Houdini 19.5 Nodes LOP nodes

Edit Properties

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

On this page
Since 17.0

Overview

By itself, this nodes doesn’t do anything. You must add spare parameters corresponding to attributes on prims in the scene graph tree. Then when you edit the spare parameters, the node authors equivalent changes to the referenced attributes.

How to

  1. In Primitives, set the path(s) to the primitive(s) you want to the edit.

  2. Click Edit Properties.

    This opens the Edit Parameter Interface window with the From USD tab selected in the source pane on the left.

  3. Find the prim you want to edit (or a prim of the same type). Click the plus button to expand it to show the properties as child items.

    (The specific primitive you drag the property out of does not matter. It doesn’t affect which primitives this node changes. The node only uses the property name. This node always and only edits the prims selected in Primitives.)

  4. Drag the property from the source tree on the left into the Existing parameters tree in the center. Drop it below “Primitive Path (primpath)” and above “Action (createprims)”.

    Dropping the item in the parameter tree will actually create two parameters: a “control” pop-up menu containing options for how to author the property, and a parameter for setting the parameter value. (For example, if you drop the size attribute from a Cube primitive, it will create both size and size_control.)

Control pop-up menus

The pop-up menu to the left of each parameter controls how the node authors the attribute:

Pop-up menu item

Meaning

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.

Block

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.)

Disconnect Input

Deletes the attribute input connection to its source. Input connections take precedence over attribute values, so disconnecting an input allows the attribute value to take effect.

Do Nothing

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

Tips

  • For each prim selected in the Primitives parameter, the node will look for properties with the same names as the properties you created spare parameters for. This node will only author properties on selected primitives if it has a matching parameter, and the control menu is set to write to the property.

    So technically you have a single Edit Properties node that applies to prims of many different types, with a long list of parameters where each parameter applies to only a few of the selected prims. You may want to avoid doing this, however, since it might be confusing to other people trying to understand your network.

  • If you make a useful editing interface you want to share, you can turn an Edit Properties node instance into a LOP digital asset. Right-click the node in the network editor and choose Create digital asset. The spare parameters become the digital asset’s parameter interface, and the node functions the same way, but as an asset that can be shared and versioned.

    Note

    Once you convert an Edit Properties node to a digital asset, you can’t add more spare parameters to an instance of the asset edit more properties. The asset only looks at its “baked in” parameters, and ignores spare parameters.

  • The USD attribute name is stored on the spare parameters as tag data.

  • In any parameter setting an attribute value, you can use the following local variables:

    @numprim ($NPRIM is deprecated)

    The total number of primitives being modified by this node.

    @prim ($PRIM is deprecated)

    Index of the primitive being modified. This value goes from 0 to @numprim-1.

    @primpath ($PRIMPATH is deprecated)

    The path of the primitive being modified.

  • Custom properties that are commonly added to primitives but which are not part of any USD schema can be specified in a file named EditPropertiesCustom.usda anywhere in your HOUDINI_PATH. This file describes a USD stage using any standard USD composition rules. The /custom primitive and all of its descendant primitives and their properties will appear in the Edit Parameter Interface window on the USD tab, under the Custom Properties branch.

  • A node of this type or any digital assets derived from this node type can also optionally have parameters that validate the node’s parameters and trigger warnings or errors if requirements are not met. As an example of this technique, the Render Settings LOP has validation parameter that trigger a warning if the node is asked to create a new primitive that is not inside the /Render branch of the scene graph hierarchy (as mandated by the USD Render Setting specification). To use this feature, two parameters are used:

    errorseverity

    An ordered menu indicating whether the validation message should be presented as a Message, Warning, or Error (using the values 0, 1, and 2 respectively).

    errormsg

    The message to be presented to the user. If this parameter returns an empty string, no message is added to the node.

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. The Edit mode has two variations. Edit will not modify primitives which have a houdini:editable attribute set to false. Force edit will modify a primitive regardless of the existence or value of this attribute. This attribute can be set on a primitive using the Configure Primitives LOP.

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

In addition to that, any connectable USD attributes (i.e., the ones in the inputs: namespace) will have menu items that allow disconnecting them from their sources.

Pop-up menu item

Meaning

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.

Block

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.)

Disconnect Input

Deletes the attribute input connection to its source. Input connections take precedence over attribute values, so disconnecting an input allows the attribute value to take effect.

