This was reported at Slashdot a couple days ago, but John Carmack has now set up his very own blog to talk about nerd stuff.

While talking about the delay of releasing the Quake 3 source under the GPL, he makes this small off-hand comment:

There are still bits of early Quake code in Half Life 2 [snip]

Of course this is getting some people in the community riled up. Valve has stated that the Source engine is 100% new technology. So how can JohnC come out with a statement like this? (Especially if he hasn’t seen the source… or has he?)

Well I can think of one possibility. That the code that is still in the engine from Quake 1 is merely code used to process input and player movement. Notice that movement in the Half-Life 2 world is very similar to that of Half-Life (and Quake), meaning there is no “bobbing” or slight movement of the player’s view to simulate walking (see games based on Quake 2 and 3 to see the difference). The rendering code is obviously new, the sound code is way more advanced than anything Quake had, Havok is a new addition, and of course Steam is a Valve original. So that leaves only the input code unspoken for. And since that code works fine, why re-write it? It certainly cannot be put in the same category as game engine technology, and that could be why there is no notice on the game box or anywhere else that Half-Life 2 contains technology licensed from id Software, like one can find on Half-Life’s box.

Disclaimer: IANAP (I am not a programmer)