Make gltf2 export normal normalization safe

This avoids introducing NaNs e.g. when the input mesh has 0-length normals

code/AssetLib/glTF/glTFExporter.cpp

@@ -348,7 +348,7 @@ void glTFExporter::GetMatColorOrTex(const aiMaterial* mat, glTF::TexProperty& pr
 
                     if (path[0] == '*') { // embedded
                         aiTexture* curTex = mScene->mTextures[atoi(&path[1])];
-						
+
                         prop.texture->source->name = curTex->mFilename.C_Str();
 
                         uint8_t *data = reinterpret_cast<uint8_t *>(curTex->pcData);

code/AssetLib/glTF2/glTF2Exporter.cpp

@@ -758,7 +758,7 @@ void glTF2Exporter::ExportMeshes()
         // Normalize all normals as the validator can emit a warning otherwise
         if ( nullptr != aim->mNormals) {
             for ( auto i = 0u; i < aim->mNumVertices; ++i ) {
-                aim->mNormals[ i ].Normalize();
+                aim->mNormals[ i ].NormalizeSafe();
             }
         }
 

test/unit/utglTF2ImportExport.cpp

@@ -446,6 +446,21 @@ TEST_F(utglTF2ImportExport, export_bad_accessor_bounds) {
     EXPECT_EQ(aiReturn_SUCCESS, exporter.Export(scene, "gltf2", ASSIMP_TEST_MODELS_DIR "/glTF2/BoxWithInfinites-glTF-Binary/BoxWithInfinites_out.gltf"));
 }
 
+TEST_F(utglTF2ImportExport, export_normalized_normals) {
+    Assimp::Importer importer;
+    Assimp::Exporter exporter;
+    const aiScene* scene = importer.ReadFile(ASSIMP_TEST_MODELS_DIR "/glTF2/BoxBadNormals-glTF-Binary/BoxBadNormals.glb", aiProcess_ValidateDataStructure);
+    ASSERT_NE(scene, nullptr);
+    EXPECT_EQ(aiReturn_SUCCESS, exporter.Export(scene, "glb2", ASSIMP_TEST_MODELS_DIR "/glTF2/BoxBadNormals-glTF-Binary/BoxBadNormals_out.glb"));
+
+    // load in again and ensure normal-length normals but no Nan's or Inf's introduced
+    scene = importer.ReadFile(ASSIMP_TEST_MODELS_DIR "/glTF2/BoxBadNormals-glTF-Binary/BoxBadNormals_out.glb", aiProcess_ValidateDataStructure);
+    for ( auto i = 0u; i < scene->mMeshes[0]->mNumVertices; ++i ) {
+        const auto length = scene->mMeshes[0]->mNormals[i].Length();
+        EXPECT_TRUE(abs(length) < 1e-6 || abs(length - 1) < 1e-6);
+    }
+}
+
 #endif // ASSIMP_BUILD_NO_EXPORT
 
 TEST_F(utglTF2ImportExport, sceneMetadata) {