Houdini 21.0 Nodes Geometry nodes

Tissue Properties Otis geometry node

Creates and modifies tissue attributes in preparation for the tissue solver.

Since 21.0

This node activates and assigns the physical properties and constraint attributes that govern the behavior of the tissue’s simulation.

Each tissue parameter injects a corresponding point attribute into the node’s output stream that the downstream Otis Muscle and Tissue Configure and Otis Solver nodes will then use to affect the constraint or material property it is tied to. In other words, this node only creates constraint attributes and material attributes.

You can assign each tissue parameter as either an Absolute or a Relative value. When a parameter is Absolute, its value is used explicitly (as an override). When a parameter is Relative, its value is used as a multiplier of whatever its current Absolute value (incoming or default value) is. If you do not specify a user-set value for a parameter, then the default value for that parameter is used.

In cases where a parameter is turned off, the incoming value for the associated attribute will be passed through the node.

Setting up tissue properties

When setting up tissue properties, think of the entire set of properties for the tissue as layers of a sort. You can make the first Tissue Properties SOP node in your tissue network the base properties layer for the tissue (the properties node that initializes and applies all the tissue properties for the entirety of the tissue), and then make all the subsequent Tissue Properties SOP nodes in the network the specialized properties layers (property nodes whose settings produce different tissue effects like saggy skin or tight skin).

You can also use the Attrib Paint SOP node to paint masks and blend layers of properties for your tissue. Using masks and chaining together a series of Tissue Properties SOP nodes can effectively composite tissue characteristics.

There are two ways that you can use the Tissue Properties SOP node:

You can also use the Mask Blend parameter to dial the strength of the composite up or down without having to adjust your painted masks.

Set-up Tips

The best ways to achieve more muscle definition is via Tissue to Muscle constraints. These will make muscle action much more evident on the tissue’s outer surface, by forcing the tissue to move along with muscles.

Parameters

Group

Specifies the geometry group to which to apply the tissue properties. If no groups are specified, then the tissue properties are applied to all the geometry groups on the tissue supplied on Input 1.

Group Type

Sets the component type for the geometry group that is specified in the Group field.

Guess from Group

Node guesses the geometry group component type.

Vertices

Group contains vertices.

Edges

Group contains edges.

Points

Group contains points.

Primitives

Group contains primitives.

Mode

Determines how the tissue properties are applied to the tissue.

Assign Values

Apply the tissue properties to all areas of the tissue.

Blend with Mask

Apply the tissue properties to only the regions on the tissue that have been painted with the attribute specified by Mask Attribute.

Mask Attribute

Identifies the mask attribute that is used by the Attribute Paint SOP node to paint this set of tissue properties on the tissue.

Invert Mask

Inverts how the tissue properties are applied to the Mask Attribute regions of the tissue.

Mask Blend

Determines what percentage of the tissue properties are applied to the Mask Attribute region of the tissue. A Mask Blend of 0.5 provides a blend of 50%. Also, you can animate this parameter.

Tissue Core Layer

These parameters define the physical properties of the Tissue Core Layer, the inner tetrahedral structure holding the outer Tissue Solid Layer together and connecting it to bones and muscles. This usually occupies the same space as bones & muscles. The core’s outer surface should be a close fit shrink wrap of muscles and bones. Tissue Solidify Otis outputs suitable tetrahedral meshes. The parameters in this tab control how the core behaves independently from the outer Tissue Solid Layer, giving finer control over internal rigidity and deformation response.

Enable

When on, activates the Shape Stiffness parameter for the core tetrahedral mesh.

Shape Stiffness

Override

When enabled, sets how much the tissue core resists changes to its shape. Higher values preserve the original shape of the tetrahedra more strongly. Only available when the Mode is set to Absolute.

Mode

Select whether the Shape Stiffness is interpreted as an absolute value or as a relative multiplier of the incoming or default value.

Relative Shape Stiffness

Multiplier

Multiplies the incoming Shape Stiffness when the mode is set to Relative.

Enable

When on, activates the Volume Stiffness parameter for the tissue core.

Volume Stiffness

Override

Controls how much the core tries to maintain its volume during deformation. Higher values result in more volume preservation. Only available when the Mode is set to Absolute.

