id Software’s John Carmack Comments on Game Engine Development

John Carmack is well known, and well respected for his work in videogames—particularly in his development of FPS game engines such as those in Doom, Quake and most recently, Rage. His engines have served as strong backbones for games like Half-Life, the Call of Duty series, and other heavy hitters.

Responding to an article on Kotaku about the beauty of Doom 3’s source code, John Carmack added some comments of his own about his thought process while developing the engine and how he thinks the code is cleaner compared to his work on C++, as he considers it “a final evolution of [his] C style, rather than the first iteration of [his] C++ style.”

He explained how he “meandered” into C++ with the newer game, basically experimenting with the coding language. He wrote about how he wished he’d read up more on the language before jumping into it.

In some ways, I still think the Quake 3 code is cleaner, as a final evolution of my C style, rather than the first iteration of my C++ style, but it may be more of a factor of the smaller total line count, or the fact that I haven’t really looked at it in a decade. I do think "good C++" is better than "good C" from a readability standpoint, all other things being equal.

I sort of meandered into C++ with Doom 3 – I was an experienced C programmer with OOP background from NeXT’s Objective-C, so I just started writing C++ without any proper study of usage and idiom. In retrospect, I very much wish I had read Effective C++ and some other material. A couple of the other programmers had prior C++ experience, but they mostly followed the stylistic choices I set.

I mistrusted templates for many years, and still use them with restraint, but I eventually decided I liked strong typing more than I disliked weird code in headers. The debate on STL is still ongoing here at Id, and gets a little spirited. Back when Doom 3 was started, using STL was almost certainly not a good call, but reasonable arguments can be made for it today, even in games.

I am a full const nazi nowadays, and I chide any programmer that doesn’t const every variable and parameter that can be.

The major evolution that is still going on for me is towards a more functional programming style, which involves unlearning a lot of old habits, and backing away from some OOP directions.

Carmack has a much longer post up on the subject at the #AltDevBlogADay blog, which you can read here.