Solid Angle Houdini To Arnold 5.1.0 / MacOSX + Linux

Compatibility

• 17.0.506
• 17.5.460
• 18.0.348
  
  

• Linux x86_64 (gcc6.3)
• Windows 7 x64 (vc14.1)
• Mac OS X 10.11+ (clang7.3)

Features

• #1128 Adding USD procedural support.  The arnold_procedural OBJ node supports rendering and visualization of USD files using the Geometry File parameter.
• #1384 IPR for the usd procedural update on frame change.
• #1380 Add the auto_instancing toggle to arnold_procedural OTL to enable auto-instancing of duplicate Arnold procedural nodes created when using .ass files.
• #1336 Add the string_replace operator which matches and replaces parts of string parameters, optionally depending on the OS Arnold is running on.
• #1369 Adding tilt/shift options for perspective render camera to control lens tilt angles with respect to the projection plane. This is useful in architectural renderings to compensate perspective transformation for vertical lines. 
• #1375 Add radial_distortion_type to perspective render camera. 

Compatibility

• 17.0.506
• 17.5.425
• 18.0.287
  
  

• Linux x86_64 (H16: gcc4.8 and H17: gcc6.3)
• Windows 7 x64 (H16: vc14 and H17: vc14.1)
• Mac OS X 10.8+ (clang7.3)

Enhancements

• IPR updates for light creation and deletion (htoa#499)
• Export materials (htoa#1315)
• Import materials (htoa#1314)
• Import materials with input component connections (htoa#1341)
• Initial Solaris support for HtoA (htoa#1329)
• Viewport proxy for arnold procedurals (htoa#1318)
• Add aov_write_vector shader to prevent clamping on specific AOVs (htoa#1235)
• Update materialx operator (htoa#1321)
• Add Role (OCIO) color space family (htoa#1348)
• Notarise the OSX HtoA installer (htoa#1292)
• Launch license manager (htoa#1308, htoa#1346)

Fixes

• Build psutil on OSX (htoa#1349)
• OSX installer crashing on extraction (htoa#1352)
• Int and Bool hydra render settings not coming through in OSX (htoa#1355)
• Crash when creating the Render Settings LOP (htoa#1353)

Fixes
- Fix switch operators from being unintentionally exported (htoa#1217)
- Remove crash when creating the ramp_rgb shader node (htoa#1218)

