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

#include "device/device.h"

#include "scene/background.h"
#include "scene/film.h"
#include "scene/integrator.h"
#include "scene/light.h"
#include "scene/mesh.h"
#include "scene/object.h"
#include "scene/scene.h"
#include "scene/shader.h"
#include "scene/shader_graph.h"
#include "scene/shader_nodes.h"
#include "scene/stats.h"

#include "integrator/shader_eval.h"

#include "util/foreach.h"
#include "util/hash.h"
#include "util/log.h"
#include "util/path.h"
#include "util/progress.h"
#include "util/task.h"

CCL_NAMESPACE_BEGIN

static void shade_background_pixels(Device *device,
                                    DeviceScene *dscene,
                                    int width,
                                    int height,
                                    vector<float3> &pixels,
                                    Progress &progress)
{
  /* Needs to be up to data for attribute access. */
  device->const_copy_to("data", &dscene->data, sizeof(dscene->data));

  const int size = width * height;
  const int num_channels = 3;
  pixels.resize(size);

  /* Evaluate shader on device. */
  ShaderEval shader_eval(device, progress);
  shader_eval.eval(
      SHADER_EVAL_BACKGROUND,
      size,
      num_channels,
      [&](device_vector<KernelShaderEvalInput> &d_input) {
        /* Fill coordinates for shading. */
        KernelShaderEvalInput *d_input_data = d_input.data();

        for (int y = 0; y < height; y++) {
          for (int x = 0; x < width; x++) {
            float u = (x + 0.5f) / width;
            float v = (y + 0.5f) / height;

            KernelShaderEvalInput in;
            in.object = OBJECT_NONE;
            in.prim = PRIM_NONE;
            in.u = u;
            in.v = v;
            d_input_data[x + y * width] = in;
          }
        }

        return size;
      },
      [&](device_vector<float> &d_output) {
        /* Copy output to pixel buffer. */
        float *d_output_data = d_output.data();

        for (int y = 0; y < height; y++) {
          for (int x = 0; x < width; x++) {
            pixels[y * width + x].x = d_output_data[(y * width + x) * num_channels + 0];
            pixels[y * width + x].y = d_output_data[(y * width + x) * num_channels + 1];
            pixels[y * width + x].z = d_output_data[(y * width + x) * num_channels + 2];
          }
        }
      });
}

/* Light */

NODE_DEFINE(Light)
{
  NodeType *type = NodeType::add("light", create);

  static NodeEnum type_enum;
  type_enum.insert("point", LIGHT_POINT);
  type_enum.insert("distant", LIGHT_DISTANT);
  type_enum.insert("background", LIGHT_BACKGROUND);
  type_enum.insert("area", LIGHT_AREA);
  type_enum.insert("spot", LIGHT_SPOT);
  SOCKET_ENUM(light_type, "Type", type_enum, LIGHT_POINT);

  SOCKET_COLOR(strength, "Strength", one_float3());

  SOCKET_POINT(co, "Co", zero_float3());

  SOCKET_VECTOR(dir, "Dir", zero_float3());
  SOCKET_FLOAT(size, "Size", 0.0f);
  SOCKET_FLOAT(angle, "Angle", 0.0f);

  SOCKET_VECTOR(axisu, "Axis U", zero_float3());
  SOCKET_FLOAT(sizeu, "Size U", 1.0f);
  SOCKET_VECTOR(axisv, "Axis V", zero_float3());
  SOCKET_FLOAT(sizev, "Size V", 1.0f);
  SOCKET_BOOLEAN(ellipse, "Ellipse", false);
  SOCKET_FLOAT(spread, "Spread", M_PI_F);

  SOCKET_INT(map_resolution, "Map Resolution", 0);
  SOCKET_FLOAT(average_radiance, "Average Radiance", 0.0f);

  SOCKET_FLOAT(spot_angle, "Spot Angle", M_PI_4_F);
  SOCKET_FLOAT(spot_smooth, "Spot Smooth", 0.0f);

  SOCKET_TRANSFORM(tfm, "Transform", transform_identity());

  SOCKET_BOOLEAN(cast_shadow, "Cast Shadow", true);
  SOCKET_BOOLEAN(use_mis, "Use Mis", false);
  SOCKET_BOOLEAN(use_camera, "Use Camera", true);
  SOCKET_BOOLEAN(use_diffuse, "Use Diffuse", true);
  SOCKET_BOOLEAN(use_glossy, "Use Glossy", true);
  SOCKET_BOOLEAN(use_transmission, "Use Transmission", true);
  SOCKET_BOOLEAN(use_scatter, "Use Scatter", true);
  SOCKET_BOOLEAN(use_caustics, "Shadow Caustics", false);

  SOCKET_INT(max_bounces, "Max Bounces", 1024);
  SOCKET_UINT(random_id, "Random ID", 0);

  SOCKET_BOOLEAN(is_shadow_catcher, "Shadow Catcher", true);
  SOCKET_BOOLEAN(is_portal, "Is Portal", false);
  SOCKET_BOOLEAN(is_enabled, "Is Enabled", true);

  SOCKET_NODE(shader, "Shader", Shader::get_node_type());

  SOCKET_STRING(lightgroup, "Light Group", ustring());

  return type;
}

Light::Light() : Node(get_node_type())
{
  dereference_all_used_nodes();
}

void Light::tag_update(Scene *scene)
{
  if (is_modified()) {
    scene->light_manager->tag_update(scene, LightManager::LIGHT_MODIFIED);
  }
}

bool Light::has_contribution(Scene *scene)
{
  if (strength == zero_float3()) {
    return false;
  }
  if (is_portal) {
    return false;
  }
  if (light_type == LIGHT_BACKGROUND) {
    return true;
  }

  const Shader *effective_shader = (shader) ? shader : scene->default_light;
  return !is_zero(effective_shader->emission_estimate);
}

/* Light Manager */

LightManager::LightManager()
{
  update_flags = UPDATE_ALL;
  need_update_background = true;
  last_background_enabled = false;
  last_background_resolution = 0;
}

