Houdini 22.0 Nodes LOP nodes

Asset Reference

Reference, Transform, and select variants of a USD Asset.

Since 19.0

This node combines the most common features of the Reference, Xform, and Set Variant LOPs into a convenient tool.

Parameters

Destination Primitive

Scene graph path where the referenced asset will be attached.

Primitive Kind

If the prim at Primitive Path doesn’t exist, this node will create it. If it has to create the prim, it will set it to have this kind.

Setting this parameter to Auto will not author a Kind on the leaf primitive where the reference is added. Instead, it will examine the Kind of the prim after setting the reference, and automatically set the Kind of ancestor prims to ensure the leaf primitive is part of a valid model hierarchy. Note that this may result in adding a Kind to ancestor prims that were not created by this node. If the referenced prim has no kind, or is not a model kind, Auto mode will not author Kind on any prim.

Parent Primitive Type

If the prim at Primitive Path doesn’t exist, this node will create it. If it has to create the prim, it will give any intermediate prims it has to create this type.

Make Instanceable

Mark the new or modified prims as instanceable (as in “native instancing”). This saves memory if you reference the same branch into multiple places, but makes the descendants of the referenced prim not editable. If this option is off, the prims are not explicitly marked as not instanceable. Instead, the current instanceable value on each prim is left unchanged.

Reference

Source

The source of the asset being referenced. By default, this node will switch to the second input, when connected, and use File otherwise. Users can also specify which source if they wish.

File

Reference in a prim from an external USD file.

Second Input

Reference in a prim from a this node’s second input.

Second Input if Connected

Reference from the Second Input if connected, otherwise from a file.

File Reference

Reference File

Click the Open floating file chooser button to load the USD file from disk you want to add as a reference.

Reference Primitive

Reference Automatically Chosen Primitive

If the referenced file has a default primitive set, use that. If there is no default prim, use the first Xform prim at the root. If there is no Xform prim at the root, use the first root prim of any type.

Reference Default Primitive

If the referenced file has a default primitive set, use that. If not, display a warning on this node.

Reference Specific Primitive

Reference in the scene graph path in the Reference Primitive Path parameter.

Reference Primitive Path

Drag a primitive from the Scene Graph Tree to this field or enter a path to the primitive you want to use as a reference.

Options

Time Offset (in Frames)

Offsets all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file.

Time Scale

Scales all time samples from the file or target primitive on the first input. You can use this to re-time animations in the references file. A value of 1 means normal speed. Values smaller than 1 make animations slower, values greater than 1 make the animation appear in slow motion.

Handle Missing Files

If the reference is to an external file, this controls what the node does if the referenced file does not exist.

Error for Missing Files

The node errors, preventing cooking the rest of the network.

Warn for Missing Files

The node shows a warning, then passes through the first input unchanged.

Ignore Missing Files

The node silently ignores the missing file, and passes through the first input unchanged.

Allow Missing Files on the Stage

Author the reference to the sublayer even if it currently doesn’t exist. This node and the following nodes will probably print warnings from the USD libraries about missing files.

Transform

Transform

How the transform parameters below apply to the primitive. (Because each USD prim can contain multiple transforms, and be affected by parent transforms, there are many different ways to apply new transforms.)

Append

Apply the parameters as a new, most local transform.

Prepend

Apply the parameters as a new, least local transform.

Overwrite or Append

If a local transform exists with the name xformOp:transform, overwrite it with the parameters. Otherwise, apply it as a new, most local transform.

If this replaces an existing transform, that transform’s order in the local transform stack is not affected.

Overwrite or Prepend

Like Overwrite or Append, but least local.

Apply Transform in World Space

Apply the parameters as a new, most local transform. However, prior to applying the transform, it is updated so that the result of the transform appears as if the transform was being applied in world space, before any local or ancestor transformations were applied to the primitive.

Replace All Local Transforms

The transform specified in the remaining transform parameters is always applied as a new transform. Prior to applying this transform, all existing transform operations on the local transform stack are cleared so that only the supplied transform remains on the local transform stack (though ancestor transforms still have an effect).

Apply XformCommonAPI

The transform specified in the remaining transform parameters will be applied as if it were appended to whatever the current transform on the prim is. But the resulting final transform will be expressed using the USD XformCommonAPI specification. Note that this specification cannot express shears, and so cannot express some transforms which may result in unexpected changes to transforms that already have shears.

