The order of evaluation of function arguments is undefined, and the order
was reversed between these compilers. This was causing regressions tests
to give different results between Linux and macOS.
If there was any specularity in the Principled BSDF, it would get a sampling
weight of one regardless of its actual impact.
This commit makes Cycles estimate the contribution of the component and adjust
the weighting accordingly, which greatly improves the noise characteristics of
the Principled BSDF in many cases.
Note that this commit might slightly change the brightness of areas when using
MultiGGX and high roughnesses, but the new brightness is more accurate and
closer to the result of Branched Path Tracing. See T51836 for details.
Differential Revision: https://developer.blender.org/D2677
The PDF of the MultiGGX sampling is approximated by the singlescattering GGX
term as well as a scaled diffuse term that makes up for the energy in the
multiscattering component that's missed by GGX.
However, there were two problems with the glossy terms: The diffuse term missed
a normalization factor, and the singlescattering term was not properly scaled
down based on the albedo estimate.
The glass term was completely wrong and has been rewritten. It uses the fresnel
factor to weight reflection vs. refraction and uses the glossy MultiGGX model
for reflection.
For refraction, the correct singlescattering term is now used, and a new
albedo approximation is used that was derived by evaluating GGX albedo for
roughnesses from 0 to 1 and IORs from 1 to 3 and fitting numerical
approximations to it. The resulting model has a mean relative error of 9e-5,
but could probably be simplified without losing noticable accuracy in the
final render.
The improved PDFs help with glossy highlights (due to better light sampling vs.
closure sampling MIS) and fix the situation described in T51836 where mixing
MultiGGX with other closures (as it happens in e.g. the Principled
BSDF) causes incorrect darkening.
The implementation originally handled four different cases:
Regular glossy, glass, metallic fresnel glossy and diffuse.
However, only the first two are actually used currently. Therefore, this commit
removes the other two, which allows to simplify the code.
Additionally, due to the Principled BSDF, the function arguments are now
identical for glossy and glass, which allows to get rid of some ugly #ifdefs.
This commit contains the first part of the new Cycles denoising option,
which filters the resulting image using information gathered during rendering
to get rid of noise while preserving visual features as well as possible.
To use the option, enable it in the render layer options. The default settings
fit a wide range of scenes, but the user can tweak individual settings to
control the tradeoff between a noise-free image, image details, and calculation
time.
Note that the denoiser may still change in the future and that some features
are not implemented yet. The most important missing feature is animation
denoising, which uses information from multiple frames at once to produce a
flicker-free and smoother result. These features will be added in the future.
Finally, thanks to all the people who supported this project:
- Google (through the GSoC) and Theory Studios for sponsoring the development
- The authors of the papers I used for implementing the denoiser (more details
on them will be included in the technical docs)
- The other Cycles devs for feedback on the code, especially Sergey for
mentoring the GSoC project and Brecht for the code review!
- And of course the users who helped with testing, reported bugs and things
that could and/or should work better!
commit 90778901c9
Merge: 76eebd93bf0026
Author: Schoen <schoepas@deher1m1598.emea.adsint.biz>
Date: Mon Apr 3 07:52:05 2017 +0200
Merge branch 'master' into cycles_disney_brdf
commit 76eebd9379
Author: Schoen <schoepas@deher1m1598.emea.adsint.biz>
Date: Thu Mar 30 15:34:20 2017 +0200
Updated copyright for the new files.
commit 013f4a152a
Author: Schoen <schoepas@deher1m1598.emea.adsint.biz>
Date: Thu Mar 30 15:32:55 2017 +0200
Switched from multiplication of base and subsurface color to blending
between them using the subsurface parameter.
commit 482ec5d1f2
Author: Schoen <schoepas@deher1m1598.emea.adsint.biz>
Date: Mon Mar 13 15:47:12 2017 +0100
Fixed a bug that caused an additional white diffuse closure call when using
path tracing.
commit 26e906d162
Merge: 0593b8c223aff9
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Feb 6 11:32:31 2017 +0100
Merge branch 'master' into cycles_disney_brdf
commit 0593b8c51b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Feb 6 11:30:36 2017 +0100
Fixed the broken GLSL shader and implemented the Disney BRDF in the
real-time view port.
