Houdini 18.5 Nodes LOP nodes

Render Settings

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

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Since 18.0


  • A UsdRenderSettings prim holds global render settings for rendering the scene, as well as a list of UsdRenderProduct prims representing the rendered files/buffers, and which purposes should be rendered.

  • Render settings prims must be somewhere under /Render in the scene graph tree.

Creating vs. editing prims

This node belongs to a class of nodes that create or edit USD prims directly. These nodes operate in Create mode or Edit mode. This is controlled by a Create primitives checkbox or a Create/Edit popup menu. In create mode, the node creates new prims. In edit mode, the node changes the attributes on an existing prim.

Parameters that correspond to a USD attribute have a pop-up menu to the left that controls how the node authors the attribute.

Pop-up menu item


Set or Create

Sets the attribute to the given value, whether it previously existed or not.

Set If Exists

Only set the attribute to the given value if it previously existed.

Use this mode to make sure an attribute is only set on primitives of the correct type. For example, only UsdGeomSphere primitives are likely to have a radius attribute.


Makes the attribute appear to not exist, so it takes on its default value. (If the attribute doesn’t already exist on the prim, this does nothing.)

Do Nothing

Ignore this parameter, don’t create or change the attribute in any way.



Whether this node should create new prims, or edit existing prims.

Primitive Path

In create mode, this lets you control where in the scene graph to create the prim(s).

The default is usually /$OS. This creates a primitive at the root level with the same name as the node (for example, /tube1). This is a useful default for preventing naming conflicts, but terrible for organization. You should try to remember to change the Primitive path to a better value when you create prims.

For example, instead of naming models after the node that created them, you might want to name them after the geometry inside, and organize them under a /Models branch.

The "Create primitives" section contains basic controls for how to create the new prim(s).


In edit mode, the node has a Primitive pattern parameter. This lets you specify the prim(s) the node should operate on. 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, including matching all prims in a collection.

Initialize Parameters For Edit

In edit mode, changes the state of all control menu parameters to Do Nothing, so that this node will not apply any changes. Also grabs the current values of each property from the first Primitives match, and sets the values of the corresponding parameters to match. This means that changing any parameter’s control menu to Set or Create mode will set the property to its current value, making it easier to apply changes to an existing value rather than setting a brand new value.

Create Primitives

This section only appears when the node is creating primitives.

For example:

  • If you want to create a new cube primitive at /world/objects/cube1 on an empty stage: Set Primitive Specifier to "Define", and the Parent Primitive Type to "Xform".

  • If you want to override the radius of a sphere at /world/objects/sphere1: Set Primitive Specifier to "Over", and the Parent Primitive Type to None. This makes sure the primitive types of any existing ancestor prims are not be modified by this node.

Primitive Count

The number of primitives to create.

Primitive Kind

Set all created prims to have this kind.

Parent Primitive Type

If any parents of a path in Primitive paths do not exist, this node will automatically create them. In this case, it will create parent nodes of this type.

Primitive Specifier

The USD operator to use when creating the new prims.


Authors a completely new prim. Use this if you want to create a brand new prim or replace an existing prim.


Authors an override of an existing prim. Attributes not explicitly authored on this prim will get their values from the existing prim on the lower layer.


Define a primitive class. This is usually not necessary unless you are doing deep USD magic.



A list of paths to UsdRenderProduct prims, representing the rendered outputs. If you don’t specify any explicit products, the renderer should by default output an RGB image using the render settings on this node, to a default display or image name.

Included Purposes

A list of purpose tokens (such as render (final render), proxy, and guide, from UsdGeomImageable). Only geometry with its purpose set to one of these tokens will be sent to the renderer. The default purpose is the purpose for all geometry that doesn’t have an explicitly set purpose, so you will usually want to include it.

(This cannot be specified per-product because it is a statement of which geometry is present.)

Material Binding Purposes

A list of material purpose tokens to consider when resolving material bindings.


Path to a USD camera (UsdGeomCamera) prim to render the scene from.


The horizontal and vertical size of the output image, in pixels.

Instantaneous Shutter

Override the camera’s Shutter close parameter to be equal to its Shutter open time, to produce a zero-width shutter interval. This is a convenient way to disable motion blur.

Aspect Ratio Conform Policy

What to do if the aspect ratio of the output image (Resolution width divided by height) doesn’t match the aspect ratio of the camera aperture (controlled by attributes on the camera). This allows a standard renderer to do something reasonable when you switch between cameras.

Expand Aperture

If necessary, expand the camera aperture to match the image.

Crop Aperture

If necessary, crop the camera aperture to match the image.

Adjust Aperture Width

If necessary, change the camera aperture width to match the image.

Adjust Aperture Height

If necessary, change the camera aperture height to match the image.

Adjust Pixel Aspect Ratio

Change the aspect ratio of the image to match the camera.