Enhancements
- GPU rendering (BETA): You can now switch between CPU and GPU render devices interactively and expect visually similar results. NVIDIA® GPUs from Turing to Maxwell architectures are supported, and Arnold will take advantage of multiple GPUs, NVLink and NVIDIA RTX hardware accelerated raytracing if available. Note that due to beta status of GPU rendering, a number of features are missing, performance is not final, and use in production is not advised. We plan to gradually improve this in subsequent releases and would appreciate your feedback.
- Improved adaptive sampling: Adaptive sampling now uses a more effective criterion. With the new metric, pixels are being dropped gradually in a smoother and much more predictable manner, resulting much lower render times for identical noise levels. In addition, the adaptive sampling criterion windowing that was previously available only in progressive rendering mode is now also available in non-progressive mode, resulting in higher quality sampling, with fewer sampling "holes". (#7972, #7950)
- Improved skydome sampling: Arnold now takes into account the normal of the shading point when importance sampling the skydome. Therefore bright areas in the skydome are less likely to "steal" samples when they are below the normal. Even for more uniformly colored skydomes, the improved sampler will waste fewer samples in directions that are below the hemisphere, allowing for lower skydome light sample rates to be used which should give a noticeable speedup. For the same number of shadow rays cast, the new sampler has just a small ~2% performance overhead. Note that skydome samples need to be lowered to 70% or less from their original value (3 instead of 4) to roughly keep the number of shadow rays and associated cost the same. (#6669)
- Visible lights: The quad_light, disk_light, cylinder_light and point_light now have a camera and a transmission attribute, allowing these lights to become visible to camera and transmission rays. These attributes are left to 0 by default, thus not changing the default behaviour of the non-visible lights. (#2269)
- Microfacet multiple scattering: The GGX microfacet BSDF used in the standard_surface shader has been improved to account for multiple scattering between the microfacets, which is more physically correct and reduces energy loss on reflection, especially at higher roughness settings. The reflection from rough metals in particular will be significantly brighter and more saturated as a result. Unfortunately there is a slight increase in noise on account of the more difficult sampling when including the multiple scattering component. Disabling the global option enable_microfacet_multiscatter will restore the previous look. (#7207)
- Improved random-walk SSS: A new randomwalk_v2 SSS mode has been added that scatters more accurately and deeply through highly-transparent/optically-thin objects, which produces SSS with more saturated colors around fine surface detail and heavily backlit regions of an object. Note that renders will be more costly and noisier than with the original method, since random walks will be on average longer and more random. (#7550)
- Anisotropy controls for coat in standard_surface: We have added two new parameters, coat_anisotropy and coat_rotation, in the standard_surface shader for finer artistic control of the coat layer. (#7935)
- Support for negative transmission_extra_roughness in standard_surface: The parameter transmission_extra_roughness in the standard_surface shader now accepts negative values, allowing separate control of the specular and transmission roughnesses for artistic purposes. (#7936)
- Linkable transmission depth in standard_surface: The transmission_depth parameter is now linkable. (#8039)
- Improved coat layer in diffuse reflections: When caustics are disabled on the reflected object, the coat layer on the standard_surface shader is now correctly taken into account. (#8016)
- Improved bump and normal mapping: Built-in shaders such as bump2d, bump3d and normal_map now correct for non-physical shading normals while preserving detail. This should be more noticeable when rendering normal-mapped ocean surfaces or using extreme normal maps. (#7639)
- Smart opaque: Built-in shaders now set the object.opaque flag automatically based on whether or not the shader settings would require disabling the opaque flag on the object to render correctly. For instance, it's no longer necessary to manually disable the opaque flag to get transparent shadows for a glass shader. Notable exceptions are curves and points when min_pixel_width is in use and OSL shaders. Custom shaders can take advantage of this setup tagging shader attributes with metadata.
- Note that setups with transparency but with the opaque flag set to false will now be considered transparent. To preserve the previous look you can make your shader opaque or use a ray switch to make it opaque only to shadows. (#5966)
- Operator connection on procedurals: Operator graphs can now be connected to procedurals through the operator parameter. Only nodes in the procedural or nested procedurals are evaluated by the graph, where everything is performed relative to the procedural's name scope such as selection expressions. Furthermore, nodes created by the operators are put in the procedural's name scope. (#7747)
- New include_graph operator: The include_graph operator allows importing operator graphs from an .ass file, where the target parameter specifies the target operator in the included sub-graph. The operator can also load shaders if they exist in the .ass file, where they are put in appropriate name scope depending on what the operator is connected to. (#7294)
- Scoped child operators: Child operators are now placed in the name scope of their parent operator, where a set of child operators can be connected to enforce a particular evaluation order. (#8075)
- MaterialX operator improvements: Updated the MaterialX library and operator (#7825). Swizzles can now be used to define the channel connections between shader nodes. Float array handling has been expanded to handle other array types such as color3array in order to support the ramp shader (#7970). The search path for the Arnold node definitions is now set automatically (#8028). The operator matches assignments in accordance with the current name scope, i.e. procedural or global namespace (#7968).
- Subdivision creases support in Alembic procedural: The Alembic procedural will now detect and translate crease data for subdivision surfaces. (#7655)
- Improved ramp_rgb shader: Several new interpolation modes were added, as well as an implicit_uvs parameter, which allows to use barycentric implicit UVs to drive the ramp, instead of regular UVs. This last option can be particularly useful with hair. (#7987)
- New time mode in ramp shaders: The ramp and ramp_rgb shaders now have an additional time mode that computes the input based on the current sg->time and the camera's start and end shutter interval. (#7925)
