Welcome to RenderMan 21.3!

This release introduces the following improvements, fixes, and miscellaneous changes.

New Features

• PxrSurface's new Diffuse Exponent (when roughness is 0.0) is a power exponent that controls the diffuse falloff.
• PxrMarschnerHair now supports Glow and improved controls with the addition of new parameters.
• PxrSurface's interior scattering introduces a Multiscatter parameter. This is required to be on for use with the PxrVCM and PxrUPBP integrators.
• LPE system now handles complex sets of LPEs more efficiently.
• Per lobe LPE has been added to PxrMarschnerHair, these will output results from: HairSpecularR, HairSpecularTT, HairSpecularTRT, HairSpecularGLINTS.

• New built-in primvars "curvature_u" and "curvature_v" -- the principal surface curvatures in the u and v directions. (As before, the "curvature" primvar is the mean surface curvature, ie. the average of curvature_u and curvature_v.)

Miscellaneous Changes

• Scenes with frequent use of EnableLightFilter may see a reduction in the amount of memory used.

• Support for changing light filter topology during IPR.

• Improved light sampling in volumes.
• Less noise is visible when using presence values less than 1.
• Time to first pixel in scenes with millions of lights has been greatly reduced.
• Added support for writing holdout shadows to the beauty alpha channel
• Some error messages for RiCurves now contain more info.
• We now allow layering of subsurface transmit gain in PxrLayer and PxrLayerMixer.

• PxrOcclusion useAlbedo now requires Bxdfs to return a valid albedo user lobe otherwise black is assumed. This may result in a change the behavior for custom Bxdfs, visible lights, and hair geometry.

• Denoiser layer groups can now override the main images variance channels using custom settings.
• Improved selection of lights when rendering anisotropic volumes.

Bug Fixes

• Fixed a bug that could cause sporadic crashes early in a multi-threaded render.

• Fixed a bug with UNC Windows file path parameters for "it"
• Fixed a bug in PxrMarschner that may cause crashes.
• Spaces in file paths can be passed to "it"
• Fixed a possible stack overflow when rendering curves.

• Fixed missing results from baking one-sided geometry.

• Fixed an error message indicating bad nesting of structs when the problem was actually just incompatible struct connections in shader graphs.

• The orientation of Nn on a sphere now matches Ngn -- there was an inconsistency for transforms with negative determinant (both for Orientation "rh" and "lh") when Option "quadric" "orientspheretotransform" is 1.

• Fixed incorrect output space for bake3d normals.
• Fixed incorrect transmission term for motion blurred volumes.

• Python RIF's now run in python3.

• Fixed a bug that could cause OSL shaders to get dropped from objects with long "identifier" attributes.

• Fixed crash in watertight dicing that could occur with some maxgridsize settings.

• Fixed single-scatter nested volumes writing direct lighting and emission results to LPE AOVs. The results are now correctly classified and written to the correct AOV.

• Geometric light patches no longer potentially get disabled when they happen to have a high enough tessellation rate.

• Matte objects now work correctly in Z-depth AOVs. Toggle off the "respects matte" property of the Z AOV if you wish to emulate the previous behavior.

• Fixed potential for crashes during direct-linked renderer shutdown at the completion of a render that used OSL.

• Fixed potential end-of-render crash when using OSL shading nodes.
• Fixed incorrect derivatives in PxrBumpManifold2D.
• Fixed out-of-sync PxrLayerSurface.args from PxrSurface.args where diffuse tranmission didn't work with PxrLayerSurface.args.
• Added missing subsurface transmit gain in PxrLayerSurface.args and PxrLayer so we can now layer subsurface transmit gain as well.

• Fixed a bug that caused textures made with pattern "single" to return black when used with bilinear and bslpine filters.

• Fixed a crash that would occur when using holdouts in scenes with no light sources.
• Fixed a bug accessing the wrong MIP level for non-square textures resulting in spurrious "T10004 {WARNING} Can't find res for xxxx" warnings and random texture read values.
• Fixed correlation artifacts in PxrDirt

Known Limitations

RenderMan Pro Server

• The PxrAovLight does not work properly with PxrUPBP.
• Analytical lights placed inside volumes may yield artifacts when made visible to the camera. As a work around, the light camera visibility should be turned off, and a geometry with a similar shape should be used (visible to camera, invisible to transmission and indirect rays), with the proper emissive bxdf.
• Using the '.' character in the handle for an OSL shader could cause unpredictable results during re-rendering.
• Instances are not supported for baking.
• 3d baking: no direct bake-to-ptex support.
• PxrBakePointCloud cannot directly render ptex.
• No RixPTC/pointcloud API (so PxrBakePointCloud cannot read ptc files).
• Sample/Display filter plug-ins do not have access to lighting services for light dependent effects, e.g. lens flare.
• Adding new mesh light on existing geometry during IPR results in double geometry.
• Camera visibility changes are not respected during Live Rendering.
• For PxrUPBP, If the light source is inside a volume, that volume needs to be defined as Volume “box”
• For PxrUPBP, To get a volume caustic, the object casting the caustic needs to have higher intersectpriority than the volume.
• For PxrUPBP, Overlapping heterogeneous volumes are not working yet. (However, overlapping homogeneous volumes do work.) This will be resolved in the future.
• PxrPortalLight may yield artifacts when generating photons for PxrVCM / PxrUPBP. This will be fixed in a future release.
• When attempting to access an array primvar, you must first check the size of the array primvar and allocate the appropriate space. Not doing so may lead to a crash.
• Points and curves cannot have mesh lights attached to them.
• Deformation motion blurred volumes don't currently work with densityFloatPrimVar or densityColorPrimVar. You will need to use a PxrPrimVar node connected to densityFloat and densityColor instead.