Previously, the Principled BSDF used the Subsurface input to scale the radius.
When it was zero, it used a diffuse closure, otherwise a subsurface closure.
This sort of scaling input makes sense, but it should be specified in distance
units, rather than a 0..1 factor, so this commit changes the unit and renames
the input to Subsurface Scale.
Additionally, it adds support for mixing diffuse and subsurface components.
This is part of e.g. the OpenPBR spec, and the logic behind it is to support
modeling e.g. dirt or paint on top of skin. Before, materials would be either
fully diffuse (radius=0) or fully subsurface.
For typical materials, this mixing factor will be either zero or one
(just like metallic or transmission), but supporting fractional inputs makes
sense for e.g. smooth transitions at boundaries.
Another change is that there is no separate Subsurface Color anymore - before,
this was mixed with the Base Color using the Subsurface input as the factor,
but this was not really useful since that input was generally very small.
And finally, the handling of how the path enters the material for random walk
subsurface scattering is changed. Before, this always used lambertian (diffuse)
transmission, but this caused some problems, like overly white edges.
Instead, two different methods are now used, depending on the selected mode.
In Fixed Radius mode, the code assumes a simple medium boundary, and performs
refraction into the material using the main Roughness and IOR inputs.
Meanwhile, when not using Fixed Radius, the code assumes a more complex
boundary (as typically found on organic materials, e.g. skin), so the entry
bounce has a 50/50 chance of being either diffuse transmission or refraction
using the separate Subsurface IOR input and a fixed roughness of 1.
Credit for this method goes to Christophe Hery.
Pull Request: https://projects.blender.org/blender/blender/pulls/110989
Overall, this commit reworks the component layering in the Principled BSDF
in order to ensure that energy is preserved and conserved.
This includes:
- Implementing support for the OSL `layer()` function
- Implementing albedo estimation for some of the closures for layering purposes
- The specular layer that the Principled BSDF uses has a proper tabulated
albedo lookup, the others are still approximations
- Removing the custom "Principled Diffuse" and replacing it with the classic
lambertian Diffuse, since the layering logic takes care of energy now
- Making the merallic component independent of the IOR
Note that this changes the look of the Principled BSDF noticeably in some
cases, but that's needed, since the cases where it looks different are the
ones that strongly violate energy conservation (mostly grazing reflections
with strong Specular).
Pull Request: https://projects.blender.org/blender/blender/pulls/110864
This adds path guiding features into Cycles by integrating Intel's Open Path
Guiding Library. It can be enabled in the Sampling > Path Guiding panel in the
render properties.
This feature helps reduce noise in scenes where finding a path to light is
difficult for regular path tracing.
The current implementation supports guiding directional sampling decisions on
surfaces, when the material contains a least one diffuse component, and in
volumes with isotropic and anisotropic Henyey-Greenstein phase functions.
On surfaces, the guided sampling decision is proportional to the product of
the incident radiance and the normal-oriented cosine lobe and in volumes it
is proportional to the product of the incident radiance and the phase function.
The incident radiance field of a scene is learned and updated during rendering
after each per-frame rendering iteration/progression.
At the moment, path guiding is only supported by the CPU backend. Support for
GPU backends will be added in future versions of OpenPGL.
Ref T92571
Differential Revision: https://developer.blender.org/D15286
These replace float3 and packed_float3 in various places in the kernel where a
spectral color representation will be used in the future. That representation
will require more than 3 channels and conversion to from/RGB. The kernel code
was refactored to remove the assumption that Spectrum and RGB colors are the
same thing.
There are no functional changes, Spectrum is still a float3 and the conversion
functions are no-ops.
Differential Revision: https://developer.blender.org/D15535
For transparency, volume and light intersection rays, adjust these distances
rather than the ray start position. This way we increment the start distance
by the smallest possible float increment to avoid self intersections, and be
sure it works as the distance compared to be will be exactly the same as
before, due to the ray start position and direction remaining the same.
Fix T98764, T96537, hair ray tracing precision issues.
Differential Revision: https://developer.blender.org/D15455
* Rename "texture" to "data array". This has not used textures for a long time,
there are just global memory arrays now. (On old CUDA GPUs there was a cache
for textures but not global memory, so we used to put all data in textures.)
* For CUDA and HIP, put globals in KernelParams struct like other devices.
* Drop __ prefix for data array names, no possibility for naming conflict now that
these are in a struct.
Move MNEE to own kernel, separate from shader ray-tracing. This does introduce
the limitation that a shader can't use both MNEE and AO/bevel, but that seems
like the better trade-off for now.
We can experiment with bigger kernel organization changes later.
Differential Revision: https://developer.blender.org/D15070
This adds support for selective rendering of caustics in shadows of refractive
objects. Example uses are rendering of underwater caustics and eye caustics.
