That is the point: the "drawing code" is perhaps 20% of a game engine. You are missing asset management (loading, streaming, caching...), audio (big enough to

That is the point: the "drawing code" is perhaps 20% of a game engine. You are missing asset management (loading, streaming, caching...), audio (big enough to split into libraries and actual audio engines), input (of different kinds), networking (big enough to split too), AI, scripting, physics...