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

#include <optional>

#include "blender/attribute_convert.h"
#include "blender/sync.h"
#include "blender/util.h"

#include "scene/attribute.h"
#include "scene/camera.h"
#include "scene/curves.h"
#include "scene/hair.h"
#include "scene/object.h"
#include "scene/scene.h"

#include "util/color.h"

#include "util/hash.h"
#include "util/log.h"

#include "DNA_meshdata_types.h"
#include "DNA_modifier_types.h"
#include "DNA_particle_types.h"

#include "BLI_listbase.h"
#include "BLI_math_matrix.h"
#include "BLI_math_vector.h"

#include "BKE_attribute.hh"
#include "BKE_curves.hh"
#include "BKE_customdata.hh"
#include "BKE_mesh_legacy_convert.hh"
#include "BKE_particle.h"

namespace blender {
struct ModifierData;
}

CCL_NAMESPACE_BEGIN

ParticleCurveData::ParticleCurveData() = default;

ParticleCurveData::~ParticleCurveData() = default;

static float shaperadius(const float shape, const float root, const float tip, const float time)
{
  assert(time >= 0.0f);
  assert(time <= 1.0f);
  float radius = 1.0f - time;

  if (shape != 0.0f) {
    if (shape < 0.0f) {
      radius = powf(radius, 1.0f + shape);
    }
    else {
      radius = powf(radius, 1.0f / (1.0f - shape));
    }
  }
  return (radius * (root - tip)) + tip;
}

/* curve functions */

static bool ObtainCacheParticleData(Hair *hair,
                                    const blender::Mesh *b_mesh,
                                    const blender::Object *b_ob,
                                    ParticleCurveData *CData,
                                    bool background)
{
  int curvenum = 0;
  int keyno = 0;

  if (!(hair && b_mesh && b_ob && CData)) {
    return false;
  }

  const Transform tfm = get_transform(b_ob->object_to_world());
  const Transform itfm = transform_inverse(tfm);

  for (const blender::ModifierData &b_mod : b_ob->modifiers) {
    if ((b_mod.type == blender::eModifierType_ParticleSystem) &&
        (background ? ((b_mod.mode & blender::eModifierMode_Render) != 0) :
                      ((b_mod.mode & blender::eModifierMode_Realtime) != 0)))
    {
      const auto *psmd = reinterpret_cast<const blender::ParticleSystemModifierData *>(&b_mod);
      blender::ParticleSystem *b_psys = psmd->psys;
      blender::ParticleSettings *b_part = b_psys->part;

      if ((b_part->ren_as == blender::PART_DRAW_PATH) && (b_part->type == blender::PART_HAIR)) {
        const int shader = clamp(b_part->omat - 1, 0, hair->get_used_shaders().size() - 1);
        const int display_step = background ? b_part->ren_step : b_part->draw_step;
        const int totparts = b_psys->totpart;
        const int totchild = background ?
                                 b_psys->totchild :
                                 (int)((float)b_psys->totchild * (float)b_part->disp / 100.0f);
        int totcurves = totchild;

        if (b_part->childtype == 0 || totchild == 0) {
          totcurves += totparts;
        }

        if (totcurves == 0) {
          continue;
        }

        int ren_step = (1 << display_step) + 1;
        if (b_part->kink == blender::PART_KINK_SPIRAL) {
          ren_step += b_part->kink_extra_steps;
        }

        CData->psys_firstcurve.push_back_slow(curvenum);
        CData->psys_curvenum.push_back_slow(totcurves);
        CData->psys_shader.push_back_slow(shader);

        const float radius = b_part->rad_scale * 0.5f;

        CData->psys_rootradius.push_back_slow(radius * b_part->rad_root);
        CData->psys_tipradius.push_back_slow(radius * b_part->rad_tip);
        CData->psys_shape.push_back_slow(b_part->shape);
        CData->psys_closetip.push_back_slow((b_part->shape_flag & blender::PART_SHAPE_CLOSE_TIP) !=
                                            0);

        int pa_no = 0;
        if (!(b_part->childtype == 0) && totchild != 0) {
          pa_no = totparts;
        }

        const int num_add = (totparts + totchild - pa_no);
        CData->curve_firstkey.reserve(CData->curve_firstkey.size() + num_add);
        CData->curve_keynum.reserve(CData->curve_keynum.size() + num_add);
        CData->curve_length.reserve(CData->curve_length.size() + num_add);
        CData->curvekey_co.reserve(CData->curvekey_co.size() + num_add * ren_step);
        CData->curvekey_time.reserve(CData->curvekey_time.size() + num_add * ren_step);

        for (; pa_no < totparts + totchild; pa_no++) {
          int keynum = 0;
          CData->curve_firstkey.push_back_slow(keyno);

          float curve_length = 0.0f;
          float3 prev_co_world = zero_float3();
          float3 prev_co_object = zero_float3();
          for (int step_no = 0; step_no < ren_step; step_no++) {
            float3 co_world = prev_co_world;
            BKE_particle_co_hair(b_psys, b_ob, pa_no, step_no, &co_world.x);
            const float3 co_object = transform_point(&itfm, co_world);
            if (step_no > 0) {
              const float step_length = len(co_object - prev_co_object);
              curve_length += step_length;
            }
            CData->curvekey_co.push_back_slow(co_object);
            CData->curvekey_time.push_back_slow(curve_length);
            prev_co_object = co_object;
            prev_co_world = co_world;
            keynum++;
          }
          keyno += keynum;