Apply Extended XformCommonAPI (with Shear + Pivot Rotate)

The transform specified in the remaining transform parameters will be applied as if it were appended to whatever the current transform on the prim is. But the resulting final transform will be expressed using a Houdini-defined extension of the USD XformCommonAPI specification. This extension is accessible through the husd.UsdHoudini.HoudiniXformCommonAPI python class. This class provides a very similar interface to pxr.UsdGeom.XformCommonAPI but allows for shears in the transform, is able to store a pivot rotation value, and can express rotations as a quaternion if the rotations are animated. Using quaternions to express rotations avoids motion blur artifacts that can occur when using Euler angles to express the rotation.

Transform Order

The order in which Houdini applies translates, rotates, and scales, and the order in which it applies rotation.

Translate

Movement amount along XYZ axes.

Rotate

Degrees rotation around XYZ axes.

Scale

Non-uniform scaling along XYZ axes.

Shear

Amount of shearing. The three values represent shearing in the X direction on the XY plane, in the X direction on the XZ plane, and in the Y direction on the YZ plane, respectively.

Uniform Scale

Scales the object uniformly along all three axes.

Align To Up Axis

When enabled, the reference will be transformed so its up axis matches the current stage.

Pivot Primitives

Pivot Translate

Moves the local origin of the object.

Pivot Rotate

Rotates the local origin of the object after translation.

Variants

Number of Variants

You can perform multiple variant selections in a single Set Variant node. Set this to the number of selections you want to make, or use the plus and minus buttons to add or remove selections.

Primitives

The primitive(s) you want to define as variants of a Variant Set. You can click the Select button beside the text box to select the primitives from the scene graph tree. You can also use primitive patterns for advanced matching.

Variant Set

The name of the variant set to select a variant from.

Variant Name

If not choosing the variant by index, this parameter is the name of the variant that should be selected within the specified variant set. If this value is an empty string, any existing variant selection specified in the active layer will be cleared. This will “reveal” any variant selection opinions authored in weaker layers. If this value is set to the special string <block>, an explicit empty variant selection will be made, blocking any variant selection opinions from weaker layers, leaving the chosen set without any variant selected. If this is set to a list of variant names (space or comma- separated), then this will use the first one that matches a valid variant name in each prim’s variant set.

LOP nodes

  • APEX Animate

    Edits the animation on an APEX scene.

  • APEX SOP Rig Builder

    Authors APEX rigs and binds them to USD primitives.

  • Add Variant

    Adds one or more variants to a variant set on a primitive. This node creates the primitive if it doesn’t exist.

  • Additional Render Vars

    Create multiple render vars.

  • Asset Reference

    Reference, Transform, and select variants of a USD Asset.

  • Assign Material

    Assigns a material to one or more USD primitives. You can use also programmatically assign materials using VEX, programmatically override material settings for each assignment, and programmatically assign materials to geometry subsets.

  • Assign Prototypes

    Switch point instances or USD instanceable prims to instance a different prototype.

  • Attribute VOP

    Create/edit USD attribute values using a VOP network.

  • Attribute Wrangle

    Create/edit USD primitive attributes using a VEX snippet.

  • Auto Select LOD

    Automatically selects a level-of-detail variant based on the primitive’s distance from the camera.

  • Bake APEX Scene

    Bakes animation from APEX scenes to point positions and transforms.

  • Bake UsdSkel Skinning

    Bakes animation driven by a UsdSkel into transforms and point positions.

  • Basis Curves

    Creates or edits a basis curves shape primitive.

  • Begin Context Options Block

    This node begins a block of LOP nodes, within which certain context options have certain values.

  • Blend

    Partially applies edits to a layer’s attributes based on a fractional weight.

  • Blend Constraint

    Blends transforms according to a list of weights specified as parameters.

  • Cache

    Caches the results of cooking the network at different times, increasing playback speed.

  • Camera

    Adds a USD camera to the scene.

  • Capsule

    Creates or edits a capsule (tube with hemispherical ends) shape primitive.

  • Collection

    Creates/edits collections using primitive patterns.

  • Component Geometry

    Geometry container or import source, in a network created by the Component Builder tool.

  • Component Geometry Variants

    Sets up geometry variants, in a network created by the Component Builder tool.

  • Component Material

    Assigns materials to geometry in a network created by the Component Builder tool.

  • Component Output

    Assembles the final Component prim, in a network created by the Component Builder tool.

  • Cone

    Creates or edits a cone shape primitive.

  • Configure APEX Rig

    Configures and attaches simple APEX rigs to USD primitives.

  • Configure Guide Deform

    Tags groom primitives with the HairDeform procedural API, configuring how they deform at render time.

  • Configure Layer

    Edits metadata on a layer.

  • Configure Primitives

    Edits various metadata on one or more primitives.

  • Configure Properties

    Configures metadata on properties (relationships and attributes).

