- Deduplicate Fisheye projection code
- Replace spherical/cartesian conversions with shared helpers
- Replace transforms from/to local coordinate systems with shared helpers
The main type of repeated transform that's not covered here is `to/from_coords`, but with separate values for xy and z (e.g. BSDFs that already computed `dot(wi, N)` earlier, so they only need `dot(wi, X)` and `dot(wi, Y)` later). Could also be replaced, but it would feel weirdly specific for a helper function.
Pull Request: https://projects.blender.org/blender/blender/pulls/125999
Previously, Cycles only supported the Henyey-Greenstein phase function for volume scattering.
While HG is flexible and works for a wide range of effects, sometimes a more physically accurate
phase function may be needed for realism.
Therefore, this adds three new phase functions to the code:
Rayleigh: For particles with a size below the wavelength of light, mostly athmospheric scattering.
Fournier-Forand: For realistic underwater scattering.
Draine: Fairly specific on its own (mostly for interstellar dust), but useful for the next entry.
Mie: Approximates Mie scattering in water droplets using a mix of Draine and HG phase functions.
These phase functions can be combined using Mix nodes as usual.
Co-authored-by: Lukas Stockner <lukas@lukasstockner.de>
Pull Request: https://projects.blender.org/blender/blender/pulls/123532
The same random number was used for sampling color channel at each step,
which leads to bias. Fixed by rescaling the random number.
Another possibility would be to scramble `rng_offset` and use a new
random number each time, similar as in subsurface scattering, but
rescaling random number should be faster than computing a new one, and
is favorable here since the precision here is not very important
Pull Request: https://projects.blender.org/blender/blender/pulls/127454
This decreases BSDF_ROUGHNESS_SQ_THRESH so that the microfacet
roughness has a cutoff at much lower values and fixes a precision
issue in the bsdf_sample code that prevented this previously.
Pull Request: https://projects.blender.org/blender/blender/pulls/125919
Fix a NaN when rendering glossy materials that can appear due to a
division by zero in bsdf_D when rendering materials with low roughness.
Thank you to Weizhen for the fix after my incorrect
first attempt.
Pull Request: https://projects.blender.org/blender/blender/pulls/125756
Setting this option to a value above zero replaces the lambertian Diffuse term
with the modified energy-preserving Oren-Nayar BSDF, which matches the OpenPBR
behavior.
Pull Request: https://projects.blender.org/blender/blender/pulls/123616
This multiscattering term comes from the OpenPBR specification and nicely
preserves energy while correctly modeling increased saturation at high
roughness.
Preparation for adding a diffuse roughness option to the Principled BSDF.
To me, the difference in output and computation seems small enough to
not need an enum for the old behavior.
Note that this also switches sampling to cosine-weighted, in my tests this
gives lower noise. I also checked doing MIS between cosine and uniform,
using the A term as a weight for how often to use cosine (since that term
is Lambertian diffuse), but always using cosine was better.
A nice consequence of that is that you don't get a huge noise jump when
going from 0.0 to 0.01 roughness.
Pull Request: https://projects.blender.org/blender/blender/pulls/123345
when ray exceeds `max_bounce`, we do not allocate any closure at
intersection. However, Ray Portal BSDF still added `SD_BSDF` flag,
resulting in undefined behavior in
`integrate_surface_bsdf_bssrdf_bounce()`.
This part of code was similar to Transparent BSDF, however, Transparent
closure was still allocated in this case.
To fix the undefined behavior, add `SD_BSDF` flag only when the Ray
Portal closure was allocated.
This is an implementation of thin film iridescence in the Principled BSDF based on "A Practical Extension to Microfacet Theory for the Modeling of Varying Iridescence".
There are still several open topics that are left for future work:
- Currently, the thin film only affects dielectric Fresnel, not metallic. Properly specifying thin films on metals requires a proper conductive Fresnel term with complex IOR inputs, any attempt of trying to hack it into the F82 model we currently use for the Principled BSDF is fundamentally flawed. In the future, we'll add a node for proper conductive Fresnel, including thin films.
- The F0/F90 control is not very elegantly implemented right now. It fundamentally works, but enabling thin film while using a Specular Tint causes a jump in appearance since the models integrate it differently. Then again, thin film interference is a physical effect, so of course a non-physical tweak doesn't play nicely with it.
- The white point handling is currently quite crude. In short: The code computes XYZ values of the reflectance spectrum, but we'd need the XYZ values of the product of the reflectance spectrum and the neutral illuminant of the working color space. Currently, this is addressed by just dividing by the XYZ values of the illuminant, but it would be better to do a proper chromatic adaptation transform or to use the proper reference curves for the working space instead of the XYZ curves from the paper.
Pull Request: https://projects.blender.org/blender/blender/pulls/118477
Transport rays that enter to another location in the scene, with
specified ray position and normal. This may be used to render portals
for visual effects, and other production rendering tricks.