          CData->curve_keynum.push_back_slow(keynum);
          CData->curve_length.push_back_slow(curve_length);
          curvenum++;
        }
      }
    }
  }

  return true;
}

static bool ObtainCacheParticleUV(Hair *hair,
                                  const blender::Mesh *b_mesh,
                                  const blender::Object *b_ob,
                                  ParticleCurveData *CData,
                                  bool background,
                                  const int uv_num)
{
  if (!(hair && b_mesh && b_ob && CData)) {
    return false;
  }

  CData->curve_uv.clear();

  for (blender::ModifierData &b_mod : b_ob->modifiers) {
    if ((b_mod.type == blender::eModifierType_ParticleSystem) &&
        (background ? ((b_mod.mode & blender::eModifierMode_Render) != 0) :
                      ((b_mod.mode & blender::eModifierMode_Realtime) != 0)))
    {
      auto *psmd = reinterpret_cast<blender::ParticleSystemModifierData *>(&b_mod);
      blender::ParticleSystem *b_psys = psmd->psys;
      blender::ParticleSettings *b_part = b_psys->part;

      if ((b_part->ren_as == blender::PART_DRAW_PATH) && (b_part->type == blender::PART_HAIR)) {
        const int totparts = b_psys->totpart;
        const int totchild = background ?
                                 b_psys->totchild :
                                 (int)((float)b_psys->totchild * (float)b_part->disp / 100.0f);
        int totcurves = totchild;

        if (b_part->childtype == 0 || totchild == 0) {
          totcurves += totparts;
        }

        if (totcurves == 0) {
          continue;
        }

        int pa_no = 0;
        if (!(b_part->childtype == 0) && totchild != 0) {
          pa_no = totparts;
        }

        const int num_add = (totparts + totchild - pa_no);
        CData->curve_uv.reserve(CData->curve_uv.size() + num_add);

        blender::MutableSpan<blender::ParticleData> b_psys_particles(b_psys->particles,
                                                                     b_psys->totpart);
        auto *b_pa = b_psys_particles.begin();
        for (; pa_no < totparts + totchild; pa_no++) {
          /* Add UVs */
          float2 uv = zero_float2();
          BKE_particle_uv_on_emitter(b_psys, nullptr, psmd, b_pa, pa_no, uv_num, &uv.x);
          CData->curve_uv.push_back_slow(uv);

          if (pa_no < totparts && b_pa != b_psys_particles.end()) {
            ++b_pa;
          }
        }
      }
    }
  }

  return true;
}

static bool ObtainCacheParticleVcol(Hair *hair,
                                    const blender::Mesh *b_mesh,
                                    const blender::Object *b_ob,
                                    ParticleCurveData *CData,
                                    bool background,
                                    const int vcol_num)
{
  if (!(hair && b_mesh && b_ob && CData)) {
    return false;
  }

  CData->curve_vcol.clear();

  for (blender::ModifierData &b_mod : b_ob->modifiers) {
    if ((b_mod.type == blender::eModifierType_ParticleSystem) &&
        (background ? ((b_mod.mode & blender::eModifierMode_Render) != 0) :
                      ((b_mod.mode & blender::eModifierMode_Realtime) != 0)))
    {
      auto *psmd = reinterpret_cast<blender::ParticleSystemModifierData *>(&b_mod);
      blender::ParticleSystem *b_psys = psmd->psys;
      blender::ParticleSettings *b_part = b_psys->part;

      if ((b_part->ren_as == blender::PART_DRAW_PATH) && (b_part->type == blender::PART_HAIR)) {
        const int totparts = b_psys->totpart;
        const int totchild = background ?
                                 b_psys->totchild :
                                 (int)((float)b_psys->totchild * (float)b_part->disp / 100.0f);
        int totcurves = totchild;

        if (b_part->childtype == 0 || totchild == 0) {
          totcurves += totparts;
        }

        if (totcurves == 0) {
          continue;
        }

        int pa_no = 0;
        if (!(b_part->childtype == 0) && totchild != 0) {
          pa_no = totparts;
        }

        const int num_add = (totparts + totchild - pa_no);
        CData->curve_vcol.reserve(CData->curve_vcol.size() + num_add);

        blender::MutableSpan<blender::ParticleData> b_psys_particles(b_psys->particles,
                                                                     b_psys->totpart);
        auto *b_pa = b_psys_particles.begin();
        for (; pa_no < totparts + totchild; pa_no++) {
          /* Add vertex colors */
          float4 vcol = make_float4(0.0f, 0.0f, 0.0f, 1.0f);
          BKE_particle_mcol_on_emitter(b_psys, nullptr, psmd, b_pa, pa_no, vcol_num, &vcol.x);
          CData->curve_vcol.push_back_slow(vcol);

          if (pa_no < totparts && b_pa != b_psys_particles.end()) {
            ++b_pa;
          }
        }
      }
    }
  }

  return true;
}

static void ExportCurveSegments(Scene *scene, Hair *hair, ParticleCurveData *CData)
{
  int num_keys = 0;
  int num_curves = 0;

  if (hair->num_curves()) {
    return;
  }

  /* compute and reserve size of arrays */
  for (int sys = 0; sys < CData->psys_firstcurve.size(); sys++) {
    for (int curve = CData->psys_firstcurve[sys];
         curve < CData->psys_firstcurve[sys] + CData->psys_curvenum[sys];
         curve++)
    {
      num_keys += CData->curve_keynum[curve];
      num_curves++;
    }
  }

  hair->resize_curves(hair->num_curves() + num_curves, hair->num_keys() + num_keys);

  packed_normal *attr_normal = nullptr;
  float *attr_intercept = nullptr;
  float *attr_length = nullptr;
  float *attr_random = nullptr;