  • Configure Stage

    Configures metadata for how to load layers into the stage and asset resolution.

  • Coordinate System

    Define named coordinate systems used in shaders.

  • Copy Property

    Copy properties from one primitive to another, or renames properties on a primitive.

  • Copy to Points

    Instances or copies primitives onto points.

  • Create LOD

    Uses the PolyReduce SOP to automatically generate multiple levels of detail from a high-res model, and stores them as USD variants.

  • Cube

    Creates or edits a cube shape primitive.

  • Cylinder

    Creates or edits a cylinder shape primitive.

  • Distant Light

    Creates or edits a USD Distant Light, representing a far-off light source such as the sun. Adds some useful Karma-specific attributes.

  • Dome Light

    Creates or edits a USD Dome Light prim. A dome light emits light inward, simulating light coming from the sky/environment surrounding the scene.

  • Draw Mode

    Sets draw mode properties on USD model assets.

  • Drop

    Runs a simulation to drop primitives under gravity.

  • Duplicate

    Creates copies of a prim (and its descendants).

  • Edit

    Interactively transforms prims in the viewer. Can use physics collisions to position props realistically.

  • Edit Context Options

  • Edit Material Network

    Allows you to edit an existing USD material by modifying parameters and shader connections. This can be useful if the existing material is on a non-editable layer.

  • Edit Material Properties

    Lets you build a spare parameter interface that reflects material or shader input attributes to directly edit their values.

  • Edit Properties

    Lets you build a spare parameter interface to directly edit attribute and relationship values.

  • Edit Properties From Node

    Lets you refer to the parameter on another node to directly edit attribute and relationship values.

  • Edit Prototypes

    Modify the prototypes of native or point instances in-place, without disturbing the instancing setup.

  • Edit Target Layer

    Allows you to apply edits directly in a lower layer, instead of overriding prims and attributes in the active layer.

  • Error

    Generates a message, warning, or error, which can show up on a parent asset.

  • Explore Variants

    Visualize, set, or extract variants on primitives.

  • Extract Instances

    Converts (heroes) an instance into a real editable prim.

  • Fetch

    Grabs the output of another LOP, potentially in another LOP network.

  • File Cache

    Caches (writes out once and then reads from) USD layers (possibly animated) to disk.

  • Follow Path Constraint

    Constrains a prim to follow a path curve.

  • For Each

    The end node of a For-Each loop block.

  • Geometry Clip Sequence

  • Geometry Color

    Adds display color and display opacity primvars to geometry.

  • Geometry Light

    Adds properties to turn geometry into lights.

  • Geometry Sequence

    Imports a sequence of geometry files into LOPs as animated geometry.

  • Geometry Subset VOP

    Creates USD geometry subsets within geometry prims (similar to groups in SOPs) based on evaluating a VEXpression or VOP network.

  • Graft Branches

    Takes prims/branches from the second input and attaches them onto branches of the scene graph tree in the first input.

  • Graft Stages

    Takes scene graph trees from other inputs and attaches them onto branches of the scene graph tree in the first input.

  • HDA Dynamic Payload

    Cooks a OBJ or SOP asset on disk and imports the animated geometry output as a USD payload.

  • Hermite Curves

    Creates or edits a hermite curves shape primitive.

  • Houdini Preview Procedurals

    Invokes Houdini Procedurals while working interactively.

  • Houdini Procedural: Crowd

    Houdini Crowd Procedural for Solaris.

  • Houdini Procedural: Feather

    Generates feathers for rendering.

  • Houdini Procedural: Hair

    Houdini Procedural: Haie for Solaris.

  • Houdini Procedural: Ocean

    Houdini Ocean Procedural for Solaris.

  • Houdini Procedural: RBD

    Houdini Procedural: RBD for Solaris.

  • Husk Image Metadata

    Add Husk Custom Metadata to Render Products and Render Vars.

  • Image Filter

    Create an Image Filter List

  • Inline USD

    Parses usda code representing a layer and adds it to the layer stack.

  • Insertion Point

    Represents a point in the node graph where nodes can be inserted.

  • Isolate Scene

    Work in masked areas of the stage.

  • Karma Background Plate

    Sets up AOVs and hold-out or matte objects that leave holes in the scene through which the background is visible. These prims still take shadows and contribute to reflections as if they were the background.

  • Karma Blocker Light Filter

    Creates or edits a USD Karma blocker light filter prim.

  • Karma Cryptomatte

    Setup Cryptomatte AOVs for Karma.

  • Karma Fog Box

    Creates a constant volume within a box.

  • Karma Physical Sky

    Creates a Karma Sky Dome and Sun Light rig.