- New uv_projection shader: This shader allows to do planar, spherical, cylindrical, ball, cubic and shrink_wrap projections. (#7280)
- New matrix_interpolate shader: This shader allows to produce motion blurred matrix parameters, by interpolating between matrix values. (#7948)
- New coord_space control in camera_projection: You can now choose to do camera projections in world or object space, or by using Pref user data, or linking any shader to the input position P parameter. (#7798)
- UV coordinates for background: During background shading, UV coordinates are now generated from the screen coordinates for camera rays. Thus it's now possible to directly link a UV-based shader to options.background such as image, checkerboard or ramp. (#8007)
- Denoising albedo: A built-in AOV with an albedo optimized for denoising has been added as denoise_albedo. Both the Arnold (noice) and OptiX™ denoisers will use the new AOV if present. (#6955, #8168, #8069)
- OptiX denoiser improvements: Updated to Optix™ 6 which brings denoising improvements in quality, memory consumption and performance on Turing™ hardware. (#7965)
- Faster sample generation: Rendering with high camera AA samples combined with large numbers of lights or other secondary samples could sometimes result in very slow startup times. For instance, a scene with AA=18 and point_light.samples=18 was taking 11 minutes to start; it now takes a fraction of a second. (#7933)
- Faster .ass file writing: Writing to .ass files, especially over some Windows networks, can be dramatically faster. One customer saw a 51x speedup. (#7801)
- Faster OSL UDIM texture reads: Reading UDIM textures in OSL is now much faster, with up to 10x reported speedups. (#7920)
- Reduced memory usage for instances of curves: The uvs and shidxs arrays in the curves node are no longer duplicated for every instance of a curves node, significantly reducing the memory footprint of instanced curves. (#7742)
- Maketx monochrome map detection: maketx now by default detects the frequent case of an RGB image that can be stored as single channel. This can result in smaller .tx files and render time memory savings. (#6671)
- Motion vectors AOV uses the camera shutter: In order to facilitate using motion vectors, the global option options.ignore_motion_blur now keeps motion keys and only sets the camera ray times to be equal to the options.reference_time – use this with motion vectors instead of setting shutter intervals to zero. The new global option options.ignore_motion will take over the pre-existing ignore_motion_blur functionality of ignoring all motion keys. (#7962)
- New OCIO role: arnold_srgb_equivalent has been added as a synonym for the older srgb_equivalent to make it clear this is an Arnold role. (#8092)
- Updated to OIIO 2.1.0: Updated to the latest OpenImageIO library in order to bring in several texture related bug fixes. (#7929)
HtoA Enhancements
- Inline OSL shader (htoa#887)
- CopyToPoints creates ginstance nodes for alembic primitives (htoa#1166)
- Alembic Instancing with CopyAndTransform SOP (htoa#1093)
- Expand top level userdata on packed primitives (htoa#1149)
- Refactor and optimise translation classes - 2.4x speedup (htoa#1165)
- MaterialX Export (htoa#1194)
- Texture baking UDIM support (htoa#1099)
- Export operator graphs connected to a procedural (htoa#1180)
- Add an option to write out relative texture and procedural paths (htoa#1183)
- Add gpu_max_texture_resolution to GPU options (htoa#1176)
- Add menu to fill gpu cache on Arnold ROP (htoa#1188)
- Use options.ignore_motion_blur to generate motion vectors AOV (htoa#1210)
Incompatible changes
- Removed legacy point clouds: An internal point cloud data structure (previously used for SSS) and its associated API have been removed. (#6358)
- Removed SSS on curves: SSS on curves was deprecated as it did not properly work and has now been removed. (#4254)
- Removed support for NVIDIA® Kepler™ GPUs: the Optix™ denoiser only supports GPUs with CUDA™ Compute Capability 5.0 and above. (#7964)
- Defaults changed for standard_surface: The specular_IOR parameter changed from 1.52 to 1.5 so that it matches the coat_IOR and thin_film_IOR. The specular_roughness changed from 0.1 to 0.2. The subsurface_type default changed from diffusion to randomwalk. (#7627, #8133)
- MaterialX shader reference type name changed: The attribute used to define the shader reference type in MaterialX documents (e.g. surfaceshader, displacementshader) has been renamed context because of changed behaviour in the MaterialX library. (#7825)
- Operator merge order reversed: The last operator wins if multiple operator inputs are merged and override the same node parameter. (#7903)
- Specular AOV: The sheen component has been removed from the specular_* AOVs. (#7522)
Fixes
- Packing packed alembics creates shader assignment discrepancy (htoa#1062)
- Houdini 17 test failures (htoa#1140)
- Fix LPE for spec AOVs (htoa#1167)
- Packed primitives gives different ass files when exporting locally vs on the farm (htoa#1168)
- Multiple GPUs listed incorrectly (htoa#1186)
- MPlay IPR not working (htoa#1195)
- Add time to ramp pattern menu (htoa#1197)
- Remove obsolete shaders (htoa#1198)
- Displaying the last AOV when denoising the beauty in GPU mode (htoa#1209)
- Error on baking one object for different uv sets (htoa#1185)
- Bake all the polymeshes generated by the selected object (htoa#1191)
- Crash writing materialx file (htoa#1213)
- Triplanar: object coord space not working during displacement (core#7401)
- Triplanar: pref not working during displacement (core#8139)
- Dxy screen differentials in displacement context are zero (core#6267)
- parallel AiMakeTx can consume too much memory (core#6376)
- OpenEXR: standard chromaticities metadata was missing in output files (core#7408)
- Arnold crashes when you try to write out render stats (core#7741)
- connected normal_map and bump2d breaks transmission (core#7750)
- Space transform screen space issue (core#7760)
- Crash when using polygon holes (core#7781)
- Operator nodes are not allowed within procedurals (core#7784)
- No diagnostic showing license server used for successful checkout (RLM parity) (core#7790)
- running multiple AiMakeTx hangs and crashes in 5.2.2.0 (core#7794)
- maketx was not automatically doing –opaque-detect (core#7808)
- transmission toon artifacts around triangle edges (core#7812)
- color shifts in randomwalk sss when far from origin (core#7905)
- Add missing camera projection features (core#7939)
- add triggers for filename, objectpath and fps changes for alembic procedural (core#7952)
- Log reason why custom procedural fails to load (core#7982)
- Add missing attributes in ramp_rgb (core#7987)
- Deep driver: append does not work with half data channels (core#8019)
- Luminance conversions should take into account working color space (core#8026)
- Add wrap_mode "none" for uv_transform (core#8097)
- Ramp in interpolation "constant" not including key positions (core#8142)
- allow smaller SSS radius (core#8170)
- Reset shader assignment using set_parameter (core#8009)

