13 December 2023

HtoA 6.2.5.0 is feature release using Arnold 7.2.5.0.

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

• Light instancing - You can now instance and render Light SOPs. Solaris lights, or lights created by a procedural, are not supported yet. (HTOA-693)

• Post Translation Hook - Added a post-translation Python callback to the Arnold ROP, With this callback, you can directly edit the Arnold universe before the render begins. (HTOA-657)

• Support multiple packed primitives per alembic - Scenes using Houdini Alembic packed primitives now generate much smaller amounts of data in Arnold, creating a single alembic node to represent multiple packed primitives. This reduces the time to process the generated secne significantly, in some cases giving a 64x speed up on scene translation, and an exponentional reduction in file sizes. See table below. (HTOA-1920)

Number of Instances	Scene Translation Time Before	Scene Translation Time After	Scene Creation Time Before	Scene Creation Time After	Scene File Size Before	Scene File Size After
2500	1m43s	1.64s	14.30s	00.13s	243M	926K
500	19.6s	0.45s	02.92s	00.11s	48M	199K
100	8.22	0.25s	00.64s	00.09s	9.7M	56K

• Arnold procedural nodes now trigger OnCreated.py scripts - As with the legacy Arnold Procedural node any new Arnold Procedural nodes can trigger the oncreated event see the houdini asset event documentation for further details (HTOA-2131)

• Support for husk thread count argument - You can set the number of render threads on the husk command line with --thread or --j. (ARNOLD-13299)

• GPU renderer overhaul: A large part of the GPU renderer was rewritten using NVIDIA OptiX 8. This allowed numerous improvements such as much faster startup times, lower GPU memory usage, better scaling on multiple GPUs, and faster renders overall. (ARNOLD-9882)

• Global light sampling in volumes: Global light sampling is now supported in volumes. The render time speedup when using global light sampling in volumes depend on the number of lights, but even scenes with only a few lights are faster to render. (ARNOLD-13095)

Below is an equal time render comparison of a scene containing 351 motion blurred mesh lights inside an atmosphere_volume.

• Improved thick curves intersector: Curves in thick mode are on average 10% faster (in some cases, more than 100% faster) and they look better in closeups. (ARNOLD-2875, ARNOLD-8549 and ARNOLD-14391)

• Distance shader in reflections: The distance shader now properly handles secondary paths such as reflections. (ARNOLD-13883)

• Overlay imager: A new imager that allows you to decorate or tag your renders by printing text over the rendered images. Overlay text can use any of the system fonts (TrueType or PostScript), or custom fonts defined via the OPENIMAGEIO_FONTS environment variable. You can include scene and system information, and render statistics, with pre-defined tokens, such as <frame_time>, <samples>, and <camera>. See the Overlay Imager documentation for the full list of tokens. (ARNOLD-14188)

• GPU denoising in Intel Open Image Denoise: The Intel denoiser was upgraded from version 1.4.1 to 2.1.0, which brings real-time denoising through NVIDIA and Intel GPU support. (ARNOLD-12547)

• Toon light-group AOVs: The toon shader now outputs AOVs for direct lighting from lights that have a label in their aov parameter. The toon light-group AOVs are named with the toon aov_prefix parameter. For example, if a light has aov = "keylight" and a toon shader has aov_prefix = "myprefix_", then the toon light-group AOV is named "myprefix_keylight". (ARNOLD-9602)

• Automatically create non-existent paths to tx file: Generating a .tx file (maketx, autotx, AiMakeTx) now works even if the paths to the output .tx file do not exist: Arnold now creates those paths. (ARNOLD-14703)

• Faster overlapping volumes: Arnold renders a few percent faster when there are many overlapping volumes. (ARNOLD-14353)

• Scene unit conversion for light intensity: Scene unit conversion is now supported for light intensity in nested procedurals. If a procedural contains a light and its scene units do not match the procedural units, the light intensity is scaled to match the procedural. Conversion is in place for Arnold ass file procedurals, but we do not yet support USD and arbitrary procedural formats. (ARNOLD-9205)

• Scene unit conversion for volume density and emission: Scene unit conversion is now supported for volume density and emission in nested procedurals. If a procedural contains a volume and its scene units do not match the procedural units, volume density and emission are scaled to match the procedural. Conversion is in place for Arnold ass file procedurals, but we do not yet support USD and arbitrary procedural formats. (ARNOLD-9206)

• Improved profiling: Procedural and volume intersection times are now listed separately, instead of being included with the parent BVH. Profiling has also been added in other areas, in particular multithreaded code where helper threads were not being accounted for. This should result in higher quality statistics. (ARNOLD-14443)

• GPU: Better compatibility with CPU rendering: The following CPU features have been ported over to the GPU.