  if (hair->need_attribute(scene, ATTR_STD_VERTEX_NORMAL)) {
    attr_normal = hair->attributes.add(ATTR_STD_VERTEX_NORMAL)->data_for_write<packed_normal>();
  }
  if (hair->need_attribute(scene, ATTR_STD_CURVE_INTERCEPT)) {
    attr_intercept = hair->attributes.add(ATTR_STD_CURVE_INTERCEPT)->data_for_write<float>();
  }
  if (hair->need_attribute(scene, ATTR_STD_CURVE_LENGTH)) {
    attr_length = hair->attributes.add(ATTR_STD_CURVE_LENGTH)->data_for_write<float>();
  }
  if (hair->need_attribute(scene, ATTR_STD_CURVE_RANDOM)) {
    attr_random = hair->attributes.add(ATTR_STD_CURVE_RANDOM)->data_for_write<float>();
  }

  int *curve_first_key = hair->get_curve_first_key().data();
  int *curve_shader = hair->get_curve_shader().data();

  packed_float3 *curve_keys = hair->get_position_for_write();
  float *curve_radius = hair->get_radius_for_write();

  num_keys = 0;
  num_curves = 0;

  /* actually export */
  for (int sys = 0; sys < CData->psys_firstcurve.size(); sys++) {
    for (int curve = CData->psys_firstcurve[sys];
         curve < CData->psys_firstcurve[sys] + CData->psys_curvenum[sys];
         curve++)
    {
      curve_first_key[num_curves] = num_keys;

      for (int curvekey = CData->curve_firstkey[curve];
           curvekey < CData->curve_firstkey[curve] + CData->curve_keynum[curve];
           curvekey++)
      {
        const float3 ickey_loc = CData->curvekey_co[curvekey];
        const float curve_time = CData->curvekey_time[curvekey];
        const float curve_length = CData->curve_length[curve];
        const float time = (curve_length > 0.0f) ? curve_time / curve_length : 0.0f;
        float radius = shaperadius(
            CData->psys_shape[sys], CData->psys_rootradius[sys], CData->psys_tipradius[sys], time);
        if (CData->psys_closetip[sys] &&
            (curvekey == CData->curve_firstkey[curve] + CData->curve_keynum[curve] - 1))
        {
          radius = 0.0f;
        }
        curve_keys[num_keys] = ickey_loc;
        curve_radius[num_keys] = radius;
        if (attr_intercept) {
          attr_intercept[num_keys] = time;
        }

        if (attr_normal) {
          /* NOTE: the geometry normals are not computed for legacy particle hairs. This hair
           * system is expected to be deprecated. */
          attr_normal[num_keys] = packed_normal(make_float3(0.0f, 0.0f, 0.0f));
        }

        num_keys++;
      }

      if (attr_length != nullptr) {
        attr_length[num_curves] = CData->curve_length[curve];
      }

      if (attr_random != nullptr) {
        attr_random[num_curves] = hash_uint2_to_float(num_curves, 0);
      }

      curve_shader[num_curves] = CData->psys_shader[sys];

      num_curves++;
    }
  }

  hair->tag_position_modified();
  hair->tag_radius_modified();
  hair->tag_curve_first_key_modified();
  hair->tag_curve_shader_modified();

  /* check allocation */
  if ((hair->num_keys() != num_keys) || (hair->num_curves() != num_curves)) {
    LOG_ERROR << "Hair memory allocation failed, clearing data.";
    hair->clear(true);
  }
}

static float4 CurveSegmentMotionCV(ParticleCurveData *CData,
                                   const int sys,
                                   const int curve,
                                   const int curvekey)
{
  const float3 ickey_loc = CData->curvekey_co[curvekey];
  const float curve_time = CData->curvekey_time[curvekey];
  const float curve_length = CData->curve_length[curve];
  const float time = (curve_length > 0.0f) ? curve_time / curve_length : 0.0f;
  float radius = shaperadius(
      CData->psys_shape[sys], CData->psys_rootradius[sys], CData->psys_tipradius[sys], time);

  if (CData->psys_closetip[sys] &&
      (curvekey == CData->curve_firstkey[curve] + CData->curve_keynum[curve] - 1))
  {
    radius = 0.0f;
  }

  /* curve motion keys store both position and radius in float4 */
  float4 mP = make_float4(ickey_loc);
  mP.w = radius;
  return mP;
}

static float4 LerpCurveSegmentMotionCV(ParticleCurveData *CData,
                                       const int sys,
                                       const int curve,
                                       const float step)
{
  assert(step >= 0.0f);
  assert(step <= 1.0f);
  const int first_curve_key = CData->curve_firstkey[curve];
  const float curve_key_f = step * (CData->curve_keynum[curve] - 1);
  int curvekey = (int)floorf(curve_key_f);
  const float remainder = curve_key_f - curvekey;
  if (remainder == 0.0f) {
    return CurveSegmentMotionCV(CData, sys, curve, first_curve_key + curvekey);
  }
  int curvekey2 = curvekey + 1;
  if (curvekey2 >= (CData->curve_keynum[curve] - 1)) {
    curvekey2 = (CData->curve_keynum[curve] - 1);
    curvekey = curvekey2 - 1;
  }
  const float4 mP = CurveSegmentMotionCV(CData, sys, curve, first_curve_key + curvekey);
  const float4 mP2 = CurveSegmentMotionCV(CData, sys, curve, first_curve_key + curvekey2);
  return mix(mP, mP2, remainder);
}

static void export_hair_motion_validate_attribute(Hair *hair,
                                                  const int motion_step,
                                                  const int num_motion_keys,
                                                  bool have_motion)
{
  Attribute *attr_P = hair->attributes.find(ATTR_STD_POSITION);
  Attribute *attr_R = hair->attributes.find(ATTR_STD_RADIUS);
  const int num_keys = hair->num_keys();

