Houdini 20.5 Nodes Object nodes

Guide Simulate object node

Runs a physics simulation on the input guides.

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Since 16.0

Extracts the required skin and guide curves from a groom object such as a Guide Groom or Guide Deform. These nodes can also write their groom data to files which can be imported by this node.

Parameters

Groom Source

Source Mode

Groom Object

Load the groom from a groom object.

Groom File

Load the groom from a file.

Groom Object

Load the groom data from this source object.

Groom File

Load the groom data from this file.

Use Object Transform

Take this object’s transform into account when simulating curves.

Dynamics

Enable Dynamics

Enables dynamics simulation.

Reset Simulation

Clears the entire simulation cache. When viewing a DOP Network in the viewport, a button will be made active above the viewport on the right hand side. Pressing that button performs exactly the same action as pressing this Reset Simulation button.

Cache Simulation

Enables the simulation cache. Many solvers will not work properly unless this option is enabled. However for very large simulations, turning off this option is the best way to guarantee the smallest possible memory footprint for the simulation.

Create External DOP Network

Copy the internal DOP network to an external one for editing.

Use External DOP Network

Fetch the simulation from an external DOP network.

Guide DOP Object

Get the simulation output from this DOP object.

Use Freeze Frame

Freeze the simulation in time.

Freeze Frame

Freeze the simulation at this frame.

Display

Display As Subdivision Curves

Subdivide curves in the viewport for smoother display.

Display Color

Display curves in this color in the viewport.

Simulation

Start Frame

The default offset time expression references this parameter to set the offset time appropriately. This allows one to set the start time in frames rather than seconds which can be more straightforward in some cases. If the start frame is set to 24, the simulation will not start cooking until frame 24. Note that if you use this, $SF and $F will no longer refer to the same thing inside the simulation.

Scale Time

Specifies a scale factor that relates global time to the simulation time for this DOP Network. A value greater than one means the simulation time advances faster than the global time. A value less than one causes the simulation to appear to run in slow motion relative to the global time. Several expression functions such as doptime exist for converting from global times to simulation times and vice versa.

Spatial Scale

Indicates the scale of the simulation. It is very important that you set this to the right value, otherwise the defaults for stiffness and damping will not work as expected.

Note

You should choose the correct Unit Length in Edit > Preferences > Hip File Options before you create your DOP network. That way, the wire solver node will automatically get the correct Spatial Scale when it’s created.

Minimum Substeps

Limits the minimum number of substeps per timestep. Higher values may be more accurate, but may require more computation.

Solve Tolerance

Determines how close to the actual value the formula must solve before continuing to solve the next frame.

A smaller value will give higher quality, but will also run slower. A larger value will run faster, but may not be as accurate.

Max Collision Resolve Passes

The maximum number of passes that are performed to resolve the collisions. When this number is set too low, there is a chance that not all collisions will be resolved, whch could result in visible penetrations.

Physical

Physical Parameters

Compute Mass

Determines if the mass will be calculated automatically from the object’s density and volume.

Density

The mass of a wire object is its volume times its density. The volume is affected by the width parameter.

Mass

The absolute mass of the object.

Width

The width of the wire object defines the diameter of each cylindrical section.

Friction

The coefficient of friction of the object. A value of 0 means the object is frictionless. This governs how much the tangential velocity is affected by collisions.

Dynamic Friction Scale

An object sliding may have a lower friction coefficient than an object at rest. This is the scale factor that relates the two. It is not a friction coefficient, but a scale between zero and one.

A value of one means that dynamic friction is equal to static friction. A scale of zero means that as soon as static friction is overcome the object acts without friction.

Elasticity

Linear Spring Constant

This parameter defines how strongly the wire resists stretching.

Linear Damping Constant

This parameter defines how strongly the wire resists oscillation due to stretch forces.

Angular Spring Constant

This parameter defines how strongly the wire resists bending.

Angular Damping Constant

This parameter defines how strongly the wire resists oscillation due to bending forces.

Adjust For Length

Enabling this parameter will adjust spring and damper strengths according to segment lengths. This allows wire flexibility behavior to be independent of segment resolution.

Adjust For Mass

Enabling this parameter will adjust spring and damper strengths according to segment masses. This allows wire flexibility behavior to be independent of mass.

Reference Matching

Values greater than zero cause all curves to behave more like curves that are as long as Reference Length. This causes hairs that are longer than the reference length to bend less and curves that are shorter to bend more.

Reference Length

The reference length used by Equal Length Behavior.

Plasticity

Stretch Threshold

This parameter defines the amount of stretching allowed before the wire is permanently stretched.

Stretch Rate

This parameter defines how quickly a wire’s permanent shape becomes stretched.

