Fix #2077 : GLTF segfault using triangle strip

code/glTF2Importer.cpp

@@ -550,9 +550,18 @@ void glTF2Importer::ImportMeshes(glTF2::Asset& r)
                     case PrimitiveMode_TRIANGLE_STRIP: {
                         nFaces = count - 2;
                         faces = new aiFace[nFaces];
-                        SetFace(faces[0], data.GetUInt(0), data.GetUInt(1), data.GetUInt(2));
-                        for (unsigned int i = 3; i < count; ++i) {
-                            SetFace(faces[i - 2], faces[i - 1].mIndices[1], faces[i - 1].mIndices[2], data.GetUInt(i));
+                        for (unsigned int i = 0; i < nFaces; ++i) {
+                            //The ordering is to ensure that the triangles are all drawn with the same orientation
+                            if ((i + 1) % 2 == 0)
+                            {
+                                //For even n, vertices n + 1, n, and n + 2 define triangle n
+                                SetFace(faces[i], data.GetUInt(i + 1), data.GetUInt(i), data.GetUInt(i + 2));
+                            }
+                            else
+                            {
+                                //For odd n, vertices n, n+1, and n+2 define triangle n
+                                SetFace(faces[i], data.GetUInt(i), data.GetUInt(i + 1), data.GetUInt(i + 2));
+                            }
                         }
                         break;
                     }
@@ -560,8 +569,8 @@ void glTF2Importer::ImportMeshes(glTF2::Asset& r)
                         nFaces = count - 2;
                         faces = new aiFace[nFaces];
                         SetFace(faces[0], data.GetUInt(0), data.GetUInt(1), data.GetUInt(2));
-                        for (unsigned int i = 3; i < count; ++i) {
-                            SetFace(faces[i - 2], faces[0].mIndices[0], faces[i - 1].mIndices[2], data.GetUInt(i));
+                        for (unsigned int i = 1; i < nFaces; ++i) {
+                            SetFace(faces[i], faces[0].mIndices[0], faces[i - 1].mIndices[2], data.GetUInt(i + 2));
                         }
                         break;
                 }
@@ -615,9 +624,18 @@ void glTF2Importer::ImportMeshes(glTF2::Asset& r)
                 case PrimitiveMode_TRIANGLE_STRIP: {
                     nFaces = count - 2;
                     faces = new aiFace[nFaces];
-                    SetFace(faces[0], 0, 1, 2);
-                    for (unsigned int i = 3; i < count; ++i) {
-                        SetFace(faces[i - 2], faces[i - 1].mIndices[1], faces[i - 1].mIndices[2], i);
+                    for (unsigned int i = 0; i < nFaces; ++i) {
+                        //The ordering is to ensure that the triangles are all drawn with the same orientation
+                        if ((i+1) % 2 == 0)
+                        {
+                            //For even n, vertices n + 1, n, and n + 2 define triangle n
+                            SetFace(faces[i], i+1, i, i+2);
+                        }
+                        else
+                        {
+                            //For odd n, vertices n, n+1, and n+2 define triangle n
+                            SetFace(faces[i], i, i+1, i+2);
+                        }
                     }
                     break;
                 }
@@ -625,8 +643,8 @@ void glTF2Importer::ImportMeshes(glTF2::Asset& r)
                     nFaces = count - 2;
                     faces = new aiFace[nFaces];
                     SetFace(faces[0], 0, 1, 2);
-                    for (unsigned int i = 3; i < count; ++i) {
-                        SetFace(faces[i - 2], faces[0].mIndices[0], faces[i - 1].mIndices[2], i);
+                    for (unsigned int i = 1; i < nFaces; ++i) {
+                        SetFace(faces[i], faces[0].mIndices[0], faces[i - 1].mIndices[2], i + 2);
                     }
                     break;
                 }
@@ -848,12 +866,6 @@ void glTF2Importer::InternReadFile(const std::string& pFile, aiScene* pScene, IO
 
     ImportNodes(asset);
 
-    // TODO: it does not split the loaded vertices, should it?
-    //pScene->mFlags |= AI_SCENE_FLAGS_NON_VERBOSE_FORMAT;
-    MakeVerboseFormatProcess process;
-    process.Execute(pScene);
-
-
     if (pScene->mNumMeshes == 0) {
         pScene->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;
     }

code/glTFImporter.cpp

@@ -740,11 +740,6 @@ void glTFImporter::InternReadFile(const std::string& pFile, aiScene* pScene, IOS
 
     ImportNodes(asset);
 
-    // TODO: it does not split the loaded vertices, should it?
-    //pScene->mFlags |= AI_SCENE_FLAGS_NON_VERBOSE_FORMAT;
-	MakeVerboseFormatProcess process;
-    process.Execute(pScene);
-
 
     if (pScene->mNumMeshes == 0) {
         pScene->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;