Houdini 18.5 Nodes LOP nodes

Mask from Bounds

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

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Since 18.5


You can use the primvar created by this node as a "mask" to select prims for other operations, and/or to create a collection of the prims "inside" the bounding volume.

This node is designed to work with polygonal meshes. For parametric shapes such as the USD Sphere and Cube prims, the node will just report 1.0 if the shape’s origin inside, and 0.0 if the origin is outside.

Tips and notes

  • When Ignore primitives outside bounds is on, the node does not author the primvar on selected prims outside the bounding box. This is faster than authoring 0.0 values.

  • The node can create a primvar containing a fractional value between 0.0 and 1.0 indicating how much of the prim was inside the bounding sphere.

  • The node can also create a property (calculated the same way as a Constant primvar), and a USD collection of the prims that are "inside".

  • You can reverse the inside/outside values with the Invert Bounds parameter.

  • You can blur the boundary between inside and outside with the Feather parameter. You can also shrink or grow the boundary without blurring using the Offset parameter.


Input Stage

The stage that contains the primitives to be affected by this LOP node.

Stage Containing Bounding Primitives

An optional stage containing the bounding primitives. (Only works when selecting by bounding primitives/geometry.)



What type of primitives to add the primvar to.

Point Instances

Specify a list of individual instances using /path[instance_index] syntax.

Primitives/Native Instances

Specify a list of prim paths, including instanceable prims.


A space-separated list of instances, using /path[instance_index] syntax (for example, /geometry/instancer[0] /geometry/instancer[1]). The index within the square brackets can be an inclusive range, for example /geometry/instancer[4-7]. You can refer to instances of nested instancers using multiple indexes, for example /geometry/instancer[2][7].


When Type is Primitives/Native Instances, a space-separated list of prim paths/patterns to add the primvar to.


Bounding Type

Choose between a box, sphere, or use external geometry prims as the boundary.


When Bounding Type is Box or Sphere, the size of the bounding volume.


Moves the bounding volume.


Rotation of the bounding volume.


When Bounding Type is Primitives, scales the bounding volume created from the external geometry.

Pivot Translate

When Bounding Type is Primitives, moves the pivot for rotating ans scaling the bounding volume created from the external geometry.

Primitive Source

When Bounding Type is Primitives, whether to get bounding primitives from the stage connected to this node’s first input or the second input.

Bounding Primitives

When Bounding Type is Primitives, a space-separated list of prim paths/patterns to use to define the bounding volume.


Creates a soft falloff between values "inside" and "outside" the bounding shape. Negative values apply the falloff inside the boundary, positive values apply falloff outside the boundary. The greater the difference from 0, the larger the falloff radius.

When this is non-zero, primvar values on points/faces (0.0 or 1.0) are multiplied by a linear gradient from 1 to 0 between the bounds and this distance.


Shrinks (negative values) or grows (positive values) the boundary shape.

Invert Bounds

Reverses the meaning of the primvar values, so 0.0 indicates inside and 1.0 indicates outside.

Ignore Primitives Outside Bounds

When this on, the node does not author the primvar on selected prims outside the bounding box. This is faster than authoring 0.0 values.


Add Primvar

Adds a primvar indicating how much of each prim is inside the bounding volume.


The name of the primvar to create.


Specify the data type for the primvar. The default is float. If you choose boolean or a number type that does not support decimals, features such as Feather will have no effect. This should be boolean, int, float, or double. Most other types won’t work (the values will all be zero).


This controls the "level" at which the node creates the primvar.


Calculates one inside/outside value for the entire mesh, by combining the values for each point using the Method below.


Sets a 1.0 or 0.0 on each face indicating whether the face is inside or outside the bounding volume.


Sets a 1.0 or 0.0 on each point.

Face Varying

Sets a 1.0 or 0.0 on each polygon corner.

Point/face values may be between 1.0 and 0.0 if you use the Feather parameter to soften the edges of the bounding volume.


In USD, Constant interpolation is equivalent to a Houdini detail attribute. Uniform interpolation is equivalent to a Houdini primitive attribute. FaceVarying interpolation is equivalent to a Houdini vertex attribute. And Vertex interpolation is (confusingly) equivalent to a Houdini point attribute.


When Interpolation is Constant, this is the node combines the point values to compute an overall value for the entire mesh. The default is Average, which is the most useful method.


Use the highest point value.


Use the lowest point value.


Use the mean (average) of all point values across the mesh.

First Match

Use the value of the first point.

Last Match

Use the value of the last point.


Don’t use point values, instead calculate if the mesh’s centroid is inside or outside.


The value to use for "inside". The default is 1.0.

Weights and Collection

Add Weights

Creates a property (not a primvar) on the prims, set to the same value as would be computed for a Constant primvar, using the Method below.

Weight Name

The name of the weight property to create.


See above.

Add Collection

Creates a new collection containing the prims that have a non-zero "weight" attribute. This is only available when Add Weights is on.

Collection Name

The name of the collection to add the primitives to. This is always created on the /collections prim (this node creates /collections if it doesn’t already exist).

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 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.

  • 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.

  • 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.