Data Window NDC

Directs the renderer to only render within this window of the entire output image. The rectangle is specified in as minX, minY, maxX, maxY, in a normalized range 0 to 1. Coordinates 0, 0 are the bottom left and 1, 1 are the top right. The default window 0, 0, 1, 1 covers the entire image (that is, is not cropped).

You can use this window to temporarily crop the render to a smaller region, for testing purposes.

You can also specify negative values and/or values greater than 1 to reveal overscan data.

Pixels are only rendered if they are fully inside the window.

The normalized coordinates map to the image after any adjustments by the Aspect ratio conform policy.

Pixel Aspect Ratio

The aspect ratio (width/height) of image pixels (not the image itself). The default is 1.0, indicating square pixels.


Show Alfred Progress

As rendering progresses, print out progress using the Alfred progress format. For multi-frame renders, this progress will be cumulative across frames (i.e. if there are 4 frames, percent complete will be 25% after the first frame finishes).

IPR Inc Random

When rendering to the Solaris viewport, this causes each render to start with a new random seed.

IPR Bucket Size

The initial bucket size for IPR rendering.

IPR Reserve Threads

When rendering in IPR mode, reserve this number of threads for other Houdini tasks.

Cache Limit

Whether to use a fixed size cache (karma:global:cachesize) or whether to use a proportion of physical memory (karma:global:cacheratio)

Cache Memory Ratio

The proportion of physical memory Karma will use for its unified cache.

For example, with the default vm_cacheratio of 0.25 and 16 Gb of physical memory, Karma will use 4 Gb for its unified cache.

The unified cache stores dynamic, unloadable data used by the render including the following:

  • 2D .rat texture tiles

  • 3D .i3d texture tiles

  • 3D .pc point cloud pages (when not preloaded into memory)

Note: This value is only used for off-line rendering, not IPR.

Cache Size (MB)

An explicit memory limit for the unified shading cache. This is deprecated in favor of using the Cache Memory Ratio.

Note: This value is only used for off-line rendering, not IPR.

Pixel Samples

The number of ray-samples sent through each pixel. More samples will result in a less noisy image.

Ray Bias

The ray-bias used for secondary rays.

Screendoor Limit

Disable Lighting

Disable all lighting and material evaluation, using only the display color to shade primitives.

Headlight AO Samples

When rendering in headlight mode, perform this many ambient occlusion samples per shade.

Headlight AO Distance

When rendering in headlight mode with ambient occlusion shading, this distance is used for occlusion testing. Smaller values will result in faster, but less accurate shading.

Headlight Fog Color

The color of the depthcue fog for disabled lighting.

Light Sampling Mode

Whether Karma should perform uniform sampling of lights or whether rendering should use the light tree. The light tree can be significantly faster for scenes that have large numbers of lights.

Light Sampling Quality

This is a global control to improve sampling quality for all lights. This acts as a multiplier on the individual light quality controls. Increasing the quality will improve direct light sampling as well as shadows/occlusion.

Color Limit

The maximum value a shading sample is allowed to contribute to an LPE image plane to reduce appearance of "fireflies" caused by undersampling of extremely bright light sources. Note that reducing this value can result in an overall reduction in the amount of light in your scene


The rendering camera.

Offscreen Quality

This parameter controls the shading quality scale factor for geometry that is not directly visible to the camera. For geometry that is outside the field of view (ie. visible only to secondary rays), karma will smoothly reduce the shading quality based on the angle between the geometry and the edge of the viewing frustum. Smaller values can increase performance particularly in scenes where the camera is within the displacement bound of nearby geometry, where it permits the hidden primitives to be diced more coarsely than those that are directly visible.

Image Filters

Image filters post-process the filtered pixels to produce the final image.

This parameter specifies a list of filters. These filters are specified as a JSON list.

Sample Filter

Sample filters are used to modify samples before they are sent to pixel filters.

This parameter specifies a list of filters. These filters are specified as a JSON list.

Pixel Oracle

When rendering, a Pixel Oracle tells karma which pixels need additional sampling and which pixels are converged.

This parameter tells karma which oracle to use.

Random Seed

This is the random seed to use for the render.

Abort Missing Texture

Enabling this option will cause karma to abort the render with an error if it encounters a missing texture map.

Export Components

A whitespace-separated list of shading component names that will be computed for export. If you have defined new component labels in your materials, these can be added to the list so that they are exported for per-component export planes. If you are not using some components, remove them from the list to improve render efficiency.

PBR light exports assume that this list is complete - that is, all components created by shaders are listed. If there are unlisted components, light exports may be missing illumination from these components.

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 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 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 a collection using selected prims.

  • Collection

    Creates/edits collections using primitive patterns.

  • 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 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.

  • 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.

  • 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.

  • 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 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).

  • 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.

  • 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

  • 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.