Stretch Hardening

This parameter defines how a wire becomes stiffer (if greater than 1) or weaker (if less than 1) when permanently stretched.

Bend Threshold

This parameter defines the amount of bending allowed before the wire is permanently bent.

Bend Rate

This parameter defines how quickly a wire’s permanent shape becomes bent.

Bend Hardening

This parameter defines how a wire becomes stiffer (if greater than 1) or weaker (if less than 1) when permanently bent.

Forces

Target

Target

Enable a force which causes curves to stick more closely to their predefined shape.

Target Stiffness

This parameter defines how strongly the wire resists deforming from the animated position.

Target Damping

This parameter defines how strongly the wire resists oscillation relative to the animated position.

Gravity

Gravity

Enable Gravity

Force

The magnitude of gravity.

Wind

Wind

Enable the wind force.

Velocity

The wind field’s velocity.

Strength

The strength with which curves adjust to the wind’s velocity.

Noise

Seed

Random seed for the noise.

Turbulence

The number of noise generations to use.

Roughness

The amplitude reduction of higher frequency noise contributions.

Exponent

Raises the noise to the given exponent.

Frequency

The scale of the noise. Decreasing frequency increases feature size.

Minimum Value

Sets the minimum value that can be generated by the noise field.

Maximum Value

Sets the maximum value that can be generated by the noise field.

Offset

Allows the noise field to be effectively moved through space.

Drag

Normal Drag

The component of drag in the directions normal to the wire. Increasing this will make the wire go along with any wind that blows against it. For realistic wire-wind interaction, the Normal Drag should be chosen larger (about 10 times larger) than the tangent drag.

Tangent Drag

The component of drag in the direction tangent to the wire. Increasing this will make the wire go along with any wind that blows tangent to the wire.

Constraints

Roots

Root Constraint

Controls the way curve roots are constrained to the input groom.

Position & Orientation

Match position and direction of roots to the input groom. This causes curves to stick out of the skin in the direction of the groom.

This sets the gluetoanimation attribute of root points to 1.

Position

Match the position of roots to the input groom. Curves will drop & swing freely as the direction is not constrained at all.

This sets the pinttoanimation attribute of root points to 1.

Clumping

Create Clump Constraints

Create constraints between guides that belong to the same clump.

Tip

You can create clumps using the Clump tool. This should be used on a Guide Groom, which can then be fed into this node. The Clump tool creates a clumpid attribute, which is used to identify clumps.

Max Guides Per Clump

Only create clump constraints for clumps that have at most this number of guides.

All the unclumped guides in a groom belong to the same clumpid. Without this limit, these guides would be considered a clump and constraints would be created between them.

Display Clump Constraints

Display clump constraints in the viewport.

Collisions

Wire-Wire

Self Collisions

Compute collisions with other parts of the same guide curve.

Wire-Geometry

Collision Handling

Determines the collision detection and resolution strategy used by the wire solver.

SDF

A strategy that supports SDF representations of rigid bodies.

Local Geometric

A collision response strategy that ignores the influence of elements distant from the collision. This strategy is faster that “Global Geometric” but may produce visual artifacts.

Global Geometric

A collision response strategy that considers the influence of all elements.

Repulsion

A repulsion force is applied to gently push apart these pieces of geometry when the two pieces of geometry overlap (including overlap of the collision width). This parameter controls the strength of the force.

Skin

Collide With Skin

Compute collisions with the skin geometry.

VDB Source

Compute From Geometry

Compute the required collision volume internally. This is done using VDB volumes.

SOP Volume

Fetch a collision volume from a specified SOP path.

Voxel Size

The voxel size to use when computing the collision volume.

Fill Interior

Computes distance values for the entire interior of the object. This ensures that collision detection works even deep inside the object, but can greatly increase the computation time and space requirements of the volume.

Interior Band

How far into the object to compute distance values when Fill Interior is disabled.

Volume SOP

The SOP path to get the collision volume from when VDB Source is set to SOP Volume.

External

Collide With External Geometry

SOP Path

The SOP path to fetch the external collision geometry from.

VDB Source

Compute From Geometry

Compute the required collision volume internally. This is done using VDB volumes.

SOP Volume

Fetch a collision volume from a specified SOP path.

Voxel Size

The voxel size to use when computing the collision volume.

Fill Interior

Computes distance values for the entire interior of the object. This ensures that collision detection works even deep inside the object, but can greatly increase the computation time and space requirements of the volume.

Interior Band

How far into the object to compute distance values when Fill Interior is disabled.

Volume SOP

The SOP path to get the collision volume from when VDB Source is set to SOP Volume.

Caching

See the File Cache SOP help for these parameters.

Locals

See also

Object nodes

  • Agent Cam

    Create and attach camera to a crowd agent.