Mode

Selects whether the Volume Stiffness is used as an absolute value or relative multiplier.

Relative Volume Stiffness

Multiplier

Multiplies the incoming Volume Stiffness when the mode is set to Relative.

Enable

Enables the Damping Ratio parameter, which affects how fast the core stabilizes after deformation.

Damping Ratio

Override

Specifies how much velocity is dissipated in the simulation of the core. Higher damping reduces oscillation and adds resistance to sudden motion. Available only in Absolute mode.

Damping Ratio Exponent

Sets the exponential scale for the Damping Ratio to help fine-tune extremely small values that are common in soft tissue dynamics.

Mode

Determines whether the Damping Ratio is used as an absolute override or a relative multiplier.

Relative Damping Ratio

Multiplier

A relative multiplier applied to the incoming Damping Ratio value.

Enable

Turns on the Mass Density parameter for the tissue core.

Mass Density

Override

Specifies the mass per unit volume for the tetrahedra in the core. This keeps mass resolution-independent and ensures consistent simulation behavior even when the mesh is refined. Available only in Absolute mode.

Mode

Switches between using an absolute mass value and a relative multiplier.

Relative Mass Density

Multiplier

Multiplies the incoming Mass Density when the mode is set to Relative.

Optional

Enable

Turns on the Fiber Stiffness parameter, enabling directionally-dependent stiffness within the tissue core (useful for anisotropic materials or muscle behavior). Tissue Solidify Otis outputs a materialW material direction attribute required to use this. The direction is always out of the surface, so higher fiberstiffness increases resistance to change in that direction.

Fiber Stiffness

Override

Defines how strongly the tissue core resists stretching or shearing along fiber directions. This is only meaningful when materialW is present and well defined. Available in Absolute mode only.

Mode

Chooses whether to interpret the Fiber Stiffness as an absolute or relative value.

Relative Fiber Stiffness

Multiplier

Multiplies the input Fiber Stiffness value when the mode is set to Relative.

Tissue Solid Layer

These parameters define the physical properties of the Tissue Solid Layer, which represents the material between muscles/bones and the skin.

Enable

When on, enables the Shape Stiffness parameter for the solid layer.

Shape Stiffness

Override

Determines how much the solid tetrahedral mesh resists changes to its shape. Higher values make the solid retain its original shape more rigidly. Only available in Absolute mode.

Mode

Chooses whether the Shape Stiffness is applied as an absolute value or as a relative multiplier.

Relative Shape Stiffness

Multiplier

Multiplies the incoming Shape Stiffness value when the mode is set to Relative.

Enable

Turns on the Volume Stiffness parameter.

Volume Stiffness

Override

Controls how strongly the tissue solid preserves its volume. A higher value means the volume resists compression or expansion more. Available in Absolute mode only.

Mode

Switches between Absolute and Relative mode for Volume Stiffness.

Relative Volume Stiffness

Multiplier

A multiplier for the incoming Volume Stiffness when using Relative mode.

Enable

Enables the Damping Ratio for the solid tetrahedral mesh.

Damping Ratio

Override

Controls how quickly energy is dissipated from the solid mesh. Higher damping results in faster settling and less oscillation. Only available in Absolute mode.

Damping Ratio Exponent

Allows you to scale the damping value across orders of magnitude. Useful for tuning extremely small damping values commonly used in soft body simulations.

Mode

Selects whether the Damping Ratio is used as an absolute override or a relative multiplier.

Relative Damping Ratio

Multiplier

Multiplies the input Damping Ratio when the mode is set to Relative.

Enable

Enables the Mass Density parameter for the solid tetrahedral mesh.

Mass Density

Override

Sets the mass per unit volume for the tetrahedra. This ensures resolution-independent simulation behavior. Only available in Absolute mode.

Mode

Determines if the Mass Density is treated as an absolute value or relative multiplier.

Relative Mass Density

Multiplier

Multiplies the input Mass Density when the mode is set to Relative.

Optional

Enable

Enables directional Fiber Stiffness for the solid mesh, allowing anisotropic behavior. Requires a materialW attribute as created by Tissue Solidify Otis.

