> [!abstract] Summary > HTOA (HtoA) is the official Arnold plugin for Houdini. Installation requires matching the exact plugin version to both your Houdini version and Python version, then pointing Houdini's environment file to the plugin paths. --- # Install HTOA ## 1. Download the Correct Version > [!warning] You must match **three things** exactly: Houdini version, Python version, and Arnold/HTOA version. A mismatch will cause the plugin to fail silently or crash. Download from the [Autodesk Arnold for Houdini downloads page](https://www.arnoldrenderer.com/arnold/download/). The filename encodes all version info, e.g.: ``` htoa-6.3.1.1_r6f505f8_houdini-20.0.653.py39 ↑ HTOA ver ↑ Houdini ver ↑ Python ver ``` Check your Houdini Python version via **Help → About Houdini** or by running `hython --version` in the terminal. ## 2. Install the Plugin Extract the archive to a stable location, e.g.: ``` C:/Program Files/Autodesk/Arnold/houdini20/ ``` ## 3. Configure the Houdini Environment File Add the following to your `houdini.env` file (located in your Houdini preferences folder, typically `~/houdini20.x/`): ```env PATH = "$PATH;C:/Program Files/Autodesk/Arnold/houdini20/htoa-6.3.1.1_r6f505f8_houdini-20.0.653.py39/scripts/bin" HOUDINI_PATH = "C:/Program Files/Autodesk/Arnold/houdini20/htoa-6.3.1.1_r6f505f8_houdini-20.0.653.py39;&" ``` > [!important] The `&` at the end of `HOUDINI_PATH` is required — it tells Houdini to also include the default path. Without it, Houdini will ignore its own default nodes and tools. ## 4. Verify Installation Launch Houdini and check: - The **Arnold** menu appears in the menu bar - Arnold render nodes are available in **ROPs** (e.g. `arnold` ROP) - The **htoa** shelf is loaded ## License Arnold requires an active license to render without watermarks. In a network environment, point to the license server via: ```env solidangle_LICENSE = port@licenseserver ``` Or set `ARNOLD_LICENSE_SERVER` depending on your RLM/FlexLM setup. --- # Troubleshooting | Issue | Likely Cause | Fix | | ----- | ------------ | --- | | Arnold menu missing | Wrong `HOUDINI_PATH` | Check env file path and `&` suffix | | Plugin loads but renders fail | Python version mismatch | Redownload matching HTOA build | | Watermarked renders | No license found | Check license server connectivity | | Nodes missing from palette | `&` missing in `HOUDINI_PATH` | Add `;&` at end of the path |