LightManager::~LightManager()
{
  foreach (IESSlot *slot, ies_slots) {
    delete slot;
  }
}

bool LightManager::has_background_light(Scene *scene)
{
  foreach (Light *light, scene->lights) {
    if (light->light_type == LIGHT_BACKGROUND && light->is_enabled) {
      return true;
    }
  }
  return false;
}

void LightManager::test_enabled_lights(Scene *scene)
{
  /* Make all lights enabled by default, and perform some preliminary checks
   * needed for finer-tuning of settings (for example, check whether we've
   * got portals or not).
   */
  bool has_portal = false, has_background = false;
  foreach (Light *light, scene->lights) {
    light->is_enabled = light->has_contribution(scene);
    has_portal |= light->is_portal;
    has_background |= light->light_type == LIGHT_BACKGROUND;
  }

  bool background_enabled = false;
  int background_resolution = 0;

  if (has_background) {
    /* Ignore background light if:
     * - If unsupported on a device
     * - If we don't need it (no HDRs etc.)
     */
    Shader *shader = scene->background->get_shader(scene);
    const bool disable_mis = !(has_portal || shader->has_surface_spatial_varying);
    if (disable_mis) {
      VLOG_INFO << "Background MIS has been disabled.\n";
    }
    foreach (Light *light, scene->lights) {
      if (light->light_type == LIGHT_BACKGROUND) {
        light->is_enabled = !disable_mis;
        background_enabled = !disable_mis;
        background_resolution = light->map_resolution;
      }
    }
  }

  if (last_background_enabled != background_enabled ||
      last_background_resolution != background_resolution) {
    last_background_enabled = background_enabled;
    last_background_resolution = background_resolution;
    need_update_background = true;
  }
}

bool LightManager::object_usable_as_light(Object *object)
{
  Geometry *geom = object->get_geometry();
  if (geom->geometry_type != Geometry::MESH && geom->geometry_type != Geometry::VOLUME) {
    return false;
  }
  /* Skip objects with NaNs */
  if (!object->bounds.valid()) {
    return false;
  }
  /* Skip if we are not visible for BSDFs. */
  if (!(object->get_visibility() & (PATH_RAY_DIFFUSE | PATH_RAY_GLOSSY | PATH_RAY_TRANSMIT))) {
    return false;
  }
  /* Skip if we have no emission shaders. */
  /* TODO(sergey): Ideally we want to avoid such duplicated loop, since it'll
   * iterate all geometry shaders twice (when counting and when calculating
   * triangle area.
   */
  foreach (Node *node, geom->get_used_shaders()) {
    Shader *shader = static_cast<Shader *>(node);
    if (shader->emission_sampling != EMISSION_SAMPLING_NONE) {
      return true;
    }
  }
  return false;
}

void LightManager::device_update_distribution(Device *,
                                              DeviceScene *dscene,
                                              Scene *scene,
                                              Progress &progress)
{
  KernelIntegrator *kintegrator = &dscene->data.integrator;

  /* Update CDF over lights. */
  progress.set_status("Updating Lights", "Computing distribution");

  /* Counts emissive triangles in the scene. */
  size_t num_triangles = 0;

  foreach (Object *object, scene->objects) {
    if (progress.get_cancel())
      return;

    if (!object_usable_as_light(object)) {
      continue;
    }

    /* Count emissive triangles. */
    Mesh *mesh = static_cast<Mesh *>(object->get_geometry());
    size_t mesh_num_triangles = mesh->num_triangles();

    for (size_t i = 0; i < mesh_num_triangles; i++) {
      int shader_index = mesh->get_shader()[i];
      Shader *shader = (shader_index < mesh->get_used_shaders().size()) ?
                           static_cast<Shader *>(mesh->get_used_shaders()[shader_index]) :
                           scene->default_surface;

      if (shader->emission_sampling != EMISSION_SAMPLING_NONE) {
        num_triangles++;
      }
    }
  }

  const size_t num_lights = kintegrator->num_lights;
  const size_t num_distribution = num_triangles + num_lights;

  /* Distribution size. */
  kintegrator->num_distribution = num_distribution;

  VLOG_INFO << "Total " << num_distribution << " of light distribution primitives.";

  if (kintegrator->use_light_tree) {
    dscene->light_distribution.free();
    return;
  }

  /* Emission area. */
  KernelLightDistribution *distribution = dscene->light_distribution.alloc(num_distribution + 1);
  float totarea = 0.0f;

  /* Triangles. */
  size_t offset = 0;
  int j = 0;

  foreach (Object *object, scene->objects) {
    if (progress.get_cancel())
      return;

    if (!object_usable_as_light(object)) {
      j++;
      continue;
    }
    /* Sum area. */
    Mesh *mesh = static_cast<Mesh *>(object->get_geometry());
    bool transform_applied = mesh->transform_applied;
    Transform tfm = object->get_tfm();
    int object_id = j;
    int shader_flag = 0;

    if (!(object->get_visibility() & PATH_RAY_CAMERA)) {
      shader_flag |= SHADER_EXCLUDE_CAMERA;
    }
    if (!(object->get_visibility() & PATH_RAY_DIFFUSE)) {
      shader_flag |= SHADER_EXCLUDE_DIFFUSE;
    }
    if (!(object->get_visibility() & PATH_RAY_GLOSSY)) {
      shader_flag |= SHADER_EXCLUDE_GLOSSY;
    }
    if (!(object->get_visibility() & PATH_RAY_TRANSMIT)) {
      shader_flag |= SHADER_EXCLUDE_TRANSMIT;
    }
    if (!(object->get_visibility() & PATH_RAY_VOLUME_SCATTER)) {
      shader_flag |= SHADER_EXCLUDE_SCATTER;
    }
    if (!(object->get_is_shadow_catcher())) {
      shader_flag |= SHADER_EXCLUDE_SHADOW_CATCHER;
    }

    size_t mesh_num_triangles = mesh->num_triangles();
    for (size_t i = 0; i < mesh_num_triangles; i++) {
      int shader_index = mesh->get_shader()[i];
      Shader *shader = (shader_index < mesh->get_used_shaders().size()) ?
                           static_cast<Shader *>(mesh->get_used_shaders()[shader_index]) :
                           scene->default_surface;

      if (shader->emission_sampling != EMISSION_SAMPLING_NONE) {
        distribution[offset].totarea = totarea;
        distribution[offset].prim = i + mesh->prim_offset;
        distribution[offset].mesh_light.shader_flag = shader_flag;
        distribution[offset].mesh_light.object_id = object_id;
        offset++;

