When modern GPU graphics are used, it's assumed that an API layer is also used. This allows the drivers to implement the API specification within approximations

When modern GPU graphics are used, it's assumed that an API layer is also used. This allows the drivers to implement the API specification within approximations appropriate to the hardware. The OS, drivers and API all collaborate to provide a consistent abstraction similar to a file system or sockets; a header file is included to use the API, and the initialization process creates a GPU context, which allows binding of resources etc. There are some examples of direct register programming, but nearly all come from gaming consoles with fixed hardware and tight performance budgets. Vulkan is simply the lowest-level approach currently available among the major APIs. Piet is an example of a rendering engine that stands on top of Vulkan: it still needs application code to be a complete renderer, but it provides higher level abstractions that speak in the desired domain language(shapes, vector data, etc.).