...

• Fixes for a case where PxrDisplacement would not work when being passed to XPU
• Make volumes respond to underlying changes in the field prim
• Fixed a bug that could sometimes hang hdPrman when processing materials with loops in the node graph
• Updated calculation of primvar calculations in curves to match RenderMan
• Fixed a camera framing issue
• Support array inputs within hdPrman's material parser
• New warning when a renderer delegate cannot be created
• Fixed issues with the fallback shader
• Add support for UsdPreviewSurface's opacityThreshold param in HdPrman
• Metallic materials should have an F0 equal to their base color in UsdPreviewSurface
• Support .args and .oso files embedded in .usdz files
• Updated UsdPreviewSurface clearcoat calculations to better match expected inputs
• Support UsdTransform2d
• Fix HdPrman support for USD Preview Material texture coordinate conventions when using a RenderMan tex format file. Inserts a UsdTransform2d if necessary to invert the T axis
• Optimize framebuffer updates for faster frame rate
• Cleaned up warnings from the stats system that would appear during interactive rendering
• Adding support for missing light parameters to hdprman (msApprox, msApproxBleed, msApproxContribution, emissionFocusNormalize)
• Updated our renderer definition with settings to allow for better integration with Solaris features
• Added support for dataWindowNDC and aspectRatioConformPolicy
• Adjust HdPrman's fallback volume shader to match Storm's. Visually, this fallback approximates something like smoke: low albedo, isotropic (i.e. scattering has no directional bias), single-scatter
• Fix HdPrman's fallback maxSamples to match the RenderMan fallback (64)
• Adds support for UsdUvTexture's "sourceColorSpace" input and fixes UsdPreviewSurface's normal mapping
• We want the ability to pass asset paths that refer to things other than .tex files on disk to prman for the lightColorMap property on lights
• Support additional clipping planes
• Add support for UsdPreviewSurface's displacement

Miscellaneous Changes

RIS

• "it": We now ignore render regions if you're using "it" for IPR. If you need render region like behavior, use the crop window feature in "it".
• Integration: A few enhancements in light selection that will provide improvements in convergence time.
• Integration: Significant speedup for RIS PxrOcclusion integrator for ambient occlusion (with "useAlbedo" off) when objects have complex pattern networks.

• OSL: simplified semantics for calling debug(). Simplify to debug(aov, "writemode", "always") and allow conditionals around the call to replace the flagval itself.  Default behavior of debug(aov) is equivalent to debug(aov, "writemode", "camerahit")

• OSL: PxrNormalMap willi now check for primvars Tn and Bn for the tangent and bitangent before using "builtin"
• Lights: Startup time improvements when many unique mesh lights are present
• Lights: Performance improvements during light selection
• API: Support for modifying data within nested mutable shading contexts
• API: If you have a custom integrator, you may need to recompile it due to an API change that was required to support Volume Aggregates.

...