Do Nothing

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

Parameters

Sampling Behavior

Cooking this node can generate many USD time samples, rather than just a single time sample at the current time. This can be equivalent to having a Cache LOP following this node, but it will evaluate much faster, and does not cache data from any other nodes. This allows animated data to be authored to USD without introducing a node time dependency which would then cause all following nodes to also be time dependent. This can vastly improve playback performance of some LOP Networks.

In all sampling modes, if a parameter on this node does not vary with time, and does not rely on other time sampled data from the stage, only a single default value will be generated in USD for the corresponding attribute. USD time samples are only generated for parameters that may vary over time.

Sample Current Frame

A single time sample will be generated for the current time.

Sample Frame Range If Input Is Not Time Dependent

If the input to this node is time dependent, this node behaves as if it is in Sample current frame mode. Otherwise it behaves as if it is in Sample frame range mode.

Sample Frame Range

The Start/End/Inc parameter is used to generate multiple times at which this node’s parameters are evaluated, and a USD time sample is created for each attribute at each one of these times.

Start/End/Inc

When the Sampling behavior is Sample frame range, this parameter controls the number and spacing of base time samples to be generated by this node. The default values of this parameter are @ropstart, @ropend, and @ropinc. These values correspond to the start, end, and step size of the global Houdini animation settings when interacting with Houdini. When using a ROP node to generate a range of frames, these values correspond to the start, end, and increment values specified on the ROP node being executed. This default ensures that a USD file written to disk will contain time samples for exactly the frame range requested by the ROP (regardless of the Houdini animation settings).

Subframe Sampling

For each primary sample generated by this node, these parameters can cuase additional samples to be generated aroudn that primary sample time. This is most often used to ensure that accurate data exists at exactly the camera shutter open and close times, as well as at the primary sample time.

Shutter

Controls the method used to specify the shutter open and close times relative to the primary sample times.

Specify Manually

The Shutter open/close parameter values provide exact offset values relative to the primary sample time.

Use Camera Prim

The Camera prim parameter provides the scene graph path of a camera primitive from which the shutter open and close times are extracted to provide the offset values relative to the primary time sample.

Shutter Open/Close

When the Shutter mode is Specify Manually, these two offset values are added to the primary sample time to indicate the shutter open and close times. The open time should be less than or equal to zero, and the close time should be greater than or equal to zero.

Camera Prim

Scene graph path of a camera prim on the input node’s stage. The shutter open and close attribute values are read from this primitive.

Samples

The number of subframe samples to create for each primary sample. These samples are evenly distributed between the shutter open and close times. Note that such an even distribution may or may not create a sample at exactly the primary sample time.

Always Include Frame Sample

Enable this option to force a sample to be created at exactly the primary sample time. If the Samples values together with the shutter open and close times already place a sample at the primary sample time, turning on this option will have no effect. Otherwise, this option will cause an addition sample to be added. This means that the actual number of samples per primary sample may in fact be one more than the number specified in the Samples parameter.

Edit Properties

Opens the Edit Parameter Interface window with the From USD tab selected in the source pane on the left.

Action

Whether this node should create new prims, or edit existing prims. In addition, the Force Edit option can be chosen to cause this node to ignore the houdini:editable attribute on prims, and always edit the specified attributes. This is in contrast to the Edit mode which will trigger a warning and not set attributes on prims with the houdini:editable attribute set to false.

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).

Primitives

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.

Primitive Specifier

The USD operator to use when creating the new prims.

Define

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

Over

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.

Class

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

Class Ancestor

If the Specifier is Define or Over, this parameter will cause some ancestor primitives to be authored with a specifier of Class. This makes it easy to create an Over or Define within a Class without having to use two separate nodes. When the Specifier is Class, this parameter is disabled because the entire primitive hierarchy is already authored as Class primitives.

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.

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.

  • 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.

  • 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.

  • Coordinate System

    Define named coordinate systems used in shaders.

  • 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 Properties

    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 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

    Summary goes here.

  • Houdini Procedural: Hair

    Houdini Hair Procedural for Solaris.

  • 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

    Create multiple render products sharing common settings.

  • Isolate Scene

    Work in masked areas of the stage.

  • Karma

    Renders the USD scene using Houdini’s Karma renderer.

  • Karma Cryptomatte

    Setup Cryptomatte AOVs for Karma.

  • Karma Fog Box

    Creates a constant volume within a box.

  • Karma Ocean

    Render an ocean with the Karma CPU renderer.

  • 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 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.

  • 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 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.

  • 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.

  • 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 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.

  • 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.

  • 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.

  • 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

  • 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.