  • Multiple render sessions with GPU (ARNOLD-14145)

  • When rendering on GPU and using per-face displacement shaders, autobump will now match the displacement shader assigned to each face. Previously, autobump would use the first shader applied. (ARNOLD-12796)

  • Motion blur on the implicit sphere primitive. (ARNOLD-12955)

  • Skydome_light.shader parameter. (ARNOLD-13641)

  • The "polygons" edge type in the wireframe. (ARNOLD-12804)

  • OSL LPE writing via debug closures. (ARNOLD-13907)

  • Image shader "file" wrap mode. (ARNOLD-12578)

  • ID mode in utility shader. (ARNOLD-14159)

  • edgelength mode in utility shader. (ARNOLD-14122)

  • The GPU renderers texture filtering logic has been improved such that there is a closer match to the CPU renderer. (ARNOLD-12578)

  • A number of fixes have been made to the GPU renderer's color management logic such that there is a closer match to the CPU renderer. (ARNOLD-12382)

• Updated Autodesk Network License Manager:: Autodesk Network License Manager (NLM) server version 11.19.4.1 is available and includes support for RHEL/Rocky Linux 9 operating systems. You can find the NLM installer in the license/installer folder, and from the Arnold License Manager. (ARNOLD-14429)

USD Enhancements

• USDZ files supported as file format: You can render usdz files with kick, and load them with the usd procedural. usd#1726.
• Orthographic cameras in Hydra: Orthographic Cameras are now supported in the Hydra render delegate. usd#612.
• Pixel Aspect Ratio in Hydra: The Arnold Render Delegate now supports the pixelAspectRatio parameter in RenderSetting primitives usd#658

API changes

• Multiple render sessions on GPU: The GPU can now render multiple render sessions at the same time. (ARNOLD-14145)
• Font API: A new API AiFontGetFamilies and AiFontGetStyles returns the list of available system fonts (e.g. "Arial", "Times New Roman") and font styles (e.g. "Regular", "Bold", "Italic"). AiFontGetFilename returns the path of the file that defines a given font family and style. (ARNOLD-14395)

Incompatible Changes

• Minimum NVIDIA driver requirements for Arnold GPU: Arnold GPU requires 535.104 or higher drivers on Linux and 537.13 or higher on Windows.
• GPU cache pre-population deprecated: The GPU cache pre-population has been deprecated and calling these functions will now do nothing. (ARNOLD-12135)

Bug Fixes

• HTOA-2282 - Fixed Python errors when exporting to MaterialX using the Arnold menu

• HTOA-2438 - Arnold Render Settings LOP should author pixel aspect ratio in the Render Settings primitive instead of the Render product

• HTOA-2297 - Added skip_alpha driver setting to allow writing out PNG with transparency

• usd#1709 - Procedural failures if schemas are present

• usd#1713 - Fix coding error "attempt to get string for GfVec4f"

• usd#1732 - Force the color AOV to be interpreted as the Arnold beauty pass

• usd#1735 - Fix usdskel geometry and motion blur interpolation outside the keyframe boundaries

• usd#1524 - Fix material binding on instances under a SkelRoot

• usd#1718 - Support primvars:arnold attributes in Arnold typed schemas

System Requirements

• Houdini, Houdini FX, Houdini Indie and Houdini Education
  • 19.0.720
  • 19.5.773
  • 20.0.547
• Linux with at least glibc 2.28 and libstdc++ 9.3.1 (gcc 9.3.1) for Houdini 19, 19.5, and 20. 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. This is equivalent to Rocky 8.
• macOS 10.13 or later, macOS 11 or later for Houdini 19.5
• Apple Mac models with M series chips:
  • Natively supported by Arnold for Houdini 19.5
  • Supported under Rosetta 2 mode for older versions of Houdini
• 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 of the Ada, Ampere, Turing, Volta, Pascal, or Maxwell architecture. We recommend using the 535.104.05 or higher drivers on Linux and 537.13, or higher on Windows. See Arnold GPU for more information.
• Optix™ denoiser requires an NVidia GPU with CUDA™ Compute Capability 5.0 and above.