Stellarium 0.12.3 . ... Renderer is composed of interface classes abstracting away low-level graphics work, and backend classes either derived from or used by the interface classes. ... It constructs other graphics classes (textures, vertex and index buffers, etc.) and sets graphics state (global color, depth test mode, etc.) ... The reason is not templating; the API class and backend are separate so the former is owned by user code, while the latter might be owned by the renderer backend. ...