  if (num_motion_keys != num_keys || !have_motion) {
    /* No motion or hair "topology" changed, remove motion steps. */
    if (num_motion_keys != num_keys) {
      LOG_DEBUG << "Hair topology changed, removing motion attribute.";
    }
    attr_P->remove_motion();
    attr_R->remove_motion();
  }
  else if (motion_step > 0) {
    /* Motion, fill up previous steps that we might have skipped because
     * they had no motion, but we need them anyway now. */
    for (int step = 1; step <= motion_step; step++) {
      packed_float3 *mP = attr_P->data_for_write<packed_float3>(step);
      std::copy_n(hair->get_position(), num_keys, mP);

      float *mR = attr_R->data_for_write<float>(step);
      std::copy_n(hair->get_radius(), num_keys, mR);
    }
  }
}

static void ExportCurveSegmentsMotion(Hair *hair, ParticleCurveData *CData, const int motion_step)
{
  /* Set motion steps on position and radius attributes. */
  Attribute *attr_P = hair->attributes.find(ATTR_STD_POSITION);
  Attribute *attr_R = hair->attributes.find(ATTR_STD_RADIUS);
  bool new_attribute = false;

  if (!attr_P->has_motion()) {
    attr_P->add_motion(hair);
    attr_R->add_motion(hair);
    new_attribute = true;
  }

  /* export motion vectors for curve keys */
  const int attr_step = motion_step + 1;
  packed_float3 *mP = attr_P->data_for_write<packed_float3>(attr_step);
  float *mR = attr_R->data_for_write<float>(attr_step);
  bool have_motion = false;
  int i = 0;
  int num_curves = 0;
  const int num_keys = hair->num_keys();

  for (int sys = 0; sys < CData->psys_firstcurve.size(); sys++) {
    for (int curve = CData->psys_firstcurve[sys];
         curve < CData->psys_firstcurve[sys] + CData->psys_curvenum[sys];
         curve++)
    {
      /* Curve lengths may not match! Curves can be clipped. */
      const int curve_key_end = (num_curves + 1 < (int)hair->get_curve_first_key().size() ?
                                     hair->get_curve_first_key()[num_curves + 1] :
                                     num_keys);
      const int num_center_curve_keys = curve_key_end - hair->get_curve_first_key()[num_curves];
      const int is_num_keys_different = CData->curve_keynum[curve] - num_center_curve_keys;

      if (!is_num_keys_different) {
        for (int curvekey = CData->curve_firstkey[curve];
             curvekey < CData->curve_firstkey[curve] + CData->curve_keynum[curve];
             curvekey++)
        {
          if (i < num_keys) {
            const float4 cv = CurveSegmentMotionCV(CData, sys, curve, curvekey);
            mP[i] = make_float3(cv);
            mR[i] = cv.w;
            if (!have_motion) {
              /* unlike mesh coordinates, these tend to be slightly different
               * between frames due to particle transforms into/out of object
               * space, so we use an epsilon to detect actual changes */
              float4 curve_key = make_float4(hair->get_position()[i]);
              curve_key.w = hair->get_radius()[i];
              if (len_squared(cv - curve_key) > 1e-5f * 1e-5f) {
                have_motion = true;
              }
            }
          }
          i++;
        }
      }
      else {
        /* Number of keys has changed. Generate an interpolated version
         * to preserve motion blur. */
        const float step_size = num_center_curve_keys > 1 ? 1.0f / (num_center_curve_keys - 1) :
                                                            0.0f;
        for (int step_index = 0; step_index < num_center_curve_keys; ++step_index) {
          const float step = step_index * step_size;
          const float4 cv = LerpCurveSegmentMotionCV(CData, sys, curve, step);
          mP[i] = make_float3(cv);
          mR[i] = cv.w;
          i++;
        }
        have_motion = true;
      }
      num_curves++;
    }
  }

  /* In case of new attribute, we verify if there really was any motion. */
  if (new_attribute) {
    export_hair_motion_validate_attribute(hair, motion_step, i, have_motion);
  }
}

/* Hair Curve Sync */

bool BlenderSync::object_has_particle_hair(blender::Object *b_ob)
{
  /* Test if the object has a particle modifier with hair. */
  for (blender::ModifierData &b_mod : b_ob->modifiers) {
    if ((b_mod.type == blender::eModifierType_ParticleSystem) &&
        (preview ? ((b_mod.mode & blender::eModifierMode_Realtime) != 0) :
                   ((b_mod.mode & blender::eModifierMode_Render) != 0)))
    {
      auto *psmd = reinterpret_cast<blender::ParticleSystemModifierData *>(&b_mod);
      blender::ParticleSystem *b_psys = psmd->psys;
      blender::ParticleSettings *b_part = b_psys->part;

      if ((b_part->ren_as == blender::PART_DRAW_PATH) && (b_part->type == blender::PART_HAIR)) {
        return true;
      }
    }
  }

  return false;
}

/* Old particle hair. */
void BlenderSync::sync_particle_hair(Hair *hair,
                                     const blender::Mesh &b_mesh,
                                     BObjectInfo &b_ob_info,
                                     bool motion,
                                     const int motion_step)
{
  if (!b_ob_info.is_real_object_data()) {
    return;
  }
  const blender::Object &b_ob = *b_ob_info.real_object;

  /* obtain general settings */
  if (b_ob.mode == blender::OB_MODE_PARTICLE_EDIT || b_ob.mode == blender::OB_MODE_EDIT) {
    return;
  }

  /* Extract particle hair data - should be combined with connecting to mesh later. */

  ParticleCurveData CData;

  ObtainCacheParticleData(hair, &b_mesh, &b_ob, &CData, !preview);

