While the multiscattering GGX code is cool and solves the darkening problem at higher roughnesses, it's also currently buggy, hard to maintain and often impractical to use due to the higher noise and render time.
In practice, though, having the exact correct directional distribution is not that important as long as the overall albedo is correct and we a) don't get the darkening effect and b) do get the saturation effect at higher roughnesses.
This can simply be achieved by adding a second lobe (https://blog.selfshadow.com/publications/s2017-shading-course/imageworks/s2017_pbs_imageworks_slides_v2.pdf) or scaling the single-scattering GGX lobe (https://blog.selfshadow.com/publications/turquin/ms_comp_final.pdf). Both approaches require the same precomputation and produce outputs of comparable quality, so I went for the simple albedo scaling since it's easier to implement and more efficient.
Overall, the results are pretty good: All scenarios that I tested (Glossy BSDF, Glass BSDF, Principled BSDF with metallic or transmissive = 1) pass the white furnace test (a material with pure-white color in front of a pure-white background should be indistinguishable from the background if it preserves energy), and the overall albedo for non-white materials matches that produced by the real multi-scattering code (with the expected saturation increase as the roughness increases).
In order to produce the precomputed tables, the PR also includes a utility that computes them. This is not built by default, since there's no reason for a user to run it (it only makes sense for documentation/reproducibility purposes and when making changes to the microfacet models).
Pull Request: https://projects.blender.org/blender/blender/pulls/107958
A couple of mistakes since the light linking commit:
- The +1 got missed in some of the refactors in the branch
- The order of arguments to the shadow path split was wrong
Pull Request: https://projects.blender.org/blender/blender/pulls/108420
The original names were `...update_position()`, but no update in
position is performed in these functions, rather, the entries in
`LightSample` are updated. Also make clear that the functions are used
by MNEE.
Only Embree CPU BVH was built in the multi-device case. However, one
Embree GPU BVH is needed per GPU, so we now reuse the same logic as in
the other backends.
Pull Request: https://projects.blender.org/blender/blender/pulls/107992
Used to be https://archive.blender.org/developer/D17123.
Internally these are already using the same code path anyways, there's no point in maintaining two distinct nodes.
The obvious approach would be to add Anisotropy controls to the Glossy BSDF node and remove the Anisotropic BSDF node. However, that would break forward compability, since older Blender versions don't know how to handle the Anisotropy input on the Glossy BSDF node.
Therefore, this commit technically removes the Glossy BSDF node, uses versioning to replace them with an Anisotropic BSDF node, and renames that node to "Glossy BSDF".
That way, when you open a new file in an older version, all the nodes show up as Anisotropic BSDF nodes and render correctly.
This is a bit ugly internally since we need to preserve the old `idname` which now no longer matches the UI name, but that's not too bad.
Also removes the "Sharp" distribution option and replaces it with GGX, sets Roughness to zero and disconnects any input to the Roughness socket.
Pull Request: https://projects.blender.org/blender/blender/pulls/104445
NanoVDB headers have unused code using "double" type, which is not supported on Arc GPUs.
Recent DPC++ changes enforced runtime verifications:
7663dc201d
which prevents execution when such type has been present even if unused.
This is a solution to avoid double to be compiled at all, similar as how it is done for Metal.
Area light sampling use special techniques to reduce noise with small
spread angles; the change in sampled area was not taken into
consideration when computing the pdf in MNEE.
Pull Request: https://projects.blender.org/blender/blender/pulls/107897
After the removal of the Shadow pass this no longer worked. Now it works by
marking the object as a shadow catcher and returning the Shadow Catcher pass.
The result is different than before, since it also takes into account indirect
light now and uses a different method to weight the contribution of lights that
is adaptive to the light strength.
This will make further changes for light linking easier, where we want to
build multiple trees specialized for each light linking set.
It's also easier to understand than the stack used previously.
Pull Request: https://projects.blender.org/blender/blender/pulls/107560
