24 July 2024

HtoA 6.3.3.0 uses Arnold 7.3.3.0 and is a minor feature release bringing a new OpenPBR surface shader, improvements to volume rendering, OIDN support for Apple Metal and AMD GPUs, and many other improvements as well as multiple bug fixes.

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

Known Issues

• HTOA-2698 - The new ramp shaders aren't translating correctly in Solaris. As a workaround, you can manually change the asset type to the v1 version of the node. This will be fixed in an upcoming release

Enhancements

• OpenPBR Surface: A new openpbr_surface shader implements the OpenPBR specification. OpenPBR Surface is an evolution of Standard Surface, developed in collaboration with Adobe and the Academy Software Foundation. It introduces many improvements, in particular a better sheen/fuzz model and improved metal reflectivity parameterization. (ARNOLD-13385)

_{image courtesy of Nikie Monteleone}

_{Convert Standard Surface shaders to OpenPBR Surfaces using the new conversion scripts}

• Classic Viewport Improvements: Viewport shader preview for OpenPBR Surface and Standard Surface in classic HtoA (HTOA-1488, HTOA-1511)

(Note: Shader parameters must be promoted for this to work in the viewport)

(Shader Developers: Custom shaders can now use the new houdini.ogl_tag metadata to automatically tag VOP parameters with OpenGL tags):

[attr diffuse]
houdini.ogl_tag STRING "ogl_diff"

• Solaris Viewport Improvements: Shader parameters and textures are now more accurately reflected in the viewport (HTOA-598, HTOA-2266)

• Scattering diffusion in volumes: Two new parameters in standard_volume improve how light is scattered in volumes. Using those parameters can help achieve high-scattering looks with fewer volume bounces and without adding energy. (ARNOLD-14482)
  • scatter_diffusion accelerates scattering in volumes.
  • scatter_diffusion_roughness accelerates scattering further on anisotropic volumes and can help achieve realistic looking clouds with fewer bounces.
  • gain and bias curves can further tweak the effect of both parameters

• Stochastic volume interpolation: The tricubic interpolation mode of AiVolumeSampleXXX() calls, such as those used by the standard_volume shader, now uses a stochastic method of interpolation that greatly reduces the amount of voxel data read in each sample call. In testing, we've seen speed ups of as much as 1.7x in certain scenes. Note that this technique does not always produce a perfectly matching image as a result, and can be toggled via the stochastic_volume_interpolation render option (default is on). (ARNOLD-3856)

• Improved quality with Intel Open Image Denoise 2.3.0: The updated Intel Denoiser improves denoising quality and can produce sharper results with less artifacts on scenes with specular reflections and transmission. For more information about changes in this version, see the OIDN release notes (ARNOLD-15059).

• OIDN support for Apple Metal and AMD GPU: The Intel OIDN denoiser now supports on macOS all Apple Metal GPUs (M1 and newer) and on Windows AMD GPUs using RDNA2 (Navi 21 only) and RDNA3 (Navi 3x) architectures. This allows for significantly faster denoising: on an M1 Max laptop we see 5-8x faster denoising. (ARNOLD-14855, ARNOLD-14856)

• GPU Many-lights support for light linking: Arnold GPU now uses Global Light Sampling for group of lights linked to a shape. This can improve rendering performance for scenes with light linking. For example, the ALab scene now renders twice as fast when you use Global Light Sampling. (ARNOLD-15050)

• GPU improved time to first pixel in scenes with many nodes: Reduced time to first pixel with Arnold GPU and scenes with many nodes. For example, we have seen a 18% improvement in time to first pixel on a simple scene with 1,000,000 instances. (ARNOLD-13652)

• Motion vector AOV on GPU: The motionvector AOV is now supported when rendering on GPU. (ARNOLD-11046)

• Ramp Shaders: Improved UI and new linkable inputs (HTOA-2629)

• 3D ramp modes: Ramp shaders have three new modes: 3d_linear, 3d_spherical, and 3d_cylindrical. These modes calculate the ramp input from the distance between the shading point and a user-defined reference point or line. (ARNOLD-15051, ARNOLD-15196)

• Ramp offset: Ramp shaders can now offset the input value, which allows you to add noise to the ramp. (ARNOLD-15052, ARNOLD-15197)

