string flags = features.create_flags();
string vertex_src = process_standard_source(standard_vertex_src, flags);
string fragment_src = process_standard_source(standard_fragment_src, flags);
string flags = features.create_flags();
string vertex_src = process_standard_source(standard_vertex_src, flags);
string fragment_src = process_standard_source(standard_fragment_src, flags);