Differential D16655 Diff 58189 intern/cycles/kernel/light/distribution.h

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intern/cycles/kernel/light/distribution.h

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				/* SPDX-License-Identifier: Apache-2.0
				* Copyright 2011-2022 Blender Foundation */

				#pragma once

				#include "kernel/light/light.h"
				#include "kernel/light/triangle.h"

				CCL_NAMESPACE_BEGIN

				/* Simple CDF based sampling over all lights in the scene, without taking into
				* account shading position or normal. */

				ccl_device int light_distribution_sample(KernelGlobals kg, ccl_private float *randu)
				{
				/* This is basically std::upper_bound as used by PBRT, to find a point light or
				* triangle to emit from, proportional to area. a good improvement would be to
				* also sample proportional to power, though it's not so well defined with
				* arbitrary shaders. */
				int first = 0;
				int len = kernel_data.integrator.num_distribution + 1;
				float r = *randu;

				do {
				int half_len = len >> 1;
				int middle = first + half_len;

				if (r < kernel_data_fetch(light_distribution, middle).totarea) {
				len = half_len;
				}
				else {
				first = middle + 1;
				len = len - half_len - 1;
				}
				} while (len > 0);

				/* Clamping should not be needed but float rounding errors seem to
				* make this fail on rare occasions. */
				int index = clamp(first - 1, 0, kernel_data.integrator.num_distribution - 1);

				/* Rescale to reuse random number. this helps the 2D samples within
				* each area light be stratified as well. */
				float distr_min = kernel_data_fetch(light_distribution, index).totarea;
				float distr_max = kernel_data_fetch(light_distribution, index + 1).totarea;
				*randu = (r - distr_min) / (distr_max - distr_min);

				return index;
				}

				template<bool in_volume_segment>
				ccl_device_noinline bool light_distribution_sample(KernelGlobals kg,
				float randu,
				const float randv,
				const float time,
				const float3 P,
				const int bounce,
				const uint32_t path_flag,
				ccl_private LightSample *ls)
				{
				/* Sample light index from distribution. */
				const int index = light_distribution_sample(kg, &randu);
				ccl_global const KernelLightDistribution *kdistribution = &kernel_data_fetch(light_distribution,
				index);
				const int prim = kdistribution->prim;

				if (prim >= 0) {
				/* Mesh light. */
				const int object = kdistribution->mesh_light.object_id;

				/* Exclude synthetic meshes from shadow catcher pass. */
				if ((path_flag & PATH_RAY_SHADOW_CATCHER_PASS) &&
				!(kernel_data_fetch(object_flag, object) & SD_OBJECT_SHADOW_CATCHER)) {
				return false;
				}

				const int shader_flag = kdistribution->mesh_light.shader_flag;
				triangle_light_sample<in_volume_segment>(kg, prim, object, randu, randv, time, ls, P);
				ls->shader \|= shader_flag;
				return (ls->pdf > 0.0f);
				}

				const int lamp = -prim - 1;

				if (UNLIKELY(light_select_reached_max_bounces(kg, lamp, bounce))) {
				return false;
				}

				if (!light_sample<in_volume_segment>(kg, lamp, randu, randv, P, path_flag, ls)) {
				return false;
				}

				ls->pdf_selection = kernel_data.integrator.distribution_pdf_lights;
				ls->pdf *= ls->pdf_selection;

				return true;
				}

				ccl_device_inline float light_distribution_pdf_lamp(KernelGlobals kg)
				{
				return kernel_data.integrator.distribution_pdf_lights;
				}

				CCL_NAMESPACE_END