• Arnold ROP - Now saves deform_keys to universe options (HTOA-2620)

AtNode* options = AiUniverseGetOptions(universe);
const int deform_keys = AiNodeGetInt(options, 'deform_keys');

• Heatmap Imager Mode: The tonemap imager now has a heatmap mode that creates a spectrum based on a looked-up AOV quantity. The color ranges from blue (at minimum) to red (at maximum). (ARNOLD-15123)

• Improved AOV memory usage in non-progressive renders: Non-progressive, adaptive renders with the box filter now use less memory. Memory usage is also reduced in non-adaptive renders when using the following filters gaussian_filter, triangle_filter, sinc_filter, catrom_filter, mitnet_filter, blackman_harris_filter. For example, in a 1080p render using adaptive with AA_samples_max 50 and 6 AOVs, the memory used by AOVs was reduced from 14GB to 730MB (-96%). Note also that AOV memory usage now remains constant as AA_samples_max increases, unlike previous releases where the memory would increase quadratically. (ARNOLD-10160)

• Improved efficiency of the Alembic procedural: The Alembic procedural now reads data in parallel, which optimizes initialization times of heavy Alembic files with many objects. We observed startup times going from 15 minutes to 4 seconds on a large production scene. (ARNOLD-14796)

• Indirect diffuse and indirect specular parameters are now linkable in the standard_surface and openpbr_surface shaders: The indirect_diffuse and indirect_specular of standard_surface and openpbr_surface shaders now support linking of shaders. This should allow better optimization in scenarios where no indirect lighting is needed. (ARNOLD-14204)

• Triplanar Nref user param: Triplanar shader now accepts an Nref user parameter, to allow specifying reference normals when in Pref mode. (ARNOLD-15063)

• AOV names used for OpenImageIO subimages: Multi-part files previously used default subimage naming for layers/subimages. Arnold now uses the names of AOV outputs for the corresponding subimage. (ARNOLD-15053)

• Triangle tessellation memory usage statistics grouped under polymesh memory usage: Arnold logs now list triangle tessellation and polymesh memory usage together in the peak CPU memory used and peak GPU memory consumed. (ARNOLD-15194)

• ZMQ - Upgraded to ZMQ 4.3.5 (HTOA-2617)

• OSL VOP - Added a manual Compile button (HTOA-1733)

• OSL VOP - Node inputs and outputs are updated on scene load, even in manual cook mode (HTOA-1733)

USD Enhancements

• Reduced memory usage when using Husk - Arnold now uses less memory for geometry when rendering a single frame through Husk. usd#1918
• Skinning on USD curves and points - Binding skeleton on BasisCurves and points will now work with the procedural. usd#1814
• User data on lights - Primvars on lights are now imported as user data on Arnold light nodes. usd#1939
• Improved quad and mesh light exports - Mesh lights are now exported as a Mesh with light attributes instead of a GeometryLight. usd#1955
• Renders abort on license fail - The render delegate used by Husk aborts a render if a license isn't found and the environment variable ARNOLD_FORCE_ABORT_ON_LICENSE_FAIL is set to 1. usd#1950

API changes

• ParallelFor API: A new AiParallelFor function allows API users to easily implement multithreading of work over an array without having to use a dedicated multi-threading library such as TBB. (ARNOLD-14966)

   // simple example that squares all the elements in an array
   void square(size_t array_index, void* data, void* payload)
   {
      float& value = *static_cast<float*>(data);
      value        = value * value;
   }
  
   std::array<float, 7> values = {1, 2, 3, 5, 8, 13, 21};
   AiParallelFor(values.data(), sizeof(values[0]), values.size(), nullptr, square);

• ParallelJobs API: A new AtParallelJobs class allows programs to run jobs in parallel through a parallel job scheduler. This has more overhead than AiParallelFor(), but is more flexible as it allows for dispatching jobs without needing to place all the jobs in an array. (ARNOLD-15091)

   AtParallelJobs jobs;
   for (size_t i = 0; i < job_count; ++i)
   {
      payload = create_your_payload_data();
      jobs.add(payload, &callback);
   }  
   jobs.wait();

  OpenVDB preview in AiProceduralViewport: The procedural viewport preview API can now return a boundary mesh for a volume when called on a procedural containing OpenVDB volumes nodes. This is useful to render a preview of a procedural with volumes in a DCC viewport. (ARNOLD-14382)

