Houdini 20.0 Nodes Render nodes

Labs Niagara ROP render node

Export point caches to be used with Unreal’s Niagara particle system.

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The Niagara ROP exports static or animated point caches to a custom json format that can be read by the Houdini Niagara plugin for Unreal. This could be used for driving particle emitters in Niagara, or creating complex simulations in Houdini that can be run in realtime through Niagara.


The Niagara ROP works with the latest version of the Houdini Niagara plugin for Unreal 4.25 and onwards.

To install the plugin please refer to the Houdini Niagara GitHub page.

You can find the latest information and links to sample files on the Houdini Niagara Updates forum thread.

Houdini to Niagara Workflow



ROP Settings

Frame Range / Time Mode

Controls whether this render node outputs the current frame (Render any frame) or the image sequence specified in the Start/End/Inc parameters (Render Frame Range).

Render Frame Range (strict) will render frames START to END when it is rendered, but will not allow frames outside this range to be rendered at all. Render Frame Range will allow outside frames to be rendered. This is used in conjunction with render dependencies. It also affects the behavior of the 'Override Frame Range' in the Render Control dialog.

Two possible cases where you'd want the strict behavior:

  • A 60 frame walk cycle written out to a geo, but part of a larger ROP net to render out a larger frame range.

  • A texture loop from 1-20.

Otherwise, you will usually set this to non-strict.

Render Current Frame

Renders a single frame, based on the value in the playbar or the frame that is requested by a connected output render node.

Render Frame Range

Renders a sequence of frames. If an output render node is connected, this range is generally ignored in favor of frames requested by the output render node.

Render Frame Range (Strict)

Renders a sequence of frames. If an output render node is connected, this range restricts its requested frames to this frame range.

Single Frame With 'time' Attribute

Renders a single frame, with the time attribute set to 0 be default. Ideal for use with point clouds that represent impact points from rbd simulations.


Specifies the range of frames to render (start frame, end frame, and increment). All values may be floating point values. The range is inclusive.

These parameters determine the values of the local variables for the output driver.

For example, if the parameters are set to:






0.5 |

…there will be 4 frames rendered (10.5, 11, 11.5, and 12), so $NRENDER will have a value of 4. $N will have the following values at each frame:











Render with Take

The output driver will switch to this take before rendering and then restore the current take when rendering is done.


use chs("take") to use this value in other parameters. See the chs expression function for more information.

Output Path

The output file should be of the type, .hbsjon, .hjson or .hcsv (this format has been deprecated).

hbjson - is a binary json file format. Ideal for faster export and import, and smaller file sizes.

hjson - an ascii json file format. Ideal for debugging the results.


Number of Renames

Rename any point attribute to match naming conventions in Unreal.

Overwrite Existing Attributes

If the specified destination attribute already exists, it is deleted and replaced by the source attribute.

Keep Attributes

A space separated list of the attributes that will be written out.

Cast Attributes

If necessary, you can cast an attribute to a type that matches the compatible types in Unreal.

Clamp Attributes That Are Outside Type Range

When an attribute is cast to a different type the value might be outside of the range of the target type. If this option is selected, the value will be clamped to the type range. If this option is not selected and an out of range value is encountered, an exception will be raised while writing out the file. Only applicable to binary format output (.hbjson)


Export Current Frame As time == 0

Overrides the time attribute to always equal 0. Disabling this will create an age attribute for the points that is relative to the current time in the playbar.

Export Start Frame As time == 0

Off by default. If the start frame of your frame range is not 1, but rather something like 1001, turn this on to use your start frame as time == 0.

Render nodes

  • Agent

    This output operator is used to write agent definition files.

  • Alembic

    Exports the scene to an Alembic archive. Alembic is a common exchange format for moving geometry and animation between different 3D software packages.

  • Archive Generator

    Generates disk-based archives which can be used by either mantra or RIB renderers.

  • Bake Animation

    Bakes animation from object transforms and CHOP overrides.

  • Bake Texture

    Generates a texture map from one or more objects' rendered appearance.

  • Batch

    Renders the input ROP in a single batch job.

  • Channel

    The Channel output operator generates clip files from a particular CHOP.

  • Composite

    Renders images from a compositing network.

  • DSM Merge

    Merges two or more deep shadow/camera map files.

  • Dem Bones Skinning Converter

    Converts any non-changing topology deforming mesh sequence into a bone-based animation.

  • Dynamics

    Saves the state of a DOP network simulation into files.

  • Fetch

    Makes a dependency link to a ROP in a different network.

  • Filmbox FBX

    Exports entire scenes to FBX files.

  • Filmbox FBX Animation

    Export animation from geometry-based skeleton to an FBX file.

  • Filmbox FBX Character

    Export a skinned character with geometry-based skeleton to an FBX file.

  • Frame Container

    Prevents frame dependency changes in the contained nodes from affecting its inputs.

  • Frame Depedency

    Allows an output frame to depend on one or more input frames.

  • GLTF Character

  • Geometry

    Generates geometry files from a SOP or DOP network.

  • Geometry Raw

    Generates raw binary files from a SOP or DOP network.

  • HQueue Render

    HQueue, or Houdini Queue, is a distributed job scheduling system.

  • HQueue Simulation

    HQueue, or Houdini Queue, is a distributed job scheduling system.

  • Hair Card Texture

    Renders hair textures for use on hair cards.

  • Karma

    Renders non-USD scenes using Houdini’s Karma renderer.

  • Labs 3D Facebook Image

    Quickly render a 3D scene to a 2.5D image that can be uploaded to Facebook.

  • Labs Flipbook Textures

    Renders, composites, and exports flipbook textures.

  • Labs JSON Exporter

    Export geometry attibutes to a JSON file.

  • Labs Marmoset Export

    The Marmoset Export ROP allows you to quickly generate an mview inside Houdini

  • Labs Niagara ROP

    Export point caches to be used with Unreal’s Niagara particle system.

  • Labs Sketchfab

    Uploads geometry to Sketchfab

  • Labs Vertex Animation Textures

    Exports a mesh and a set of textures to be used with a shader for complex real-time effects, such as: soft-body deformation, rigid-body dynamics, dynamically remeshed geometries, and particle sprites.

  • MDD Point Cache

    This output operator is used to write an MDD animation file.

  • Mantra

    Renders the scene using Houdini’s standard mantra renderer and generates IFD files.

  • Mantra Archive

    Generates disk-based archives which can be used by mantra.

  • Merge

    Merges several render dependencies into one.

  • Net Barrier

    Blocks the ROP network until synchronization occurs.

  • Null

    Does nothing.

  • OpenGL

    Render an image using the hardware-accelerated 3D viewport renderer.

  • Pre Post

    Renders ROPs before and after a main job.

  • Shell

    Runs an external command.

  • Subnetwork

    The SubNetwork output operator provides an easy way to manage large number of output operators.

  • Switch

    Renders one of several inputs.

  • Tractor

    Tractor is a program shipped out with Pixar’s distribution of RenderMan.

  • USD

    Renders a LOP network out to one or more USD files. This node is available as render node or as a LOP.

  • USD Render

    Renders an output image from the stage generated by a LOP network.

  • USD Stitch

    Merges USD files representing individual frames by composing them.

  • USD Stitch Clips

    Merges multiple value clips representing individual frames.

  • USD Zip

    Assembles USDZ archive files from existing USD files.

  • Wedge

    Re-renders the same ROP multiple times with different settings

  • Wren

    This output operator is used to drive the Wren rendering program.

  • glTF