Compatibility
16.5.634
17.0.416
17.0.459
Linux x86_64 (H16: gcc4.8 and H17: gcc6.3)
Windows 7 x64 (H16: vc14 and H17: vc14.1)
Mac OS X 10.8+ (clang7.3)
Fixes
CopyToPoints and CopyTransform instancing fix (htoa#1159)
Houdini locks up during TX file generation (htoa#1151, core#7794)

Enhancements
- Round corners shader: This shader modifies the shading normals near edges to give the appearance of a round corner. The simpler way to use this shader is to connect its output normal to standard_surface.normal or standard_surface.coat_normal (core#7517)
- Normal map blending: A new normal_map blending mode was added to the layer_rgba shader. This makes easier to create fine details and is more efficient than connecting multiple bump or normal mapping nodes. (core#7523)
- Faster adaptive subdivision: Faster adaptive subdivision due to more efficient computation of irregular patches: x2 speedup in some cases. (core#7344, core#7444, core#7488)
- Faster operator evaluation: Operator evaluation is now up to 20x faster on large scenes thanks to expression caching and graph pre-processing. (core#7001, core#7508)
- JSON log file additions: The JSON stats file has more info, such as the hardware used. (core#7196)
- LPE image metadata: Output image metadata now includes the full light path expression for each layer. (core#7499)
- Alembic archives: The Alembic procedural will reuse alembic file handles, keeping up to 8 file handles open for better cache handling in parallel node initialisation. (core#7071)
Incompatible changes
- Range shader gain: The gain parameter on the range shader is now inverted for consistency with the AiGain() API function (core#7477)
- JSON stats change: The JSON stats format has changed in order to resolve some ambiguities with nested fields. (core#7074, core#7530)
- JSON stats version: The JSON stats file now has a "JSON log version" field that will be incremented each time a breaking change is made to the JSON stats format. (core#7530)
Fixes
Alembic packed primitive translation optimisations motion (htoa#1023)
Optimisations for rendering multiple alembic primitives (htoa#1106, core#7493)
MaterialX generated shaders are scoped under their node graph names. (core#7443)
Unexpected missing parameter warning on custom procedural instances. (core#7548)
Copy id to child alembic nodes. (core#7442)
Shaders should check that samples are always strictly positive. (core#7573)
Alembic geometry has incorrect transform with make_instance enabled. (core#7567)
Alembic transform/deformation motion blur mismatch. (core#7539)
The first parameter of OSL nodes is not initialized to the default value. (core#7524)
Remove the OptiX dependency on mac. (core#7520)
User parameters not properly propagated or read from parent procedural. (core#7516)
Alembic Crash with arbGeoParam array property. (core#7507)
Autobump (and bump) disappear for some pixels. (core#7505)
Alembic procedural expansion with make_instance on using an object_transform parameter. (core#7501)
Noice: when looking for feature AOVs prioritize AOVs with the correct filter. (core#7497)
Kick -laovs should not grab a license. (core#7495)
Add sheen AOV labels. (core#7492, htoa#1105)
Texture baking: small triangles can cause artifacts. (core#7480)
Gain function in range shader is inverted. (core#7477)
Alembic object transform fix. (core#7475)
Curves memory report missing some entries. (core#7474)
Shadow group is not inherited in ginstance. (core#7472)
D'Eon BCSDF must be evaluated when `base_color` is small. (core#7470)
Render callback does not support an "empty" callback. (core#7467)
MaterialX: Supported parameter arrays are not processed by operator and node definition generation. (core#7466)
Adaptive camera samples higher than expected. (core#7461)
Thread safety of alembic procedural tokenize function. (core#7456)
Cell noise time not evaluated when linked. (core#7445)
Volume AOVs: shadow rays interfere with new Z and ID AOVs. (core#7432)
Volumes: register new AOV volume_Z. (core#7431)
Transform motion in procedural that only contains lights can give invalid lights. (core#7422)
Make flatness check for quad_light more robust. (core#7419)
Noice: skip denoising AOVs with no associated variance. (core#7418)
Noice: support additional channel suffixes and warn if the suffix is unsupported. (core#7417)
Noice: incorrect handling of variance AOVs in a separate file. (core#7416)
Noice: issues with certain crop windows combinations. (core#7415)
Alembic files with single entry array attributes should be considered not arrays. (core#7413)
Metadata lexer should ignore more than three # in a row. (core#7388)
Nested timing stats are ambiguous in json output. (core#7074)
Recover from failed optix launches. (core#6727)
Export full path instead of node name when writing to .ass while expanding procedurals. (core#6221)
Alembic transform incorrect with motion blur. (core#7579)
Alembic with make_instance and parallel node init enabled causes disappearing geometry. (core#7478)
Alembic crash with make_instance enabled and changing frames. (core#7446)

This is a bug fix release, bringing alembic procedural improvements.

Compatibility:

This release uses Arnold 5.2.0.1 and OpenVDB 4.0.0.