This acts much like a Transparent BSDF. Render passes are passed
through, and this is affected by light path max transparent bounces.
Pull Request: https://projects.blender.org/blender/blender/pulls/114386
This is a regression in 4.1, caused by 36e603c430.
For unbiased MIS weight in light tree, we should use sd->N for
mis_origin_n, since sc->N is not available in NEE.
The change also makes it so we do not sample lights below sd->N even
when bump map correction is disabled. This diverges from the original
idea of giving full control to artists, but ensures the internal math
is happy.
Pull Request: https://projects.blender.org/blender/blender/pulls/120216
The original bug report was that the Glossy Toon BSDF behaves incorrectly
when mixed with other closures.
The underlying issue here was that the eval function didn't check whether
the reflection angle is inside the valid cone and always returned its PDF,
which is very high compared to e.g. the diffuse closure's PDF for small
sizes (since the cone is supposed to be quite tight) and therefore breaks
MIS mixing.
However, while looking into this, I found a number of other issues, and so
this commit also contains several other changes to the Toon BSDFs:
- The angle that was used to compute the intensity wasn't the actual angle
between the vectors. From what I can see, the formula that was used goes
back all the way to the initial commit 12 years ago, so this probably was
something that happened to work with one particular cone sampling method.
Now, however, it caused weird asymmetric highlights, so replace it with
the actual angle (which we already compute anyways).
- Setting size to zero caused the BSDF to go black, so clamp to 1e-5.
- The code was overall a bit repetitive, so I've cleaned it up a bit.
for a camera ray, compute the actual range of the hair width that the
current pixel covers, and only integrate that subset, to prevent a
ribbon-like appearance in close-up looks.
When the hair covers less than one pixel on the screen or when the ray
is not camera ray, the model works the same as before.
Pull Request: https://projects.blender.org/blender/blender/pulls/116094
The valid interval from incoming direction was shared between
`...eval_r()` and `...eval_residual()`, so compute that in `...eval()` instead.
The valid interval from outgoing direction was computed for
`...eval_r()` to further reduce the integration interval. This part is
removed because the check `dot(wo, wm) > 0` is relatively cheap inside the loop.
The geometry normal of the curve might not be precisely orthogonal to
the tangent due to interpolation. Previously, the tangent was adjusted
to be orthogonal to the normal. However, the normal is linearly
interpolated, which is less accurate than the tangent computed using Catmull-Rom.
This commit keeps the tangent and adjust the normal instead, besides
better accuracy, it ensures a smooth transition when the cross-section
shifts between circular and elliptical.
The pre-4.0 Principled BSDF had a special diffuse BSDF that contained
the roughness value from the node. Since 4.0, the regular Diffuse BSDF is used,
so we need to ignore it when determining the roughness value for baking.
Along with the 4.1 libraries upgrade, we are bumping the clang-format
version from 8-12 to 17. This affects quite a few files.
If not already the case, you may consider pointing your IDE to the
clang-format binary bundled with the Blender precompiled libraries.
Fix issues related to NaN normals in some situations by trying
to detect when these cases might occur and just reverting back
to default normals.
As a side effect of these changes, OSL now behaves correctly
when given a non-normalized normal.
Pull Request: https://projects.blender.org/blender/blender/pulls/114960
While this code is suspect, better to go back to the old state for now,
as there is no simple fix that doesn't introduce other issues.
Fix#115022Fix#115414
This reverts commit 063a9e8964.
The increased amount of BSDF code from Principled BSDF v2 and the
microfacet BSDF led to a big performance regression on Metal and AMD.
We have not been able to find a good workaround for all scenes.
This change disables the Principled Hair BSDF code when it is not used
in the scene. This makes common benchmark scenes faster, but
performance is still bad in scenes that do use it.
Ref #112596
Pull Request: https://projects.blender.org/blender/blender/pulls/113904
Cycles implements the "Taming the Shadow Terminator" paper by Matt Jen-Yuan
Chiang to solve shadow terminator issues when a bump map is applied, as well
as similar approach for the glossy reflection to ensure ray does not get
reflected to inside of the object.
This correction term is applied unconditionally, which makes it harder to have
full control over shading via normals for stylistic reasons.
This change exposes this corrective term as an option called "Bump Map
Correction" which is available in the shader settings next to the
"Transparent Shadows".
The reason to make it per-shader rather than per-object is to allow flexibility
of a control: it is possible that an object has multiple shaders attached to it,
and only some of them used for bump mapping. Another, and possibly stronger
reason to have it per-shader is ease of assets control: shader brings settings
which are needed for its proper behavior. So if material at some point
decides to take over normals, artists would not need to update settings on
every asset which uses that material.
The option is enabled by default, so there is no changes for existing setups.
Pull Request: https://projects.blender.org/blender/blender/pulls/113480
