Houdini Environment Setup

Houdini Environment Setup


Houdini environment setup for you and your team so that you can deliver tools and integrate scripts easily. Automate the setup in a team setting and add callbacks to manage scene preferences and source control.

What is the Houdini environment?

Houdini has specific environment variables that defines where it looks for scripts and resources.
Add your own paths to these variables to store scripts and resources wherever we want.

Houdini environment scripts

Historically, the most common way to modify the Houdini environment is through a file in the preference directory, namely houdini.env. Houdini evaluates this file during boot and thus presents an opportunity to inject paths for our tool environment. The problem is that this file gets extremely messy when everything uses this file to bootstrap.

“What if I want to organize my add ons so I can easily turn things on and off? ”
“As a tech artist, I don’t want to deal with pre existing configuration information when I modify the end user’s Houdini environment.”

Houdini Packages

Luckily there is a new alternative and a better way – namely packages and as of Houdini 17.5.467 and Houdini 18.0.315 the packages functionality can also daisy chain. In my mind, SideFx has achieved nirvana of environment modification.

A Houdini package is a .json file that exists inside a “packages” directory to modify the Houdini environment. The package syntax supports relative paths, os environment variables, version and os checks, so you can get very specific and complex with your packages. Read more about the specifics in the SideFx documentation on this.

Create a .json file in a packages directory in the Houdini preference directory.

In the package file, specify a path (HOUDINI_PATH) to a “Houdini site” folder. To the right you see the structure of the site folder I use.

The sub folder names “otls”, “presets”, “python_panels”, “python2.7libs”, “scripts”, “toolbar”, and “packages” are some commonly key-worded folders that automatically gets added to the Houdini environment during startup as a result of adding the path in the package.


Houdini Site

Manually implementing a package

First, go to the Houdini user preference directory and create a folder called “packages”.

Next, create a .json file inside the packages folder you just created (I name mine LCG.json). Put the content below in the .json file, and change the paths how you see fit.


Here is the really cool thing. If you are part of a team, using source control to distribute tools and assets, the data we put in the end users preference folder is extremely minimal and never really have to change.

We add a path (adding to the “HOUDINI_PATH” variable) to our distributed Houdini site and trigger the site’s packages via the package_path variable. We add complexity and additions to those packages as things need to change and distribute them via source control. The end user takes no action to receive these updates – their environment will just update.

Verifying the Houdini environment

Start up Houdini, copy and paste the code below into the python shell and run it to verify that the paths have been added to your environment.

Thanks to Houdini packages, we append, prepend or replace the Houdini environment without dealing with houdini.env. Create as many packages as you want. One per project/team/game/freelance job – the sky is the limit.

Now let’s talk about the things we can add “for free” to the environment at this point. By just creating these key worded folders in the HOUDINI_PATH, we add certain types resources to the environment. These are some of the most useful I have found so far….

  • otls – save Houdini Digital Assets (HDAs) here
  • packages – I place additional packages here to keep consistency with the folder naming convention. The packages in this folder are not automatically executed, but called via the “package_path” variable in the package that added this parent folder to the HOUDINI_PATH.
  • presets – save parameter value presets on any node and distribute them by saving them here.
  • python_panels – drop in custom tool UIs and they will show up in a drop down menu in the python panel.
  • python2.7libs – home of “pythonrc.py” – executed on Houdini boot up, so it provides a hook to add in python paths, create custom variables and any number of other things you can accomplish with Python in Houdini.
  • toolbar – distribute your custom toolbars (shelves for the Maya users out there)
  • vex – start adding your custom and reusable vex functions to a “include” sub-folder. Name the vex code file yourName.h
  • scripts – another folder that can contain certain keyworded python scripts. beforescenesave.py will automatically be run…you guessed it….before your scene is saved.
  • dso – drop in custom compiled plug ins for easy distribution.
  • viewer_states – custom written Python viewer states that includes custom manipulators and tool interfaces into the 3d viewport.
“I want to automate the creation of this setup for my team(s)? ”
“I want the Houdini site and my tools stored in any random location for each member of the team.

Automate install & uninstall with Houdini Digital Assets

Set this up is via a Houdini Digital Asset (HDA) – an extremely capable and versatile technology that is a core part of Houdini and the future is being written on it’s shoulders. It is flexible, easy to maintain and simple to implement.

Think of an HDA as a tool container. If you come from Maya, you can also think of it as a reference because anything that you put into an HDA is in a way referenced into every scene that you add this HDA node into. Change the HDA – all the instances of this node will update. Another key feature of the HDA that we will use for our purposes here, is the “on create” callback. It allows us to execute a Python script when the node is created.