        Mesh::Triangle t = mesh->get_triangle(i);
        if (!t.valid(&mesh->get_verts()[0])) {
          continue;
        }
        float3 p1 = mesh->get_verts()[t.v[0]];
        float3 p2 = mesh->get_verts()[t.v[1]];
        float3 p3 = mesh->get_verts()[t.v[2]];

        if (!transform_applied) {
          p1 = transform_point(&tfm, p1);
          p2 = transform_point(&tfm, p2);
          p3 = transform_point(&tfm, p3);
        }

        totarea += triangle_area(p1, p2, p3);
      }
    }

    j++;
  }

  const float trianglearea = totarea;

  /* Lights. */
  int light_index = 0;

  if (num_lights > 0) {
    float lightarea = (totarea > 0.0f) ? totarea / num_lights : 1.0f;
    foreach (Light *light, scene->lights) {
      if (!light->is_enabled)
        continue;

      distribution[offset].totarea = totarea;
      distribution[offset].prim = ~light_index;
      distribution[offset].mesh_light.object_id = OBJECT_NONE;
      distribution[offset].mesh_light.shader_flag = 0;
      totarea += lightarea;

      light_index++;
      offset++;
    }
  }

  /* normalize cumulative distribution functions */
  distribution[num_distribution].totarea = totarea;
  distribution[num_distribution].prim = 0;
  distribution[num_distribution].mesh_light.object_id = OBJECT_NONE;
  distribution[num_distribution].mesh_light.shader_flag = 0;

  if (totarea > 0.0f) {
    for (size_t i = 0; i < num_distribution; i++)
      distribution[i].totarea /= totarea;
    distribution[num_distribution].totarea = 1.0f;
  }

  if (progress.get_cancel())
    return;

  /* Update integrator state. */
  kintegrator->use_direct_light = (totarea > 0.0f);

  /* Precompute pdfs for distribution sampling.
   * Sample one, with 0.5 probability of light or triangle. */
  kintegrator->distribution_pdf_triangles = 0.0f;
  kintegrator->distribution_pdf_lights = 0.0f;

  if (trianglearea > 0.0f) {
    kintegrator->distribution_pdf_triangles = 1.0f / trianglearea;
    if (num_lights) {
      kintegrator->distribution_pdf_triangles *= 0.5f;
    }
  }

  if (num_lights) {
    kintegrator->distribution_pdf_lights = 1.0f / num_lights;
    if (trianglearea > 0.0f) {
      kintegrator->distribution_pdf_lights *= 0.5f;
    }
  }

  /* Copy distribution to device. */
  dscene->light_distribution.copy_to_device();
}

void LightManager::device_update_tree(Device *,
                                      DeviceScene *dscene,
                                      Scene *scene,
                                      Progress &progress)
{
  KernelIntegrator *kintegrator = &dscene->data.integrator;

  if (!kintegrator->use_light_tree) {
    dscene->light_tree_nodes.free();
    dscene->light_tree_emitters.free();
    dscene->light_to_tree.free();
    dscene->object_lookup_offset.free();
    dscene->triangle_to_tree.free();
    return;
  }

  /* Update light tree. */
  progress.set_status("Updating Lights", "Computing tree");

  /* Add both lights and emissive triangles to this vector for light tree construction. */
  vector<LightTreePrimitive> light_prims;
  light_prims.reserve(kintegrator->num_distribution);
  vector<LightTreePrimitive> distant_lights;
  distant_lights.reserve(kintegrator->num_distant_lights);
  vector<uint> object_lookup_offsets(scene->objects.size());

  /* When we keep track of the light index, only contributing lights will be added to the device.
   * Therefore, we want to keep track of the light's index on the device.
   * However, we also need the light's index in the scene when we're constructing the tree. */
  int device_light_index = 0;
  int scene_light_index = 0;
  foreach (Light *light, scene->lights) {
    if (light->is_enabled) {
      if (light->light_type == LIGHT_BACKGROUND || light->light_type == LIGHT_DISTANT) {
        distant_lights.emplace_back(scene, ~device_light_index, scene_light_index);
      }
      else {
        light_prims.emplace_back(scene, ~device_light_index, scene_light_index);
      }

      device_light_index++;
    }

    scene_light_index++;
  }

  /* Similarly, we also want to keep track of the index of triangles that are emissive. */
  size_t total_triangles = 0;
  int object_id = 0;
  foreach (Object *object, scene->objects) {
    if (progress.get_cancel())
      return;

    if (!object_usable_as_light(object)) {
      object_id++;
      continue;
    }

    object_lookup_offsets[object_id] = total_triangles;

    /* Count emissive triangles. */
    Mesh *mesh = static_cast<Mesh *>(object->get_geometry());
    size_t mesh_num_triangles = mesh->num_triangles();

    for (size_t i = 0; i < mesh_num_triangles; i++) {
      int shader_index = mesh->get_shader()[i];
      Shader *shader = (shader_index < mesh->get_used_shaders().size()) ?
                           static_cast<Shader *>(mesh->get_used_shaders()[shader_index]) :
                           scene->default_surface;

      if (shader->emission_sampling != EMISSION_SAMPLING_NONE) {
        light_prims.emplace_back(scene, i, object_id);
      }
    }

    total_triangles += mesh_num_triangles;
    object_id++;
  }

  /* Append distant lights to the end of `light_prims` */
  std::move(distant_lights.begin(), distant_lights.end(), std::back_inserter(light_prims));