  /* add hair geometry */
  if (motion) {
    ExportCurveSegmentsMotion(hair, &CData, motion_step);
  }
  else {
    ExportCurveSegments(scene, hair, &CData);
  }

  /* generated coordinates from first key. we should ideally get this from
   * blender to handle deforming objects */
  if (!motion) {
    if (hair->need_attribute(scene, ATTR_STD_GENERATED)) {
      float3 loc;
      float3 size;
      mesh_texture_space(b_mesh, loc, size);

      Attribute *attr_generated = hair->attributes.add(ATTR_STD_GENERATED);
      packed_float3 *generated = attr_generated->data_for_write<packed_float3>();

      for (size_t i = 0; i < hair->num_curves(); i++) {
        const float3 co = hair->get_position()[hair->get_curve(i).first_key];
        generated[i] = co * size - loc;
      }
    }
  }

  /* create vertex color attributes */
  if (!motion) {
    blender::Vector<blender::StringRef> vcol_names;
    b_mesh.attributes().foreach_attribute([&](const blender::bke::AttributeIter &iter) {
      if (iter.data_type != blender::bke::AttrType::ColorByte) {
        return;
      }
      if (iter.domain != blender::bke::AttrDomain::Corner) {
        return;
      }
      vcol_names.append(iter.name);
    });

    for (const int vcol_num : vcol_names.index_range()) {
      const ustring name = ustring(std::string_view(vcol_names[vcol_num]));
      if (!hair->need_attribute(scene, name)) {
        continue;
      }

      ObtainCacheParticleVcol(hair, &b_mesh, &b_ob, &CData, !preview, vcol_num);

      Attribute *attr_vcol = hair->attributes.add(name, TypeRGBA, ATTR_ELEMENT_CURVE);

      float4 *fdata = attr_vcol->data_for_write<float4>();

      if (fdata) {
        size_t i = 0;

        /* Encode vertex color using the sRGB curve. */
        for (size_t curve = 0; curve < CData.curve_vcol.size(); curve++) {
          fdata[i++] = color_srgb_to_linear_v4(CData.curve_vcol[curve]);
        }
      }
    }
  }

  /* create UV attributes */
  if (!motion) {
    const blender::VectorSet<blender::StringRefNull> uv_names = b_mesh.uv_map_names();
    const ustring default_name = ustring(std::string_view(b_mesh.default_uv_map_name()));
    for (const int uv_num : uv_names.index_range()) {
      const ustring name = ustring(std::string_view(uv_names[uv_num]));
      const bool active_render = name == default_name;
      const AttributeStandard std = (active_render) ? ATTR_STD_UV : ATTR_STD_NONE;

      /* UV map */
      if (hair->need_attribute(scene, name) || hair->need_attribute(scene, std)) {
        Attribute *attr_uv;

        ObtainCacheParticleUV(hair, &b_mesh, &b_ob, &CData, !preview, uv_num);

        if (active_render) {
          attr_uv = hair->attributes.add(std, name);
        }
        else {
          attr_uv = hair->attributes.add(name, TypeFloat2, ATTR_ELEMENT_CURVE);
        }

        float2 *uv = attr_uv->data_for_write<float2>();

        if (uv) {
          size_t i = 0;

          for (size_t curve = 0; curve < CData.curve_uv.size(); curve++) {
            uv[i++] = CData.curve_uv[curve];
          }
        }
      }
    }
  }

  hair->curve_shape = scene->params.hair_shape;
}

static void attr_create_motion_from_velocity(Hair *hair,
                                             const blender::Span<blender::float3> src,
                                             const float motion_scale)
{
  const int num_curve_keys = hair->num_keys();

  /* Override motion steps to fixed number. */
  hair->set_motion_steps(3);

  /* Set motion steps on position attribute. Radius doesn't change for
   * velocity-based motion. */
  Attribute *attr_P = hair->attributes.find(ATTR_STD_POSITION);
  attr_P->add_motion(hair);
  const packed_float3 *P = hair->get_position();

  /* Only export previous and next frame, we don't have any in between data. */
  const float motion_times[2] = {-1.0f, 1.0f};
  for (int step = 1; step <= 2; step++) {
    const float relative_time = motion_times[step - 1] * 0.5f * motion_scale;
    packed_float3 *mP = attr_P->data_for_write<packed_float3>(step);

    for (int i = 0; i < num_curve_keys; i++) {
      mP[i] = float3(P[i]) + make_float3(src[i][0], src[i][1], src[i][2]) * relative_time;
    }
  }
}

static AttributeElement blender_domain_to_attr_element(const blender::bke::AttrDomain b_domain)
{
  switch (b_domain) {
    case blender::bke::AttrDomain::Point:
      return ATTR_ELEMENT_CURVE_KEY;
      break;
    case blender::bke::AttrDomain::Curve:
      return ATTR_ELEMENT_CURVE;
      break;
    default:
      assert(false);
      return ATTR_ELEMENT_NONE;
  }
}

static void attr_create_generic(Scene *scene,
                                Hair *hair,
                                const blender::bke::CurvesGeometry &b_curves,
                                const bool need_motion,
                                const float motion_scale)
{
  const blender::bke::AttributeAccessor b_attributes = b_curves.attributes();

  AttributeSet &attributes = hair->attributes;
  static const ustring u_velocity("velocity");
  const bool need_uv = hair->need_attribute(scene, ATTR_STD_UV);
  bool have_uv = false;

  b_attributes.foreach_attribute([&](const blender::bke::AttributeIter &iter) {
    const ustring name{std::string_view(iter.name)};

    const blender::bke::AttrDomain b_domain = iter.domain;
    const blender::bke::AttrType b_data_type = iter.data_type;

    if (need_motion && name == u_velocity) {
      const blender::VArraySpan b_attr = *iter.get<blender::float3>(
          blender::bke::AttrDomain::Point);
      attr_create_motion_from_velocity(hair, b_attr, motion_scale);
      return;
    }

