Houdini 20.0


Properties let you set up flexible and powerful hierarchies of rendering, shading, lighting, and camera parameters.

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Properties supply options to the renderer, such as camera parameters, light positions and parameters, shader names, and so on.

Many properties are renderer-specific, though some properties that are common to all renderers, such as camera focal length, will be the same for all renderers and automatically translated into the appropriate renderer option by the properties system. Basically, the properties system maintains a list of properties the renderer knows about, and list of properties defined in Houdini, and maps between them.

The new properties-aware mantra, RenderMan, Alfred, and other render driver nodes use Python scripts at render time to translate the scene data and properties sent from Houdini into IFD (for mantra) or RIB. The combination of property inheritance and scriptability makes the property system extremely flexible.


The key feature of properties is inheritance. You can properties at any of several levels, and properties at more specific levels override properties at more general levels.

The inheritance order is:

  • Renderer defaults – if you don’t specify a property, the renderer uses its built-in (or configured) default value.

  • Output driver

  • Material

  • Objects

  • Primitives – See per-primitive properties below.

At each level you can specify properties specific to that level. Any properties you define at higher levels are inherited by lower levels, so you can specify a default shader at the output driver level. Even though the shader definition is meaningless on an output driver, it’s inherited as the default by all objects rendered through that driver.

Properties at a lower level override properties at a higher level, so for example you can specify a surface shader on the object, and override it per-primitive.

In practice, inheritance is somewhat limited by the fact that, for convenience, Houdini automatically adds common properties, such as light mask and default shader, to every object created, so every object will override any light mask or default shader you add higher up the chain (such as on the camera or output driver). However, a TD can edit the list of default properties added to new objects. See advanced uses below.

Editing, adding or removing properties

Technically, properties are spare parameters. You can add them to a node using the Edit Parameter Interface window.

See the section on Inherence above for the different “levels” at which you can add properties.

  1. Select the node you want to edit.

  2. In the parameter editor, open the Gear menu and choose Edit Rendering Parameters.

See the Edit Parameter Interface window help for information on how to add and remove properties.

Once you've added render properties you can edit their values in the parameter editor.

You can attach them to renderable nodes (such as objects). You can also use a Properties SHOP to hold properties and refer to it from renderable objects.

Houdini decides what default properties to create on new objects. There are usually more properties available than just the defaults. You can add properties, or remove properties to clean up the interface, allow inheritance, or save memory.

Per-primitive properties

  • The Properties shader lets you attach arbitrary properties. Houdini will apply the shader’s properties to any object or primitive that uses the shader.

  • Use the Material Palette to apply shaders per-primitive. The Material node replaces the old Shader surface node.


The properties system enables many useful and powerful scenarios:

  • Override the object shader at the primitive level.

    • To set properties on primitives, create a Properties SHOP with just the properties you care about, and assign it as to the primitives you want to affect. Other primitive inherit their properties from the object.

    • Per-primitive shaders and light mask.

    • Per-primitive displacement bounds! This can be a huge performance boost: only increase the displacement bounds property on highly displaced primitives.

  • Point instancing

    • You can bind properties to points, and when geometry is instanced onto the point, the point’s properties are inherited by the instanced geometry.

    • Scatter points that will be instanced as an asteroid field. You can set properties on the individual points to control the look of the instanced geometry.

    • Use a procedural shader to instance geometry onto points, with properties on the points controlling the operation of the shader.


  • Define properties at the highest level that’s practical. The lower the level at which you set things, the more places you’ll have to edit when you want to change something.

Advanced uses

  • You can bypass properties (that is, have Houdini pretend the property isn’t present on a node) using a flag of the opparm HScript command.

  • The Python scripts responsible for generating IFD/RIB are in $HFS/Houdini/soho.

  • The dialog scripts in $HFS/Houdini/soho/parameters control the list of all available properties, as well as what properties are added to new objects.

    Each file includes a parameters/scriptname.user.ds file. If you have such a file in your Houdini path, it will get imported, which gives you the opportunity to override parameter definitions and define symbols which control the operation of the parent scripts.


Houdini 20.0

Getting started

Using Houdini

  • Geometry

    How Houdini represents geometry and how to create and edit it.

