This header contains declarations for functions in the HoloPlayCore dynamic library, which handles communication with the HoloPlay Service runtime.
A programmer looking to design a custom renderer for Looking Glass devices ought only to need the functions declared in this header file. They have simple arguments and return types, and are designed to be easily bound from any programming language and dropped into custom rendering pipelines.
Nearly all of them map directly to combinations of functions declared in libHoloPlayCore.h; they are provided for developer convenience and simple cross-language binding of functions that might return structs or opaque object pointers. For insight on how these work under the hood and more direct access to the data they provide, see that page.