15 May 2025

HtoA 6.4.2.0 is a minor feature release using Arnold 7.4.2.0.

Installation

• Download Arnold for Houdini from your Autodesk Account. See Download Arnold for more information about downloading HtoA from your Autodesk Account.

• Follow these installation instructions

Enhancements

• Selection highlight in Solaris (HTOA-2903):

  

• Faster polymesh node init: Time needed for polymesh node initialization has been reduced when there are many meshes being initialized at the same time on machines with many CPU cores. For instance, the Activision Caldera scene went from 63s to initialize to 8.7s on a 120-core Windows machine. (ARNOLD-16008)

• Parallel instancer initialization: Multiple instancer nodes can now initialize at the same time. On a 120-core Windows machine the scene init time for the Intel Jungle USD scene went from 115s to 43s. (ARNOLD-16120)

• Minor Imager performance improvement: Enhanced memory copy operations within the Imager framework, resulting in improved performance. Stress tests demonstrate a reduction of 60 milliseconds per Imager chain. (ARNOLD-16256)

• parallel_init metadata: A warning is now printed when the parallel_init metadata is missing from a procedural. Missing metdata results in parallel_init being disabled for the procedural, which can result in slower scene initialization for those procedurals that could have safely benefited from parallel initialization. (ARNOLD-7051)

• Update Autodesk Desktop Licensing: Autodesk Desktop Licensing is updated to v15.3.0.1298. See the release notes for more information on this release. (ARNOLD-16104)

• Upgrade OIIO components: Various components used by OpenImageIO have been upgraded to more recent versions. In particular, jpeg files should now load and write noticeably faster than before. (ARNOLD-7892, ARNOLD-15771)

• Upgrade Customer Error Reporting (CER): CER was upgraded to 7.1.8 to address security vulnerabilities. (ARNOLD-16144)

• Upgrade Autodesk Analytics Program: Arnold includes a newer version of the Autodesk Analytics Program (ADP), which brings stability and performance improvements. (ARNOLD-16031)

USD Enhancements

• Optimize invisible primitives: Don't translate invisible primitives to Arnold when using the render delegate, which can significantly reduce the scene memory used. usd#2264
• Optimize unused child nodes: Destroy child nodes in the Hydra procedural instead of disabling them. This reduces the memory footprint on some scenes. usd#2277
• Update default interactive FPS: Improve the default interactive Frames Per Second settings in the render delegate, allowing faster maximum FPS and slower minimum FPS. usd#2276
• Optimize display driver creation: The render delegate now uses a single display driver for all AOVs, instead of using one driver per AOV. This reduces initialisation and render time. usd#2284
• Angular velocity: The point instancer angular velocity now works in the render delegate. usd#2285

Incompatible changes

Removed options.gpu_sparse_textures: The gpu_sparse_textures option has been removed as the functionality behind it had already been removed in a previous release of Arnold. (ARNOLD-16237)

Bug Fixes

• HTOA-2863 - Improved performance when loading/copying complex Arnold Material Builder graphs
• usd#2298 - Fix a potential crash when multiple Hydra renders initialize concurrently.
• usd#2300 - Animated sequences render an incorrect filename in Hydra mode
• usd#2260 - Deepexr settings were not set properly with husk renders
• usd#2231 - Fix velocity motion blur coherence when there is varying number of instances
• usd#2287 - Fix mismatch in default value for GI_transmission_depth between USD and Hydra

System Requirements

• Houdini, Houdini FX, Houdini Indie and Houdini Education
  • 19.5.805
  • 20.0.896
  • 20.5.550
  • 20.5.582
• Linux with at least glibc 2.28 and libstdc++ 9.3.1 (gcc 9.3.1) for Houdini 19.5, 20 and 20.5. This is equivalent to RHEL/CentOS 7.
• Linux with at least glibc 2.17 and libstdc++ 11.2.1 (gcc 11.2.1) for Houdini 20/20.5. This is equivalent to Rocky 8.
• macOS 11 or later
• Apple Mac models with M series chips are natively supported by HtoA
• x86-64 CPUs need to support the SSE4.1 instruction set. Apple Mac models with M series chip are supported natively mode.
• GPU rendering works on Windows and Linux only and requires an NVIDIA GPU with the Maxwell architecture or later.
  • On Linux, we recommend 560.35.03 or higher drivers.
  • On Windows, we recommend 560.76 or higher drivers.
• Optix™ denoiser requires an NVidia GPU with CUDA™ Compute Capability 5.0 and above.
• Intel OIDN GPU support is limited to:
  • MacOS
    • Apple native CPUs (M1 and newer)
  • Windows
    • Intel Xe dedicated and integrated GPUs
    • NVIDIA GPUs using Turing or newer architectures