Houdini 18.0 Nodes LOP nodes

Scene Import

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

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Overview

This lets you bring work done in Houdini into the a LOP network for layout, lighting, and rendering.

Tips and notes

  • By default this node does not import anything because the Objects list is blank. You must specify a list of node paths/patterns in this field to import objects.

  • Containment relationships (object subnets containing other objects) at the object level are translated into prim hierarchy in USD.

  • Wiring relationships (objects wired into other object to specify parenting) at the object level are also translated into prim hierarchy unless you turn on Ignore inputs.

Parameters

General

Import All Time Samples

Imports animated data for each frame within the range specified below. For any animated parameter or SOP geometry, this creates time samples on the resulting USD attributes.

Since this immediately stores all time samples within USD attribute data, the node doesn’t become time-dependent and doesn’t need to be recooked when scrubbing to a different frame.

Depending on the amount of animated data, the import can take a lot longer than the import of just the current frame, which occurs when this toggle is disabled.

Frame Range

When Import all time samples is on, the range of frames to import. By default the parameters have expressions that set this to the full frame range of the timeline.

Substeps

When Import all time samples is on, the number of substeps between frames.

Objects

Import Objects

Whether to import Object nodes (models, cameras, and lights) into USD, mapping as many parameter values as possible to standard USD attributes.

Destination Path

Prefix the node path of each imported object with this path to create its scene graph path. The default is /, which imports objects at the root level.

Shared Materials Path

When importing materials attached to imported objects, prefix their scene graph paths with this path.

Root Object

Only look at Object nodes inside this node network path. The default is /obj, which means the node will try to import all Object nodes.

Objects

A list of node paths to import. If this is blank (the default), the node imports nothing. Set this to * to try to import all Object nodes.

Filter

Choose whether to import all Object node types, or only Cameras, only Lights, or only Geometry objects.

Make Conflicting Paths Unique

When this is on, the node will add numbers to names to ensure prims at the same level have unique names. When this is off, conflicting names will make the node stop cooking and show an error.

Name conflicts most often occur when Flatten Hierarchy is enabled, but can also happen because by default the scene graph path is built from both containment and wiring relationships at the object level.

Flatten Hierarchy

Imports every object directly under the Destination Path, ignoring containment and wiring.

Ignore Inputs

Don’t use the parent-child wiring relationships between object nodes to create prim hierarchy.

Import SOP Geometry

Import the geometry generated by SOP nodes inside Geometry objects as USD geometry. Turning this off might be useful if you only want to import the transform hierarchy from the objects, and want to treat actual geometry separately.

Set Subdivision Scheme to Match Object Parameters

When Import SOP geometry is on, check for rendering properties that control subdivision on the object, and set the USD Subdivision Scheme to match.

Set SOP Path Attribute

When Import SOP geometry is on, use a SOP string primitive attribute (usually path or name) to generate/name additional prim hierarchy. (Geometry in Houdini has no inherent hierarchy otherwise.)

For example, the polygonal mesh inside a Geometry object named Lamp might normally be imported as /Lamp/mesh_0. However, if some faces in the mesh have a name attribute set to bulb, those faces would be imported as a separate mesh at /Lamp/bulb.

SOP Path Attribute

When Set SOP path attribute is on, the name of a SOP string primitive attribute to use to generate/name additional prim hierarchy (usually name or path).

Materials

Import Materials

Whether to import materials (either from the list below, or materials assigned to imported objects).

Destination Path

Prefix the node path of each imported material with this path to create its scene graph path.

Flatten Hierarchy

Imports every material directly under the scene graph path in Materials ▸ Destination Path, ignoring any intermediate subnets or input object.

Materials Assigned to Objects

Import any materials assigned to imported objects.

Materials Assigned to SOP Geometry

Import any materials assigned at the geometry level inside imported objects.

Additional Materials

Import any material VOP node paths listed in this parameter.

See also

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.

  • 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 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 Skinning

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

  • 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.

  • 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 a collection using selected prims.

  • 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.

  • 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.

  • 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 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.

  • Extract Instances

    Converts 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 Subset VOP

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

  • Graft

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

  • Inline USD

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

  • Instancer

    Instances or copies primitives onto points.

  • Karma Procedural

    Sets up render-time instantiation for Karma.

  • Karma Render Properties

    Configure Render Properties for Karma (Beta).

  • Karma Standard Render Vars

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

  • LOP nodes

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

  • Layer Break

    Starts a new active sublayer that subsequent nodes will edit.

  • 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 Linker

    Creates USD light link properties based on rules.

  • Light Mixer

    Lets you interactively edit USD properties for multiple lights.

  • Load Layer

  • Look At Constraint

    Constrains a prim to always point toward a target.

  • Material Library

    Imports Material VOP nodes as USD material prims.

  • 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.

  • Modify Point Instances

    Modify 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 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.

  • 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).

  • 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 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.

  • 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 ROP

  • USD Render ROP

  • 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.

  • attribvop