Welcome to RenderMan 23.6!

This release introduces improvements to RenderMan. 

Please dive right into the release notes below for more detailed information on the latest version of your favorite renderer!

New Features in 23.6

• There are two new optional controls for path-traced subsurface scattering - Attribute "trace" "int sssautobias" and "trace" "float sssbias". In the rare cases where the automatically computed bias for
  path-traced subsurface scattering needs tweaking, one can set "sssautobias" to 0 and "sssbias" to a desired value such as 1e-6. The default values are 1 for "sssautobias" and 1e-4 for "sssbias".

• Allow volumes to output their aovs via PxrTee.

• The PxrPrimvar built-in names "curvature_u" and "curvature_v" for principal curvatures can now also be written "curvatureU" and "curvatureV". This is for forward compatibility with the OSL version of PxrPrimvar in RenderMan 24.

• Deprecate the behavior where connecting a utility pattern to a PxrSurface node forces uncached opacity computations. This has been seen to be a major performance detriment, but can be re-enabled with Option "user" "int utilityPatternForcesOpacity" [1]

• Added support for OpenEXR Arbitrary Metadata
• PxrAttribute has a new resultI output to allow users to chain PxrAttribute nodes.

Fixes

• Fix for renders from recovery were taking > 20x longer than when uninterrupted

• Fixed bugs batched trace() with multiple shader groups in the hits.

• Fixed a bug that could return garbage derivatives on failed texture lookups from OSL.

• Fixed a bug that could result in bad texture derivatives at UDIM boundaries.

• Fixed offscreen decimation of dicing rate incorrect behavior with a custom ScreenWindow

• Fixed out-of-bounds vector access when a OSL spline is provided with only a single control point.

• Fixed incorrect default for the number of textures in PxrTileManifold and PxrRandomTextureManifold.

• Fixed rare holes in alpha channel due to missing ray hits on subdivision surfaces with intricate detail. (The holes were visible when looking at the alpha channel with gamma=0.)

• Fixed a bug where derivatives where uninitialized when fetching uniform attributes and options with OSL getattribute().

• PxrSwitch artifact when connecting a pattern to the index parameter.

• Fixed cases where texture3d() could lead to uninitialized values in derivatives.

• Fixed a bug where AreaScale of mesh lights was not properly updated during interactive updates.

• Fix for shadow bump terminator index error in PxrDiffuse and PxrDisney
• Fix for uninitialized direction in sampleMarschnerGLINTS()

• Optimized a pathological case for nested instancing on scene ingestion that can dramatically reduce render startup in certain cases.

• Fixed a bug that could cause intermittent crashes in non-deforming curves.
  

Miscellaneous Changes

• Added improvements to light selection learning

• Improve the behavior of denoised Marschner by changing how the albedo is calculated

• Improve the degree of noise in scenes with spotlights or ies profiles
• LocalQueue log improvements