  /* Update integrator state. */
  kintegrator->use_direct_light = !light_prims.empty();

  /* TODO: For now, we'll start with a smaller number of max lights in a node.
   * More benchmarking is needed to determine what number works best. */
  LightTree light_tree(light_prims, kintegrator->num_distant_lights, 8);

  /* We want to create separate arrays corresponding to triangles and lights,
   * which will be used to index back into the light tree for PDF calculations. */
  const size_t num_lights = kintegrator->num_lights;
  uint *light_array = dscene->light_to_tree.alloc(num_lights);
  uint *object_offsets = dscene->object_lookup_offset.alloc(object_lookup_offsets.size());
  uint *triangle_array = dscene->triangle_to_tree.alloc(total_triangles);

  for (int i = 0; i < object_lookup_offsets.size(); i++) {
    object_offsets[i] = object_lookup_offsets[i];
  }

  /* First initialize the light tree's nodes. */
  const vector<LightTreeNode> &linearized_bvh = light_tree.get_nodes();
  KernelLightTreeNode *light_tree_nodes = dscene->light_tree_nodes.alloc(linearized_bvh.size());
  KernelLightTreeEmitter *light_tree_emitters = dscene->light_tree_emitters.alloc(
      light_prims.size());
  for (int index = 0; index < linearized_bvh.size(); index++) {
    const LightTreeNode &node = linearized_bvh[index];

    light_tree_nodes[index].energy = node.energy;

    light_tree_nodes[index].bbox.min = node.bbox.min;
    light_tree_nodes[index].bbox.max = node.bbox.max;

    light_tree_nodes[index].bcone.axis = node.bcone.axis;
    light_tree_nodes[index].bcone.theta_o = node.bcone.theta_o;
    light_tree_nodes[index].bcone.theta_e = node.bcone.theta_e;

    light_tree_nodes[index].bit_trail = node.bit_trail;
    light_tree_nodes[index].num_prims = node.num_prims;

    /* Here we need to make a distinction between interior and leaf nodes. */
    if (node.is_leaf()) {
      light_tree_nodes[index].child_index = -node.first_prim_index;

      for (int i = 0; i < node.num_prims; i++) {
        int emitter_index = i + node.first_prim_index;
        LightTreePrimitive &prim = light_prims[emitter_index];

        light_tree_emitters[emitter_index].energy = prim.energy;
        light_tree_emitters[emitter_index].theta_o = prim.bcone.theta_o;
        light_tree_emitters[emitter_index].theta_e = prim.bcone.theta_e;

        if (prim.is_triangle()) {
          light_tree_emitters[emitter_index].mesh_light.object_id = prim.object_id;

          int shader_flag = 0;
          Object *object = scene->objects[prim.object_id];
          Mesh *mesh = static_cast<Mesh *>(object->get_geometry());
          Shader *shader = static_cast<Shader *>(
              mesh->get_used_shaders()[mesh->get_shader()[prim.prim_id]]);

          if (!(object->get_visibility() & PATH_RAY_CAMERA)) {
            shader_flag |= SHADER_EXCLUDE_CAMERA;
          }
          if (!(object->get_visibility() & PATH_RAY_DIFFUSE)) {
            shader_flag |= SHADER_EXCLUDE_DIFFUSE;
          }
          if (!(object->get_visibility() & PATH_RAY_GLOSSY)) {
            shader_flag |= SHADER_EXCLUDE_GLOSSY;
          }
          if (!(object->get_visibility() & PATH_RAY_TRANSMIT)) {
            shader_flag |= SHADER_EXCLUDE_TRANSMIT;
          }
          if (!(object->get_visibility() & PATH_RAY_VOLUME_SCATTER)) {
            shader_flag |= SHADER_EXCLUDE_SCATTER;
          }
          if (!(object->get_is_shadow_catcher())) {
            shader_flag |= SHADER_EXCLUDE_SHADOW_CATCHER;
          }

          light_tree_emitters[emitter_index].prim = prim.prim_id + mesh->prim_offset;
          light_tree_emitters[emitter_index].mesh_light.shader_flag = shader_flag;
          light_tree_emitters[emitter_index].emission_sampling = shader->emission_sampling;
          triangle_array[prim.prim_id + object_lookup_offsets[prim.object_id]] = emitter_index;
        }
        else {
          light_tree_emitters[emitter_index].prim = prim.prim_id;
          light_tree_emitters[emitter_index].mesh_light.shader_flag = 0;
          light_tree_emitters[emitter_index].mesh_light.object_id = OBJECT_NONE;
          light_tree_emitters[emitter_index].emission_sampling = EMISSION_SAMPLING_FRONT_BACK;
          light_array[~prim.prim_id] = emitter_index;
        }

        light_tree_emitters[emitter_index].parent_index = index;
      }
    }
    else {
      light_tree_nodes[index].child_index = node.right_child_index;
    }
  }

  /* Copy arrays to device. */
  dscene->light_tree_nodes.copy_to_device();
  dscene->light_tree_emitters.copy_to_device();
  dscene->light_to_tree.copy_to_device();
  dscene->object_lookup_offset.copy_to_device();
  dscene->triangle_to_tree.copy_to_device();
}

static void background_cdf(
    int start, int end, int res_x, int res_y, const vector<float3> *pixels, float2 *cond_cdf)
{
  int cdf_width = res_x + 1;
  /* Conditional CDFs (rows, U direction). */
  for (int i = start; i < end; i++) {
    float sin_theta = sinf(M_PI_F * (i + 0.5f) / res_y);
    float3 env_color = (*pixels)[i * res_x];
    float ave_luminance = average(env_color);

    cond_cdf[i * cdf_width].x = ave_luminance * sin_theta;
    cond_cdf[i * cdf_width].y = 0.0f;

    for (int j = 1; j < res_x; j++) {
      env_color = (*pixels)[i * res_x + j];
      ave_luminance = average(env_color);

      cond_cdf[i * cdf_width + j].x = ave_luminance * sin_theta;
      cond_cdf[i * cdf_width + j].y = cond_cdf[i * cdf_width + j - 1].y +
                                      cond_cdf[i * cdf_width + j - 1].x / res_x;
    }

    const float cdf_total = cond_cdf[i * cdf_width + res_x - 1].y +
                            cond_cdf[i * cdf_width + res_x - 1].x / res_x;

