distribution.h

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/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
 *
 * SPDX-License-Identifier: Apache-2.0 */
 
#pragma once
 
#include "kernel/globals.h"
 
#include "kernel/light/common.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, const float rand)
{
  /* 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;
 
  do {
    const int half_len = len >> 1;
    const int middle = first + half_len;
 
    if (rand < 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. */
  const int index = clamp(first - 1, 0, kernel_data.integrator.num_distribution - 1);
 
  return index;
}
 
ccl_device_noinline bool light_distribution_sample(KernelGlobals kg,
                                                   const float rand,
                                                   ccl_private LightSample *ls)
{
  /* Sample light index from distribution. */
  ls->emitter_id = light_distribution_sample(kg, rand);
  ls->pdf_selection = kernel_data.integrator.distribution_pdf_lights;
  return true;
}
 
ccl_device_inline float light_distribution_pdf_lamp(KernelGlobals kg)
{
  return kernel_data.integrator.distribution_pdf_lights;
}
 
CCL_NAMESPACE_END