tiny_gltf.h - register MSFT_lod with the model's used extensions

tiny_gltf.h

@@ -8334,6 +8334,32 @@ static void SerializeGltfModel(const Model *model, detail::json &o) {
     }
   }
 
+  // MSFT_lod
+
+  // Look if there is a node that employs MSFT_lod
+  auto msft_lod_nodes_it = std::find_if(
+    model->nodes.begin(), model->nodes.end(),
+    [](const Node& node) { return !node.lods.empty(); });
+
+  // Look if there is a material that employs MSFT_lod
+  auto msft_lod_materials_it = std::find_if(
+    model->materials.begin(), model->materials.end(),
+    [](const Material& material) {return !material.lods.empty(); });
+
+  // If either a node or a material employ MSFT_lod, then we need
+  // to add MSFT_lod to the list of used extensions.
+  if (msft_lod_nodes_it != model->nodes.end() || msft_lod_materials_it != model->materials.end()) {
+    // First check if MSFT_lod is already registered as used extension
+    auto has_msft_lod = std::find_if(
+      extensionsUsed.begin(), extensionsUsed.end(),
+      [](const std::string &s) { return (s.compare("MSFT_lod") == 0); });
+
+    // If MSFT_lod is not registered yet, add it
+    if (has_msft_lod == extensionsUsed.end()) {
+      extensionsUsed.push_back("MSFT_lod");
+    }
+  }
+
   // Extensions used
   if (extensionsUsed.size()) {
     SerializeStringArrayProperty("extensionsUsed", extensionsUsed, o);