Houdini 18.0 Nodes LOP nodes

Modify Point Instances

Modify point transforms and property values for individual point instances.

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Overview

This node can modify point instance transforms and properties in a few ways:

  • You can set transform and property values using parameters and expressions.

  • You can compute property values using VEX snippets.

  • You can create a SOP network inside this node (or elsewhere in the Houdini node hierarchy) that generates a point cloud where each point corresponds to an instance and SOP attributes on the points correspond to properties. See point cloud editing below.

This node is useful, for example, if you wnat to transform instances from the results of an RBD simulation. At the same time, you could use property editing to update the velocities and angularVelocities attributes.

Point cloud editing

This node lets you build a SOP network to modify instance transforms and properties by processing geometry that represents the instances. Points in the geometry correspond to instances, and the SOP attributes on the points correspond to instance properties.

You can set the node to get transforms and/or individual properties by processing a SOP network.

  • If you choose "Internal SOP", the node uses the nodes you build in the SOP subnet inside this node.

    In this mode, the points are created for you and fed through the network (connect the output of Sub-Network Input #1 to the first node in your processing network).

    Each point has a path SOP attribute set to the scene graph path of the instancer.

  • If you choose "External SOP", you can specify a SOP network anywhere in the Houdini node hierarchy. However, the network must generate the points with the proper attributes somehow.

    • The points must have a path SOP attribute set to the scene graph path of the instancer.

    • By default, the node will try to match points up with instances by matching point numbers to instance indices. This will probably only work you are processing every instance in a single instancer. Otherwise, you should turn on Match by ID and set the id SOP attribute on each point to the index of the corresponding instance.

  • SOP attribute names and types must match the corresponding property names set up on this node (although some names can be remapped automatically, see Tips below).

  • Beside the point position (P), SOP point instancing attributes, such as scale, pscale, orient, N, and up, are translated back into the instance transform. See instancing attributes for more information.

Tips and notes

  • If you try to edit the USD velocities, angularVelocities, and/or acceleration attributes, the node will show an option to remap from the corresponding SOP attributes (v, w, and accel).

  • In VEX snippets, you can use @ variable names containing colons (:). This makes it easier to automatically bind certain USD attribute names (for example i@primvars:foo). (These names are not normally legal in names in VEX source code. The node automatically encodes these kinds of names when used in a snippet.)

Parameters

Point instances

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].

Transform

Edit Transform

Author new transforms on the selected instances. If this is off, the node will not override the existing transforms.

Source

How to compute the transform for each selected instance. "Internal SOP" uses the SOP subnet inside this node to process points representing the instances. "External SOP" uses an external SOP network that must generate points representing the instances from scratch. (See point cloud editing above.) "Uniform" gets the transform from parameters (which can be driven by expressions).

Match By ID

When Source is "External SOP" and this is on, the node looks for id SOP attributes on the generated points. The id should be the index of the corresponding instance. (When this is off, the node matches point numbers to instance indices, which only works if you process every instance in a single instancer.)

SOP Path

When Source is "External SOP", the node path to the geometry node to cook to get the generated points. Each point in the output should correspond to one of the selected instances.

Group

When Source is "External SOP", if this is not blank, only consider points in this point group from the geometry node’s output.

Transform order

The order in which Houdini applies translates, rotates, and scales, and the order in which it applies rotation.

Translate

Movement amount along XYZ axes.

Rotate

Degrees rotation around XYZ axes.

Scale

Non-uniform scaling along XYZ axes.

Uniform scale

Scales the object uniformly along all three axes.

Shear

Amount of shearing in the XY plane, the XZ plane, and the YZ plane.

Pivot Transform

Pivot translate

Moves the local origin of the object.

Pivot rotate

Rotates the local origin of the object after translation.

Properties

Get Properties

Click to automatically fill in the Properties multi-parm. (The node assumes any array attribute on the instancer with an array length the same as the number of instances contains per-instance values.) If you want to re-do this, click Clear in the multi-parm, then click this button again.

Enable

For each property, the node only computes a new value if this is checked.

Name

The name of the property to edit or create. You can choose an existing attribute from the pop-up menu to the right of this field. (The node assumes any array attribute on the instancer with an array length the same as the number of instances contains per-instance values.)

Type

The USD type of the attribute to create/edit. If you chose the Name from the pop-up list, this is automatically set to the correct type.

Source

How to compute the attribute value for each selected instance. "Internal SOP" uses the SOP subnet inside this node to process points representing the instances. "External SOP" uses an external SOP network that must generate points representing the indices from scratch. (See point cloud editing above.) "Uniform" gets the value from a parameter (which can be driven by expressions).

Use Snippet

When Source is "Uniform", get the value for each instance by evaluating a VEX snippet. The snippet should write the value to the value variable. You can use the variables typically available to an Attribute Wrangle SOP. @ptnum is the index of the current point. You can use npoints(0) to get the total number of points. You can use @Frame and @Time to make the snippet time-dependent.

Value

When Source is "Uniform", the value to set the attribute to for each instance. (This can be driven by an expression.)

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