forked from bartvdbraak/blender
fdc2962beb
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
84 lines
2.5 KiB
C
84 lines
2.5 KiB
C
/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
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*
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* SPDX-License-Identifier: Apache-2.0 */
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#pragma once
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#include "kernel/sample/mapping.h"
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CCL_NAMESPACE_BEGIN
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/* Light Sample Result */
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typedef struct LightSample {
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float3 P; /* position on light, or direction for distant light */
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packed_float3 Ng; /* normal on light */
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float t; /* distance to light (FLT_MAX for distant light) */
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float3 D; /* direction from shading point to light */
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float u, v; /* parametric coordinate on primitive */
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float pdf; /* pdf for selecting light and point on light */
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float pdf_selection; /* pdf for selecting light */
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float eval_fac; /* intensity multiplier */
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int object; /* object id for triangle/curve lights */
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int prim; /* primitive id for triangle/curve lights */
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int shader; /* shader id */
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int lamp; /* lamp id */
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int group; /* lightgroup */
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LightType type; /* type of light */
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int emitter_id; /* index in the emitter array */
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} LightSample;
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/* Utilities */
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ccl_device_inline float3 ellipse_sample(float3 ru, float3 rv, float2 rand)
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{
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const float2 uv = sample_uniform_disk(rand);
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return ru * uv.x + rv * uv.y;
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}
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ccl_device_inline float3 rectangle_sample(float3 ru, float3 rv, float2 rand)
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{
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return ru * (2.0f * rand.x - 1.0f) + rv * (2.0f * rand.y - 1.0f);
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}
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ccl_device float3 disk_light_sample(float3 n, float2 rand)
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{
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float3 ru, rv;
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make_orthonormals(n, &ru, &rv);
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return ellipse_sample(ru, rv, rand);
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}
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ccl_device float light_pdf_area_to_solid_angle(const float3 Ng, const float3 I, float t)
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{
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float cos_pi = dot(Ng, I);
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if (cos_pi <= 0.0f)
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return 0.0f;
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return t * t / cos_pi;
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}
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/* Visibility flag om the light shader. */
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ccl_device_inline bool is_light_shader_visible_to_path(const int shader, const uint32_t path_flag)
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{
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if ((shader & SHADER_EXCLUDE_ANY) == 0) {
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return true;
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}
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if (((shader & SHADER_EXCLUDE_DIFFUSE) && (path_flag & PATH_RAY_DIFFUSE)) ||
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((shader & SHADER_EXCLUDE_GLOSSY) && ((path_flag & (PATH_RAY_GLOSSY | PATH_RAY_REFLECT)) ==
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(PATH_RAY_GLOSSY | PATH_RAY_REFLECT))) ||
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((shader & SHADER_EXCLUDE_TRANSMIT) && (path_flag & PATH_RAY_TRANSMIT)) ||
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((shader & SHADER_EXCLUDE_CAMERA) && (path_flag & PATH_RAY_CAMERA)) ||
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((shader & SHADER_EXCLUDE_SCATTER) && (path_flag & PATH_RAY_VOLUME_SCATTER)))
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{
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return false;
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}
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return true;
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}
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CCL_NAMESPACE_END
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