commit 8c7e11423b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Feb 3 14:24:05 2017 +0100
Fix to comply strict compiler flags and some code cleanup
commit 17724e9d2d
Merge: 379ba34520afa2
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jan 24 09:59:58 2017 +0100
Merge branch 'master' into cycles_disney_brdf
commit 379ba346b0
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jan 24 09:28:56 2017 +0100
Renamed the Disney BSDF to Principled BSDF.
commit f80dcb4f34
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Dec 2 13:55:12 2016 +0100
Removed reflection call when roughness is low because of artifacts.
commit 732db8a57f
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Nov 16 09:22:25 2016 +0100
Indication if to use fresnel is now handled via the type of the BSDF.
commit 0103659f5e
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Nov 11 13:04:11 2016 +0100
Fixed an error in the clearcoat where it appeared too bright for default
light sources (like directional lights)
commit 0aa68f5335
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Nov 7 12:04:38 2016 +0100
Resolved inconsistencies in using tabs and spaces
commit f5897a9494
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Nov 7 08:13:41 2016 +0100
Improved the clearcoat part by using GTR1 instead of GTR2
commit 3dfc240e61
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Oct 31 11:31:36 2016 +0100
Use reflection BSDF for glossy reflections when roughness is 0.0 to
reduce computational expense and some code cleanup
Code cleanup includes:
- Code style cleanup and removed unused code
- Consolidated code in the bsdf_microfacet_multi_impl.h to reduce
some computational expense
commit a2dd0c5faf
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Oct 26 08:51:10 2016 +0200
Fixed glossy reflections and refractions for low roughness values and
cleaned up the code.
For low roughness values, the reflections had some strange behavior.
commit 9817375912
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Oct 25 12:37:40 2016 +0200
Removed default values in setup functions and added extra functions for
GGX with fresnel.
commit bbc5d9d452
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Oct 25 11:09:36 2016 +0200
Switched from uniform to cosine hemisphere sampling for the diffuse and
the sheen part.
commit d52d8f2813
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Oct 24 16:17:13 2016 +0200
Removed the color parameters from the diffuse and sheen shader and use
them as closure weights instead.
commit 8f3d927385
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Oct 24 09:57:06 2016 +0200
Fixed the issue with artifacts when using anisotropy without linking the
tangent input to a tangent node.
commit d93f680db9
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Oct 24 09:14:51 2016 +0200
Added subsurface radius parameter to control the per color channel
effection radius of the subsurface scattering.
commit c708c3e53b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Oct 24 08:14:10 2016 +0200
Rearranged the inputs of the shader.
commit dfbfff9c38
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Oct 21 09:27:05 2016 +0200
Put spaces in the parameter names of the shader node
commit e5a748ced1
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Oct 21 08:51:20 2016 +0200
Removed code that isn't in use anymore
commit 75992bebc1
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Oct 21 08:50:07 2016 +0200
Code style cleanup
commit 4dfcf455f7
Merge: 243a0e32cd6a89
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Thu Oct 20 10:41:50 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit 243a0e3eb8
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Thu Oct 20 10:01:45 2016 +0200
Switching between OSL and SVM is more consistant now when using Disney
BSDF.
There were some minor differences in the OSL implementation, e.g. the
refraction roughness was missing.
commit 2a5ac50922
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 27 09:17:57 2016 +0200
Fixed a bug that caused transparency to be always white when using OSL and
selecting GGX as distribution of the Disney BSDF
commit e1fa862391
Merge: d0530a87f76f6f
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 27 08:59:32 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit d0530a8af0
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 27 08:53:18 2016 +0200
Cleanup the Disney BSDF implementation and removing unneeded files.
