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test2/intern/cycles/kernel/integrator/state_template.h
Weizhen Huang fdc2962beb Fix #114634: correlated samples in volume when using equiangular sampling and light tree 
The same random number was used when sampling from the volume segment
and from the direct scattering position, causing correlation issues with
light tree.

To solve this problem, we ensure the same light is picked for
volume segment/direct scattering, equiangular/distance sampling by
sampling the light tree only once in volume segment. From the direct
scattering position in volume, we sample a position on the picked light
as usual. If sampling from the light tree fails, we continue with
indirect scattering.
For unbiased MIS weight for forward sampling, we retrieve the `P`, `D`
and `t` used in volume segment for traversing the light tree.

The main changes are:
1. `light_tree_sample()` and `light_distribution_sample()` now only pick
lights. Sampling a position on light is done separately via
`light_sample()`.
2. `light_tree_sample()` is now only called only once from volume
segment. For direct lighting we call `light_sample()`.
3. `light_tree_pdf()` now has a template `<in_volume_segment>`.
4. A new field `emitter_id` is added to struct `LightSample`, which just
stores the picked emitter index.
5. Additional field `previous_dt = ray->tmax - ray->tmin` is added to
`state->ray`, because we need this quantity for computing the pdf.
6. Distant/Background lights are also picked by light tree in volume
segment now, because we have no way to pick them afterwards. The direct
sample event for these lights will be handled by
`VOLUME_SAMPLE_DISTANCE`.
7. Original paper suggests to use the maximal importance, this results
in very poor sampling probability for distant and point lights therefore
excessive noise. We have a minimal importance for surface to balance, we
could do the same for volume but I do not want to spend much time on
this now. Just doing `min_importance = 0.0f` seems to do the job
okayish. This way we still won't sample the light with zero
`max_importance`.

The current solution might perform worse with distance sampling, because
the light tree measure is biased towards equiangular sampling. However,
it is difficult to perform MIS between equiangular and distance sampling
if different lights are picked for each method. This is something we can
look into in the future if proved to be a serious regression.

Pull Request: https://projects.blender.org/blender/blender/pulls/119389
2024-03-25 18:50:52 +01:00