  • Copying and instancing

    How to use copies (real geometry) and instances (loaded or created at render time).

  • Animation

    How to create and keyframe animation in Houdini.

  • Digital assets

    Digital assets let you create reusable nodes and tools from existing networks.

  • Import and export

    How to get scene, object, and other data in and out of Houdini.

  • Executing tasks with PDG/TOPs

    How to define dependencies and schedule tasks using TOP networks.

  • MPlay viewer

    Using Houdini’s stand-alone image viewer.

Character FX

  • Character

    How to rig and animate characters in Houdini.

  • Crowd simulations

    How to create and simulate crowds of characters in Houdini.

  • Muscles and tissue

    How to create and simulate muscles, tissue, and skin in Houdini.

  • Hair and fur

    How to create, style, and add dynamics to hair and fur.

  • Feathers

    How to create highly realistic and detailed feathers for your characters.


  • Dynamics

    How to use Houdini’s dynamics networks to create simulations.

  • Vellum

    Vellum uses a Position Based Dynamics approach to cloth, hair, grains, fluids, and softbody objects.

  • Pyro

    How to simulate smoke, fire, and explosions.

  • Fluids

    How to set up fluid and ocean simulations.

  • Oceans and water surfaces

    How to set up ocean and water surface simulations.

  • Destruction

    How to break different types of materials.

  • Grains

    How to simulate grainy materials (such as sand).

  • Particles

    How to create particle simulations.

  • Finite elements

    How to create and simulate deformable objects


  • OBJ - Object nodes

    Object nodes represent objects in the scene, such as character parts, geometry objects, lights, cameras, and so on.

  • SOP - Geometry nodes

    Geometry nodes live inside Geo objects and generate geometry.

  • DOP - Dynamics nodes

    Dynamics nodes set up the conditions and rules for dynamics simulations.

  • VOP - Shader nodes

    VOP nodes let you define a program (such as a shader) by connecting nodes together. Houdini then compiles the node network into executable VEX code.

  • LOP - USD nodes

    LOP nodes generate USD describing characters, props, lighting, and rendering.

  • ROP - Render nodes

    Render nodes either render the scene or set up render dependency networks.

  • CHOP - Channel nodes

    Channel nodes create, filter, and manipulate channel data.

  • COP2 - Compositing nodes

    Composite nodes create, filter, and manipulate image data.

  • TOP - Task nodes

    TOP nodes define a workflow where data is fed into the network, turned into work items and manipulated by different nodes. Many nodes represent external processes that can be run on the local machine or a server farm.

Lighting, rendering, and compositing

  • Solaris

    Solaris is the umbrella name for Houdini’s scene building, layout, lighting, and rendering tools based on the Universal Scene Description (USD) framework.

  • Rendering

    How to render images and animation from the 3D scene.

  • HQueue

    HQueue is Houdini’s free distributed job scheduling system.

  • Materials

    How to assign materials and create custom materials for shading.

  • Compositing

    Houdini’s compositing networks let you create and manipulate images such as renders.


  • Menus

    Explains each of the items in the main menus.

  • Viewers

    Viewer pane types.

  • Panes

    Documents the options in various panes.

  • Windows

    Documents the options in various user interface windows.

  • Stand-alone utilities

    Houdini includes a large number of useful command-line utility programs.

  • APIs

    Lists all the reference documentation for the ways you can program Houdini.

  • Python scripting

    How to script Houdini using Python and the Houdini Object Model.

  • Expression functions

    Expression functions let you compute the value of parameters.

  • HScript commands

    HScript is Houdini’s legacy scripting language.

  • VEX

    VEX is a high-performance expression language used in many places in Houdini, such as writing shaders.

  • Properties

    Properties let you set up flexible and powerful hierarchies of rendering, shading, lighting, and camera parameters.

  • Galleries

    Pre-made materials included with Houdini.

  • Houdini packages

    How to write and combine multiple environment variable definition files for different plug-ins, tools, and add-ons.

  • Houdini Engine

    Documents the Houdini Engine C, Python APIs, and Houdini Engine plugins

  • hwebserver

    Functions and classes for running a web server inside a graphical or non-graphical Houdini session.