Binaries available for the following Houdini, Houdini FX, Houdini Indie and Houdini Education production builds:
-16.5.496
-16.5.536
-16.5.571
and for the following platforms:
-Windows 7 x64 (vc14)
-Please note that Houdini Apprentice does not support third-party renderers and thus cannot run HtoA.
Enhancements

-Translate volume shader for custom procedurals (htoa#1095)

Fixes:
-Fixed alembic procedural motion vectors pass (htoa#1087)
-alembic packed primitive motion blur issue with SOP transform (htoa#1101)
-Fixed alembic traversal threading issue (htoa#1103, core#7456)
-alembic crash fixed with make_instance enabled and changing frames (core#7446)
-alembic files with single entry array attributes should be considered not arrays (core#7413)
-Copy id to child alembic nodes (core#7442)
-Texture baking uv layer fix (htoa#1102)
-Update state_int node interface (htoa#1096)
-Gain function in range shader is inverted (core#7477)

Incompatible changes:
-Unpacking alembic packed primitives affected by a scaling transform SOP will affect object space, requiring an adjustment to the displacement scale (htoa#1049)

Fixes
Procedural node no longer translates primitive material in error (htoa#947)

Fixed a bug where MPlay created a frame per progressive pass (htoa#969)

Now we detect and report invalid color spaces in the OCIO config (htoa#981)

Remove an exception occurring when displaying volumes as bounding box (htoa#983)
Removed an error with license checking in batch mode (htoa#985)
Phantom instances conflicting with beauty is fixed (htoa#987)

AiMakeTx() no longer fails with single channel input images and DWAA compression (htoa#988)

Save to disk in background is fixed (htoa#990)

Fixed a crash connecting MtoA Ramp shader in HtoA (htoa#993)
Array parameters now update correctly in IPR (htoa#994)

Fixed a memory leak when destroying custom procedurals (core#6624)

Fixed standard_hair no longer creates the 'hair' LPE label (core#6537)

OSL shader param cannot link to alpha component of RGBA shader (core#6568)

Color Manager: fix python binding for AiColorManagerTransform return value (core#6582)

Allow IOR below 1.0 (core#6585)

Number of image tags too low (core#6646)

Provide simple constructor for matrix in Python API (core#6555)

Compatibility
This release uses Arnold 5.0.2.3 and OpenVDB 4.0.0.

Binaries available for the following Houdini, Houdini FX, Houdini Indie and Houdini Education production builds:

16.0.736
16.5.268
16.5.323


and for the following platforms:

Linux x86_64 (gcc4.8)
Windows 7 x64 (vc14)
Mac OS X 10.8+ (clang7.3)


Please note that Houdini Apprentice does not support third-party renderers and thus cannot run HtoA.

Enhancements
CLM license server not detected at startup (htoa#964)

AiMakeTx Issues on Windows (htoa#967)

Crash using the light blocker with a spotlight (htoa#968)

Fixes
UDIMs: incorrect character substitutions (core#6511)
Crash during accel construction with invalid or invisible geometry (core#6481)
error building BVH over procedurals with no visible objects (core#6500)
Properly warn when there are more than 15 per-light AOVs (core#6516)
maketx and AiMakeTx are extremely slow or crash with certain large images (core#6527)

Compatibility
This release uses Arnold 5.0.2.2 and OpenVDB 4.0.0.
Binaries available for the following Houdini, Houdini FX, Houdini Indie and Houdini Education production builds:
16.0.705
16.0.736
16.5.268

and for the following platforms:
Linux x86_64 (gcc4.8)
Windows 7 x64 (vc14)
Mac OS X 10.8+ (clang7.3)

Please note that Houdini Apprentice does not support third-party renderers and thus cannot run HtoA.
Enhancements
Use explicit default color spaces in Arnold ROP (htoa#963)
Disable parameter linking with environment variable (htoa#959)
Implement standard shader UI logic (htoa#958)
Fixes
Fix for s/t wrap with <attr> expressions set in the image node filename (core#6257)
Excessive memory use with compressed UVs (core#6411)
Small polymesh memory leak at render shutdown (core#6417)
OSL raytype mismatch (core#6422)
Handle invalid characters when image tokens are resolved (core#6440)
Backfacing normals not supported in normal_map (core#6441)
Chained bumps using bump2d isn't working (core#6442)
Custom procedurals cannot create nodes before proc_init (core#6453)
Crash with linear subdivision, vertex normals, and deformation blur (code#6454)

Compatibility
This release uses Arnold 5.0.2.1 and OpenVDB 4.0.0.
Binaries available for the following Houdini, Houdini FX, Houdini Indie and Houdini Education production builds:
16.0.705
16.0.736
16.5.268

and for the following platforms:
Linux x86_64 (gcc4.8)
Windows 7 x64 (vc14)
Mac OS X 10.8+ (clang7.3)

