update the calculation and orthogonalization for bitangent

code/PostProcessing/CalcTangentsProcess.cpp

@@ -191,9 +191,9 @@ bool CalcTangentsProcess::ProcessMesh(aiMesh *pMesh, unsigned int meshIndex) {
         tangent.x = (w.x * sy - v.x * ty) * dirCorrection;
         tangent.y = (w.y * sy - v.y * ty) * dirCorrection;
         tangent.z = (w.z * sy - v.z * ty) * dirCorrection;
-        bitangent.x = (w.x * sx - v.x * tx) * dirCorrection;
-        bitangent.y = (w.y * sx - v.y * tx) * dirCorrection;
-        bitangent.z = (w.z * sx - v.z * tx) * dirCorrection;
+        bitangent.x = (- w.x * sx + v.x * tx) * dirCorrection;
+        bitangent.y = (- w.y * sx + v.y * tx) * dirCorrection;
+        bitangent.z = (- w.z * sx + v.z * tx) * dirCorrection;
 
         // store for every vertex of that face
         for (unsigned int b = 0; b < face.mNumIndices; ++b) {
@@ -201,7 +201,7 @@ bool CalcTangentsProcess::ProcessMesh(aiMesh *pMesh, unsigned int meshIndex) {
 
             // project tangent and bitangent into the plane formed by the vertex' normal
             aiVector3D localTangent = tangent - meshNorm[p] * (tangent * meshNorm[p]);
-            aiVector3D localBitangent = bitangent - meshNorm[p] * (bitangent * meshNorm[p]);
+            aiVector3D localBitangent = bitangent - meshNorm[p] * (bitangent * meshNorm[p]) - localTangent * (bitangent * localTangent);
             localTangent.NormalizeSafe();
             localBitangent.NormalizeSafe();