  • Karma Render Products

    Create multiple render products sharing common settings.

  • Karma Render Settings

    Configure Render Settings for Karma.

  • Karma Shadow Catcher

    Configure render-time hold-out or matte objects.

  • Karma Sky Atmosphere

    Creates or edits a Karma Sky Atmosphere.

  • Karma Sky Dome Light

    Creates or edits a Karma Sky Dome Light.

  • Karma Standard Render Vars

    Create standard karma render vars (AOVs/Image Planes).

  • Karma Texture Baker

    Create a Render Settings primitive to create texture maps that define shading states for an object.

  • LPE Tag

    Manage Lights' LPE Tags.

  • Labs Biome Plant Scatter Import

    Import a biome plant scatter from SOPs to LOPs.

  • Labs Karma

    Renders USD stages using Karma with integrated caching, wedging, and TOPs workflows.

  • Labs Karma AOVs for RenderMan Denoiser

    Generates AOVs for the Pixar RenderMan denoiser.

  • Labs ML CV Directory Variant

    Creates a variant set from USD assets in a directory.

  • Labs ML CV Dome Camera

    Generates a camera from one of the random positions within a specified 3D camera dome and frames the focus object within the camera’s view.

  • Labs ML CV Synthetics Karma Rop

    Renders RGB image or ID EXR file for segmentation masking.

  • Labs Relight GSplats

    Relights Gaussian Splats using USD lights and a BSDF shader.

  • Labs ZibraVDB Import

    References ZibraVDB data on disk into a volume prim containing field prims.

  • Layer Break

    Starts a new active sublayer that subsequent nodes will edit, and indicates all previous layers will be discarded when saving to disk.

  • Layer Replace

    Replaces all uses of a certain layer with a substitute layer from its second input.

  • Light

    Creates or edits a USD Light prim. This node also adds some useful Karma-specific attributes.

  • Light Filter Library

    Authors USD light filter primitives from VOP nodes.

  • Light Linker

    Creates USD light link properties based on rules.

  • Light Mixer

    Lets you interactively edit USD properties for multiple lights.

  • Live Render

    Launches renders which react to upstream LOP changes and send the image to the Render Gallery.

  • Load Layer for Editing

  • Loft Payload Info

    Adds basic information from inside a payload to the primitive that loads the payload.

  • Look At Constraint

    Constrains a prim to always point toward a target.

  • Mask from Bounds

    Sets a primvar based on whether/by how much selected prims are inside a bounding shape.

  • Match Size

    Resizes and recenters the input geometry to match a reference bounding box.

  • Material Library

    Authors USD material primitives from shader VOP nodes.

  • Material Linker

    Creates material assignments based on rules.

  • Material Variation

    Creates attributes/primvars to override material parameters per-prim/instance.

  • Merge

    Merges the layers from incoming stages into a unified layer stack.

  • Merge PointInstancers

    Merges point instancers into a single consolidated point instancer.

  • Mesh

    Creates or edits a mesh shape primitive.

  • Modify Paths

    Modify asset path attribute values.

  • Modify Point Instances

    Modifies point transforms and property values for individual point instances.

  • Motion Blur

    Adds time samples to allow motion blur when rendering.

  • Null

    This node does nothing. It can be useful to insert a Null into a network as a fixed point in the network that you can refer to by name in expressions/scripts.

  • Output

    Represents the output of a subnetwork. Allows you to design a node asset with multiple outputs.

  • Paint Instances

    Provides tools for populating a scene with USD assets in a point instancer. You can place individual instances, paint/scatter instances in different ways using customizable brushes, and edit existing instances.

  • Parent Constraint

    Makes a primitive appear to inherit the transform hierarchy of another prim somewhere else in the tree.

  • Plane

    Creates or edits a plane shape primitive.

  • PointInstancer

    Creates or edits USD PointInstancer prims from SOP points.

  • Points

    Creates or edits a Points shape primitive.

  • Points Constraint

    Position and Orient primitives using point positions from a geometry.

  • Portal Light

    Creates or edits a USD Portal Light prim. A portal light is used in conjunction with a Dome Light to restrict the parts of the dome light that are sampled to illuminate a scene.

  • Primitive

    Bulk-creates one or more attributes of a certain type.

  • Prune

    Hides or deactivates primitives and point instances.

  • Python Script

    Lets you write Python code in the node to use the USD API to directly manipulate the stage.

  • RBD Destruction

    An example for a fracturing simulation in USD, also useful as a canned effect.

  • Reference

    References the contents of a external USD files and/or layers created by other LOP nodes into a branch of the existing scene graph tree. Can also remove or replace existing references.

