Houdini 19.0 Nodes LOP nodes

Material Library

Authors USD material primitives from shader VOP nodes.

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Since 17.0


This node translates shader VOP nodes into USD material primitives.

A newly created Material Library node uses a pattern asterisk in the Material VOP parameter to match children VOP nodes inside the LOP and translate them into USD materials. See USD materials below.

Alternatively, this LOP can also import Houdini VOP materials from other VOP networks (such as /mat), using Auto-fill Materials button.


  • You can use patterns in Material VOP parameter

  • You can define a common USD path for all materials, using Material Path Prefix parameter. Any material whose Material Path multi-parm instance is not an absolute path will use it as a prefix.

  • The Material Path Prefix parameter can be used to specify either the ancestor primitive (if the path ends with a slash), or the ancestor path and the shader primitive name prefix (if the path does not end with a slash).

  • If you want to re-do importing all materials (for example, to grab new materials), click Clear in the multi-parm, then click Auto-fill materials again.

  • Even though this node allows you to assign the material at the same time you import it, we recommend you use a separate node (Material Linker or Assign Material) to assign materials. Keeping the two operations separate makes your network easier to understand for others.

USD materials

Inside the Material Library LOP, the VOP nodes, their parameters, and inputs represent USD shaders, their attributes and input connectors. For example, a Principled Shader VOP represents a Karma material, and the Pxr Surface VOP represents a USD RenderMan shader.

The Collect VOP can gather several shaders for different renderers to create a USD material that contains all of them.

You can connect the shader VOPs can be connected to one another, and the node will translate these as USD shader connections. (For example, if you connect the output of a USD UV Texture VOP to the input of USD Preview Surface VOP.)


To import materials from inside this node, set the Material network to . (a single period).


You can use Visualize VOP ('x' hotkey) to debug the shader node network. If the shader translator for a given shader node supports output value visualization via the Visualize VOP node, then the USD Material will be authored in such a way that geometry will be shaded using the value of the shader node feeding into the Visualize VOP.


Material Network

Node path to the VOP network containing material nodes to import. The node looks for materials here when you click Auto-fill materials. Set this to . (a single period) to use the VOP subnet inside this node.

This is a hidden parameter, which is set and used by Auto-fill button.

Container Path

The default parent scene graph path of newly created materials. This is prefixed to the material names to get the material prim path when you click Auto-fill materials.

This is a hidden parameter, which is set and used by Auto-fill button.

Auto-fill Materials

Click this to automatically create instances of the multi-parm for each material node in the Material network.

This button will bring up a pop-up dialog prompting for the material network inside which to look for nodes with material flag turned on. Each such node will be filled into own multi-parm instance. The dialog also asks for the USD path at which to author the USD material translated from that node.

Auto-generate Preview Surface Shaders

When possible, the LOP will generate a USD Preview Surface shader primitive. This shader type is part of the USD standard and should be implemented by all USD renderers, so this shader (which may be an approximation of the original shader) should show up in any renderer, even if the renderer doesn’t understand the original shader type.

Note, if textures are involved, the auto-generated preview network will wire the alpha output of a USD Texture Reader primitive to the opacity input of a USD Preview Surface shader primitive. Some renderers, like Storm, are known to mishandle the opacity, leading to artifacts in the viewport. To workaround such cases, you can turn this toggle off and then you can manually create a USD Preview network inside, feeding it to the Collect VOP along with the original surface shader.

Allow Shader Parameter Animation

When it is turned off, all USD values are assumed non-animatable and will be authored at a default time code. And, with this option turned on, shader node parameters that are time-dependent will get translated to USD values at non-default time codes, while time-independent parameters will still author a value at a default time code.

Note, checking parameter time dependency can be costly and may add up to a large portion of the shader translation time. Since the vast majority of shader nodes don’t have animated parameters, this toggle is off by default to save the work involved in checking it.

Parent Primitive Type

If the intermediate prims in a material path don’t exist, the node will create them. This controls the type of the intermediate prims this node creates.

Material Path Prefix

This is automatically prefixed to any material paths that are not absolute (do not start with a slash). This lets you specify relative material paths in the multi-parm, and set their common parent hierarchy in this one parameter.

Number of Materials

The number of materials to import. Set the number or click the plus and minus buttons to add or remove material imports.

Include Only VOPs with Material Flag Set

If Material VOP is a pattern, this excludes nodes that don’t have the Material flag on. Default is off.

Material VOP

The Houdini node path to a VOP node representing a shader or material. This can be a node pattern, in which case this node will import all matched nodes as USD materials.

Material Path

The USD scene graph path at which to create the material prim. If this is an absolute path (starts with a slash), it is used as-is. If this path is relative, it is relative to the path in the Material path prefix parameter.

Assign to Geometry

When this is on, you can assign the newly imported material to USD geometry prims using the Geometry path parameter below.

Geometry Path

When Assign to geometry is on, assign the newly imported material to the primitives listed in this parameter.

LOP nodes

  • 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.

  • 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.

  • Background Plate

    Sets up 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.

  • Bake 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 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.

  • Copy Property

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

  • 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.

  • 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

    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 Prototype

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

  • 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.

  • Follow Path Constraint

    Constrains a prim to follow a path curve.

  • For Each

    The end node of a For-Each loop block.

  • 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.

  • 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.

  • Instancer

    Instances or copies primitives onto points.

  • Instancer

    Creates a constant volume within a box.

  • Instancer

    Create multiple render products sharing common settings.

  • Karma

    Renders the USD scene using Houdini’s Karma renderer.

  • Karma Procedural

    Sets up render-time instantiation for Karma.

  • Karma Render Properties

    Configure Render Properties for Karma.

  • Karma Standard Render Vars

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

  • LOP nodes

    LOP nodes generate USD describing characters, props, lighting, and rendering.

  • LPE Tag

    Manage Lights LPE Tags.

  • Labs RizomUV Optimize

  • Labs RizomUV Rectangularize

  • Labs RizomUV Unwrap

  • 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.

  • Layout

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

  • Light

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

  • Light Linker

    Creates USD light link properties based on rules.

  • Light Mixer

    Lets you interactively edit USD properties for multiple lights.

  • 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.

  • 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 LOP

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

  • 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.

  • 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.

  • Parent Constraint

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

  • Points

    Creates or edits a Points shape primitive.

  • Points Constraint

    Position and Orient primitives using point positions from a geometry.

  • 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 of how to a fracturing simulation in USD, also useful as a canned effect.

  • Reference

    References the contents of an external USD file into a branch of the existing scene graph tree, or removes/replaces existing references.

  • Render Geometry Settings

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

  • 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 Character Import

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

  • 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 Crowd Import

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

  • SOP Import

    Imports geometry 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.

  • 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.

  • 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 Point Instancers

    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.

  • 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.

  • 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.


  • 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.