Method update

core/progress.cpp:20–26

  }

  void Progress::update(size_t delta)
  {
    std::lock_guard<std::mutex> lock(mutex);
    current = std::min(current + delta, total);
    if (!func(userPtr, double(current) / double(total)))
      cancel();
  }

  void Progress::submitUpdate(Engine* engine, const Ref<Progress>& progress, size_t delta)
  {