    /* stuff the total into the brightness value for the last entry, because
     * we are going to normalize the CDFs to 0.0 to 1.0 afterwards */
    cond_cdf[i * cdf_width + res_x].x = cdf_total;

    if (cdf_total > 0.0f) {
      const float cdf_total_inv = 1.0f / cdf_total;
      for (int j = 1; j < res_x; j++) {
        cond_cdf[i * cdf_width + j].y *= cdf_total_inv;
      }
    }

    cond_cdf[i * cdf_width + res_x].y = 1.0f;
  }
}

void LightManager::device_update_background(Device *device,
                                            DeviceScene *dscene,
                                            Scene *scene,
                                            Progress &progress)
{
  KernelIntegrator *kintegrator = &dscene->data.integrator;
  KernelBackground *kbackground = &dscene->data.background;
  Light *background_light = NULL;

  bool background_mis = false;

  /* find background light */
  foreach (Light *light, scene->lights) {
    if (light->light_type == LIGHT_BACKGROUND && light->is_enabled) {
      background_light = light;
      background_mis |= light->use_mis;
    }
  }

  kbackground->portal_weight = kintegrator->num_portals > 0 ? 1.0f : 0.0f;
  kbackground->map_weight = background_mis ? 1.0f : 0.0f;
  kbackground->sun_weight = 0.0f;

  /* no background light found, signal renderer to skip sampling */
  if (!background_light || !background_light->is_enabled) {
    kbackground->map_res_x = 0;
    kbackground->map_res_y = 0;
    kbackground->use_mis = (kbackground->portal_weight > 0.0f);
    return;
  }

  progress.set_status("Updating Lights", "Importance map");

  int2 environment_res = make_int2(0, 0);
  Shader *shader = scene->background->get_shader(scene);
  int num_suns = 0;
  float sun_average_radiance = 0.0f;
  foreach (ShaderNode *node, shader->graph->nodes) {
    if (node->type == EnvironmentTextureNode::get_node_type()) {
      EnvironmentTextureNode *env = (EnvironmentTextureNode *)node;
      if (!env->handle.empty()) {
        ImageMetaData metadata = env->handle.metadata();
        environment_res.x = max(environment_res.x, (int)metadata.width);
        environment_res.y = max(environment_res.y, (int)metadata.height);
      }
    }
    if (node->type == SkyTextureNode::get_node_type()) {
      SkyTextureNode *sky = (SkyTextureNode *)node;
      if (sky->get_sky_type() == NODE_SKY_NISHITA && sky->get_sun_disc()) {
        /* Ensure that the input coordinates aren't transformed before they reach the node.
         * If that is the case, the logic used for sampling the sun's location does not work
         * and we have to fall back to map-based sampling. */
        const ShaderInput *vec_in = sky->input("Vector");
        if (vec_in && vec_in->link && vec_in->link->parent) {
          ShaderNode *vec_src = vec_in->link->parent;
          if ((vec_src->type != TextureCoordinateNode::get_node_type()) ||
              (vec_in->link != vec_src->output("Generated"))) {
            environment_res.x = max(environment_res.x, 4096);
            environment_res.y = max(environment_res.y, 2048);
            continue;
          }
        }

        /* Determine sun direction from lat/long and texture mapping. */
        float latitude = sky->get_sun_elevation();
        float longitude = M_2PI_F - sky->get_sun_rotation() + M_PI_2_F;
        float3 sun_direction = make_float3(
            cosf(latitude) * cosf(longitude), cosf(latitude) * sinf(longitude), sinf(latitude));
        Transform sky_transform = transform_inverse(sky->tex_mapping.compute_transform());
        sun_direction = transform_direction(&sky_transform, sun_direction);

        /* Pack sun direction and size. */
        float half_angle = sky->get_sun_size() * 0.5f;
        kbackground->sun = make_float4(
            sun_direction.x, sun_direction.y, sun_direction.z, half_angle);

        /* empirical value */
        kbackground->sun_weight = 4.0f;
        sun_average_radiance = sky->get_sun_average_radiance();
        environment_res.x = max(environment_res.x, 512);
        environment_res.y = max(environment_res.y, 256);
        num_suns++;
      }
    }
  }

  /* If there's more than one sun, fall back to map sampling instead. */
  if (num_suns != 1) {
    kbackground->sun_weight = 0.0f;
    environment_res.x = max(environment_res.x, 4096);
    environment_res.y = max(environment_res.y, 2048);
  }

  /* Enable MIS for background sampling if any strategy is active. */
  kbackground->use_mis = (kbackground->portal_weight + kbackground->map_weight +
                          kbackground->sun_weight) > 0.0f;

  /* get the resolution from the light's size (we stuff it in there) */
  int2 res = make_int2(background_light->map_resolution, background_light->map_resolution / 2);
  /* If the resolution isn't set manually, try to find an environment texture. */
  if (res.x == 0) {
    res = environment_res;
    if (res.x > 0 && res.y > 0) {
      VLOG_INFO << "Automatically set World MIS resolution to " << res.x << " by " << res.y
                << "\n";
    }
  }
  /* If it's still unknown, just use the default. */
  if (res.x == 0 || res.y == 0) {
    res = make_int2(1024, 512);
    VLOG_INFO << "Setting World MIS resolution to default\n";
  }
  kbackground->map_res_x = res.x;
  kbackground->map_res_y = res.y;

  vector<float3> pixels;
  shade_background_pixels(device, dscene, res.x, res.y, pixels, progress);

  if (progress.get_cancel())
    return;