  • Relocates

    Authors relocate source-target mappings to the active layer.

  • Render Geometry Settings

    Applies renderer-specific geometry settings to geometry in the scene graph.

  • Render Pass

    Creates or edits a UsdRenderPass prim, which represents a render pass, with attributes configuring the content of the pass, and how to configure the renderer to generate the pass.

  • Render Product

    Creates or edits a UsdRenderProduct prim, which represents an output of a renderer (such as a rendered image file or other file-like artifact produced by a renderer), with attributes configuring how to generate the product.

  • Render Settings

    Creates or edits a UsdRenderSettings prim, which holds the general settings for rendering the scene.

  • Render Var

    Specifies a custom variable computed by the renderer and/or shaders, either a shader output or a light path expression (LPE).

  • Resample Transforms

    Generates interpolated transform time samples from existing time samples on USD prims.

  • Restructure Scene Graph

    This node has various operations for editing prim paths, variant sets, and composition arcs.

  • Retime Instances

    Offsets and/or scales the timing of animation on selected instances.

  • SOP Create

    Lets you create geometry in a SOP subnetwork inside this node, so you can create geometry in-place in the LOP network instead of needing a separate SOP network.

  • SOP Import

    Imports geometry from a SOP network into the USD scene graph.

  • SOP Import APEX Scene

    Imports an APEX scene or character from a SOP network into the USD scene graph.

  • SOP Import Crowd

    Imports a crowd from a SOP network into the USD scene graph.

  • SOP Import UsdSkel Character

    Imports a character or animation from a SOP network into the USD scene graph.

  • SOP Modify

    Converts USD geometry into SOP geometry, runs the SOP subnet inside this node on the geometry, and converts the changes back to USD overrides.

  • Scatter Instances

    Hydra generative procedural and LOP node for scattering instances.

  • Scene Doctor

    Validates primitives on a USD stage.

  • Scene Import

    Imports models, materials, and lights from the Object level into the LOP network.

  • Scope

    Creates a scope primitive. Scope is the simplest form of grouping, and does not have a transform. Scopes can be useful for organizing the scene tree.

  • Set Extents

    Sets the bounding box metadata of selected primitives.

  • Set Variant

    Selects (switches to) one of the variants stored in a variant set on a primitive.

  • Shot Layer Edit

    Part of the Shot Builder Toolset, targets a specific layer for all shots that match the give pattern.

  • Shot Load

    Part of the Shot Builder Toolset, load USD data for your project.

  • Shot Output

    Part of the Shot Builder Toolset, outputs USD data and /or rendered images to your project.

  • Shot Split

    Passes through the input node’s stage, but may alter the shot context option depending on which output branch is being cooked.

  • Shot Switch

    Passes through one of several inputs, based on the shot context option.

  • Simulation Proxy

    Generates low-poly collison geometry suitable for physical simulation and creates a proxy relationship to the original model.

  • Sphere

    Creates or edits a sphere shape primitive.

  • Split PointInstancers

    Splits a point instancer into two or more instances, which divide up the original instances.

  • Split Primitive

    Splits USD geometry prims into child primitives based on geometry subsets or primvar values.

  • Split Scene

    This node splits a scene graph into two disjoint sets of primitives.

  • Stage Manager

    Provides a convenient interface to reference in many files at once and place them in the scene graph tree.

  • Store Parameter Values

    Lets you store temporary (unsaved) data in the stage.

  • Sublayer

    Imports from USD files or other LOP node chains into as sublayers, or removes/replaces/reorders existing sublayers.

  • Subnet

    Encapsulates a LOP subnetwork, allowing you to organize and hide parts of the network.

  • Surface Constraint

    Constrain a prim to stick to a surface.

  • Switch

    Passes through one of several inputs, based on a parameter choice or expression.

  • Texture Material Library

    Authors USD material primitives whose texture inputs are driven by COPs.

  • TimeShift

    Outputs the stage as it is at a different point in the timeline.

  • Transform

    Edits the transforms of selected USD primitives.

  • Transform UV

    Moves, rotates, and scales texture coordinates on USD primitives.

  • Transform by SOP Points

    Transforms USD primitives by SOP points with transform attributes.

  • USD ROP

  • USD Render ROP

  • Unassign Material

    Unbinds a material from one or more USD primitives.

  • Value Clip

  • Vary Material Assignment

    Assign different materials across a number of prims to create variation.

  • Volume

    References volume data on disk into a volume prim containing field prims.

  • Xform

    Creates or edits an Xform prim. Xform (and its sub-classes) represents a transform in the scene tree.