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blender-archive/intern/cycles/kernel/integrator/integrator_state_template.h
Brecht Van Lommel a94343a8af Cycles: improve SSS Fresnel and retro-reflection in Principled BSDF 
For details see the "Extending the Disney BRDF to a BSDF with Integrated
Subsurface Scattering" paper.

We split the diffuse BSDF into a lambertian and retro-reflection component.
The retro-reflection component is always handled as a BSDF, while the
lambertian component can be replaced by a BSSRDF.

For the BSSRDF case, we compute Fresnel separately at the entry and exit
points, which may have different normals. As the scattering radius decreases
this converges to the BSDF case.

A downside is that this increases noise for subsurface scattering in the
Principled BSDF, due to some samples going to the retro-reflection component.
However the previous logic (also in 2.93) was simple wrong, using a
non-sensical view direction vector at the exit point. We use an importance
sampling weight estimate for the retro-reflection to try to better balance
samples between the BSDF and BSSRDF.

Differential Revision: https://developer.blender.org/D12801
2021-10-11 18:22:54 +02:00

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/*
* Copyright 2011-2021 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/************************************ Path State *****************************/
KERNEL_STRUCT_BEGIN(path)
/* Index of a pixel within the device render buffer where this path will write its result.
* To get an actual offset within the buffer the value needs to be multiplied by the
* `kernel_data.film.pass_stride`.
*
* The multiplication is delayed for later, so that state can use 32bit integer. */
KERNEL_STRUCT_MEMBER(path, uint32_t, render_pixel_index, KERNEL_FEATURE_PATH_TRACING)
/* Current sample number. */
KERNEL_STRUCT_MEMBER(path, uint16_t, sample, KERNEL_FEATURE_PATH_TRACING)
/* Current ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current diffuse ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, diffuse_bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current glossy ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, glossy_bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current transmission ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, transmission_bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current volume ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, volume_bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current volume bounds ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, volume_bounds_bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current transparent ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, transparent_bounce, KERNEL_FEATURE_PATH_TRACING)
/* DeviceKernel bit indicating queued kernels.
* TODO: reduce size? */
KERNEL_STRUCT_MEMBER(path, uint32_t, queued_kernel, KERNEL_FEATURE_PATH_TRACING)
/* Random number generator seed. */
KERNEL_STRUCT_MEMBER(path, uint32_t, rng_hash, KERNEL_FEATURE_PATH_TRACING)
/* Random number dimension offset. */
KERNEL_STRUCT_MEMBER(path, uint32_t, rng_offset, KERNEL_FEATURE_PATH_TRACING)
/* enum PathRayFlag */
KERNEL_STRUCT_MEMBER(path, uint32_t, flag, KERNEL_FEATURE_PATH_TRACING)
/* Multiple importance sampling
* The PDF of BSDF sampling at the last scatter point, and distance to the
* last scatter point minus the last ray segment. This distance lets us
* compute the complete distance through transparent surfaces and volumes. */
KERNEL_STRUCT_MEMBER(path, float, mis_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(path, float, mis_ray_t, KERNEL_FEATURE_PATH_TRACING)
/* Filter glossy. */
KERNEL_STRUCT_MEMBER(path, float, min_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
/* Throughput. */
KERNEL_STRUCT_MEMBER(path, float3, throughput, KERNEL_FEATURE_PATH_TRACING)
/* Ratio of throughput to distinguish diffuse and glossy render passes. */
KERNEL_STRUCT_MEMBER(path, float3, diffuse_glossy_ratio, KERNEL_FEATURE_LIGHT_PASSES)
/* Denoising. */
KERNEL_STRUCT_MEMBER(path, float3, denoising_feature_throughput, KERNEL_FEATURE_DENOISING)
/* Shader sorting. */
/* TODO: compress as uint16? or leave out entirely and recompute key in sorting code? */
KERNEL_STRUCT_MEMBER(path, uint32_t, shader_sort_key, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END(path)
/************************************** Ray ***********************************/
KERNEL_STRUCT_BEGIN(ray)
KERNEL_STRUCT_MEMBER(ray, float3, P, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float3, D, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, t, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, time, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, dP, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, dD, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END(ray)
