message: implement a "default obj" material for the obj importer
diff: @@ -142,6 +142,9 @@ namespace ospray::sg {
  materialRegistry.add(defaultMat);
  ////////////////////////////////////
  + defaultMat = createNode("obj_default", "material_obj");
  + materialRegistry.add(defaultMat);
  +
  size_t baseMaterialOffset = materialRegistry.children().size();
  for (auto m : materialNodes)
  @@ -216,7 +219,7 @@ namespace ospray::sg {
  std::transform(shape.mesh.material_ids.begin(),
  shape.mesh.material_ids.end(),
  mIDs.begin(),
  - [](int i) { return i + 1; });
  + [](int i) { return i + 2; });
  mesh.createChildData("material", mIDs);
  #endif
  