• Dynamic editing of AOVs and LPEs. Add them, remove them, or edit them – all without restarting your Live Renders. This is perfect for lighters and TDs tweaking shots
• Dynamically change resolutions without having to restart your render – especially useful when using viewport renders with tools like Maya and Houdini
• Quicker artist feedback via a new capability to control how the first iterations are updated to the screen

Interactivity in heavy scenes

When making rapid edits to heavy scenes and this setting is non-zero, the renderer will try to reduce tearing by updating the whole screen progressively with a dissolve-like effect using a new option we call "decidither" but is exposed as Interactive Refinement in bridge products where possible to allow updates to the technique without changing the artist workflow.

Enhanced adaptive sampling and a new default

Important improvements to how RenderMan performs adaptive sampling have been made.

• The default approach has changed to how the adaptive sampler works.  In the past, we used the notion of contrast changes in the pixel to determine when to stop sampling.  This had the advantage that it was more memory efficient.  However, it had the disadvantage that it would sometimes do the wrong thing in areas of significant change on a surface.  The new approach uses statistical variance to determine when to stop sampling the pixel.  The new approach will give more consistent levels of noise across an image (and across a variety of images) compared to previous versions of RenderMan.  This means that you will need to put fewer renders back on the farm because they contain noisy regions
• Pixel variance tests are done in a perceptual space.  This improves reliability of the sampler and makes it behave closer to what the human eye sees.  This will result in more even noise across areas in the image with varying exposure
  • Testing in a perceptual space has allowed us to remove darkfalloff as a parameter that controls the new RenderMan 23 adaptive sampling metrics (though it does remain for our compatibility metric, "contrast-v22")
• The default value of the PixelVariance option is changing.  For the old RenderMan contrast based metric, 0.005 was the default.  0.015 is the default for the new variance metric
• New controls for "exposure bracketing".  To provide more flexibility during compositing, you can tell RenderMan to sample more in darker and lighter regions of an image so that you can change the exposure of the image without bringing more noise into the image.  The units are in stops.
• If you load an old scene, double check the value of PixelVariance and adaptivemetric.  0.015 for "variance", and 0.005 for "contrast-v22".  You will need to experiment with values other than these to find a good balance of render time and quality, you can find out more about this under Sampling
• You can choose the "contrast-v22" adaptive sampling metric to revert RenderMan back to its old behavior.  This metric is deprecated and will be removed from a future release.

All of these enhancements will likely mean that you will need to rethink your adaptive sampling defaults if you tweaked them in an older version.  Because minor tweaks may be made between the RenderMan 23.0 beta and the release, you may want to revisit your defaults again at that time.

Important Differences

• The plugin API has been updated, so all plugins need to be recompiled in order to function in version 23.x
• RenderMan has been updated to support VFX Reference Platform CY2018
  • C++14 is now the minimum requirement for developers writing plugins
  • GCC6.3 is now the minimum supported Linux compiler
  • OpenVDB has been updated to 5.2
  • Alembic has been updated to 1.7.11
  • Support for python3 bindings are available for 3.4 and 3.5
• RMANCONFIG option and its behavior have been removed
  • It is no longer possible to use the "RMANCONFIG" environment variable to override the configuration defaults file (${RMANTREE}/etc/rendermn.ini). Configurations are now customized using the "RMAN_CONFIG_OVERRIDE" environment variable. This variable specifies a directory where additional configuration files can be found, e.g. a site-specific rendermn.ini file
  • The search order for the "rendermn.ini" defaults file is as follows:
    • 1. ${RMANTREE}/etc/rendermn.ini
    • 2. ${RMAN_CONFIG_OVERRIDE}/rendermn.ini
    • 3. ${HOME}/.rendermn.ini
    • 4. ${HOME}/rendermn.ini
    • 5. ./rendermn.ini

• The RDIR option behavior, becomes RMAN_CONFIG_OVERRIDE

• The renderer no longer internally converts separate "facevarying float s" and "facevarying float t" primvars into a fused "facevarying float[2] st". As a result, any discontinuities in facevarying s will no longer automatically be propagated to facevarying t and vice versa. If your application still emits separate "facevarying s" and "t", for predictable texturing on subdivision surfaces, it is highly recommended that your application outputs "facevarying float[2] st" instead

More information can be found in the Developer Section of the documentation. These changes may impact your scripts, plugins, pipeline, and more, changes to your workflows in 23 have been kept to a minimum to allow easier migration.