    /* Weak, use first float2 attribute as standard UV. */
    if (need_uv && !have_uv && b_data_type == blender::bke::AttrType::Float2 &&
        b_domain == blender::bke::AttrDomain::Curve)
    {
      Attribute *attr = attributes.add(ATTR_STD_UV, name);

      const blender::VArraySpan b_attr = *iter.get<blender::float2>();

      static_assert(sizeof(blender::float2) == sizeof(float2));
      const blender::Span src = b_attr.cast<float2>();
      std::copy(src.begin(), src.end(), attr->data_for_write<float2>());
      have_uv = true;
      return;
    }

    if (!hair->need_attribute(scene, name)) {
      return;
    }
    if (attributes.find(name)) {
      return;
    }

    const blender::bke::GAttributeReader b_attr = iter.get();

    blender::bke::attribute_math::to_static_type(b_attr.varray.type(), [&]<typename BlenderT>() {
      using Converter = typename ccl::AttributeConverter<BlenderT>;
      using CyclesT = typename Converter::CyclesT;
      if constexpr (!std::is_void_v<CyclesT>) {
        const blender::VArray<BlenderT> src_varray = b_attr.varray.typed<BlenderT>();
        const blender::CommonVArrayInfo info = b_attr.varray.common_info();

        if (info.type == blender::CommonVArrayInfo::Type::Single) {
          const auto &single_value = *static_cast<const BlenderT *>(info.data);
          Attribute *attr = attributes.add(name, Converter::type_desc, ATTR_ELEMENT_MESH);
          CyclesT *data = reinterpret_cast<CyclesT *>(attr->data_for_write());
          *data = Converter::convert(single_value);
          return;
        }

        const AttributeElement element = blender_domain_to_attr_element(b_attr.domain);
        if constexpr (Converter::layout_compatible) {
          if (src_varray.is_span() && b_attr.sharing_info) {
            attributes.add_shared(name,
                                  Converter::type_desc,
                                  element,
                                  info.data,
                                  src_varray.size(),
                                  b_attr.sharing_info);
            return;
          }
        }

        Attribute *attr = attributes.add(name, Converter::type_desc, element);
        CyclesT *data = reinterpret_cast<CyclesT *>(attr->data_for_write());

        const blender::VArraySpan src = src_varray;
        for (const int i : src.index_range()) {
          data[i] = Converter::convert(src[i]);
        }
      }
    });
  });
}

static float4 curve_point_as_float4(const blender::Span<blender::float3> b_positions,
                                    const blender::Span<float> b_radius,
                                    const int index)
{
  float4 mP = make_float4(
      b_positions[index][0], b_positions[index][1], b_positions[index][2], 0.0f);
  mP.w = b_radius.is_empty() ? 0.005f : b_radius[index];
  return mP;
}

static float4 interpolate_curve_points(const blender::Span<blender::float3> b_positions,
                                       const blender::Span<float> b_radius,
                                       const int first_point_index,
                                       const int num_points,
                                       const float step)
{
  const float curve_t = step * (num_points - 1);
  const int point_a = clamp((int)curve_t, 0, num_points - 1);
  const int point_b = min(point_a + 1, num_points - 1);
  const float t = curve_t - (float)point_a;
  return mix(curve_point_as_float4(b_positions, b_radius, first_point_index + point_a),
             curve_point_as_float4(b_positions, b_radius, first_point_index + point_b),
             t);
}

static void export_hair_curves(Scene *scene,
                               Hair *hair,
                               const blender::bke::CurvesGeometry &b_curves,
                               const bool need_motion,
                               const float motion_scale)
{
  const blender::Span<blender::float3> positions = b_curves.positions();
  const blender::OffsetIndices points_by_curve = b_curves.points_by_curve();
  const blender::bke::AttributeAccessor b_attributes = b_curves.attributes();

  hair->resize_curves(points_by_curve.size(), positions.size());

  /* Sync positions, sharing with Blender when possible. */
  sync_attribute_from_blender(
      hair->attributes,
      ATTR_STD_POSITION,
      b_attributes.lookup<blender::float3>("position", blender::bke::AttrDomain::Point),
      positions.size());
  hair->tag_position_modified();

  /* Sync radius, sharing with Blender when possible, or filling default. */
  if (sync_attribute_from_blender(
          hair->attributes,
          ATTR_STD_RADIUS,
          b_attributes.lookup<float>("radius", blender::bke::AttrDomain::Point),
          positions.size()))
  {
    hair->tag_radius_modified();
  }
  else {
    float *curve_radius = hair->get_radius_for_write();
    std::fill(curve_radius, curve_radius + positions.size(), 0.005f);
  }

  int *curve_first_key = hair->get_curve_first_key().data();
  int *curve_shader = hair->get_curve_shader().data();