  /* build row distributions and column distribution for the infinite area environment light */
  int cdf_width = res.x + 1;
  float2 *marg_cdf = dscene->light_background_marginal_cdf.alloc(res.y + 1);
  float2 *cond_cdf = dscene->light_background_conditional_cdf.alloc(cdf_width * res.y);

  double time_start = time_dt();

  /* Create CDF in parallel. */
  const int rows_per_task = divide_up(10240, res.x);
  parallel_for(blocked_range<size_t>(0, res.y, rows_per_task),
               [&](const blocked_range<size_t> &r) {
                 background_cdf(r.begin(), r.end(), res.x, res.y, &pixels, cond_cdf);
               });

  /* marginal CDFs (column, V direction, sum of rows) */
  marg_cdf[0].x = cond_cdf[res.x].x;
  marg_cdf[0].y = 0.0f;

  for (int i = 1; i < res.y; i++) {
    marg_cdf[i].x = cond_cdf[i * cdf_width + res.x].x;
    marg_cdf[i].y = marg_cdf[i - 1].y + marg_cdf[i - 1].x / res.y;
  }

  float cdf_total = marg_cdf[res.y - 1].y + marg_cdf[res.y - 1].x / res.y;
  marg_cdf[res.y].x = cdf_total;

  float map_average_radiance = cdf_total * M_PI_2_F;
  if (sun_average_radiance > 0.0f) {
    /* The weighting here is just a heuristic that was empirically determined.
     * The sun's average radiance is much higher than the map's average radiance,
     * but we don't want to weight the background light too much because
     * visibility is not accounted for anyway. */
    background_light->set_average_radiance(0.8f * map_average_radiance +
                                           0.2f * sun_average_radiance);
  }
  else {
    background_light->set_average_radiance(map_average_radiance);
  }

  if (cdf_total > 0.0f)
    for (int i = 1; i < res.y; i++)
      marg_cdf[i].y /= cdf_total;

  marg_cdf[res.y].y = 1.0f;

  VLOG_WORK << "Background MIS build time " << time_dt() - time_start << "\n";

  /* update device */
  dscene->light_background_marginal_cdf.copy_to_device();
  dscene->light_background_conditional_cdf.copy_to_device();
}

void LightManager::device_update_lights(Device *device, DeviceScene *dscene, Scene *scene)
{
  /* Counts lights in the scene. */
  size_t num_lights = 0;
  size_t num_portals = 0;
  size_t num_background_lights = 0;
  size_t num_distant_lights = 0;
  bool use_light_mis = false;

  foreach (Light *light, scene->lights) {
    if (light->is_enabled) {
      num_lights++;

      if (light->light_type == LIGHT_DISTANT) {
        num_distant_lights++;
      }
      else if (light->light_type == LIGHT_POINT || light->light_type == LIGHT_SPOT) {
        use_light_mis |= (light->size > 0.0f && light->use_mis);
      }
      else if (light->light_type == LIGHT_AREA) {
        use_light_mis |= light->use_mis;
      }
      else if (light->light_type == LIGHT_BACKGROUND) {
        num_distant_lights++;
        num_background_lights++;
      }
    }
    if (light->is_portal) {
      num_portals++;
    }
  }

  /* Update integrator settings. */
  KernelIntegrator *kintegrator = &dscene->data.integrator;
  kintegrator->use_light_tree = scene->integrator->get_use_light_tree() &&
                                device->info.has_light_tree;
  kintegrator->num_lights = num_lights;
  kintegrator->num_distant_lights = num_distant_lights;
  kintegrator->num_background_lights = num_background_lights;
  kintegrator->use_light_mis = use_light_mis;

  kintegrator->num_portals = num_portals;
  kintegrator->portal_offset = num_lights;

  /* Create KernelLight for every portal and enabled light in the scene. */
  KernelLight *klights = dscene->lights.alloc(num_lights + num_portals);

  int light_index = 0;
  int portal_index = num_lights;

  foreach (Light *light, scene->lights) {
    /* Consider moving portals update to their own function
     * keeping this one more manageable. */
    if (light->is_portal) {
      assert(light->light_type == LIGHT_AREA);

      float3 extentu = light->axisu * (light->sizeu * light->size);
      float3 extentv = light->axisv * (light->sizev * light->size);

      float len_u, len_v;
      float3 axis_u = normalize_len(extentu, &len_u);
      float3 axis_v = normalize_len(extentv, &len_v);
      float area = len_u * len_v;
      if (light->ellipse) {
        area *= -M_PI_4_F;
      }
      float invarea = (area != 0.0f) ? 1.0f / area : 1.0f;
      float3 dir = light->dir;

      dir = safe_normalize(dir);

      klights[portal_index].co = light->co;
      klights[portal_index].area.axis_u = axis_u;
      klights[portal_index].area.len_u = len_u;
      klights[portal_index].area.axis_v = axis_v;
      klights[portal_index].area.len_v = len_v;
      klights[portal_index].area.invarea = invarea;
      klights[portal_index].area.dir = dir;
      klights[portal_index].tfm = light->tfm;
      klights[portal_index].itfm = transform_inverse(light->tfm);

      portal_index++;
      continue;
    }

    if (!light->is_enabled) {
      continue;
    }

    float3 co = light->co;
    Shader *shader = (light->shader) ? light->shader : scene->default_light;
    int shader_id = scene->shader_manager->get_shader_id(shader);
    int max_bounces = light->max_bounces;
    float random = (float)light->random_id * (1.0f / (float)0xFFFFFFFF);

    if (!light->cast_shadow)
      shader_id &= ~SHADER_CAST_SHADOW;