commit 3f4fc826bd
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 27 08:36:07 2016 +0200
Unified the OSL implementation of the Disney clearcoat as a simple
microfacet shader like it was previously done in SVM
commit 4d3a0032ec
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Sep 26 12:35:36 2016 +0200
Enhanced performance for Disney materials without subsurface scattering
commit 3cd5eb56cf
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Sep 16 08:47:56 2016 +0200
Fixed a bug in the Disney BSDF that caused specular reflections to be too
bright and diffuse is now reacting to the roughness again
- A normalization for the fresnel was missing which caused the specular
reflections to become too bright for the single-scatter GGX
- The roughness value for the diffuse BSSRDF part has always been
overwritten and thus always 0
- Also the performance for refractive materials with roughness=0.0 has
been improved
commit 7cb37d7119
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Thu Sep 8 12:24:43 2016 +0200
Added selection field to the Disney BSDF node for switching between
"Multiscatter GGX" and "GGX"
In the "GGX" mode there is an additional parameter for changing the
refraction roughness for materials with smooth surfaces and rough interns
(e.g. honey). With the "Multiscatter GGX" this effect can't be produced at
the moment and so here will be no separation of the two roughness values.
commit cdd29d06bb
Merge: 02c315ab40d1c1
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 6 15:59:05 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit 02c315aeb0
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Sep 6 15:16:09 2016 +0200
Implemented the OSL part of the Disney shader
commit 5f880293ae
Merge: 630b80eb399a6d
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Sep 2 10:53:36 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit 630b80e08b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Sep 2 10:52:13 2016 +0200
Fresnel in the microfacet multiscatter implementation improved
commit 0d9f4d7acb
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Aug 26 11:11:05 2016 +0200
Fixed refraction roughness problem (refractions were always 100% rough)
and set IOR of clearcoat to 1.5
commit 9eed34c7d9
Merge: ef29aaeae475e3
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Aug 16 15:22:32 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit ef29aaee1a
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Aug 16 15:17:12 2016 +0200
Implemented the fresnel in the multi-scatter GGX for the Disney BSDF
- The specular/metallic part uses the multi-scatter GGX
- The fresnel of the metallic part is controlled by the specular value
- The color of the reflection part when using transparency can be
controlled by the specularTint value
commit 88567af085
Merge: cc267e5285e082
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Aug 3 15:05:09 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit cc267e52f2
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Aug 3 15:00:25 2016 +0200
Implemented the Disney clearcoat as a variation of the microfacet bsdf,
removed the transparency roughness again and added an input for
anisotropic rotations
commit 81f6c06b1f
Merge: ece5a087065022
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Aug 3 11:42:02 2016 +0200
Merge branch 'master' into cycles_disney_brdf
commit ece5a08e0d
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jul 26 16:29:21 2016 +0200
Base color now applied again to the refraction of transparent Disney
materials
commit e3aff6849e
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jul 26 16:05:19 2016 +0200
Added subsurface color parameter to the Disney shader
commit b3ca6d8a2f
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jul 26 12:30:25 2016 +0200
Improvement of the SSS in the Disney shader
* Now the bump normal is correctly used for the SSS.
* SSS in Disney uses the Disney diffuse shader
commit d68729300e
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jul 26 12:23:13 2016 +0200
Better calculation of the Disney diffuse part
Now the values for NdotL und NdotV are clamped to 0.0f for a better look
when using normal maps
commit cb6e500b12
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Jul 25 16:26:42 2016 +0200
Now one can disable specular reflactions again by setting specular and
metallic to 0 (cracked this in the previous commit)
commit bfb9cb11b5
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Jul 25 16:11:07 2016 +0200
fixed the Disney SSS and cleaned the initialization of the Disney shaders
commit 642c0fdad1
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Jul 25 16:09:55 2016 +0200
fixed an error that was caused by the missing LABEL_REFLECT in the Disney
diffuse shader
commit c10b484dca
Author: Jens Verwiebe <info@jensverwiebe.de>
Date: Fri Jul 22 01:15:21 2016 +0200
Rollback attempt to fix sss crashing, it prevented crash by disabling sss completely, thus useless
commit 462bba3f97
Author: Jens Verwiebe <info@jensverwiebe.de>
Date: Thu Jul 21 23:11:59 2016 +0200
Add an undef for sc_next for safety
commit 32d348577d
Author: Jens Verwiebe <info@jensverwiebe.de>
Date: Thu Jul 21 00:15:48 2016 +0200
Attempt to fix Disney SSS
commit dbad91ca6d
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed Jul 20 11:13:00 2016 +0200
Added a roughness parameter for refractions (for scattering of the rays
within an object)
With this, one can create a translucent material with a smooth surface and
with a milky look.
