consider aiProcess_FlipWindingOrder in aiProcess_GenNormals & aiProcess_GenSmoothNormals

code/PostProcessing/GenFaceNormalsProcess.cpp

@@ -70,6 +70,7 @@ GenFaceNormalsProcess::~GenFaceNormalsProcess() {
 // Returns whether the processing step is present in the given flag field.
 bool GenFaceNormalsProcess::IsActive(unsigned int pFlags) const {
     force_ = (pFlags & aiProcess_ForceGenNormals) != 0;
+    flippedWindingOrder_ = (pFlags & aiProcess_FlipWindingOrder) != 0;
     return (pFlags & aiProcess_GenNormals) != 0;
 }
 
@@ -134,6 +135,8 @@ bool GenFaceNormalsProcess::GenMeshFaceNormals(aiMesh *pMesh) {
         const aiVector3D *pV1 = &pMesh->mVertices[face.mIndices[0]];
         const aiVector3D *pV2 = &pMesh->mVertices[face.mIndices[1]];
         const aiVector3D *pV3 = &pMesh->mVertices[face.mIndices[face.mNumIndices - 1]];
+        if (flippedWindingOrder_)
+            std::swap( pV2, pV3 );
         const aiVector3D vNor = ((*pV2 - *pV1) ^ (*pV3 - *pV1)).NormalizeSafe();
 
         for (unsigned int i = 0; i < face.mNumIndices; ++i) {

code/PostProcessing/GenFaceNormalsProcess.h

@@ -80,6 +80,7 @@ public:
 private:
     bool GenMeshFaceNormals(aiMesh* pcMesh);
     mutable bool force_ = false;
+    mutable bool flippedWindingOrder_ = false;
 };
 
 } // end of namespace Assimp

code/PostProcessing/GenVertexNormalsProcess.cpp

@@ -70,6 +70,7 @@ GenVertexNormalsProcess::~GenVertexNormalsProcess() {
 // Returns whether the processing step is present in the given flag field.
 bool GenVertexNormalsProcess::IsActive(unsigned int pFlags) const {
     force_ = (pFlags & aiProcess_ForceGenNormals) != 0;
+    flippedWindingOrder_ = (pFlags & aiProcess_FlipWindingOrder) != 0;
     return (pFlags & aiProcess_GenSmoothNormals) != 0;
 }
 
@@ -142,6 +143,8 @@ bool GenVertexNormalsProcess::GenMeshVertexNormals(aiMesh *pMesh, unsigned int m
         const aiVector3D *pV1 = &pMesh->mVertices[face.mIndices[0]];
         const aiVector3D *pV2 = &pMesh->mVertices[face.mIndices[1]];
         const aiVector3D *pV3 = &pMesh->mVertices[face.mIndices[face.mNumIndices - 1]];
+        if (flippedWindingOrder_)
+            std::swap( pV2, pV3 );
         const aiVector3D vNor = ((*pV2 - *pV1) ^ (*pV3 - *pV1)).NormalizeSafe();
 
         for (unsigned int i = 0; i < face.mNumIndices; ++i) {

code/PostProcessing/GenVertexNormalsProcess.h

@@ -104,6 +104,7 @@ private:
     /** Configuration option: maximum smoothing angle, in radians*/
     ai_real configMaxAngle;
     mutable bool force_ = false;
+    mutable bool flippedWindingOrder_ = false;
 };
 
 } // end of namespace Assimp