ee89f213de
Uses a light tree to more effectively sample scenes with many lights. This can significantly reduce noise, at the cost of a somewhat longer render time per sample. Light tree sampling is enabled by default. It can be disabled in the Sampling > Lights panel. Scenes using light clamping or ray visibility tricks may render different as these are biased techniques that depend on the sampling strategy. The implementation is currently disabled on AMD HIP. This is planned to be fixed before the release. Implementation by Jeffrey Liu, Weizhen Huang, Alaska and Brecht Van Lommel. Ref T77889
81 lines
3.0 KiB
C++
81 lines
3.0 KiB
C++
/* SPDX-License-Identifier: Apache-2.0
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* Copyright 2011-2022 Blender Foundation */
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#pragma once
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#include "kernel/light/light.h"
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#include "kernel/light/triangle.h"
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CCL_NAMESPACE_BEGIN
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/* Simple CDF based sampling over all lights in the scene, without taking into
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* account shading position or normal. */
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ccl_device int light_distribution_sample(KernelGlobals kg, ccl_private float &randu)
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{
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/* This is basically std::upper_bound as used by PBRT, to find a point light or
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* triangle to emit from, proportional to area. a good improvement would be to
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* also sample proportional to power, though it's not so well defined with
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* arbitrary shaders. */
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int first = 0;
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int len = kernel_data.integrator.num_distribution + 1;
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float r = randu;
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do {
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int half_len = len >> 1;
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int middle = first + half_len;
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if (r < kernel_data_fetch(light_distribution, middle).totarea) {
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len = half_len;
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}
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else {
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first = middle + 1;
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len = len - half_len - 1;
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}
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} while (len > 0);
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/* Clamping should not be needed but float rounding errors seem to
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* make this fail on rare occasions. */
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int index = clamp(first - 1, 0, kernel_data.integrator.num_distribution - 1);
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/* Rescale to reuse random number. this helps the 2D samples within
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* each area light be stratified as well. */
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float distr_min = kernel_data_fetch(light_distribution, index).totarea;
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float distr_max = kernel_data_fetch(light_distribution, index + 1).totarea;
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randu = (r - distr_min) / (distr_max - distr_min);
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return index;
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}
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ccl_device_noinline bool light_distribution_sample(KernelGlobals kg,
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ccl_private float &randu,
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const float randv,
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const float time,
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const float3 P,
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const int bounce,
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const uint32_t path_flag,
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ccl_private int &emitter_object,
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ccl_private int &emitter_prim,
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ccl_private int &emitter_shader_flag,
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ccl_private float &emitter_pdf_selection)
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{
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/* Sample light index from distribution. */
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const int index = light_distribution_sample(kg, randu);
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ccl_global const KernelLightDistribution *kdistribution = &kernel_data_fetch(light_distribution,
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index);
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emitter_object = kdistribution->mesh_light.object_id;
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emitter_prim = kdistribution->prim;
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emitter_shader_flag = kdistribution->mesh_light.shader_flag;
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emitter_pdf_selection = kernel_data.integrator.distribution_pdf_lights;
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return true;
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}
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ccl_device_inline float light_distribution_pdf_lamp(KernelGlobals kg)
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{
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return kernel_data.integrator.distribution_pdf_lights;
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}
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CCL_NAMESPACE_END
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