Please note that Houdini Apprentice does not support third-party renderers and thus cannot run HtoA.
Enhancements
New sub-surface scattering algorithm: A new, more accurate way of calculating SSS has been added. Unlike the current empirical BSSRDF method based on diffusion theory, this new method actually traces below the surface with a real random walk and makes no assumptions about the geometry being locally flat. This means it can take into account anisotropic scattering like brute-force volume rendering and produces much better results around concavities and small details. It can also be substantially faster for large scattering radius (i.e. large mean free path) compared to the old method. On the other hand, the new method can be slower in dense media (i.e. small mfp), does not support sss_setname for blending two surfaces together, may require redialing materials to achieve a similar look, and is more sensitive to non-closed meshes, "mouth bags", and internal geometry potentially casting shadows. This new algorithm is exposed in the standard_surface shader via the new parameters subsurface_type (with enum values diffusion and randomwalk) and subsurface_anisotropy(Henyey-Greenstein's eccentricity g from -1.0 to +1.0). The default is to use the old empirical diffusion method in order not to break the look of existing scenes. (core#5005, core#6363)
Car paint shader: We are now shipping a dedicated shader for car paint, which can be thought of as the combination of a simplified version of the standard_surface and flakes shaders. This shader can create a wide range of car paint looks without having to connect several nodes. For example, a pearlescent effect can be easily added to both the specular and flakes layers by simply tweaking a few parameters such as specular_flip_flop and flake_flip_flop. An arbitrary number of layers of flakes can be used (flake_layers). The flakes at a deep layer are covered by the ones closer to the surface and more tinted by pigments (specified by the transmission_color parameter). A few presets are available to get started quickly (core#6238)
Subdivision frustum culling: Subdivision patches outside the view or dicing camera frustum will not be subdivided. This is useful for any extended surface that is only partially visible as only the directly visible part will be subdivided. Similarly, no subdivision work will happen if a mesh is not directly visible. This can be turned on globally by setting options.subdiv_frustum_culling true and can be turned off for specific meshes with polymesh.subdiv_frustum_ignore true. The global options.subdiv_frustum_padding adds a world space padding to the frustum that can be increased as needed to minimize artifacts from out-of-view objects in cast shadows, reflections, etc. Note that motion blur is not yet taken into account and moving objects might require some additional padding. (core#4451, core#6304, core#6336)
Improved flakes shader: The size parameter is replaced by the density parameter, which makes it easy to control the size and number of flakes. Alpha channel can be used as a mask. The new flakes shader supports non-disc shapes and 3D flakes, which are useful to render gemstone inclusions like goldstone, for example. (core#6061)
Improved shadow_matte shader: We have revamped and simplified the shader to make it easier to use, and fixed a number of long-standing issues: Indirect illumination now fills the global diffuse_indirect and specular_indirect AOVs, so we have removed the shader’s (confusingly named) indirect_diffuse and indirect_specular AOVs. Self-reflections are no longer rendered. A new specular_IOR parameter was added that controls Fresnel reflection. Parameters offscreen_color and background_type were removed. The new enum parameter background can be set to either scene_background (default) or background_color, which allows to connect a specific texture in the background_color parameter slot. Parameter alpha_mask was added to control whether the alpha must be opaque or if it has to contain the shadow mask. (core#6245, core#6248, core#6249, core#6250, core#6256)
Celullar option in triplanar shader: The triplanar shader now supports projection through Voronoi cells using the new cell parameter. The rotation angle of the projected texture for each cell can be controlled with the cell_rotate parameter. Cells can be smoothly blended using the cell_blend parameter. (core#6130)
Faster triplanar shader: Texture filtering in the triplanar shader has been improved, giving better antialiasing and up to a 2x speedup, specially when using high-resolution texture maps. (core#6187)
Option for exporting shader assignments: A new option has been created on the Archive section of the ROP called Export Shader Assignments . This determines whether to create the shader assignments when the Export Shaders option is off. The default matches the previous behaviour of always exporting the shader assignments. However now shader assignments can be turned off, for exporting ass files without shader connections if required. (htoa#954)
Transmit AOVs and Alpha: The standard_surface shader with transmission can now pass through AOVs, by enabling the transmit_aovs parameter. If the background is transparent, then the transmissive surface will become transparent so that it can be composited over another background. Light path expression AOVs will be passed through, so that for example a diffuse surface seen through a transmissive surface will end up in the diffuse AOV. Other AOVs can also be passed straight through (without any opacity blending), which can be used for creating masks for example. (core#5588)
OCIO Color families: The image node, the output color space parameters on the ROP, the render and LDR color spaces all now include a color family drop down to help select color spaces from an OCIO profile (htoa#916)
Display / view colorspace: OCIO Display/View tuples can now be selected as an output color space. (htoa#916)
Custom procedural namespaces: Procedurals can now declare a custom namespace using the new namespace parameter. This custom namespace can be used instead of the procedural name, to reference contents through absolute or relative paths. Multiple procedurals can share the same namespace by using the same custom name. Also, they can declare an empty name and they will use the global namespace. (core#6085)
Improved procedural namespace memory usage: Reduced memory used by procedural namespacing by about 28KB per procedural primitive, so that procedurals now use very little additional memory. In a scene with 100K procedurals, this gave about a 2.7GB reduction in memory use. (core#6086)
Faster AiNodeDestroy: we have optimized removal time for nodes contained in procedurals, greatly reducing the shutdown time at the end of a render in complex scenes. (core#6137)
Improved accuracy of UV coords: Mesh UV coordinates are now handled with higher numerical precision, fixing jagged artifacts that sometimes appeared when using high-resolution UDIM textures over very wide UV ranges. (core#5514)
Improved volume sampling of low-spread lights: Low-spread quad and disk lights should now produce less noise and show increased performance when participating in atmospheric scattering effects. (core#5128)
Faster opacity masks: Texture map-based opacity masks will now be faster to render. Testing indicates around 3-13% faster. (core#6153)
Accurate dielectric Fresnel: The Fresnel formula in the microfacet and microfacet refraction BSDFs now use the accurate dielectric instead of Shlick Fresnel. The old formula could give much too bright reflections for low IOR values near 1.0, like in the interface between ice and water. (core#5371)
Support for more OSL attributes: OSL shaders now support getattribute() lookups of standard camera attributes (e.g. camera:fov, camera:resolution, etc) as well as the geometry attributes geom:type, geom:name, geom:bounds, and geom:objbounds on objects. (core#6172)