• Shader API A new function to query whether an object is opaque or not. (ARNOLD-4919)

   AI_API AI_PURE bool AiShaderGlobalsIsObjectOpaque(const AtShaderGlobals *sg);

• Enum values You can now define enum values that start with a digit. (ARNOLD-15165)

   const char *enum_myparam[] = { "2d_space", "3d_space", NULL }; 
   AiParameterEnum("myparam", 0, enum_myparam); 

• Critical Section API Added compile guards around native_handle() references in ai_critsec.h because it no longer exists in the STL shipped with Visual Studio v17.8+ (MSVC v14.38+).

• Node API Added new API to declare an update dependency between two nodes (a dependency is when a node uses data from another node during its update). (ARNOLD-15211)

   AI_API void AiNodeAddDependency(AtNode* node, const AtNode* dependency);

Incompatible Changes

• Triangle tessellation memory usage statistics grouped under polymesh memory usage: Arnold memory usage statistics no longer groups triangle tesselation memory usage under the triangle tessellation section. You can now find the memory usage under polymesh memory usage in peak CPU memory used or peak GPU memory consumed. (ARNOLD-15194)
• heatmap_filter deprecated: With the improved heatmap workflow via imagers, the heatmap_filter is now deprecated and may be removed in the future. (ARNOLD-15123)
• No forced scene update after options modifications: Instead of forcing a full scene update when the options node is modified, a node that uses data from the options node in its node_update function should declare this dependency with the new AiNodeAddDependency API. (ARNOLD-14973)
• force_update metadata deprecated: We are deprecating this functionality, which might be removed completely on a future release. Instead of using force_update, nodes are expected to declare dependencies on other nodes using the new AiNodeAddDependency API, to optimize scene updates (ARNOLD-14901)

Bug Fixes

• HTOA-2619 - Changed Arnold Light contribution max limit to a soft limit
• HTOA-2624 - The Arnold ROP default denoiser imager network is no longer hidden
• HTOA-2647 - Added ass.gz to file pattern in Arnold Procedural node
• ARNOLD-14779 - AtProfiledLockable not compiling on Windows in newer MSVC due to Mutex::native_handle_type
• ARNOLD-15041 - Arnold does not run on Linux distros with glibc 2.39 (RHEL 9.4)
• ARNOLD-15060 - Arnold should not catch C++ exceptions it did not generate
• ARNOLD-15087 - uv_projection shader uses corrupt UVs for evaluating its default_color shader
• ARNOLD-15121 - [GPU] crash when CUDA error has no message
• ARNOLD-15122 - Crash destroying a light that is part of a light group
• ARNOLD-15136 - Random hang when parallel initializing scene
• ARNOLD-15269 - Output sheared in negative AA passes when using OptiX denoiser with odd-numbered render resolution sizes
• ARNOLD-15277 - [GPU] crash when using shadow groups
• ARNOLD-15025 - [GPU] Outdated GPU support metadata on min_pixel_width parameter
• usd#1861 - Fix BasisCurves disappearing on interactive updates
• usd#1927 - Fix procedural updates during interactive changes of non-leaf primitives
• usd#1661 - In the procedural the subdivision meshes will use the normals generated by the subdivision algorithm instead of the normal primvar.
• usd#1919 - Fix rendering multiple frames with husk.
• usd#1952 - Don't write camera aperture parameters if they're already set
• usd#1902 - Fix sporadic invalid Cache ID error

System Requirements

• Houdini, Houdini FX, Houdini Indie and Houdini Education
  • 19.5.805
  • 20.0.751
  • 20.5.278
• 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 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 with the Maxwell architecture or later.
  • On Linux, we recommend 535.104 or higher drivers.
  • On Windows, we recommend 537.13 or higher drivers.
• Optix™ denoiser requires an NVidia GPU with CUDA™ Compute Capability 5.0 and above.
• Intel OIDN GPU support is limited to:
  • Apple native CPUs (M1 and newer)
  • Intel Xe dedicated and integrated GPUs
  • NVIDIA GPUs using Turing or newer architectures
  • AMD GPUs with RDNA2 (Navi 21 only) and RDNA3 (Navi 3x) architectures