  /* Add requested attributes. */
  float *attr_intercept = nullptr;
  float *attr_length = nullptr;

  if (hair->need_attribute(scene, ATTR_STD_VERTEX_NORMAL)) {
    /* Get geometry normals. */
    packed_normal *attr_normal =
        hair->attributes.add(ATTR_STD_VERTEX_NORMAL)->data_for_write<packed_normal>();
    vector<blender::float3> point_normals(positions.size());
    blender::bke::curves_normals_point_domain_calc(
        b_curves, {point_normals.data(), int64_t(point_normals.size())});
    for (const int i : positions.index_range()) {
      attr_normal[i] = packed_normal(
          make_float3(point_normals[i][0], point_normals[i][1], point_normals[i][2]));
    }
  }

  if (hair->need_attribute(scene, ATTR_STD_CURVE_INTERCEPT)) {
    attr_intercept = hair->attributes.add(ATTR_STD_CURVE_INTERCEPT)->data_for_write<float>();
  }
  if (hair->need_attribute(scene, ATTR_STD_CURVE_LENGTH)) {
    attr_length = hair->attributes.add(ATTR_STD_CURVE_LENGTH)->data_for_write<float>();
  }
  if (hair->need_attribute(scene, ATTR_STD_CURVE_RANDOM)) {
    float *attr_random = hair->attributes.add(ATTR_STD_CURVE_RANDOM)->data_for_write<float>();
    for (const int i : points_by_curve.index_range()) {
      attr_random[i] = hash_uint2_to_float(i, 0);
    }
  }

  std::copy(points_by_curve.data().data(),
            points_by_curve.data().data() + points_by_curve.size(),
            curve_first_key);
  std::fill(curve_shader, curve_shader + points_by_curve.size(), 0);

  /* Compute per-curve length and per-point intercept along the curve. */
  if (attr_length || attr_intercept) {
    for (const int curve : points_by_curve.index_range()) {
      const blender::IndexRange points = points_by_curve[curve];

      float3 prev_co = zero_float3();
      float length = 0.0f;

      for (const int point : points) {
        const float3 co = make_float3(
            positions[point][0], positions[point][1], positions[point][2]);

        if (point != points.first()) {
          length += len(co - prev_co);
        }
        prev_co = co;

        if (attr_intercept) {
          attr_intercept[point] = length;
        }
      }

      /* Normalized 0..1 attribute along curve. */
      if (attr_intercept && length > 0.0f) {
        for (const int point : points.drop_front(1)) {
          attr_intercept[point] /= length;
        }
      }

      /* Curve length. */
      if (attr_length) {
        attr_length[curve] = length;
      }
    }
  }

  attr_create_generic(scene, hair, b_curves, need_motion, motion_scale);
}

static bool hair_topology_matches(const Hair *hair, const blender::bke::CurvesGeometry &b_curves)
{
  const blender::OffsetIndices points_by_curve = b_curves.points_by_curve();
  if (size_t(b_curves.points_num()) != hair->num_keys() ||
      size_t(points_by_curve.size()) != hair->num_curves())
  {
    return false;
  }
  for (const int i : points_by_curve.index_range()) {
    if (points_by_curve[i].size() != hair->get_curve(i).num_keys) {
      return false;
    }
  }
  return true;
}

static void export_hair_curves_motion(Hair *hair,
                                      const blender::bke::CurvesGeometry &b_curves,
                                      const int motion_step)
{
  /* Set motion steps on position and radius attributes. */
  Attribute *attr_P = hair->attributes.find(ATTR_STD_POSITION);
  Attribute *attr_R = hair->attributes.find(ATTR_STD_RADIUS);
  bool new_attribute = false;

  if (!attr_P->has_motion()) {
    attr_P->add_motion(hair);
    attr_R->add_motion(hair);
    new_attribute = true;
  }

  const size_t num_keys = hair->num_keys();
  const int attr_step = motion_step + 1;
  const blender::bke::AttributeAccessor b_attributes = b_curves.attributes();

  bool have_motion = false;
  int num_motion_keys = 0;

  if (hair_topology_matches(hair, b_curves)) {
    /* Fast path: topology unchanged, sync the whole step from Blender, sharing
     * the buffer when possible. */
    sync_attribute_motion_step_from_blender(
        *attr_P,
        attr_step,
        b_attributes.lookup<blender::float3>("position", blender::bke::AttrDomain::Point));
    if (!sync_attribute_motion_step_from_blender(
            *attr_R,
            attr_step,
            b_attributes.lookup<float>("radius", blender::bke::AttrDomain::Point)))
    {
      float *mR = attr_R->data_for_write<float>(attr_step);
      std::fill(mR, mR + num_keys, 0.005f);
    }

    /* If a buffer is shared from Blender and unchanged across frames, the
     * pointer matches the center step's, so the memcmp is skipped. */
    const packed_float3 *motion_P = attr_P->data<packed_float3>(attr_step);
    const packed_float3 *center_P = hair->get_position();
    const float *motion_R = attr_R->data<float>(attr_step);
    const float *center_R = hair->get_radius();
    have_motion = (motion_P != center_P &&
                   std::memcmp(motion_P, center_P, num_keys * sizeof(packed_float3)) != 0) ||
                  (motion_R != center_R &&
                   std::memcmp(motion_R, center_R, num_keys * sizeof(float)) != 0);
    num_motion_keys = num_keys;
  }
  else {
    /* Slow path: topology has changed, copy with per-curve interpolation. */
    const size_t num_curves = hair->num_curves();
    packed_float3 *mP = attr_P->data_for_write<packed_float3>(attr_step);
    float *mR = attr_R->data_for_write<float>(attr_step);
    int curve_index = 0;

    const blender::Span<blender::float3> b_positions = b_curves.positions();
    const blender::OffsetIndices points_by_curve = b_curves.points_by_curve();
    const blender::VArraySpan b_radius = *b_attributes.lookup<float>(
        "radius", blender::bke::AttrDomain::Point);

    for (const int i : points_by_curve.index_range()) {
      const blender::IndexRange points = points_by_curve[i];
      if (curve_index >= num_curves) {
        break;
      }

      const Hair::Curve curve = hair->get_curve(curve_index);
      curve_index++;

      if (points.size() == curve.num_keys) {
        /* Number of keys matches. */
        for (const int i : points.index_range()) {
          const int point = points[i];

