Previously, we used precomputed Gaussian fits to the XYZ CMFs, performed
the spectral integration in that space, and then converted the result
to the RGB working space.
That worked because we're only supporting dielectric base layers for
the thin film code, so the inputs to the spectral integration
(reflectivity and phase) are both constant w.r.t. wavelength.
However, this will no longer work for conductive base layers.
We could handle reflectivity by converting to XYZ, but that won't work
for phase since its effect on the output is nonlinear.
Therefore, it's time to do this properly by performing the spectral
integration directly in the RGB primaries. To do this, we need to:
- Compute the RGB CMFs from the XYZ CMFs and XYZ-to-RGB matrix
- Resample the RGB CMFs to be parametrized by frequency instead of wavelength
- Compute the FFT of the CMFs
- Store it as a LUT to be used by the kernel code
However, there's two optimizations we can make:
- Both the resampling and the FFT are linear operations, as is the
XYZ-to-RGB conversion. Therefore, we can resample and Fourier-transform
the XYZ CMFs once, store the result in a precomputed table, and then just
multiply the entries by the XYZ-to-RGB matrix at runtime.
- I've included the Python script used to compute the table under
`intern/cycles/doc/precompute`.
- The reference implementation by the paper authors [1] simply stores the
real and imaginary parts in the LUT, and then computes
`cos(shift)*real + sin(shift)*imag`. However, the real and imaginary parts
are oscillating, so the LUT with linear interpolation is not particularly
good at representing them. Instead, we can convert the table to
Magnitude/Phase representation, which is much smoother, and do
`mag * cos(phase - shift)` in the kernel.
- Phase needs to be unwrapped to handle the interpolation decently,
but that's easy.
- This requires an extra trig operation in the kernel in the dielectric case,
but for the conductive case we'll actually save three.
Rendered output is mostly the same, just slightly different because we're
no longer using the Gaussian approximation.
[1] "A Practical Extension to Microfacet Theory for the Modeling of
Varying Iridescence" by Laurent Belcour and Pascal Barla,
https://belcour.github.io/blog/research/publication/2017/05/01/brdf-thin-film.html
Pull Request: https://projects.blender.org/blender/blender/pulls/140944
Supporting this on the Metallic BSDF will require some extra work,
and on the Glossy BSDF it doesn't make much sense conceptually
(for that kind of shader setup, we'll want to support layering in SVM),
but Glass BSDF just needs to be hooked up so might as well do that.
Pull Request: https://projects.blender.org/blender/blender/pulls/140832
Detect which volume attributes nodes have a linear mapping to their usage
as density / color / temperature in volume shader nodes, and use stochastic
sampling for them.
Pull Request: https://projects.blender.org/blender/blender/pulls/132908
Stochastically turn a tricubic filter into a trilinear one. This
reduces the number of taps from 64 to 8. It combines ideas from
the "Stochastic Texture Filtering" paper and our previous GPU
sampling of 3D textures.
This is currently only used in a few places where we know stochastic
interpolation is valid or close enough in practice.
* Principled volume density, color and temperature
* Motion blur velocity
On an Macbook Pro M3 with the openvdb_smoke.blend regression test
and cubic sampling, this gives a ~2x speedup for CPU and ~4x speedup
for GPU. However it also increases noise, usually only a little. Equal
time renders for this scene show a clear reduction in noise for both
CPU and GPU.
Note we can probably get a bigger speedup with acceptable noise trade-off
using full stochastic sampling, but will investigate that separately.
Pull Request: https://projects.blender.org/blender/blender/pulls/132908
All GPU backends now support NanoVDB, using our own kernel side code
that is easily portable. This simplifies kernel and device code.
Volume bounds are now built from the NanoVDB grid instead of OpenVDB,
to avoid having to keep around the OpenVDB grid after loading.
While this reduces memory usage, it does have a performance impact,
particularly for the Cubic filter. That will be addressed by
another commit.
Pull Request: https://projects.blender.org/blender/blender/pulls/132908
This PR is a more extensive follow on from #123551 (removal of AMD and Intel GPU support).
All supported Apple GPUs have Metal 3 and tier 2 argument buffer support. The invariant resource properties `gpuAddress` and `gpuResourceID` can be written directly into GPU structs once at setup time rather than once per dispatch. More background info can be found in [this article](https://developer.apple.com/documentation/metal/improving-cpu-performance-by-using-argument-buffers?language=objc).
Code changes:
- All code relating to `MTLArgumentEncoder` is removed
- `KernelParamsMetal` updates are directly written into `id<MTLBuffer> launch_params_buffer` which is used for the "static" dispatch arguments
- Dynamic dispatch arguments are small enough to be encoded using the `MTLComputeCommandEncoder.setBytes` function, eliminating the need for cycling temporary arg buffers
Pull Request: https://projects.blender.org/blender/blender/pulls/140671
Multi-bounce was mainly disabled for disk sampling where the probability of
hitting something is relatively low even with high albedo, but this is not so
much an issue with random walk.
