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  /** @file  BlenderModifier.cpp
   *  @brief Implementation of some blender modifiers (i.e subdivision, mirror).
   */
  
  #ifndef ASSIMP_BUILD_NO_BLEND_IMPORTER
  
  #include "BlenderModifier.h"
  #include <assimp/SceneCombiner.h>
  #include <assimp/Subdivision.h>
  #include <assimp/scene.h>
  #include <memory>
  
  #include <functional>
  
  using namespace Assimp;
  using namespace Assimp::Blender;
  
  template <typename T>
  BlenderModifier *god() {
      return new T();
  }
  
  // add all available modifiers here
  typedef BlenderModifier *(*fpCreateModifier)();
  static const fpCreateModifier creators[] = {
      &god<BlenderModifier_Mirror>,
      &god<BlenderModifier_Subdivision>,
  
      nullptr // sentinel
  };
  
  // ------------------------------------------------------------------------------------------------
  struct SharedModifierData : ElemBase {
      ModifierData modifier;
  };
  
  // ------------------------------------------------------------------------------------------------
  void BlenderModifierShowcase::ApplyModifiers(aiNode &out, ConversionData &conv_data, const Scene &in, const Object &orig_object) {
      size_t cnt = 0u, ful = 0u;
  
      // NOTE: this cast is potentially unsafe by design, so we need to perform type checks before
      // we're allowed to dereference the pointers without risking to crash. We might still be
      // invoking UB btw - we're assuming that the ModifierData member of the respective modifier
      // structures is at offset sizeof(vftable) with no padding.
      const SharedModifierData *cur = static_cast<const SharedModifierData *>(orig_object.modifiers.first.get());
      for (; cur; cur = static_cast<const SharedModifierData *>(cur->modifier.next.get()), ++ful) {
          ai_assert(cur->dna_type);
  
          const Structure *s = conv_data.db.dna.Get(cur->dna_type);
          if (!s) {
              ASSIMP_LOG_WARN("BlendModifier: could not resolve DNA name: ", cur->dna_type);
              continue;
          }
  
          // this is a common trait of all XXXMirrorData structures in BlenderDNA
          const Field *f = s->Get("modifier");
          if (!f || f->offset != 0) {
              ASSIMP_LOG_WARN("BlendModifier: expected a `modifier` member at offset 0");
              continue;
          }
  
          s = conv_data.db.dna.Get(f->type);
          if (!s || s->name != "ModifierData") {
              ASSIMP_LOG_WARN("BlendModifier: expected a ModifierData structure as first member");
              continue;
          }
  
          // now, we can be sure that we should be fine to dereference *cur* as
          // ModifierData (with the above note).
          const ModifierData &dat = cur->modifier;
  
          const fpCreateModifier *curgod = creators;
          std::vector<BlenderModifier *>::iterator curmod = cached_modifiers->begin(), endmod = cached_modifiers->end();
  
          for (; *curgod; ++curgod, ++curmod) { // allocate modifiers on the fly
              if (curmod == endmod) {
                  cached_modifiers->push_back((*curgod)());
  
                  endmod = cached_modifiers->end();
                  curmod = endmod - 1;
              }
  
              BlenderModifier *const modifier = *curmod;
              if (modifier->IsActive(dat)) {
                  modifier->DoIt(out, conv_data, *static_cast<const ElemBase *>(cur), in, orig_object);
                  cnt++;
  
                  curgod = nullptr;
                  break;
              }
          }
          if (curgod) {
              ASSIMP_LOG_WARN("Couldn't find a handler for modifier: ", dat.name);
          }
      }
  
      // Even though we managed to resolve some or all of the modifiers on this
      // object, we still can't say whether our modifier implementations were
      // able to fully do their job.
      if (ful) {
          ASSIMP_LOG_DEBUG("BlendModifier: found handlers for ", cnt, " of ", ful, " modifiers on `", orig_object.id.name,
                  "`, check log messages above for errors");
      }
  }
  
  // ------------------------------------------------------------------------------------------------
  bool BlenderModifier_Mirror ::IsActive(const ModifierData &modin) {
      return modin.type == ModifierData::eModifierType_Mirror;
  }
  
  // ------------------------------------------------------------------------------------------------
  void BlenderModifier_Mirror ::DoIt(aiNode &out, ConversionData &conv_data, const ElemBase &orig_modifier,
          const Scene & /*in*/,
          const Object &orig_object) {
      // hijacking the ABI, see the big note in BlenderModifierShowcase::ApplyModifiers()
      const MirrorModifierData &mir = static_cast<const MirrorModifierData &>(orig_modifier);
      ai_assert(mir.modifier.type == ModifierData::eModifierType_Mirror);
  
      conv_data.meshes->reserve(conv_data.meshes->size() + out.mNumMeshes);
  
      // XXX not entirely correct, mirroring on two axes results in 4 distinct objects in blender ...
  
