typedef int PK_SHELL_type_t; This datatype indicates the type of a shell. One of these values: PK_SHELL_type_acorn_c shell has a single acorn vertex PK_SHELL_type_wireframe_c shell has one or more wireframe edges PK_SHELL_type_wireframe_free_c shell has no wireframe edges, but one or more faces PK_SHELL_type_mixed_c shell has both wireframe edges and faces