message: Initialize progressCallback...
diff: @@ -256,7 +256,7 @@ namespace ospray {
  /* TODO
  std::function<int(void*, const float)>
  progress_fcn { [](void*, const float){ return 1; } };*/
  - OSPProgressFunc progressCallback;
  + OSPProgressFunc progressCallback {nullptr};
  void *progressUserPtr;
  std::mutex progressMutex; // protect user callback function
  