30 Mar 2022

HtoA 6.1.0.0 is a feature release using Arnold 7.1.0.0.

Please download the .py3 version of the HtoA installer when installing the Python 3 versions of Houdini.

Installation

1. Download Arnold for Houdini

2. Follow these installation instructions

## System Requirements

Houdini, Houdini FX, Houdini Indie and Houdini Education

• 18.0.597

• 18.5.759

• 19.0.531

• Windows 10 or later, with the Visual Studio 2019 redistributable.

• Linux with at least glibc 2.17 and libstdc++ 4.8.5 (gcc 4.8.5). This is equivalent to RHEL/CentOS 7.

• macOS 10.13 or later.

• CPUs need to support the SSE4.1 instruction set. Apple Mac models with M series chips are supported under Rosetta 2 mode.

• GPU rendering works on Windows and Linux only and requires an NVIDIA GPU of the Ampere, Turing, Volta, Pascal, or Maxwell architecture.

• Optix™ denoiser requires an NVidia GPU with CUDA™ Compute Capability 5.0 and above.

• We recommend using the 511.09 (Quadro), 511.09 (GeForce), or higher on Windows and 495.46 or higher drivers on Linux. See Arnold GPU for more information.

• The driver type must be set to DCH.

^{I n the driver page select "Windows Driver Type:" DCH}

The cache will also need to be re-populated after installing a new Arnold version, updating to a new NVIDIA driver, or changing the hardware configuration of GPUs on the system. More information can be found here.

Enhancements

• htoa#1592 - Add atmosphere and background render settings LOP parameters

• htoa#1894 - Add triplanar options for inputY and inputZ

• htoa#1906 - Ship OSL includes

• Improved IPR interactivity: GPU and CPU interactivity is improved. ARNOLD-11981, ARNOLD-12007

• Stability improvements: We've improved the stability of Arnold, especially when using multiple render sessions.

• Per axis texture in triplanar: The triplanar shader can now optionally use different textures for each axis. ARNOLD-11708.

A wide range of shading effects such as snow, dust, sand, and moss, can be achieved using input_per_axis (Y).

^{Rollover images to view with and without triplanar.input_per_axis (Y)}

A video that shows how to use the input_per_axis can be found here.

• Flip_on_opposite_direction in triplanar: A new parameter called flip_on_opposite_direction can also be used to control the behavior of the shader on faces facing the corresponding negative axis. ARNOLD-11615.

• Reduced overhead of running Imagers in IPR: Imagers will no longer always run after every progressive pass or bucket update. This can give a substantial speedup with expensive to run imagers. ARNOLD-11760

• Better startup and update times with atmosphere shader: Starting renders and updating parameters when using a high number of AA samples with a volume_scatter atmosphere shader should now be much faster. ARNOLD-5503

  Render times of a simple scene with volume_scatter.samples=30:

| AA | AA_max | Arnold 7.0 | Arnold 7.1 |
| --- | --- | --- | --- |
| 4 | 50 | 5:28min (node update: 5:20min) | 8 sec (node update: 0 sec) |

• Case insensitive output image file extension: AiFindDriverType() is now case insensitive, so asking, for instance, for a "png", "PNG", or "Png" will all return the png driver. This can be observed with kick -o, which will now work for different case types. ARNOLD-11934

• Updated MaterialX to 1.38.3: We now use MaterialX 1.38.3. Surface materials defined in a nodegraph are now supported. ARNOLD-10534, ARNOLD-11903

• Updated Alembic to 1.8.3: The alembic procedural has been upgraded to use version 1.8.3 of the alembic library. ARNOLD-11973

• Faster TextureResolveUseExistingTx: The TextureResolveUseExistingTx stage is now much faster when many threads are trying to open textures for the first time with the use existing tx option enabled. On a 128-core machine we saw about an 8x speedup. ARNOLD-11689

• Faster per-pixel imagers: We removed overhead in imagers that can execute independently on each pixel. The exposure and tonemap imagers, for instance, are now significantly faster. This likely will be most noticed when interacting in IPR with small buckets. Note that bloom and denoising imagers require access to all pixels and so will not benefit from this optimization. ARNOLD-12011

• Faster bloom imager: The bloom imager has been optimized. In one test we saw a 10% performance improvement. ARNOLD-11568

• AOV denoising with the OptiX denoiser: Upgraded from the Optix 6 to Optix 7 denoiser. This newer denoiser supports denoising AOVs in a way that allows the denoised result to be compositable. Prevoius OptiX denoisers had no guarantees that the denoised results would combine correctly. ARNOLD-11726

  Original beauty	Denoised beauty	Denoised diffuse AOV	Denoised specular AOV	Denoised diffuse + denoised specular

• Upgraded OIIO to 2.4.0: This allowed for fixing several defects listed in the Bug Fixes section. ARNOLD-11651, ARNOLD-11785, ARNOLD-11790

• Invert view and display transform for textures using OCIO: When using an explicit OCIO or the default color manager, it is possible to specify both a display and view transform when writing outputs, using the View ( Display ) syntax. It is now possible to use the same syntax for input color transforms as well. For example, reading a texture using the ACES 1.0 SDR-video ( sRGB ) color space will correctly invert a file with a view transform baked in. (ARNOLD-11961).