    if (!light->use_camera) {
      shader_id |= SHADER_EXCLUDE_CAMERA;
    }
    if (!light->use_diffuse) {
      shader_id |= SHADER_EXCLUDE_DIFFUSE;
    }
    if (!light->use_glossy) {
      shader_id |= SHADER_EXCLUDE_GLOSSY;
    }
    if (!light->use_transmission) {
      shader_id |= SHADER_EXCLUDE_TRANSMIT;
    }
    if (!light->use_scatter) {
      shader_id |= SHADER_EXCLUDE_SCATTER;
    }
    if (!light->is_shadow_catcher) {
      shader_id |= SHADER_EXCLUDE_SHADOW_CATCHER;
    }

    klights[light_index].type = light->light_type;
    klights[light_index].strength[0] = light->strength.x;
    klights[light_index].strength[1] = light->strength.y;
    klights[light_index].strength[2] = light->strength.z;

    if (light->light_type == LIGHT_POINT) {
      shader_id &= ~SHADER_AREA_LIGHT;

      float radius = light->size;
      float invarea = (radius > 0.0f) ? 1.0f / (M_PI_F * radius * radius) : 1.0f;

      if (light->use_mis && radius > 0.0f)
        shader_id |= SHADER_USE_MIS;

      klights[light_index].co = co;
      klights[light_index].spot.radius = radius;
      klights[light_index].spot.invarea = invarea;
    }
    else if (light->light_type == LIGHT_DISTANT) {
      shader_id &= ~SHADER_AREA_LIGHT;

      float angle = light->angle / 2.0f;
      float radius = tanf(angle);
      float cosangle = cosf(angle);
      float area = M_PI_F * radius * radius;
      float invarea = (area > 0.0f) ? 1.0f / area : 1.0f;
      float3 dir = light->dir;

      dir = safe_normalize(dir);

      if (light->use_mis && area > 0.0f)
        shader_id |= SHADER_USE_MIS;

      klights[light_index].co = dir;
      klights[light_index].distant.invarea = invarea;
      klights[light_index].distant.radius = radius;
      klights[light_index].distant.cosangle = cosangle;
    }
    else if (light->light_type == LIGHT_BACKGROUND) {
      uint visibility = scene->background->get_visibility();

      dscene->data.background.light_index = light_index;

      shader_id &= ~SHADER_AREA_LIGHT;
      shader_id |= SHADER_USE_MIS;

      if (!(visibility & PATH_RAY_DIFFUSE)) {
        shader_id |= SHADER_EXCLUDE_DIFFUSE;
      }
      if (!(visibility & PATH_RAY_GLOSSY)) {
        shader_id |= SHADER_EXCLUDE_GLOSSY;
      }
      if (!(visibility & PATH_RAY_TRANSMIT)) {
        shader_id |= SHADER_EXCLUDE_TRANSMIT;
      }
      if (!(visibility & PATH_RAY_VOLUME_SCATTER)) {
        shader_id |= SHADER_EXCLUDE_SCATTER;
      }
    }
    else if (light->light_type == LIGHT_AREA) {
      float3 extentu = light->axisu * (light->sizeu * light->size);
      float3 extentv = light->axisv * (light->sizev * light->size);

      float len_u, len_v;
      float3 axis_u = normalize_len(extentu, &len_u);
      float3 axis_v = normalize_len(extentv, &len_v);
      float area = len_u * len_v;
      if (light->ellipse) {
        area *= -M_PI_4_F;
      }
      float invarea = (area != 0.0f) ? 1.0f / area : 1.0f;
      float3 dir = light->dir;

      /* Clamp angles in (0, 0.1) to 0.1 to prevent zero intensity due to floating-point precision
       * issues, but still handles spread = 0 */
      const float min_spread = 0.1f * M_PI_F / 180.0f;
      const float half_spread = light->spread == 0 ? 0.0f : 0.5f * max(light->spread, min_spread);
      const float tan_half_spread = light->spread == M_PI_F ? FLT_MAX : tanf(half_spread);
      /* Normalization computed using:
       * integrate cos(x) * (1 - tan(x) / tan(a)) * sin(x) from x = 0 to a, a being half_spread.
       * Divided by tan_half_spread to simplify the attenuation computation in `area.h`. */
      const float normalize_spread = 1.0f / (tan_half_spread - half_spread);

      dir = safe_normalize(dir);

      if (light->use_mis && area != 0.0f)
        shader_id |= SHADER_USE_MIS;

      klights[light_index].co = co;
      klights[light_index].area.axis_u = axis_u;
      klights[light_index].area.len_u = len_u;
      klights[light_index].area.axis_v = axis_v;
      klights[light_index].area.len_v = len_v;
      klights[light_index].area.invarea = invarea;
      klights[light_index].area.dir = dir;
      klights[light_index].area.tan_half_spread = tan_half_spread;
      klights[light_index].area.normalize_spread = normalize_spread;
    }
    else if (light->light_type == LIGHT_SPOT) {
      shader_id &= ~SHADER_AREA_LIGHT;

      float3 len;
      float3 axis_u = normalize_len(light->axisu, &len.x);
      float3 axis_v = normalize_len(light->axisv, &len.y);
      float3 dir = normalize_len(light->dir, &len.z);
      if (len.z == 0.0f) {
        dir = zero_float3();
      }

      float radius = light->size;
      float invarea = (radius > 0.0f) ? 1.0f / (M_PI_F * radius * radius) : 1.0f;
      float cos_half_spot_angle = cosf(light->spot_angle * 0.5f);
      float spot_smooth = (1.0f - cos_half_spot_angle) * light->spot_smooth;

      if (light->use_mis && radius > 0.0f)
        shader_id |= SHADER_USE_MIS;

      klights[light_index].co = co;
      klights[light_index].spot.axis_u = axis_u;
      klights[light_index].spot.radius = radius;
      klights[light_index].spot.axis_v = axis_v;
      klights[light_index].spot.invarea = invarea;
      klights[light_index].spot.dir = dir;
      klights[light_index].spot.cos_half_spot_angle = cos_half_spot_angle;
      klights[light_index].spot.len = len;
      klights[light_index].spot.spot_smooth = spot_smooth;
    }