          if (num_motion_keys < num_keys) {
            const float4 cv = curve_point_as_float4(b_positions, b_radius, point);
            mP[num_motion_keys] = make_float3(cv);
            mR[num_motion_keys] = cv.w;

            if (!have_motion) {
              float4 curve_key = make_float4(hair->get_position()[num_motion_keys]);
              curve_key.w = hair->get_radius()[num_motion_keys];
              have_motion = !(cv == curve_key);
            }
            num_motion_keys++;
          }
        }
      }
      else {
        /* Number of keys has changed. Generate an interpolated version
         * to preserve motion blur. */
        const float step_size = curve.num_keys > 1 ? 1.0f / (curve.num_keys - 1) : 0.0f;
        for (int i = 0; i < curve.num_keys; i++) {
          const float step = i * step_size;
          const float4 cv = interpolate_curve_points(
              b_positions, b_radius, points.start(), points.size(), step);
          mP[num_motion_keys] = make_float3(cv);
          mR[num_motion_keys] = cv.w;
          num_motion_keys++;
        }
        have_motion = true;
      }
    }
  }

  /* In case of new attribute, verify if there really was any motion. */
  if (new_attribute) {
    export_hair_motion_validate_attribute(hair, motion_step, num_motion_keys, have_motion);
  }
}

/* Hair object. */
void BlenderSync::sync_hair(Hair *hair, BObjectInfo &b_ob_info, bool motion, const int motion_step)
{
  /* Motion blur attribute is relative to seconds, we need it relative to frames. */
  const bool need_motion = object_need_motion_attribute(b_ob_info, scene);
  const float motion_scale = (need_motion) ? scene->motion_shutter_time() /
                                                 (b_scene->r.frs_sec / b_scene->r.frs_sec_base) :
                                             0.0f;

  /* Convert Blender hair to Cycles curves. */
  const blender::bke::CurvesGeometry &b_curves(
      blender::id_cast<const blender::Curves *>(b_ob_info.object_data)->geometry.wrap());
  if (motion) {
    export_hair_curves_motion(hair, b_curves, motion_step);
  }
  else {
    export_hair_curves(scene, hair, b_curves, need_motion, motion_scale);
  }

  const blender::VArray<int8_t> b_types = b_curves.curve_types();
  /* This does not handle cases where the curve type is not the same across all curves */
  if (!b_types.is_empty() && b_types[0] == blender::CURVE_TYPE_POLY) {
    hair->curve_shape = CURVE_THICK_LINEAR;
  }
  else {
    hair->curve_shape = scene->params.hair_shape;
  }
}

void BlenderSync::sync_hair(BObjectInfo &b_ob_info, Hair *hair)
{
  /* make a copy of the shaders as the caller in the main thread still need them for syncing the
   * attributes */
  array<Node *> used_shaders = hair->get_used_shaders();

  Hair new_hair;
  new_hair.set_used_shaders(used_shaders);

  if (view_layer.use_hair) {
    if (GS(b_ob_info.object_data->name) == blender::ID_CV) {
      /* Hair object. */
      sync_hair(&new_hair, b_ob_info, false);
    }
    else {
      /* Particle hair. */
      blender::Mesh *b_mesh = object_to_mesh(b_ob_info);

      if (b_mesh) {
        sync_particle_hair(&new_hair, *b_mesh, b_ob_info, false);
        free_object_to_mesh(b_ob_info, *b_mesh);
      }
    }

    if (scene->need_motion() == Scene::MOTION_PASS_INTERACTIVE &&
        hair->num_keys() == new_hair.num_keys())
    {
      new_hair.set_motion_steps(2);

      Attribute *attr_P = hair->attributes.find(ATTR_STD_POSITION);
      Attribute *new_attr_P = new_hair.attributes.find(ATTR_STD_POSITION);
      if (attr_P->has_motion()) {
        new_attr_P->take_motion_from(*attr_P);
      }
      else {
        new_attr_P->add_motion(&new_hair);
        new_hair.copy_center_to_motion_step(0);
      }
    }
  }

  /* update original sockets */

  for (const SocketType &socket : new_hair.type->inputs) {
    /* Those sockets are updated in sync_object, so do not modify them. */
    if (socket.name == "use_motion_blur" || socket.name == "used_shaders") {
      continue;
    }
    hair->set_value(socket, new_hair, socket);
  }

  hair->attributes.update(std::move(new_hair.attributes));

  hair->curve_shape = new_hair.curve_shape;

  /* tag update */

  /* Compares curve_keys rather than strands in order to handle quick hair
   * adjustments in dynamic BVH - other methods could probably do this better. */
  const bool rebuild = (hair->position_is_modified() || hair->radius_is_modified());

  hair->tag_update(scene, rebuild);
}

void BlenderSync::sync_hair_motion(BObjectInfo &b_ob_info, Hair *hair, const int motion_step)
{
  /* Skip if nothing exported. */
  if (hair->num_keys() == 0) {
    return;
  }

  /* Export deformed coordinates. */
  if (ccl::BKE_object_is_deform_modified(b_ob_info, *b_scene, preview)) {
    if (GS(b_ob_info.object_data->name) == blender::ID_CV) {
      /* Hair object. */
      sync_hair(hair, b_ob_info, true, motion_step);
      return;
    }

    /* Particle hair. */
    blender::Mesh *b_mesh = object_to_mesh(b_ob_info);
    if (b_mesh) {
      sync_particle_hair(hair, *b_mesh, b_ob_info, true, motion_step);
      free_object_to_mesh(b_ob_info, *b_mesh);
      return;
    }
  }

  /* No deformation on this frame, copy coordinates if other frames did have it. */
  hair->copy_center_to_motion_step(motion_step);
}

CCL_NAMESPACE_END