      // take all input meshes and clone them
      for (unsigned int i = 0; i < out.mNumMeshes; ++i) {
          aiMesh *mesh;
          SceneCombiner::Copy(&mesh, conv_data.meshes[out.mMeshes[i]]);
  
          const float xs = mir.flag & MirrorModifierData::Flags_AXIS_X ? -1.f : 1.f;
          const float ys = mir.flag & MirrorModifierData::Flags_AXIS_Y ? -1.f : 1.f;
          const float zs = mir.flag & MirrorModifierData::Flags_AXIS_Z ? -1.f : 1.f;
  
          if (mir.mirror_ob) {
              const aiVector3D center(mir.mirror_ob->obmat[3][0], mir.mirror_ob->obmat[3][1], mir.mirror_ob->obmat[3][2]);
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mVertices[j];
  
                  v.x = center.x + xs * (center.x - v.x);
                  v.y = center.y + ys * (center.y - v.y);
                  v.z = center.z + zs * (center.z - v.z);
              }
          } else {
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mVertices[j];
                  v.x *= xs;
                  v.y *= ys;
                  v.z *= zs;
              }
          }
  
          if (mesh->mNormals) {
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mNormals[j];
                  v.x *= xs;
                  v.y *= ys;
                  v.z *= zs;
              }
          }
  
          if (mesh->mTangents) {
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mTangents[j];
                  v.x *= xs;
                  v.y *= ys;
                  v.z *= zs;
              }
          }
  
          if (mesh->mBitangents) {
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mBitangents[j];
                  v.x *= xs;
                  v.y *= ys;
                  v.z *= zs;
              }
          }
  
          const float us = mir.flag & MirrorModifierData::Flags_MIRROR_U ? -1.f : 1.f;
          const float vs = mir.flag & MirrorModifierData::Flags_MIRROR_V ? -1.f : 1.f;
  
          for (unsigned int n = 0; mesh->HasTextureCoords(n); ++n) {
              for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                  aiVector3D &v = mesh->mTextureCoords[n][j];
                  v.x *= us;
                  v.y *= vs;
              }
          }
  
          // Only reverse the winding order if an odd number of axes were mirrored.
          if (xs * ys * zs < 0) {
              for (unsigned int j = 0; j < mesh->mNumFaces; ++j) {
                  aiFace &face = mesh->mFaces[j];
                  for (unsigned int fi = 0; fi < face.mNumIndices / 2; ++fi)
                      std::swap(face.mIndices[fi], face.mIndices[face.mNumIndices - 1 - fi]);
              }
          }
  
          conv_data.meshes->push_back(mesh);
      }
      unsigned int *nind = new unsigned int[out.mNumMeshes * 2];
  
      std::copy(out.mMeshes, out.mMeshes + out.mNumMeshes, nind);
      std::transform(out.mMeshes, out.mMeshes + out.mNumMeshes, nind + out.mNumMeshes,
              [&out](unsigned int n) { return out.mNumMeshes + n; });
  
      delete[] out.mMeshes;
      out.mMeshes = nind;
      out.mNumMeshes *= 2;
  
      ASSIMP_LOG_INFO("BlendModifier: Applied the `Mirror` modifier to `",
              orig_object.id.name, "`");
  }
  
  // ------------------------------------------------------------------------------------------------
  bool BlenderModifier_Subdivision ::IsActive(const ModifierData &modin) {
      return modin.type == ModifierData::eModifierType_Subsurf;
  }
  
  // ------------------------------------------------------------------------------------------------
  void BlenderModifier_Subdivision ::DoIt(aiNode &out, ConversionData &conv_data, const ElemBase &orig_modifier,
          const Scene & /*in*/,
          const Object &orig_object) {
      // hijacking the ABI, see the big note in BlenderModifierShowcase::ApplyModifiers()
      const SubsurfModifierData &mir = static_cast<const SubsurfModifierData &>(orig_modifier);
      ai_assert(mir.modifier.type == ModifierData::eModifierType_Subsurf);
  
      Subdivider::Algorithm algo;
      switch (mir.subdivType) {
      case SubsurfModifierData::TYPE_CatmullClarke:
          algo = Subdivider::CATMULL_CLARKE;
          break;
  
      case SubsurfModifierData::TYPE_Simple:
          ASSIMP_LOG_WARN("BlendModifier: The `SIMPLE` subdivision algorithm is not currently implemented, using Catmull-Clarke");
          algo = Subdivider::CATMULL_CLARKE;
          break;
  
      default:
          ASSIMP_LOG_WARN("BlendModifier: Unrecognized subdivision algorithm: ", mir.subdivType);
          return;
      };
  
      std::unique_ptr<Subdivider> subd(Subdivider::Create(algo));
      ai_assert(subd);
      if (conv_data.meshes->empty()) {
          return;
      }
      aiMesh **const meshes = &conv_data.meshes[conv_data.meshes->size() - out.mNumMeshes];
      std::unique_ptr<aiMesh *[]> tempmeshes(new aiMesh *[out.mNumMeshes]());
  
      subd->Subdivide(meshes, out.mNumMeshes, tempmeshes.get(), std::max(mir.renderLevels, mir.levels), true);
      std::copy(tempmeshes.get(), tempmeshes.get() + out.mNumMeshes, meshes);
  
      ASSIMP_LOG_INFO("BlendModifier: Applied the `Subdivision` modifier to `",
              orig_object.id.name, "`");
  }
  
  #endif // ASSIMP_BUILD_NO_BLEND_IMPORTER
  