[Bf-cycles] Cycles at Blender Conference 2017

[Brecht Van Lommel]

Hi all,

Here's some Cycles development updates from the Blender Conference. Feel
free to add anything I missed.


PRESENTATIONS

Tangent Animation (Stefan): https://www.youtube.com/watch?v=_2Ia4h8q3xs
Theory Studios (Lukas): https://www.youtube.com/watch?v=r_Gjx-rrIG0
Agent 327: https://www.youtube.com/watch?v=JKlgCnp_57M


MEETING

We had a meeting with Cycles developers present at the Blender conference.
Mostly we exchanged what everyone was working on and discussed some
implementation details. The roadmap has been updated:
https://wiki.blender.org/index.php/Dev:Source/Render/Cycles/Roadmap


DESIGN

Some notes from discussions with other developers:

* Embree is planned to be integrated, replacing our BVH building code. Main
speedups would be for motion blur and hair. For GPU BVH traversal we would
translate the BVH to our own data structures and keep our own traversal.
For the CPU it's not clear yet if it will end up being better to keep our
own traversal code, depends on code complexity and performance. For more
details on Embree benefits see Stefan's presentation.

* Adaptive sampling: there's a few challenges in implementing this,
particularly around sharing information between neighboring tiles, and
keeping the GPU occupied. Idea would be to do a basic (CPU) implementation
that doesn't share information between tiles, but only to looks at
denoising passes in neighborhood around pixel within a tile, to decide on
the number of samples. Then we can evaluate what kind of artifacts there
are compared to rendering with one big tile, and if the additional
complexity is needed. If needed, sharing information between tiles could
use the same mechanism as denoising to map neighboring tiles, perhaps just
once after the minimum number of samples is taken.

* Denoising animations. We'll try to get a minimum viable implementation
working, which would likely be a button in the Blender UI to denoise an
sequence of rendered EXR files. The compositor will need to run afterwards,
reading the denoising EXR files from disk with the Render Layers node. This
is currently not supported, and will also be useful for compositing without
re-rendering in general.

* Bevel shader using raytracing is ok to be added, even if it's probably
too slow to advise using for animation rendering. We will add warnings
about this in the documentation and the release notes.

* We'd like to make the code style more consistent, using clang-tidy. The
main issue with such changes is that it can be a pain to merge existing
branches. However, conflict resolution can be automated by running
clang-tidy on the new code, so hopefully it would not be so bad.
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