I don''t think you''re using the term singleton correctly - singleton refers to a particular object-oriented design pattern.

In order for singleton to be at all useful, it must use polymorphism (and consequentially inheritence). Otherwise, it''s just a glorified global variable, which is the typical (ab)use.


...
The graphics engine is still written in C, the new ID game programmers think he''s crazy and finished the game using C++. ID uses a pipelined development process, Carmack does research and develops the next graphics engine, while the normal programmers finish the actual game (and then Carmack begins work on the next project).