of Waves

Determines how many waves to generate for the Volume Wave texture type. The larger this number the more random looking and slower the texture.

Color Balance

Corrects the color or intensity of a texture.

Note

These attributes are only available from the fluidTextureShape tab in the Attribute Editor when a Fluid Texture 2D or Fluid Texture 3D render node is used with fluid.

Default Color

If you map a texture to a material in such a way that it that does not cover the entire surface, the file node's Default Color shows through. To select a different color, click the color bar to open the Color Chooser. To change the texture's coverage, use the placement options.

Alpha Gain

Only has an effect if the texture is used as a bump or displacement. Scaling factor applied to the texture's outAlpha channel. The default value is 1 (no effect).

Alpha Offset

Only has an effect if the texture is used as a bump or displacement. Offset factor applied to the texture's outAlpha channel. For example, if the Alpha Gain value is -1 and the Alpha Offset value is 1, the outAlpha channel is inverted. The default value is 0 (no effect).

Lighting

(Not available on fluid texture.)

Self Shadow

Turn this option on to compute self-shadowing. A single directional light at -1,-1,-1 is used to compute self-shadowing.

Hardware Shadow

Turn this option on to self-shadow the fluid (the fluid casts shadows on itself) during the simulation (hardware draw). Shading > Hardware Texturing must be turned on to see this effect.

Shadow Opacity

Use this attribute to brighten or darken shadows cast from the fluid.

When Shadow Opacity is 0.5, the shadows are attenuated in exact proportion to the transparency of the fluid.

When Shadow Opacity is zero, no shadowing occurs.

When Shadow Opacity is 1.0, shadows are completely black and the fluid is totally in shadow.

Values less than 0.5 can help make thick clouds appear more translucent.

Values greater than 0.5 make the clouds unnaturally opaque to lights, but may be useful to accentuate self shadowing.

Shadow Diffusion

Controls the softness of the fluid's internal shadow, simulating local light scattering. Shadow Diffusion can only be seen in the scene view not in a rendered fluid. Shadow Diffusion can also be used to reduce banding artifacts in the hardware display of fluid self shadowing.

To use Shadow Diffusion effects in your finalized fluid, you can use Playblast to output simulated frames.

Light Type

Sets the type of internal light used with the fluid when displaying the fluid in the scene view. If Real Lights is off, the selected internal light is also used to light the fluid for rendering. Using internal lights decreases fluid render times.

Diagonal

Sets the internal light type to a diagonal light that cuts through the X and Y origin of the fluid container.

The Diagonal light is provided for playing back fluid simulations created in Maya 2010 or earlier versions. The effect of the Diagonal light on your fluid is only visible in the scene view. The light is slightly more efficient to compute than other lights, but it only shines in a fixed direction. If Use Real Lights is off, fluids rendered with the Diagonal light appear as if the light type were set to Directional.

Directional

Sets the internal light to a directional light. Directional lights simulate a distance point light source shining along the direction vector. See Create > Lights > Directional Light.

Point

Sets the internal light to a point light. A point light shines evenly in all directions from an infinitely small point in space. See Create > Lights > Point Light.

Light Brightness

Sets the brightness of the internal Diagonal, Directional, and Point lights. See Intensity.

Light Color

Sets the color of the internal Diagonal, Directional, and Point lights. See Color.

Ambient Brightness

Sets the brightness of the internal ambient light. The internal ambient lighting appears in the scene view and in the rendered fluid regardless of whether or not Real Light is turned off. See Intensity.

Ambient Diffusion

Controls how the ambient light is diffused into the fluid density. Using Ambient Diffusion adds details to the shadowed areas of your fluid effect.

When Ambient Diffusion is set to 0, the ambient light is uniformly added to all voxels in the fluid. At low Ambient Diffusion values, the ambient light is scaled by the opacity of the fluid so that there is less light where the fluid is more opaque. At high Ambient Diffusion values, ambient light is still affected by the fluid's opacity, but it is diffused enough to approximate global occlusion of ambient lighting and can be computed quickly.

You can see the effects of Ambient Diffusion in the scene view and when your simulation is rendered using mental ray for Maya renderer. Ambient Diffusion is not supported by the Maya Software renderer.

Ambient Color

Sets the color of the internal ambient light. Ambient Color appears in the scene view and in the rendered fluid regardless of whether or not Real Light is turned off. See Color.

Real Lights

Turn on Real Lights to use the lights in your scene for rendering. Turn off Real Lights to ignore the scene lights and instead use the selected internal Light Type for rendering.

When Real Lights is off, fluid is rendered using the internal light's Light Brightness, Light Color, and position values. Using internal lighting is faster, especially for self shadowing. It does not cast shadows or light onto other objects. Fluids using the internal light do not receive shadows from other objects.

Directional Light

Sets the X, Y, and Z components of the internal directional light when Directional is selected as the Light Type.

Point Light

Sets the X, Y, and Z components of the internal point light when Point is selected as the Light Type.

Point Light Decay

See Decay Rate.

Render Stats

See Render Stats.

Not available on fluid texture or shader.

Object Display

For details, see Display.

Node Behavior

For details, see Node behavior.

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