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  Open Asset Import Library (assimp)
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    copyright notice, this list of conditions and the
    following disclaimer.
  
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  */
  
  /** @file Implementation of the post processing step to invert
   * all normals in meshes with infacing normals.
   */
  
  // internal headers
  #include "FixNormalsStep.h"
  #include <assimp/StringUtils.h>
  #include <assimp/DefaultLogger.hpp>
  #include <assimp/postprocess.h>
  #include <assimp/scene.h>
  #include <stdio.h>
  
  
  using namespace Assimp;
  
  
  // ------------------------------------------------------------------------------------------------
  // Constructor to be privately used by Importer
  FixInfacingNormalsProcess::FixInfacingNormalsProcess()
  {
      // nothing to do here
  }
  
  // ------------------------------------------------------------------------------------------------
  // Destructor, private as well
  FixInfacingNormalsProcess::~FixInfacingNormalsProcess()
  {
      // nothing to do here
  }
  
  // ------------------------------------------------------------------------------------------------
  // Returns whether the processing step is present in the given flag field.
  bool FixInfacingNormalsProcess::IsActive( unsigned int pFlags) const
  {
      return (pFlags & aiProcess_FixInfacingNormals) != 0;
  }
  
  // ------------------------------------------------------------------------------------------------
  // Executes the post processing step on the given imported data.
  void FixInfacingNormalsProcess::Execute( aiScene* pScene)
  {
      ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess begin");
  
      bool bHas( false );
      for (unsigned int a = 0; a < pScene->mNumMeshes; ++a) {
          if (ProcessMesh(pScene->mMeshes[a], a)) {
              bHas = true;
          }
      }
  
      if (bHas) {
          ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. Found issues.");
      } else {
          ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. No changes to the scene.");
      }
  }
  
  // ------------------------------------------------------------------------------------------------
  // Apply the step to the mesh
  bool FixInfacingNormalsProcess::ProcessMesh( aiMesh* pcMesh, unsigned int index)
  {
      ai_assert(nullptr != pcMesh);
  
      // Nothing to do if there are no model normals
      if (!pcMesh->HasNormals()) {
          return false;
      }
  
      // Compute the bounding box of both the model vertices + normals and
      // the unmodified model vertices. Then check whether the first BB
      // is smaller than the second. In this case we can assume that the
      // normals need to be flipped, although there are a few special cases ..
      // convex, concave, planar models ...
  
      aiVector3D vMin0 (1e10f,1e10f,1e10f);
      aiVector3D vMin1 (1e10f,1e10f,1e10f);
      aiVector3D vMax0 (-1e10f,-1e10f,-1e10f);
      aiVector3D vMax1 (-1e10f,-1e10f,-1e10f);
  
      for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
      {
          vMin1.x = std::min(vMin1.x,pcMesh->mVertices[i].x);
          vMin1.y = std::min(vMin1.y,pcMesh->mVertices[i].y);
          vMin1.z = std::min(vMin1.z,pcMesh->mVertices[i].z);
  
          vMax1.x = std::max(vMax1.x,pcMesh->mVertices[i].x);
          vMax1.y = std::max(vMax1.y,pcMesh->mVertices[i].y);
          vMax1.z = std::max(vMax1.z,pcMesh->mVertices[i].z);
  
          const aiVector3D vWithNormal = pcMesh->mVertices[i] + pcMesh->mNormals[i];
  
          vMin0.x = std::min(vMin0.x,vWithNormal.x);
          vMin0.y = std::min(vMin0.y,vWithNormal.y);
          vMin0.z = std::min(vMin0.z,vWithNormal.z);
  
          vMax0.x = std::max(vMax0.x,vWithNormal.x);
          vMax0.y = std::max(vMax0.y,vWithNormal.y);
          vMax0.z = std::max(vMax0.z,vWithNormal.z);
      }
  
      const float fDelta0_x = (vMax0.x - vMin0.x);
      const float fDelta0_y = (vMax0.y - vMin0.y);
      const float fDelta0_z = (vMax0.z - vMin0.z);
  
      const float fDelta1_x = (vMax1.x - vMin1.x);
      const float fDelta1_y = (vMax1.y - vMin1.y);
      const float fDelta1_z = (vMax1.z - vMin1.z);
  
      // Check whether the boxes are overlapping
      if ((fDelta0_x > 0.0f) != (fDelta1_x > 0.0f))return false;
      if ((fDelta0_y > 0.0f) != (fDelta1_y > 0.0f))return false;
      if ((fDelta0_z > 0.0f) != (fDelta1_z > 0.0f))return false;
  
      // Check whether this is a planar surface
      const float fDelta1_yz = fDelta1_y * fDelta1_z;
  
      if (fDelta1_x < 0.05f * std::sqrt( fDelta1_yz ))return false;
      if (fDelta1_y < 0.05f * std::sqrt( fDelta1_z * fDelta1_x ))return false;
      if (fDelta1_z < 0.05f * std::sqrt( fDelta1_y * fDelta1_x ))return false;
  
      // now compare the volumes of the bounding boxes
      if (std::fabs(fDelta0_x * fDelta0_y * fDelta0_z) < std::fabs(fDelta1_x * fDelta1_yz)) {
          if (!DefaultLogger::isNullLogger()) {
              ASSIMP_LOG_INFO("Mesh ", index, ": Normals are facing inwards (or the mesh is planar)", index);
          }
  
          // Invert normals
          for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
              pcMesh->mNormals[i] *= -1.0f;
  
          // ... and flip faces
          for (unsigned int i = 0; i < pcMesh->mNumFaces;++i)
          {
              aiFace& face = pcMesh->mFaces[i];
              for( unsigned int b = 0; b < face.mNumIndices / 2; b++)
                  std::swap( face.mIndices[b], face.mIndices[ face.mNumIndices - 1 - b]);
          }
          return true;
      }
      return false;
  }
  