HDA Creation - tips & tricks

Check out this blog post for a number of handy things that I constantly utilize when creating HDAs

Create the install.hda

First, create the digital asset that will act as our installer.

  1. In obj context, create a null.
    Houdini Environment HDA Create Null

    Houdini Installer HDA Create Null

  2. With the null selected, click the Create Subnet button
    Houdini Environment HDA Create Subnet

    Houdini Installer HDA – Create Subnet

  3. Right click on the newly created subnet and select Create Digital Asset…
    Houdini Environment HDA Create Digital Asset

    Houdini Installer HDA – Create Digital Asset

  4. In the Creation Dialog for Operator Name, put your  digital assets into a unique namespace (lcg), followed by nodeName, and version number. The Label is the human readable label. Save this particular digital asset outside of the otl folder, because in the end, the user browse to this digital asset to install our framework.
    Houdini Environment HDA Creation Settings

    Houdini Installer HDA – Creation Settings

  5. Dive inside of the digital asset and delete the null. We only need the shell of the HDA for the installer.

Basic Properties

Select some cool icon – I choose the plug because it seems fitting to what this HDA will do.

Houdini Environment Hda Set Icon

Houdini Installer HDA – Set Icon

Parameters Properties

Create 2 string parameters. Name them “houdini_path” & “package_path”. These will show the user, the paths we added. For info display, I like to disable the parameters so they will not be able to be edited by the end user – we make them read only.

We do this by writing an expression on the “Disable When” – we use something that will always be true – { 0 < 1 }

HDA properties

HDA Properties

Scripts Properties

Go to the scripts area and on the “Event Handler” drop down, select “Python Module” and “On Created”. This creates 2 internal Python modules to the HDA (make sure that the “Edit as” drop down is set to Python for the On Created callback module). Check the Python snippets below as far as what code goes into each module.

Extra files properties

We get the package json code from the “Extra Files” section of the HDA as well as the formatted success message for the pop up window.

Go to the “Extra Files” tab -> type “PACKAGE_TEMPLATE” in the “Section Name” field and click the “Add Empty Section” button. Repeat this process for a SUCCESS_MESSAGE section.

Houdini Environment HDA Create Extra files

Houdini Installer HDA Create Extra files

The SUCCESS_MESSAGE section looks like the below. Since this can contain HTML tags, it was practically impossible to show it in text form on this web site 🙂

Houdini Environment HDA Success message section

Houdini Installer HDA Success message section

Execution flow of the hda

When the node is created, the “on_created” Python function will trigger. The function creates the package file (and folder if it does not exist) and messages what happened to the user.

Since the script queries where it is being run from, put your tool framework anywhere and this will “just work” since the user will browse to this HDA.

In a Houdini session, click file->Import Houdini digital asset…

Super cool tip – double click the Installer HDA outside a Houdini session, and the latest version of Houdini will automatically launch and create the node. We figure out the root path, where the user is running our framework from and build the path to our Houdini folder.

This is actually all we need to get our entire frame work up and running, but we need to drop in a key script to really get it to sing.

Framework Structure

For our example, our framework structure looks like the below image.

  1. Houdini site that we have added via the package mechanism.
  2. Python script that will be automatically run when Houdini starts up.  Add our framework’s python root to the system path so that we can import and run our own python code.
  3. Another key worded folder and Python script. This script will trigger before the scene is saved. Perfect opportunity to add logic and handle automatic source control check outs of your hip files.
  4. Python root. Notice, the other blue source folder called lib. We will also add it to the sys.path – contains third party modules and packages.
  5. Location to save our installer.hda file.

Below you will find the Python code that is in pythonrc.py. This is the python file that runs when Houdini starts up. Find all the other key worded scripts you can drop in to make things happen post save or when Houdini opens a scene. SideFx documentation.

Houdini Environment Framework

Framework Structure


Create a copy of the install hda and make the name changes shown below. To bring up the initial window, right click on the install  HDA and choose -> Show in asset manager. Then right click -> Copy…

Houdini environment copy hda

Copy hda

The callback on_create python function is shown below and I tweaked the success message to fit the action of uninstalling.

Steps to installing / uninstalling

Houdini Environment Installing

Houdini Environment Installing

Houdini Environment Uninstalling

Houdini Environment Uninstalling


This approach is simple to implement and very easy to maintain. Since we are automatically calling all the packages inside our Houdini site packages directory, it is very simple to add in new hda directories (OTL_SCAN_PATH) whenever we need to.

I hope this article is useful to you. If it is, please drop me a comment below. Feel free to share your own experience and how you go about dealing with the Houdini environment setup.


About the Author

Christian Akesson

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Senior Technical Artist at Amazon Game Studios. Maya user since beta 1 in 1999. Mostly in Houdini these days...