2022-10-18 Render & Cycles Meeting


  • Brecht Van Lommel (Blender)
  • Weizhen Huang (Blender)
  • Christophe Hery (Meta)
  • Brian Savery (AMD)
  • Nikita Sirgienko (Intel)
  • Xavier Hallade (Intel)
  • Sebastian Herholz (Intel)


  • Path Guiding
    • Update to OpenPGL 0.4 will happen soon.
    • Deterministic sampling will remain enabled for now even if it has some performance impact and there are some issues on the Blender side that make results non-deterministic (multithreaded normal and tangent computation). We want this to become fully deterministic eventually but is not a blocker for the release.
    • MNEE compatibility will require change in OpenPGL, will be discussed by Christophe and Sebastian.
    • Still a bug with volume direct light sampling to be fixed.
  • Many Lights Sampling:
    • Some progress in the past weeks. Main open issues are importance for resampling with adaptive splitting, volume support, sub-optimal results with two sided emission on triangles, and distant lights. All are planned to be worked on.
  • Hair BSDF
    • Weizhen published a paper this year on a more accurate microfacet based hair BSDF. Some discussion was had on practical issues to make this production ready, like albedo inversion to match existing hair BSDFs.
    • Christophe will looking into sharing code for a far field approximation of the current Principled Hair shader. This can help reduce noise with few samples and not close ups of individual hairs are needed. In more complex light setups there is less benefit.
  • Intel OneAPI: host memory fallback still under development.
  • AMD HIP: performance regression in 3.3 and new compiler for new GPU support still being looked into, mainly waiting on the compiler team. For the performance regression a workaround in the Cycles code will be looked into.

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.