The release archive contains everything you need to run HtoA, including the Arnold libraries, executables, and Python modules.

Houdini Compatibility

  • The HtoA build must match exactly your Houdini install, down to the build number, or random crashes and glitches will occur.
  • HtoA requires a 64-bit Houdini, Houdini FX, or Houdini Education.

Houdini Apprentice, unfortunately, cannot run HtoA as they lack support for third-party renderers, see Houdini products comparison.

Please download the .py3 version of the HtoA installer when installing the Python 3 version of Houdini 18.5, for example, Houdini 18.5.596.py3 

Setting up HtoA with the installer

Here are step-by-step instructions to install HtoA for the current user.  

  • Download the installer matching your exact Houdini version and platform from Downloads.
  • Launch the installer:

  • Select the folder where you want the HtoA files to be extracted:

  • You can choose to either have the installer set up your Houdini config file for HtoA automatically for you or just extract the contents to do a manual installation. The automatic installation will modify a few lines in your houdini.env file and create a backup.
  • You need to accept the End User License Agreement to continue the installation:

  • You are now ready to install HtoA on your computer:

  • The actual installation is then performed:

  • Done! You can now launch Houdini and start using Arnold:

Setting up HtoA manually

If you need to have complete control of the HtoA installation, you can select to only extract the contents of the installer and configure Houdini to pick up HtoA as shown below.

Note the render delegate for Solaris is added automatically for Houdini versions 18.0 and above, so no action is required when using the installer.

Modifying the HOUDINI_PATH

The installation boils down to inserting the HtoA folder first in the HOUDINI_PATH environment variable. On Windows, you also need to update the PATH environment variable. 

The path to the HtoA folder must be inserted before the factory Houdini folders in the HOUDINI_PATH. We suggest you put it first.

Setting up the Hydra render delegate for Solaris

Note that from HtoA 5.1.1 and Houdini 18.0.391, the render delegate for Solaris is installed into the dso/usd_plugins directory so it is no longer necessary to set the PXR_PLUGINPATH_NAME either in the houdini.env file or as an environment variable.

For previous versions, the Arnold hydra render delegate was added automatically by the installer to the houdini.env file, by adding the PXR_PLUGINPATH_NAME variable, set to the location of the hydra folder within the HtoA install tree as below.

Simple installation with houdini.env

The simplest installation is to insert the HtoA folder path to the houdini.env file. This file is created by Houdini after your first run, its location varies per platform:

WindowsC:\Documents and Settings\<username>\My Documents\houdini18.0\houdini.env

On Linux and Mac, append a single line to enable HtoA for the user: 

houdini.env (Linux)
HOUDINI_PATH = /path/to/htoa/htoa-5.0.2_raba8949_houdini-18.0.348;&
houdini.env (Mac)
HOUDINI_PATH = /path/to/htoa/htoa-5.0.2_raba8949_houdini-18.0.348;&

On Windows
, you need to set the PATH to point to the scripts/bin as well:

houdini.env (Windows)
PATH = "$PATH;C:/path/to/htoa/htoa-5.0.2_raba8949_houdini-18.0.348/scripts/bin"
HOUDINI_PATH = "C:/path/to/htoa/htoa-5.0.2_raba8949_houdini-18.0.348;&"
  • Prior to Houdini 15.5.559, must use forward slashes ("/") on Windows instead of backslashes as path separators. For example: "C:/htoadeploy/12".
  • In the PATH, the HtoA binaries folder must be appended (not prepended) to avoid issues with the Houdini Engine plugin in other applications.

Using a Wrapper Script

The most flexible way to deploy HtoA is to use a wrapper to launch Houdini. On Linux for example, you could use this script:
# Sample bash script to launch Houdini with HtoA enabled

# edit these to suit your environment

# source houdini environment
source houdini_setup
cd - &> /dev/null

# View docs in the default browser
# launch houdini
houdini $@  

Modifying individual HOUDINI_*_PATHs

If you have already used the individual HOUDINI_*_PATH environments for other plugins and scripts, you may find you need to set them for HtoA instead of using only the HOUDINI_PATH environment.

In case you also set one of the following environment variables, make sure you are appending ";@;&", at the end of its value, or alternatively, add the corresponding HtoA subfolder path to it:

Environment variableSub-folderNotes
HOUDINI_DSO_PATH <htoa_folder>/dso
HOUDINI_SOHO_PATH<htoa_folder>/sohoIt is critical that the HtoA soho sub-folder be placed before the factory Houdini folder.

Modifying the Houdini install path

On OSX installing Houdini to a location other than the default install path e.g. /Applications/Houdini/Houdini 18.5.696 will result in an error whilst rendering:

unable to load dynamic library: dlopen(<htoa_folder>/arnold/drivers/driver_houdini.dylib, 5): Library not loaded: @rpath/libHoudiniUT.dylib
Referenced from: <htoa_folder>/arnold/drivers/driver_houdini.dylib
Reason: image not found

If this is a requirement it is possible to update the rpath in libHoudiniUT.dylib to reference the libHoudiniUT.dylib in the new install location for example given an installation of Houdini in /Volumes/Houdini instead you can use:

install_name_tool -change @rpath/libHoudiniUT.dylib /Volumes/Houdini/Houdini18.5.696/Frameworks/Houdini.framework/Versions/18.5/Libraries/libHoudiniUT.dylib <htoa_folder>/arnold/drivers/driver_houdini.dylib

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