    klights[light_index].shader_id = shader_id;

    klights[light_index].max_bounces = max_bounces;
    klights[light_index].random = random;
    klights[light_index].use_caustics = light->use_caustics;

    klights[light_index].tfm = light->tfm;
    klights[light_index].itfm = transform_inverse(light->tfm);

    auto it = scene->lightgroups.find(light->lightgroup);
    if (it != scene->lightgroups.end()) {
      klights[light_index].lightgroup = it->second;
    }
    else {
      klights[light_index].lightgroup = LIGHTGROUP_NONE;
    }

    light_index++;
  }

  VLOG_INFO << "Number of lights sent to the device: " << num_lights;

  dscene->lights.copy_to_device();
}

void LightManager::device_update(Device *device,
                                 DeviceScene *dscene,
                                 Scene *scene,
                                 Progress &progress)
{
  if (!need_update())
    return;

  scoped_callback_timer timer([scene](double time) {
    if (scene->update_stats) {
      scene->update_stats->light.times.add_entry({"device_update", time});
    }
  });

  VLOG_INFO << "Total " << scene->lights.size() << " lights.";

  /* Detect which lights are enabled, also determines if we need to update the background. */
  test_enabled_lights(scene);

  device_free(device, dscene, need_update_background);

  device_update_lights(device, dscene, scene);
  if (progress.get_cancel())
    return;

  if (need_update_background) {
    device_update_background(device, dscene, scene, progress);
    if (progress.get_cancel())
      return;
  }

  device_update_distribution(device, dscene, scene, progress);
  if (progress.get_cancel())
    return;

  device_update_tree(device, dscene, scene, progress);
  if (progress.get_cancel())
    return;

  device_update_ies(dscene);
  if (progress.get_cancel())
    return;

  update_flags = UPDATE_NONE;
  need_update_background = false;
}

void LightManager::device_free(Device *, DeviceScene *dscene, const bool free_background)
{
  /* TODO: check if the light tree member variables need to be wrapped in a conditional too. */
  dscene->light_tree_nodes.free();
  dscene->light_tree_emitters.free();
  dscene->light_to_tree.free();
  dscene->triangle_to_tree.free();

  dscene->light_distribution.free();
  dscene->lights.free();
  if (free_background) {
    dscene->light_background_marginal_cdf.free();
    dscene->light_background_conditional_cdf.free();
  }
  dscene->ies_lights.free();
}

void LightManager::tag_update(Scene * /*scene*/, uint32_t flag)
{
  update_flags |= flag;
}

bool LightManager::need_update() const
{
  return update_flags != UPDATE_NONE;
}

int LightManager::add_ies_from_file(const string &filename)
{
  string content;

  /* If the file can't be opened, call with an empty line */
  if (filename.empty() || !path_read_text(filename.c_str(), content)) {
    content = "\n";
  }

  return add_ies(content);
}

int LightManager::add_ies(const string &content)
{
  uint hash = hash_string(content.c_str());

  thread_scoped_lock ies_lock(ies_mutex);

  /* Check whether this IES already has a slot. */
  size_t slot;
  for (slot = 0; slot < ies_slots.size(); slot++) {
    if (ies_slots[slot]->hash == hash) {
      ies_slots[slot]->users++;
      return slot;
    }
  }

  /* Try to find an empty slot for the new IES. */
  for (slot = 0; slot < ies_slots.size(); slot++) {
    if (ies_slots[slot]->users == 0 && ies_slots[slot]->hash == 0) {
      break;
    }
  }

  /* If there's no free slot, add one. */
  if (slot == ies_slots.size()) {
    ies_slots.push_back(new IESSlot());
  }

  ies_slots[slot]->ies.load(content);
  ies_slots[slot]->users = 1;
  ies_slots[slot]->hash = hash;

  update_flags = UPDATE_ALL;
  need_update_background = true;

  return slot;
}

void LightManager::remove_ies(int slot)
{
  thread_scoped_lock ies_lock(ies_mutex);

  if (slot < 0 || slot >= ies_slots.size()) {
    assert(false);
    return;
  }

  assert(ies_slots[slot]->users > 0);
  ies_slots[slot]->users--;

  /* If the slot has no more users, update the device to remove it. */
  if (ies_slots[slot]->users == 0) {
    update_flags |= UPDATE_ALL;
    need_update_background = true;
  }
}

void LightManager::device_update_ies(DeviceScene *dscene)
{
  /* Clear empty slots. */
  foreach (IESSlot *slot, ies_slots) {
    if (slot->users == 0) {
      slot->hash = 0;
      slot->ies.clear();
    }
  }

  /* Shrink the slot table by removing empty slots at the end. */
  int slot_end;
  for (slot_end = ies_slots.size(); slot_end; slot_end--) {
    if (ies_slots[slot_end - 1]->users > 0) {
      /* If the preceding slot has users, we found the new end of the table. */
      break;
    }
    else {
      /* The slot will be past the new end of the table, so free it. */
      delete ies_slots[slot_end - 1];
    }
  }
  ies_slots.resize(slot_end);

  if (ies_slots.size() > 0) {
    int packed_size = 0;
    foreach (IESSlot *slot, ies_slots) {
      packed_size += slot->ies.packed_size();
    }

    /* ies_lights starts with an offset table that contains the offset of every slot,
     * or -1 if the slot is invalid.
     * Following that table, the packed valid IES lights are stored. */
    float *data = dscene->ies_lights.alloc(ies_slots.size() + packed_size);

    int offset = ies_slots.size();
    for (int i = 0; i < ies_slots.size(); i++) {
      int size = ies_slots[i]->ies.packed_size();
      if (size > 0) {
        data[i] = __int_as_float(offset);
        ies_slots[i]->ies.pack(data + offset);
        offset += size;
      }
      else {
        data[i] = __int_as_float(-1);
      }
    }

    dscene->ies_lights.copy_to_device();
  }
}

CCL_NAMESPACE_END