This reduces darkening artifacts at the cost of some extra render time. The
difference is mainly visible when using a high radius.
Pull Request: https://projects.blender.org/blender/blender/pulls/140665
This was broken by !138632, the refactor of the microfacet code to no longer
check the "geometric normal", which in reality was the smoothed normal.
Since the logic is now the same for all closure types, it seemed weird that
the light leak only affects Microfacet closures, not Diffuse.
Turns out that for diffuse closures, the relevant paths were rejected by
the initial hemisphere check in the smooth bump terminator code, which also
incorporates the smoothed but non-bump/normal-mapped normal sd->N.
So, we can detect and prevent the new light leaks by extending this check to
all closure types for the eval case. Sampling already has stricter checks,
so this doesn't apply there.
With this change, we can revert the two test cases back to their pre-refactor
version. In hindsight it was a mistake to just shrug off these changes as okay,
I should have looked closer into the difference.
Pull Request: https://projects.blender.org/blender/blender/pulls/140415
In Blender 3.3 (1) the individual combine and separate color nodes were
combined together into a single combine/separate color node.
To ensure legacy addons still worked, the old nodes were left in
Blender, but hidden from the Add menus.
It has been nearly 3 years since that change was made, most if not all
addons should have been updated by now. So this commit removes these
hidden legacy nodes.
(1) blender/blender@82df48227b
Pull Request: https://projects.blender.org/blender/blender/pulls/135376
This is replaced by geometry nodes, where volumes can now be generated from
point clouds and meshes with more control, and more efficient rendering as a
sparse volume.
No backwareds compatibility is provided, as this would be complicated, and
probably this feature was not used much in the past few years.
This node was supported in Cycles only, not by EEVEE.
Pull Request: https://projects.blender.org/blender/blender/pulls/140292
The 2D->2D, 3D->3D, 4D->4D hash functions used in Voronoi node were
using quite an expensive hash function. Switch these to dedicated
2D/3D/4D hash functions (pcg2d, pcg3d, pcg4d) -- these are still very
good quality, but the hash function itself is 3x-4x faster.
Which makes Voronoi node calculation overall be around 2x faster. In
some cases when using OSL, the speedup is even larger.
This visibly changes output of the Voronoi noise however. The actual
noise "behaves" the same, just if someone was depending on the noise
pattern being exactly like it was before, this will change the pattern.
Images, more performance results and details wrt OSL are in the PR.
Pull Request: https://projects.blender.org/blender/blender/pulls/139520
a degenerate triangle could produce a tangent that is antiparallel to
the normal, resulting the mapped normal to be zero, and becomes NaN when
normalized in `object_normal_transform()`. Fixed by falling back to
unperturbed normal in this case.
Fixes an assertion in the attic benchmark scene.
Pull Request: https://projects.blender.org/blender/blender/pulls/140135
This reverts commit 23c762e388 in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.
Ref blender/blender#139836
This reverts commit 64dc9cc98c in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.
Ref blender/blender#139836
This reverts commit a6015e1411 in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.
Ref blender/blender#139836
This reverts commit 5abf42012d in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.
Ref blender/blender#139836
This reverts commit 0e7a696819 in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.
Ref blender/blender#139836
This is required to make ray differentials work correctly for OSL custom
cameras.
But it also lets us simplify the implementation, and makes the OSL
functionality more complete, such as implementing all noise types.
Pull Request: https://projects.blender.org/blender/blender/pulls/138161
With these changes, we can now mark devices which are expected to work as
performant as possible, and devices which were not optimized for some reason.
For example, because the device was released after the Blender release,
making it impossible for developers to optimize for devices in already
released unchangeable code. This is primarily relevant for the LTS versions,
which are supported for two years and require proper communication about
optimization status for the new devices released during this time.
This is implemented for oneAPI devices. Other device types currently are
marked as optimized for compatibility with old behavior, but may implement
the same in the future.
Pull Request: https://projects.blender.org/blender/blender/pulls/139751
e.g. stands for "exempli gratia" in Latin which means "for example".
The best way to make sure it makes sense when writing is to just expand
it to "for example". In these cases where the text was "for e.g.", that
leaves us with "for for example" which makes no sense. This commit fixes
all 110 cases, mostly just just replacing the words with "for example",
but also restructuring the text a bit more in a few cases, mostly by
moving "e.g." to the beginning of a list in parentheses.
Pull Request: https://projects.blender.org/blender/blender/pulls/139596
Several small speedups for Voronoi node (no behavior change). This
affects Cycles and CPU execution of Voronoi node e.g. in Compositor.
- F1 mode: when evaluating distance for Voronoi cells, use a faster
distance estimation, and only do final distance calculation on the
resulting closest cell. This is only really relevant for the default
Euclidian distance, where this saves a square root per evaluated cell
(in 3D Voronoi case saves 26 square roots; in 4D case saves 80 square
roots).