GPU Enhancements

• Improved GPU IPR interactivity: GPU IPR rendering is now more interactive. ARNOLD-11981

USD Enhancements

• Point Instancer improvements : Per-instance primvars and nested instancers are now handled both in the procedural usd#944 as well as the render delegate usd#482.
• Mesh builtin normals : The procedural now reads the builtin USD description for mesh normals usd#962 usd#986
• Curves UVs : The procedural now supports UVs on curves, for per-strand primvars usd#975
• Light-linking : ignoreRoots wasn't supported correctly for light / shadow links in the procedural usd#987
• Shadow parameters : The procedural now reads shadow parameters (enable, color) from USD lights usd#945
• Shader connections to array attributes : The render delegate now supports rendering shader connection to an array attribute. This is needed e.g. to have shader connections on ramps usd#970
• Render tags : Render tags are now taken into account by the render delegate usd#883
• Procedural search path : USD is now properly considering the options procedural_search_path when loading nested procedurals #usd942
• Motion blur with UsdSkel : the procedural now extends the interval used to bake the skinning, so that it includes surrounding integer frames usd#951

Incompatible Changes

• Warnings about deprecated API usage enabled by default: Warnings about deprecated API usage are controlled by the AI_ENABLE_DEPRECATION_WARNINGS macro, which is now set to 1 by default. This will help you find any use of old Arnold API that might be causing issues. If you still need to disable them for some specific part of your code, they can be disabled by setting AI_ENABLE_DEPRECATION_WARNINGS to 0. (ARNOLD-11751).
• Changes in node_initialize/node_update : Those functions now receive a new parameter for the render session where the node is being rendered. This render session can be used for any API call requiring it to be specified. (ARNOLD-11817)
• Changes in logging API : Logging functions have been modified so that log messages are associated with a universe instead of a render session. This means the AiMsgSetLogFileFlags, AiMsgSetConsoleFlags, AiMsgGetLogFileFlags and AiMsgGetConsoleFlags API functions will now require a universe pointer instead of a render session pointer. Also, the log callback will receive a universe pointer parameter (called "universe") instead of a render session pointer. (ARNOLD-11983)
• Autodesk Network Licensing version : Arnold 7.1 switches to ARNOL_2023 licensing.
  • Single-user subscriptions will work with Arnold 7.1. The plugin installers automatically register the new version. If you do not use a plugin, then after you download Arnold, open the Arnold License Manager and click Register .
  • Existing network licenses will not work with Arnold 7.1. Log on to your Autodesk account to generate your new ARNOL_2023 licenses.

Bug Fixes

• htoa#1393 - Propagate exr autocrop option to AOVs

• hota#1581 - Fix ramp element connections in Solaris

• hota#1874 - Husk loads hdArnold.so on Linux in Houdini 19

• hota#1891 - Fix volume velocity motion blur so it responds to shutter interval

• hota#1895 - Update Arnold ROP onCreate script for python 3

• hota#1896 - Fix licensing issue on Windows

• hota#1897 - Set the colorspace of image nodes with tx files to the render colorspace

• hota#1898 - Fix to hush startup log if the HTOA_STARTUP_LOG env is set to 0

• hota#1902 - Set logging on translation universe

• hota#1910 - Fix image.filename USD metadata

• ARNOLD-11958 - Color correct shader produces incorrect values with small gamma values

• ARNOLD-11852 - Memory leak with imagers when rendering multiple frames

• ARNOLD-11835 - Full frame imagers crash with negative render region

• ARNOLD-11827 - Intel Alder Lake CPUs did not always use high performance cores in Windows

• ARNOLD-11795 - Spotlight penumbra should affect the specular intensity

• ARNOLD-11667 - GPU and CPU+FIS filtering generated sampling patterns that could alias

• ARNOLD-11242 - 'n' key was no longer toggling AI denoisers in kick IPR

• ARNOLD-10400 - Volume motion blur advection computation was incorrect

• ARNOLD-10391 - Volume motion blur used incorrect motion/shutter intervals

• ARNOLD-11889 - Maketx --monochrome-detect should generate Y not R image for exr formats

• ARNOLD-11968 - AiUniverseGetRenderSession returns invalid pointer instead of null if the session was previously destroyed

• ARNOLD-11982 - Texture invalidation in Linux and macOS occurred even when texture was not modified

• ARNOLD-12055 - [GPU] Crash switching from CPU to GPU with optix denoiser

• ARNOLD-10577 - [GPU] Textured skydome_light leaks memory over multiple frames in a session