/*************************** Intersection result ******************************/
/* Result from scene intersection. */
KERNEL_STRUCT_BEGIN(isect)
KERNEL_STRUCT_MEMBER(isect, float, t, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(isect, float, u, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(isect, float, v, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(isect, int, prim, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(isect, int, object, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(isect, int, type, KERNEL_FEATURE_PATH_TRACING)
/* TODO: exclude for GPU. */
KERNEL_STRUCT_MEMBER(isect, float3, Ng, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END(isect)
/*************** Subsurface closure state for subsurface kernel ***************/
KERNEL_STRUCT_BEGIN(subsurface)
KERNEL_STRUCT_MEMBER(subsurface, float3, albedo, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_MEMBER(subsurface, float3, radius, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_MEMBER(subsurface, float, anisotropy, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_END(subsurface)
/********************************** Volume Stack ******************************/
KERNEL_STRUCT_BEGIN(volume_stack)
KERNEL_STRUCT_ARRAY_MEMBER(volume_stack, int, object, KERNEL_FEATURE_VOLUME)
KERNEL_STRUCT_ARRAY_MEMBER(volume_stack, int, shader, KERNEL_FEATURE_VOLUME)
KERNEL_STRUCT_END_ARRAY(volume_stack,
KERNEL_STRUCT_VOLUME_STACK_SIZE,
KERNEL_STRUCT_VOLUME_STACK_SIZE)
/********************************* Shadow Path State **************************/
KERNEL_STRUCT_BEGIN(shadow_path)
/* Current ray bounce depth. */
KERNEL_STRUCT_MEMBER(shadow_path, uint16_t, bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current transparent ray bounce depth. */
KERNEL_STRUCT_MEMBER(shadow_path, uint16_t, transparent_bounce, KERNEL_FEATURE_PATH_TRACING)
/* DeviceKernel bit indicating queued kernels.
* TODO: reduce size? */
KERNEL_STRUCT_MEMBER(shadow_path, uint32_t, queued_kernel, KERNEL_FEATURE_PATH_TRACING)
/* enum PathRayFlag */
KERNEL_STRUCT_MEMBER(shadow_path, uint32_t, flag, KERNEL_FEATURE_PATH_TRACING)
/* Throughput. */
KERNEL_STRUCT_MEMBER(shadow_path, float3, throughput, KERNEL_FEATURE_PATH_TRACING)
/* Throughput for shadow pass. */
KERNEL_STRUCT_MEMBER(shadow_path, float3, unshadowed_throughput, KERNEL_FEATURE_SHADOW_PASS)
/* Ratio of throughput to distinguish diffuse and glossy render passes. */
KERNEL_STRUCT_MEMBER(shadow_path, float3, diffuse_glossy_ratio, KERNEL_FEATURE_LIGHT_PASSES)
/* Number of intersections found by ray-tracing. */
KERNEL_STRUCT_MEMBER(shadow_path, uint16_t, num_hits, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END(shadow_path)
/********************************** Shadow Ray *******************************/
KERNEL_STRUCT_BEGIN(shadow_ray)
KERNEL_STRUCT_MEMBER(shadow_ray, float3, P, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(shadow_ray, float3, D, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(shadow_ray, float, t, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(shadow_ray, float, time, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(shadow_ray, float, dP, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END(shadow_ray)
/*********************** Shadow Intersection result **************************/
/* Result from scene intersection. */
KERNEL_STRUCT_BEGIN(shadow_isect)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, float, t, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, float, u, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, float, v, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, int, prim, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, int, object, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, int, type, KERNEL_FEATURE_PATH_TRACING)
/* TODO: exclude for GPU. */
KERNEL_STRUCT_ARRAY_MEMBER(shadow_isect, float3, Ng, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_END_ARRAY(shadow_isect,
INTEGRATOR_SHADOW_ISECT_SIZE_CPU,
INTEGRATOR_SHADOW_ISECT_SIZE_GPU)
/**************************** Shadow Volume Stack *****************************/
KERNEL_STRUCT_BEGIN(shadow_volume_stack)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_volume_stack, int, object, KERNEL_FEATURE_VOLUME)
KERNEL_STRUCT_ARRAY_MEMBER(shadow_volume_stack, int, shader, KERNEL_FEATURE_VOLUME)
KERNEL_STRUCT_END_ARRAY(shadow_volume_stack,
KERNEL_STRUCT_VOLUME_STACK_SIZE,
KERNEL_STRUCT_VOLUME_STACK_SIZE)
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