message: fix plane in example viewer
diff: @@ -189,7 +189,6 @@ void parseCommandLineSG(int ac, const char **&av, sg::Node &root)
  void addPlaneToScene(sg::Node& world)
  {
  - #if 0
  auto bbox = world.bounds();
  if (bbox.empty()) {
  bbox.lower = vec3f(-5,0,-5);
  @@ -208,23 +207,26 @@ void addPlaneToScene(sg::Node& world)
  auto position = std::make_shared<sg::DataArray3f>((vec3f*)&vertices[0],
  size_t(4),
  false);
  + position->setName("vertex");
  +
  osp::vec3i *triangles = new osp::vec3i[2];
  triangles[0] = osp::vec3i{0,1,2};
  triangles[1] = osp::vec3i{1,2,3};
  auto index = std::make_shared<sg::DataArray3i>((vec3i*)&triangles[0],
  size_t(2),
  false);
  + index->setName("index");
  +
  auto &plane = world.createChild("plane", "Instance");
  auto &mesh = plane.child("model").createChild("mesh", "TriangleMesh");
  auto sg_plane = mesh.nodeAs<sg::TriangleMesh>();
  - sg_plane->vertex = position;
  - sg_plane->index = index;
  + sg_plane->add(position);
  + sg_plane->add(index);
  auto &planeMaterial = mesh["material"];
  planeMaterial["Kd"].setValue(vec3f(0.5f));
  planeMaterial["Ks"].setValue(vec3f(0.6f));
  planeMaterial["Ns"].setValue(2.f);
  - #endif
  }
  int main(int ac, const char **av)
  