Improved multi-threaded render time stats: Render times when using more than one thread did not really work. We have improved this so that render times are now much more reliable and useful and can now be confidently used to determine what parts of Arnold are the most expensive. In particular, the subdivision and displacement times will now show how much total time was used as well as what fraction of that time was spent with threads unable to do useful work. This "threads blocked" time can often be lowered by using larger buckets or the randombucket_scanning ordering. (core#6218)
maketx version info: The custom maketx binary that ships with Arnold now reports, both in the command-line and in the embedded EXR headers, that it was built specifically for "OpenImageIO-Arnold", to distinguish it from the official "OpenImageIO" one. (core#6118)
maketx color spaces: The custom maketx that ships with Arnold now supports OCIO and SynColor (when available) through the colorengine, colorconfig and colorconvert flags. See maketx --help. (core#5908)
AiMakeTx reports info messages: AiMakeTx now also prints out OIIO informational messages (generated in verbose mode, for instance) in addition to errors. (core#6148)
AiMakeTx releases input file lock sooner: AiMakeTx will now close the input texture as soon as possible instead of waiting for all the maketx jobs to finish. (core#6240)
AiMakeTx and maketx optimized flags: Both AiMakeTx and maketx now always run with the flags --monochrome-detect --opaque-detect --constant-color-detect --fixnan box3 --oiio, which can result in smaller .tx files that are faster to load and take less memory. (core#6261)
Report when textures are changed during render: The log files now report when texture modifications during a render cause a texture read error, which can happen in certain pipelines. (core#6246)
.ass metadata from compressed files: We now support loading metadata from .ass.gz files through the AiMetadataStoreLoadFromASS() API function. (core#6197)
Fixes
HtoA ZeroMQ library fix for older OSX versions (htoa#950)
Set the ginstance matte attribute from a point attribute (htoa#951)
Alpha not fully opaque in output images (core#3319)
Non-linkable light colors should have the linkable metadata disabled (core#4559)
Distant light not motion blurring direction (core#5974)
Incorrect melanin absorption values for wide gamut rendering color spaces (core#5981)
maketx fails when run on Windows with read only (mandatory) user profiles (core#6087)
Deep EXR output of light path expressions missing volumes (core#6089)
artifacts in latlong skydome_light (core#6094)
Fresnel discontinuity in diffuse term when texture is connected to specular_color (core#6095)
Subdiv: duplicate vertex index in face causes crash (core#6097)
Quad lights do not work with projected textures (core#6104)
Warn that images will be watermarked if license authorization fails (core#6116)
mesh_light crashing when provided non-mesh node (core#6124)
curvature shading differences when seen through glossy transmission/reflection (core#6128)
crash during accel construction if there are over 65k overlapping primitives (core#6135)
Indirect sample clamp not visible in AOVs (core#6136)
Light groups not supported by volume shapes and surface shader interiors (core#6138)
"A" AOV is black when 8 light AOVs are used (core#6141)
AiShaderGlobalsGetVertexUVs not working for uvsets in free render mode (core#6143)
Black AOV output due to conflicting AOV type redefinition (core#6151)
AiShaderGlobalsGetPositionAtTime, AiTraceBackground, and AiVolumeSample crash in background shading context (core#6162)
AiM4Scaling does not work in python (core#6166)
Wireframe artifacts when not in raster-space (core#6177)
MotionVector AOV empty for negative motion start / end (core#6182)
Triplanar uses wrong mipmap level for some parts of the object (core#6186)
Triplanar uses overly high res mipmaps (core#6187)
Crash when removing and recreating a procedural instance (core#6192)
counter overflow crash in big scanline EXR images (core#6202)
photometric_light filename does not support environment variable expansion (core#6219)
Metallic BSDF albedo is always white (core#6222)
Crash when removing a procedural node (core#6242)
Shadow_matte AOVs (core#6245)
Remove offscreen_color from shadow_matte (core#6248)
Remove shadow_matte background_type (core#6249)
Re-introduce background_color in shadow_matte (core#6250)
Shadow_matte self-reflections / self-shadowing (core#6251)
trace_set: crash when destroying shader (core#6254)
sss_irradiance_shader fails with closure-based shaders (core#6255)
Add alpha_mask in shadow_matte (core#6256)
Volume shader: crash when connected as atmosphere shader (core#6286)
Crash with invalid options.atmosphere and options.background shaders (core#6287)
Miscellaneous crashes (empty nurbs, empty implicit, atmosphere shadow_matte) (core#6288)
Deep Driver: write errors hang the render (core#6292)
Deep driver: append does not work with overscan renders (core#6293)
Bucket call back: user bucket coords should be snapped to bucket grid (core#6294)
Crash when saving empty ginstance with open_procs enabled (core#6295)
Camera differential evaluation can cause crashes or hangs with OSL shaders linked to camera#6313crash when 4-channel opacity texture has no alpha=0 (core#6297)
Crash on Windows when loading plugins without .dll extension (core#6331)
"host app" metadata item not readable by AiMetadataStoreLoadFromASS (core#6174)
Range shader can sometimes ouput infinite or nan (core#6258)
Support upper and mixed case versions of .ass / .ass.gz extensions (core#6303)
ASS metadata load is too slow (core#6409)
Crash when setting an array user parameter with its current value (core#6412)
Incompatible Changes
autotile disabled by default: We found that the autotile code in OIIO does not scale with high-resolution textures. In order to avoid very slow loading of untiled textures (such as JPEG) when autotile was enabled, we have now changed the autotile default setting to 0, which effectively disables it. In very rare cases, when rendering with a large number of high-resolution untiled textures, this change might degrade performance as the texture cache will blow up. The real solution is to never use untiled files, and instead convert all untiled textures to .tx tiled files. (core#5116)
maketx dependencies: The custom maketx that ships with Arnold now depends dynamically on libai.so and optionally on syncolor_shader.so, therefore to work correctly it needs to be run from its installation folder, like kick, or alternatively the new dependencies should be copied to where maketx is running from. (core#5908)
Light groups and volume shading: Just like with surface shapes, Arnold now obeys light group assignment on volume shapes and surfaces with volumetric interiors. While in many cases desirable, this can produce an unexpected change in the final image in scenes with light group assignments. (core#6138)
flakes shader: It was not easy to control the number of flakes with the size and scale parameters because they were mutually dependent. Now this can be easily done using the new density parameter. The shape of each flake has been changed from disc to Voronoi cell, which is more suitable to render inclusions of gem stones. The shader output type has been changed from RGB to RGBA to support a mask. (core#6061)
motionvector AOV: The motion vector scaling factor in the built-in motionvector AOV has changed. This was required to fix a bug that caused zero motion vectors for certain shutter positions. The output from the motion_vector shader is unchanged: it can be used as a workaround in your old scenes if you require the previous scaling. (core#6182)
shadow_matte changes: The shader AOVs indirect_diffuse and indirect_specular were removed, since the shader now fills the corresponding built-in AOVs. Parameters offscreen_color and background_type were removed. See notes in the enhancements section above.

