2023-05-02 Render & Cycles Meeting


  • Brecht Van Lommel (Blender)
  • Weizhen Huang (Blender)
  • Thomas Dinges (Blender)
  • Lukas Stockner (Blender)
  • Patrick Mours (NVIDIA)
  • William Leeson
  • Brian Savery (AMD)
  • Nikita Sirgienko (Intel)
  • Christophe Hery (Meta)


  • Principled v2 will be moved to Blender 4.0 due to scheduling issues for Lukas, but he plans to resume work on it now. The next pull request will be for albedo scaling for GGX, to replace the slower and more noisy multiscatter GGX. Then after that the plan is to add the new BSDF’s internal implementation (like Sheen), and make them available to OSL.
  • Weizhen submitted a PR for the micorfacet hair BSDF, which supports elliptical hair and uses a far field model to reduce noise. This BSDF has energy loss that makes rendering e.g. blonde hair not work as well as the existing Principled Hair. The plan is to use the same albedo scaling approach as Principled v2 to address this. Weizhen got an initial implementation of this working, but it’s not giving correct results and needs some investigation.
  • The light linking branches got more improvements, mainly in UI and for shadow linking. A challenge is to get shadow linking working correctly with multiple importance sampling, for which Sergey implemented an initial solution to trace a dedicated secondary shadow ray instead of piggy backing on the GI ray.
  • Intel hardware ray-tracing support and the upgrade to Emrbee 4 were merged. Some bugs reported, but overall seems to be in good shape.
  • AMD HIP-RT code was merged, but is not yet enabled due to issues found in testing. Brian will send an updated HIP-RT SDK, and mention the right drivers to use for testing the the pull request. Brecht will then make a new build and test.
  • AMD ROCm 5.5 was released, which should enable us to re-enable HIP on Linux by upgrading to this compiler version. Brecht will test it. This driver release should also fix viewport crashes with RDNA2 graphics card. It may take a bit for Linux distributions to upgrade to this version.
  • For optimized multi-device geometry updates, William addressed most code review comments. He also just got an alternative implementation working that tries to abstract multi-threaded device copying in the multi-device code as requested by Brecht, however it’s not clear this is the best solution. Brecht will review and check what the best solution is.

Practical Info

This is a weekly video chat meeting for planning and discussion of Blender rendering development. Any contributor (developer, UI/UX designer, writer, …) working on rendering in Blender is welcome to join and add proposed items to the agenda.

For users and other interested parties, we ask to read the meeting notes instead so that the meeting can remain focused.