i thought i knew, but im not so sure now. when someone says that like a game(lets say wolfenstein) was made from the quake 3 engine, what exactly happened? does that mean that they took the q3 source and modified it? or is it a set of methods that i would use in programming to make?
Anyone who ever writes a game from scratch immediately realizes that 95% of what he has done is generic and could be used again. Those who go on to game #2 actually get to share about 50%, after massive rewriting of game #1. those who get to game #3 might share 75%, after massive rewrites of games 1 and 2. About this time, they decide they have a game engine and start trying to convince others to just use their engine rather than going through the whole series of iterations.
Starting with some existing game engine can be a good idea, especially if the game engine in question has a lot of games under it’s belt, and the game you want to write has similar structure. You will save a lot of time, but you won’t (have to) learn as much of the nitty gritty.
If you want to write your own game engine, the thing to do is write a game and then save as much code as you can. If you just make a game engine, you end up with a bunch of stuff you don’t need and not the stuff that you do need.