Fiber Stiffness

Override

Sets how strongly the tissue solid resists deformation along defined fiber directions. Only available in Absolute mode.

Mode

Chooses between Absolute and Relative interpretation for Fiber Stiffness.

Relative Fiber Stiffness

Multiplier

A relative multiplier applied to the incoming Fiber Stiffness value.

Tissue Muscle Attachment

These parameters define how the tissue attaches to nearby muscle geometry via soft constraints. These constraints are created from the tissue’s inner surface (which should be a tightly fitting shrink-wrap over muscles and bones) to muscles.

Enable

Enables the stiffness setting for the tissue-to-muscle attachment constraint.

Stiffness

Override

Controls how strongly the tissue adheres to nearby muscles. A higher stiffness results in a tighter connection. Only available when in Absolute mode.

Mode

Sets the Stiffness mode to either Absolute or Relative.

Relative Stiffness

Multiplier

A relative multiplier applied to the incoming tissue-to-muscle Stiffness when in Relative mode.

Enable

Enables the damping behavior for the tissue-to-muscle attachment constraint.

Damping

Override

Determines how quickly motion is dampened between tissue and muscle attachments. High damping values result in quicker stabilization. Only available in Absolute mode.

Tissue to Muscle Damping Exponent

Use this multiplier to scale the damping value over orders of magnitude for finer control.

Mode

Selects the application mode (Absolute or Relative) for damping.

Relative Damping

Multiplier

A multiplier for damping when using Relative mode.

Enable

Enables the Distance Threshold for creating tissue-to-muscle attachment constraints.

Distance Threshold

Override

Defines the maximum distance at which tissue points will be attached to muscle geometry. Only available in Absolute mode.

Mode

Sets whether the Distance Threshold is used as an Absolute value or a Relative multiplier.

Relative Distance Threshold

Multiplier

A multiplier applied to the incoming Distance Threshold in Relative mode.

Tissue Bone Attachment

These parameters define how the tissue attaches to bone geometry, similar to muscle attachments but typically stiffer and more rigid.

Enable

Enables the stiffness setting for tissue-to-bone attachment constraints.

Stiffness

Override

Controls how firmly the tissue adheres to nearby bone geometry. High values result in rigid connections. Only available in Absolute mode.

Mode

Sets the stiffness value mode (Absolute or Relative).

Relative Stiffness

Multiplier

Multiplies the existing stiffness value when Relative mode is enabled.

Enable

Enables the damping setting for tissue-to-bone attachments.

Damping

Override

Determines how rapidly motion between tissue and bone is stabilized. Only available in Absolute mode.

Tissue to Bone Damping Exponent

Adjusts damping across multiple scales for precise control over damping behavior.

Mode

Chooses between Absolute and Relative mode for damping.

Relative Damping

Multiplier

A multiplier used to scale damping in Relative mode.

Enable

Enables the distance threshold for determining which tissue points attach to bones.

Distance Threshold

Override

Sets the maximum attachment range from tissue points to bones. Available in Absolute mode only.

Mode

Chooses between Absolute or Relative distance threshold mode.

Relative Distance Threshold

Multiplier

A relative multiplier applied to the Distance Threshold.

Shrinkage

These parameters control the rest scale (shrinkage or expansion) of the tissue and core geometry layers, affecting their resting size relative to the original geometry.

Enable

Enables the application of a rest scale to the tissue surface layer.

Tissue Rest Scale

Override

Sets the rest scale factor for the tissue solid layer. Values less than 1 shrink the tissue, values greater than 1 expand it. Only available in Absolute mode.

Mode

Selects whether the Tissue Rest Scale is applied as an Absolute value or a Relative multiplier.

Relative Tissue Rest Scale

Multiplier

Multiplies the existing Tissue Rest Scale value when in Relative mode.

Enable

Enables the application of a rest scale to the tissue core layer.

Core Rest Scale

Override

Sets the rest scale factor for the core layer, shrinking or expanding the core geometry at rest. Only available in Absolute mode.

Mode

Determines whether the Core Rest Scale is Absolute or Relative.

Relative Core Rest Scale

Multiplier

Multiplies the existing Core Rest Scale value when in Relative mode.

See also

Geometry nodes