2021-12-7 Blender Rendering Meeting


  • Brecht Van Lommel (Blender)
  • Kévin Dietrich (Blender)
  • William Leeson (Blender)
  • Thomas Dinges (Blender)
  • Patrick Mours (NVIDIA)
  • Roman Zulak (NVIDIA)
  • Brian Savery (AMD)
  • Michael Jones (Apple)
  • Feng Xie (Facebook)



  • 3.0 has been released (Brecht).
  • For 3.1 there are a few more weeks left to include new features (Brecht)
  • 8 patches to review: Metal D13503, Temporal de-noising D11442
    , Light groups D12871, Ray Offsetting removal D12954, Baking improvements D11345 D11502, Point clouds T92573, OpenSubdiv. The deadline for new features is 29th Dec. (Brecht)
  • Point clouds have a performance impact with CUDA and HIP due to the point primitive. It currently add about ~2% and needs optimisation. (Brecht)
  • Ray offsetting removal is very close now just a few tweaks and it should be in. The performance impact is 1%-2% depending on the scene. It should fix many issues. (William)
  • A patch for 3.1 to enable new architectures is coming. (Brian)
  • Working on AMD Linux support for 3.1. (Brian)
  • Conversation with Feng on improving multi-device support CPU + GPU. It improves the allocation between CPU and GPU and is coming by the end of the year. (Brian)
  • Working on support for more devices. (Brian)
  • NVIDIA is interested in contributing USD / Hydra support, based on updating the Tangent Studios implementation for cycles-x. Brecht agrees this is something we would like to have as part of the Cycles core and would be accepted in the main repository. (Patrick, Roman)
  • It would be good to clean up the Cycles API as this would make work like this easier and make it easier to use Cycles in different contexts such as Hydra. (Feng)
  • Looking at code for adding light weight multi-device implementation. We need an accurate timer implementation to do this and would like to use the scoped timers. (Feng)
  • Metal T92212 final host side patch to get this working has landed. It is still disabled in the code base and needs build options and UI to be usable. We would like to get this in quickly as a work in progress so as to get feedback. Many improvements are still coming this is just the first iteration. We will work with Brecht to get this in. (Michael)

Eevee & Viewport

  • Opensubdiv D12406 getting close it needs a review and a patch to fix a regression. (Kevin)

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.

  • Agenda
  • Google Meet
  • Time: Tuesday 5 to 6 PM Amsterdam Time
  • Next Meeting: January 4, 2022

Last meeting’s note said MNEE would be submitted “soon”, will it make it before this deadline?

EDIT: Patch here: ⚙ D13533 Adding Manifold Next Event Estimation Sampling Technique


Time to bring it home on the OpenSubDiv patch, it is literally the last thing needed to make the new Blender objectively better across the board than the old one (2.7x).

It is almost done, please don’t release version 3.1 without it.


I would think there is a good chance of it getting in but unfortunately Christophe was not at the last meeting so I don’t have an update from him.


Is there a speed or quality advantage of the new algorithm for rendering outside of focal dispersion over the traditional algorithm?

I presume you are referring to MNEE. It is a specialised technique for rendering refractive caustics so I would assume not. However, in principal the technique could be extended to other surface types.


Exciting to see Metal backend is close to release state!

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Is there patch/task page for this?


Yes please, I would love to follow/test the hydra delegate, this is amazing news,

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How soon can we expect Metal backend in Alpha?

I am sorry I don’t have a definite date for you but it’s probably in the coming weeks.

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Sorry I only have the link above and no task or patch.

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Oh, that’s totally ok!

Regarding USD / Hydra, I’ve updated the notes to clarify this. There is no actual patch yet, there is interest from NVIDIA in contributing this and when it becomes concrete we’ll make a task.


Just to make sure I get it right: are the upcoming improved caustics a result of overall improved light transport in Cycles, like bidirectional path tracing / VCM, or is MNEE a trick to only improve caustics?

You can find the MNEE patch here: ⚙ D13533 Adding Manifold Next Event Estimation Sampling Technique

From the looks of it, it seems MNEE in that patch a trick to improve caustics, not an “overall improvement to Cycles light transport”.

There was a task created for path guiding (⚓ T92571 Cycles: path guiding) that should bring improvements to the convergence of reflective and refractive caustics. This is more likely to be a “overall improved light transport in Cycles”. However, we need to wait for a patch for this to be made.


Thanks for the info and links. So the MNEE implementation is not a replacement of the path guiding initiative, but a method to improve caustics, while improved overall light transport will still be implemented?

MNEE is an implementation that specifically helps with certain refractive caustics (at least in it’s current form). Reflective caustics are not covered.

From my understanding other improvements to Cycles light transport (like path guiding) is still planned for the future. However this is just my interpretation of things. You’d want comments form the Cycles developers for exact plans.

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Instead of bi-directional path tracing, Metropolis Light Transport directly, a god renderer is born

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These algorithms have their own issues. Metropolis Light Transport has incorrect brightness issues (shown in the Practical Path Guiding paper’s kitchen scene comparison), MNEE has issues with more complex shapes (In the MNEE paper there is a “failed case”), Path Guiding according to SNEE’s paper seems to also have its own issue that I don’t quite understand.

The more I read the more I realize that there is just no one perfect algorithm. But hopefully some algorithms are complementary like MNEE and Path Guiding, let’s wait and see how it goes.