1 files changed, 21 insertions, 11 deletions
diff --git a/code/PostProcessing/OptimizeGraph.cpp b/code/PostProcessing/OptimizeGraph.cpp
index 709f465e2..43bd7a3ee 100644
--- a/code/PostProcessing/OptimizeGraph.cpp
+++ b/code/PostProcessing/OptimizeGraph.cpp
@@ -47,6 +47,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "OptimizeGraph.h"
 #include "ProcessHelper.h"
+#include "ConvertToLHProcess.h"
 #include <assimp/Exceptional.h>
 #include <assimp/SceneCombiner.h>
 #include <stdio.h>
@@ -135,7 +136,7 @@ void OptimizeGraphProcess::CollectNewChildren(aiNode *nd, std::list<aiNode *> &n
 		nodes.push_back(nd);
 
 		// Now check for possible optimizations in our list of child nodes. join as many as possible
-		aiNode *join_master = NULL;
+		aiNode *join_master = nullptr;
 		aiMatrix4x4 inv;
 
 		const LockedSetType::const_iterator end = locked.end();
@@ -172,7 +173,7 @@ void OptimizeGraphProcess::CollectNewChildren(aiNode *nd, std::list<aiNode *> &n
 			join_master->mName.length = ::ai_snprintf(join_master->mName.data, MAXLEN, "$MergedNode_%i", count_merged++);
 
 			unsigned int out_meshes = 0;
-			for (std::list<aiNode *>::iterator it = join.begin(); it != join.end(); ++it) {
+			for (std::list<aiNode *>::const_iterator it = join.cbegin(); it != join.cend(); ++it) {
 				out_meshes += (*it)->mNumMeshes;
 			}
 
@@ -183,17 +184,26 @@ void OptimizeGraphProcess::CollectNewChildren(aiNode *nd, std::list<aiNode *> &n
 					*tmp++ = join_master->mMeshes[n];
 				}
 
-				for (std::list<aiNode *>::iterator it = join.begin(); it != join.end(); ++it) {
-					for (unsigned int n = 0; n < (*it)->mNumMeshes; ++n) {
+				for (const aiNode *join_node : join) {
+					for (unsigned int n = 0; n < join_node->mNumMeshes; ++n) {
 
-						*tmp = (*it)->mMeshes[n];
+						*tmp = join_node->mMeshes[n];
 						aiMesh *mesh = mScene->mMeshes[*tmp++];
 
+						// Assume the transformation is affine
 						// manually move the mesh into the right coordinate system
-						const aiMatrix3x3 IT = aiMatrix3x3((*it)->mTransformation).Inverse().Transpose();
+
+						// Check for odd negative scale (mirror)
+						if (join_node->mTransformation.Determinant() < 0) {
+							// Reverse the mesh face winding order
+                            FlipWindingOrderProcess::ProcessMesh(mesh);
+						}
+
+                        // Update positions, normals and tangents
+						const aiMatrix3x3 IT = aiMatrix3x3(join_node->mTransformation).Inverse().Transpose();
 						for (unsigned int a = 0; a < mesh->mNumVertices; ++a) {
 
-							mesh->mVertices[a] *= (*it)->mTransformation;
+							mesh->mVertices[a] *= join_node->mTransformation;
 
 							if (mesh->HasNormals())
 								mesh->mNormals[a] *= IT;
@@ -204,7 +214,7 @@ void OptimizeGraphProcess::CollectNewChildren(aiNode *nd, std::list<aiNode *> &n
 							}
 						}
 					}
-					delete *it; // bye, node
+					delete join_node; // bye, node
 				}
 				delete[] join_master->mMeshes;
 				join_master->mMeshes = meshes;
@@ -304,7 +314,7 @@ void OptimizeGraphProcess::Execute(aiScene *pScene) {
 	ai_assert(nodes.size() == 1);
 
 	if (dummy_root->mNumChildren == 0) {
-		pScene->mRootNode = NULL;
+		pScene->mRootNode = nullptr;
 		throw DeadlyImportError("After optimizing the scene graph, no data remains");
 	}
 
@@ -318,11 +328,11 @@ void OptimizeGraphProcess::Execute(aiScene *pScene) {
 		// Remove the dummy root node again.
 		pScene->mRootNode = dummy_root->mChildren[0];
 
-		dummy_root->mChildren[0] = NULL;
+		dummy_root->mChildren[0] = nullptr;
 		delete dummy_root;
 	}
 
-	pScene->mRootNode->mParent = NULL;
+	pScene->mRootNode->mParent = nullptr;
 	if (!DefaultLogger::isNullLogger()) {
 		if (nodes_in != nodes_out) {
 			ASSIMP_LOG_INFO_F("OptimizeGraphProcess finished; Input nodes: ", nodes_in, ", Output nodes: ", nodes_out);