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/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
*
* SPDX-License-Identifier: Apache-2.0 */
/************************************ 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, uint32_t, sample, KERNEL_FEATURE_PATH_TRACING)
/* Current ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, bounce, KERNEL_FEATURE_PATH_TRACING)
/* Current transparent ray bounce depth. */
KERNEL_STRUCT_MEMBER(path, uint16_t, transparent_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)
/* DeviceKernel bit indicating queued kernels. */
KERNEL_STRUCT_MEMBER(path, uint16_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, uint16_t, rng_offset, KERNEL_FEATURE_PATH_TRACING)
/* enum PathRayFlag */
KERNEL_STRUCT_MEMBER(path, uint32_t, flag, KERNEL_FEATURE_PATH_TRACING)
/* enum PathRayMNEE */
KERNEL_STRUCT_MEMBER(path, uint8_t, mnee, KERNEL_FEATURE_PATH_TRACING)
/* Multiple importance sampling
* The PDF of BSDF sampling at the last scatter point, which is at ray distance
* zero and distance. Note that transparency and volume attenuation increase
* the ray tmin but keep P unmodified so that this works. */
KERNEL_STRUCT_MEMBER(path, float, mis_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
/* Object at last scatter point for light linking. */
KERNEL_STRUCT_MEMBER(path, int, mis_ray_object, KERNEL_FEATURE_LIGHT_LINKING)
/* Normal at last scatter point for light tree. */
KERNEL_STRUCT_MEMBER(path, packed_float3, mis_origin_n, KERNEL_FEATURE_PATH_TRACING)
/* Filter glossy. */
KERNEL_STRUCT_MEMBER(path, float, min_ray_pdf, KERNEL_FEATURE_PATH_TRACING)
/* Continuation probability for path termination. */
KERNEL_STRUCT_MEMBER(path, float, continuation_probability, KERNEL_FEATURE_PATH_TRACING)
/* Throughput. */
KERNEL_STRUCT_MEMBER(path, PackedSpectrum, throughput, KERNEL_FEATURE_PATH_TRACING)
/* Factor to multiple with throughput to get remove any guiding PDFS.
* Such throughput without guiding PDFS is used for Russian roulette termination. */
KERNEL_STRUCT_MEMBER(path, float, unguided_throughput, KERNEL_FEATURE_PATH_GUIDING)
/* Ratio of throughput to distinguish diffuse / glossy / transmission render passes. */
KERNEL_STRUCT_MEMBER(path, PackedSpectrum, pass_diffuse_weight, KERNEL_FEATURE_LIGHT_PASSES)
KERNEL_STRUCT_MEMBER(path, PackedSpectrum, pass_glossy_weight, KERNEL_FEATURE_LIGHT_PASSES)
/* Denoising. */
KERNEL_STRUCT_MEMBER(path, PackedSpectrum, 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, packed_float3, P, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, packed_float3, D, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, tmin, KERNEL_FEATURE_PATH_TRACING)
KERNEL_STRUCT_MEMBER(ray, float, tmax, 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)
#ifdef __LIGHT_TREE__
KERNEL_STRUCT_MEMBER(ray, float, previous_dt, KERNEL_FEATURE_PATH_TRACING)
#endif
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)
KERNEL_STRUCT_END(isect)
/*************** Subsurface closure state for subsurface kernel ***************/
KERNEL_STRUCT_BEGIN(subsurface)
KERNEL_STRUCT_MEMBER(subsurface, PackedSpectrum, albedo, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_MEMBER(subsurface, PackedSpectrum, radius, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_MEMBER(subsurface, float, anisotropy, KERNEL_FEATURE_SUBSURFACE)
KERNEL_STRUCT_MEMBER(subsurface, packed_float3, N, 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)
/************************************ Path Guiding *****************************/
KERNEL_STRUCT_BEGIN(guiding)
#ifdef __PATH_GUIDING__
/* Current path segment of the random walk/path. */
KERNEL_STRUCT_MEMBER(guiding,
openpgl::cpp::PathSegment *,
path_segment,
KERNEL_FEATURE_PATH_GUIDING)
#else
/* Current path segment of the random walk/path. */
KERNEL_STRUCT_MEMBER(guiding, uint64_t, path_segment, KERNEL_FEATURE_PATH_GUIDING)
#endif
/* If surface guiding is enabled */
KERNEL_STRUCT_MEMBER(guiding, bool, use_surface_guiding, KERNEL_FEATURE_PATH_GUIDING)
/* Random number used for additional guiding decisions (e.g., cache query, selection to use guiding
* or BSDF sampling) */
KERNEL_STRUCT_MEMBER(guiding, float, sample_surface_guiding_rand, KERNEL_FEATURE_PATH_GUIDING)
/* The probability to use surface guiding (i.e., diffuse sampling prob * guiding prob)*/
KERNEL_STRUCT_MEMBER(guiding, float, surface_guiding_sampling_prob, KERNEL_FEATURE_PATH_GUIDING)
/* Probability of sampling a BSSRDF closure instead of a BSDF closure. */
KERNEL_STRUCT_MEMBER(guiding, float, bssrdf_sampling_prob, KERNEL_FEATURE_PATH_GUIDING)
/* If volume guiding is enabled */
KERNEL_STRUCT_MEMBER(guiding, bool, use_volume_guiding, KERNEL_FEATURE_PATH_GUIDING)
/* Random number used for additional guiding decisions (e.g., cache query, selection to use guiding
* or BSDF sampling) */
KERNEL_STRUCT_MEMBER(guiding, float, sample_volume_guiding_rand, KERNEL_FEATURE_PATH_GUIDING)
/* The probability to use surface guiding (i.e., diffuse sampling prob * guiding prob). */
KERNEL_STRUCT_MEMBER(guiding, float, volume_guiding_sampling_prob, KERNEL_FEATURE_PATH_GUIDING)
KERNEL_STRUCT_END(guiding)
/******************************* Shadow linking *******************************/
KERNEL_STRUCT_BEGIN(shadow_link)
KERNEL_STRUCT_MEMBER(shadow_link, float, dedicated_light_weight, KERNEL_FEATURE_SHADOW_LINKING)
/* Copy of primitive and object from the last main path intersection. */
KERNEL_STRUCT_MEMBER(shadow_link, int, last_isect_prim, KERNEL_FEATURE_SHADOW_LINKING)
KERNEL_STRUCT_MEMBER(shadow_link, int, last_isect_object, KERNEL_FEATURE_SHADOW_LINKING)
KERNEL_STRUCT_END(shadow_link)
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