The final refraction roughness has to be calculated using the surface
roughness and the refraction roughness because those two are correlated
for refractions. If a ray hits a rough surface of a translucent material,
it is scattered while entering the surface. Then it is scattered further
within the object. The calculation I'm using is the following:
RefrRoughnessFinal = 1.0 - (1.0 - Roughness) * (1.0 - RefrRoughness)
commit 50ea5e3e34
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue Jun 7 10:24:50 2016 +0200
Disney BSDF is now supporting CUDA
commit 10974cc826
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 31 11:18:07 2016 +0200
Added parameters IOR and Transparency for refractions
With this, the Disney BRDF/BSSRDF is extended by the BTDF part.
commit 218202c090
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon May 30 15:08:18 2016 +0200
Added an additional normal for the clearcoat
With this normal one can simulate a thin layer of clearcoat by applying a
smoother normal map than the original to this input
commit dd139ead7e
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon May 30 12:40:56 2016 +0200
Switched to the improved subsurface scattering from Christensen and
Burley
commit 11160fa4e1
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon May 30 10:16:30 2016 +0200
Added Disney Sheen shader as a preparation to get to a BSSRDF
commit cee4fe0cc9
Merge: 4f955d06b5bab6
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon May 30 09:08:09 2016 +0200
Merge branch 'cycles_disney_brdf' of git.blender.org:blender into cycles_disney_brdf
Conflicts:
intern/cycles/kernel/closure/bsdf_disney_clearcoat.h
intern/cycles/kernel/closure/bsdf_disney_diffuse.h
intern/cycles/kernel/closure/bsdf_disney_specular.h
intern/cycles/kernel/closure/bsdf_util.h
intern/cycles/kernel/osl/CMakeLists.txt
intern/cycles/kernel/osl/bsdf_disney_clearcoat.cpp
intern/cycles/kernel/osl/bsdf_disney_diffuse.cpp
intern/cycles/kernel/osl/bsdf_disney_specular.cpp
intern/cycles/kernel/osl/osl_closures.h
intern/cycles/kernel/shaders/node_disney_bsdf.osl
intern/cycles/render/nodes.cpp
intern/cycles/render/nodes.h
commit 4f955d0523
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 24 16:38:23 2016 +0200
SVM and OSL are both working for the simple version of the Disney BRDF
commit 1f5c41874b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 24 09:58:50 2016 +0200
Disney node can be used without SVM and started to cleanup the OSL implementation
There is still some wrong behavior for SVM for the Schlick Fresnel part at the
specular and clearcoat
commit d4b814e930
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 18 10:22:29 2016 +0200
Switched from a parameter struct for Disney parameters to ShaderClosure params
commit b86a1f5ba5
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 18 10:19:57 2016 +0200
Added additional variables for storing parameters in the ShaderClosure struct
commit 585b886236
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 17 12:03:17 2016 +0200
added output parameter to the DisneyBsdfNode
That has been forgotten after removing the inheritance of BsdfNode
commit f91a286398
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 17 10:40:48 2016 +0200
removed BsdfNode class inheritance for DisneyBsdfNode
That's due to a naming difference. The Disney BSDF uses the name 'Base Color'
while the BsdfNode had a 'Color' input. That caused a text message to be
printed while rendering.
commit 30da91c9c5
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 4 16:08:10 2016 +0200
disney implementation cleaned
commit 30d41da0f0
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 4 13:23:07 2016 +0200
added the disney brdf as a shader node
commit 1f099fce24
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 3 16:54:49 2016 +0200
added clearcoat implementation
commit 00a1378b98
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Apr 29 22:56:49 2016 +0200
disney diffuse und specular implemented
commit 6baa7a7eb7
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Apr 18 15:21:32 2016 +0200
disney diffuse is working correctly
commit d8fa169bf3
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Apr 18 08:41:53 2016 +0200
added vessel for disney diffuse shader
commit 6b5bab6cec
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 18 10:22:29 2016 +0200
Switched from a parameter struct for Disney parameters to ShaderClosure params
commit f6499c2676
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 18 10:19:57 2016 +0200
Added additional variables for storing parameters in the ShaderClosure struct
commit 7100640b65
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 17 12:03:17 2016 +0200
added output parameter to the DisneyBsdfNode
That has been forgotten after removing the inheritance of BsdfNode
commit 419ee54411
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 17 10:40:48 2016 +0200
removed BsdfNode class inheritance for DisneyBsdfNode
That's due to a naming difference. The Disney BSDF uses the name 'Base Color'
while the BsdfNode had a 'Color' input. That caused a text message to be
printed while rendering.