This is based on "Manifold Next Event Estimation", a method developed for
production rendering. The idea is to selectively enable shadow caustics on a
few objects in the scene where they have a big visual impact, without impacting
render performance for the rest of the scene.
The Shadow Caustic option must be manually enabled on light, caustic receiver
and caster objects. For such light paths, the Filter Glossy option will be
ignored and replaced by sharp caustics.
Currently this method has a various limitations:
* Only caustics in shadows of refractive objects work, which means no caustics
from reflection or caustics that outside shadows. Only up to 4 refractive
caustic bounces are supported.
* Caustic caster objects should have smooth normals.
* Not currently support for Metal GPU rendering.
In the future this method may be extended for more general caustics.
TECHNICAL DETAILS
This code adds manifold next event estimation through refractive surface(s) as a
new sampling technique for direct lighting, i.e. finding the point on the
refractive surface(s) along the path to a light sample, which satisfies Fermat's
principle for a given microfacet normal and the path's end points. This
technique involves walking on the "specular manifold" using a pseudo newton
solver. Such a manifold is defined by the specular constraint matrix from the
manifold exploration framework [2]. For each refractive interface, this
constraint is defined by enforcing that the generalized half-vector projection
onto the interface local tangent plane is null. The newton solver guides the
walk by linearizing the manifold locally before reprojecting the linear solution
onto the refractive surface. See paper [1] for more details about the technique
itself and [3] for the half-vector light transport formulation, from which it is
derived.
[1] Manifold Next Event Estimation
Johannes Hanika, Marc Droske, and Luca Fascione. 2015.
Comput. Graph. Forum 34, 4 (July 2015), 87–97.
https://jo.dreggn.org/home/2015_mnee.pdf
[2] Manifold exploration: a Markov Chain Monte Carlo technique for rendering
scenes with difficult specular transport Wenzel Jakob and Steve Marschner.
2012. ACM Trans. Graph. 31, 4, Article 58 (July 2012), 13 pages.
https://www.cs.cornell.edu/projects/manifolds-sg12/
[3] The Natural-Constraint Representation of the Path Space for Efficient
Light Transport Simulation. Anton S. Kaplanyan, Johannes Hanika, and Carsten
Dachsbacher. 2014. ACM Trans. Graph. 33, 4, Article 102 (July 2014), 13 pages.
https://cg.ivd.kit.edu/english/HSLT.php
The code for this samping technique was inserted at the light sampling stage
(direct lighting). If the walk is successful, it turns off path regularization
using a specialized flag in the path state (PATH_MNEE_SUCCESS). This flag tells
the integrator not to blur the brdf roughness further down the path (in a child
ray created from BSDF sampling). In addition, using a cascading mechanism of
flag values, we cull connections to caustic lights for this and children rays,
which should be resolved through MNEE.
This mechanism also cancels the MIS bsdf counter part at the casutic receiver
depth, in essence leaving MNEE as the only sampling technique from receivers
through refractive casters to caustic lights. This choice might not be optimal
when the light gets large wrt to the receiver, though this is usually not when
you want to use MNEE.
This connection culling strategy removes a fair amount of fireflies, at the cost
of introducing a slight bias. Because of the selective nature of the culling
mechanism, reflective caustics still benefit from the native path
regularization, which further removes fireflies on other surfaces (bouncing
light off casters).
Differential Revision: https://developer.blender.org/D13533
* Replace license text in headers with SPDX identifiers.
* Remove specific license info from outdated readme.txt, instead leave details
to the source files.
* Add list of SPDX license identifiers used, and corresponding license texts.
* Update copyright dates while we're at it.
Ref D14069, T95597
Remove small ray offsets that were used to avoid self intersection, and leave
that to the newly added primitive object/prim comparison. These changes together
significantly reduce artifacts on small, large or far away objects.
The balance here is that overlapping primitives are not handled well and should
be avoided (though this was already an issue). The upside is that this is
something a user has control over, whereas the other artifacts had no good
manual solution in many cases.
There is a known issue where the Blender particle system generates overlapping
objects and in turn leads to render differences between CPU and GPU. This will
be addressed separately.
Differential Revision: https://developer.blender.org/D12954
We need to increase GPU memory usage a bit. Unfortunately we can't get away
with writing either reflection or transmission passes because these BSDFs may
scatter in either direction but still must be in a fixed reflection or
transmission category to match up with the color passes.
Remove prefix of filenames that is the same as the folder name. This used
to help when #includes were using individual files, but now they are always
relative to the cycles root directory and so the prefixes are redundant.
For patches and branches, git merge and rebase should be able to detect the
renames and move over code to the right file.