AOV EXR Precision Output bug fix (htoa#948)
Crash when removing a procedural node (core#6242)
Removed crash when destroying trace_set shader (core#6254)
sss_irradiance_shader no longer fails with closure-based shaders (core#6255)
Crash fixed when connecting a volume shader as an atmosphere shader (core#6286)
Miscellaneous crashes fixed (empty NURBS, empty implicit, atmosphere shadow_matte) (core#6288)
driver_deepexr driver append fixed with overscan renders (core#6293)
Crash when saving empty ginstance with open_procs enabled (core#6295)
Camera differential evaluation crashes and hangs fixed for OSL shaders linked to camera (core#6297)
The range shader no longer occasionally outputs infinite or nan floats (core#6258)

Enhancements
When exporting an .ass file, the bounding box is now written as bounds metadata in the .ass file itself instead of being written as a separate .asstoc file. Exporting .asstoc files is still possible but is now disabled by default. We will remove .asstoc support entirely in a future release (htoa#910)
Fixes
Curvature shading differences when seen through glossy transmission/reflection (core#6128)
Crash during accel construction if there are over 65k overlapping primitives (core#6135)
Alpha not fully opaque in output images (core#3319)
Quad lights do not work with projected textures (core#6104)
Indirect sample clamp not visible in AOVs (core#6136)
Black AOV output due to conflicting AOV type redefinition (core#6151)
AiM4Scaling() does not work in Python (core#6166)
Crash creating motion blurred min_pixel_width inside a procedural (core#6170)

Compatibility
This release uses Arnold 5.0.1.1 and OpenVDB 4.0.0.
Binaries available for the following Houdini, Houdini FX, Houdini Indie and Houdini Education production builds:
16.0.600
16.0.633
16.0.671

and for the following platforms:
Linux x86_64 (gcc4.8)
Windows 7 x64 (vc14)
Mac OS X 10.8+ (clang7.3)

Please note that Houdini Apprentice does not support third party renderers and thus cannot run HtoA.
Enhancements
IPR Shader Translation: Adding and rewiring of surface and volume shaders is supported during IPR rendering, including previously isolated shader nodes. (htoa#924)
IPR Output Nodes: Rewiring connections to the surface and volume material output node (htoa#925)
Fixes
IPR Shader Rewiring: Fixes for rewiring of shaders during IPR rendering including node creation and undo. (htoa#907)

See also the Arnold 5.0.1.1 release notes for the full list of core enhancements and fixes.