commit 6006f91e87
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 4 16:08:10 2016 +0200
disney implementation cleaned
commit 0ed0895914
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Wed May 4 13:23:07 2016 +0200
added the disney brdf as a shader node
commit 0630b742d7
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Tue May 3 16:54:49 2016 +0200
added clearcoat implementation
commit 9f3d39744b
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Fri Apr 29 22:56:49 2016 +0200
disney diffuse und specular implemented
commit 9b26206376
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Apr 18 15:21:32 2016 +0200
disney diffuse is working correctly
commit 4711a3927d
Author: Pascal Schoen <pascal_schoen@gmx.net>
Date: Mon Apr 18 08:41:53 2016 +0200
added vessel for disney diffuse shader
Differential Revision: https://developer.blender.org/D2313
The idea is to make include statements more explicit and obvious where the
file is coming from, additionally reducing chance of wrong header being
picked up.
For example, it was not obvious whether bvh.h was refferring to builder
or traversal, whenter node.h is a generic graph node or a shader node
and cases like that.
Surely this might look obvious for the active developers, but after some
time of not touching the code it becomes less obvious where file is coming
from.
This was briefly mentioned in T50824 and seems @brecht is fine with such
explicitness, but need to agree with all active developers before committing
this.
Please note that this patch is lacking changes related on GPU/OpenCL
support. This will be solved if/when we all agree this is a good idea to move
forward.
Reviewers: brecht, lukasstockner97, maiself, nirved, dingto, juicyfruit, swerner
Reviewed By: lukasstockner97, maiself, nirved, dingto
Subscribers: brecht
Differential Revision: https://developer.blender.org/D2586
Mostly this is making inlining match CUDA 7.5 in a few performance critical
places. The end result is that performance is now better than before, possibly
due to less register spilling or other CUDA 8.0 compiler improvements.
On benchmarks scenes, there are 3% to 35% render time reductions. Stack memory
usage is reduced a little too.
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D2269
In the triangle intersection refinement code, rays that are parallel to the triangle caused a divide by zero.
These rays might initially hit the triangle due to the watertight intersection test, but are very rare - therefore, just skipping the refinement for them works fine.
Also, a few remaining issues in the MultiGGX code are fixed that were caused by rays parallel to the surface (which happened more often there due to smooth shading).
As far as I can see, the second issue there was that the functions receive a pointer to a member variable of the
ShaderData, which is stored in global memory. However, this means that the pointer points to global memory as well,
therefore OpenCL requires the ccl_addr_space "keyword" in front of the pointer.
With this commit, the OpenCL kernels build on Linux with the Intel CPU OpenCL runtime - however, they already did
without the change and I don't have an AMD card, so I can't really test whether the AMD runtime is happy as well now.
This commit adds a new distribution to the Glossy, Anisotropic and Glass BSDFs that implements the
multiple-scattering microfacet model described in the paper "Multiple-Scattering Microfacet BSDFs with the Smith Model".
Essentially, the improvement is that unlike classical GGX, which only models single scattering and assumes
the contribution of multiple bounces to be zero, this new model performs a random walk on the microsurface until
the ray leaves it again, which ensures perfect energy conservation.
In practise, this means that the "darkening problem" - GGX materials becoming darker with increasing
roughness - is solved in a physically correct and efficient way.
The downside of this model is that it has no (known) analytic expression for evalation. However, it can be
evaluated stochastically, and although the correct PDF isn't known either, the properties of MIS and the
balance heuristic guarantee an unbiased result at the cost of slightly higher noise.
Reviewers: dingto, #cycles, brecht
Reviewed By: dingto, #cycles, brecht
Subscribers: bliblubli, ace_dragon, gregzaal, brecht, harvester, dingto, marcog, swerner, jtheninja, Blendify, nutel
Differential Revision: https://developer.blender.org/D2002