  • Alembic Archive

    Loads the objects from an Alembic scene archive (.abc) file into the object level.

  • Alembic Xform

    Loads only the transform from an object or objects in an Alembic scene archive (.abc).

  • Ambient Light

    Adds a constant level of light to every surface in the scene (or in the light’s mask), coming from no specific direction.

  • Auto Bone Chain Interface

    The Auto Bone Chain Interface is created by the IK from Objects and IK from Bones tools on the Rigging shelf.

  • Blend

    Switches or blends between the transformations of several input objects.

  • Blend Sticky

    Computes its transform by blending between the transforms of two or more sticky objects, allowing you to blend a position across a polygonal surface.

  • Bone

    The Bone Object is used to create hierarchies of limb-like objects that form part of a hierarchy …

  • Camera

    You can view your scene through a camera, and render from its point of view.

  • Common object parameters

  • Dop Network

    The DOP Network Object contains a dynamic simulation.

  • Environment Light

    Environment Lights provide background illumination from outside the scene.

  • Extract Transform

    The Extract Transform Object gets its transform by comparing the points of two pieces of geometry.

  • Fetch

    The Fetch Object gets its transform by copying the transform of another object.

  • Formation Crowd Example

    Crowd example showing a changing formation setup

  • Fuzzy Logic Obstacle Avoidance Example

  • Fuzzy Logic State Transition Example

  • Geometry

    Container for the geometry operators (SOPs) that define a modeled object.

  • Groom Merge

    Merges groom data from multiple objects into one.

  • Guide Deform

    Moves the curves of a groom with animated skin.

  • Guide Groom

    Generates guide curves from a skin geometry and does further processing on these using an editable SOP network contained within the node.

  • Guide Simulate

    Runs a physics simulation on the input guides.

  • Hair Card Generate

    Converts dense hair curves to a polygon card, keeping the style and shape of the groom.

  • Hair Card Texture Example

    An example of how to create a texture for hair cards.

  • Hair Generate

    Generates hair from a skin geometry and guide curves.

  • Handle

    The Handle Object is an IK tool for manipulating bones.

  • Indirect Light

    Indirect lights produce illumination that has reflected from other objects in the scene.

  • Instance

    Instance Objects can instance other geometry, light, or even subnetworks of objects.

  • LOP Import

    Imports transform data from a USD primitive in a LOP node.

  • LOP Import Camera

    Imports a USD camera primitive from a LOP node.

  • Labs Fire Presets

    Quickly generate and render fire simulations using presets for size varying from torch to small to 1m high and low

  • Light

    Light Objects cast light on other objects in a scene.

  • Light template

    A very limited light object without any built-in render properties. Use this only if you want to build completely custom light with your choice of properties.

  • Microphone

    The Microphone object specifies a listening point for the SpatialAudio CHOP.

  • Mocap Acclaim

    Import Acclaim motion capture.

  • Mocap Biped 1

    A male character with motion captured animations.

  • Mocap Biped 2

    A male character with motion captured animations.

  • Mocap Biped 3

    A male character with motion captured animations.

  • Null

    Serves as a place-holder in the scene, usually for parenting. this object does not render.

  • Path

    The Path object creates an oriented curve (path)

  • PathCV

    The PathCV object creates control vertices used by the Path object.

  • Python Script

    The Python Script object is a container for the geometry operators (SOPs) that define a modeled object.

  • Ragdoll Run Example

    Crowd example showing a simple ragdoll setup.

  • Reference Image

    Container for the Compositing operators (COP2) that define a picture.

  • Rivet

    Creates a rivet on an objects surface, usually for parenting.

  • Simple Biped

    A simple and efficient animation rig with full controls.

  • Simple Female

    A simple and efficient female character animation rig with full controls.

  • Simple Male

    A simple and efficient male character animation rig with full controls.

  • Sound

    The Sound object defines a sound emission point for the Spatial Audio chop.

  • Stadium Crowds Example

    Crowd example showing a stadium setup

  • Stereo Camera Rig

    Provides parameters to manipulate the interaxial lens distance as well as the zero parallax setting plane in the scene.

  • Stereo Camera Template

    Serves as a basis for constructing a more functional stereo camera rig as a digital asset.

  • Sticky

    Creates a sticky object based on the UV’s of a surface, usually for parenting.

  • Street Crowd Example

    Crowd example showing a street setup with two agent groups

  • Subnet

    Container for objects.

  • Switcher

    Acts as a camera but switches between the views from other cameras.

  • TOP Network

    The TOP Network operator contains object-level nodes for running tasks.

  • VR Camera

    Camera supporting VR image rendering.

  • Viewport Isolator

    A Python Script HDA providing per viewport isolation controls from selection.

  • glTF