- N-Sphere Radius mode: speedup by doing squared distance calculations.
We only need to find the closest one, so again doing the square root
per cell is not needed here.
Something like 5%-10% speedup for F1 3D Voronoi; more performance details
in the PR.
Pull Request: https://projects.blender.org/blender/blender/pulls/139490
In detail:
- Direct accesses of state attributes are replaced with the INTEGRATOR_STATE and INTEGRATOR_STATE_WRITE macros.
- Unified the checks for the __PATH_GUIDING define to use # if defined (__PATH_GUIDING__).
- Even if __PATH_GUIDING__ is defined, we now check if the feature is enabled using if ((kernel_data.kernel_features & KERNEL_FEATURE_PATH_GUIDING)) {. This is important for later GPU ports.
- The kernel usage of the guiding field, surface, and volume sampling distributions is wrapped behind macros for each specific device (atm only CPU). This will make it easier for a GPU port later.
Embree 4.4 introduces an improvement in the Embree GPU
implementation by dropping shared memory usage in favor
of direct controllable memory transfers. This should allow
addressing several problems spotted in Blender regarding
multithreading and memory corruption when BVH and rendering
happen at the same time. However, to implement such
improvements, the API has changed for several functions, and
this commit adopts Blender code to these changes, making Blender
buildable and functional with all existing Embree 4.X
versions, before and after 4.4.
No functional changes in Blender behavior are expected if
using Embree versions below 4.4.
Pull Request: https://projects.blender.org/blender/blender/pulls/139061
In Cycles, the convention is that reflection vs. refraction are classified
based on the hemisphere defined by the *shading* normal (N).
In general, most closure code uses the shading normal for most operations,
as is expected since using the geometric normal (Ng) would break normal maps
and smooth shading.
However, there are two places that use Ng: On the one hand, BSDF sampling
functions generally reject reflections that fall below the Ng hemisphere, since
they'd intersect the geometry when tracing the bounce. This is required, and
we can't do much about it.
On the other hand, the Microfacet evaluation code also checked that the ray
is in the same hemisphere w.r.t. both shading and geometric normal.
Theoretically, this is the right thing to do, since sampling and evaluation code
are supposed to be consistent. However, doing so breaks smooth shading, since
now direct light evaluation near the terminator will sometimes be rejected.
This didn't cause problems in practice because of another inconsistency: While
the parameter of the eval functions was named Ng, the caller actually provided
N (unclear whether by mistake or as a hacky workaround to the terminator).
When this was fixed in 063a9e89, users quickly reported issues with the shadow
terminator, so it was reverted to the hacky inconsistency in 1c50dd8b.
So, let's clean this mess up properly. If we don't want to do the Ng hemisphere
check in _eval, then instead of passing in a misleading value that ends up
making it a no-op, just remove the check. After all, the other closures don't
perform it either.
This way, we avoid the mislabeled Ng, we get rid of the special case for
microfacets, and the shadow terminator continues to be fine.
Technically, we still have the _sample vs. _eval mismatch. However, this is just
unavoidable, and is irrelevant in practice: For a strongly directional light
that makes the shadow terminator noticeable, the MIS weights will be massively
in favor of eval, to the point that it doesn't really matter what sample does.
To support this argument: You can actually reproduce a broken shadow terminator
in pretty much every Cycles version going back to 2011 by just setting up a
small intense mesh emitter, turning off MIS on it to disable _eval, and then
rendering a diffuse smooth-shaded sphere with >100000 samples so that the
fireflies resolve into somewhat consistent lighting.
If nobody has complained about this affecting all closures for 11 years,
I guess it's fine.
Pull Request: https://projects.blender.org/blender/blender/pulls/138632
This commit makes it so CUDA 11 is used to compile the compute_75
PTX CUDA kernels.
This is being done because PTX kernels have much stricter minimum
driver requirements than standard kernels, so using the latest CUDA
toolkit to compile PTX kernels can result in the PTX kernels being
inaccessible to users with drivers that are only a few months old.
This is important because in some situations, it's either impossible
(E.g. Renting certain cloud services), or difficult to update the GPU
drivers on some machines. And we want to make sure the PTX kernels
are usable by as many people as possible
Original Author: Sergey Sharybin <sergey@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/138879
Add a new shader node to control volume coefficients (scattering,
absorption and emission) directly, making it easier to model existing
volumes with measured data.
Pull Request: https://projects.blender.org/blender/blender/pulls/136287
Note: this is a partial fix, that makes NEE and forward path consistent
only when `max_transparent_bounce > 0`. It is much more involved to make
forward path tracing support a max transparent bounce of 0, but since we
don't expect people to set up a very low number of transparent bounces,
it is less important to support that specific case.
Pull Request: https://projects.blender.org/blender/blender/pulls/138098
