Well, I guess it's partly because I'm not too great at understanding other people's code... even heavily commented. In theory, I suppose I might be able to learn more interesting/useful stuff if I work with the fs2_open engine, but for the time being, I'm going to wait to do that.
Another big thing is that this game takes place in four distinct areas of combat (in theory there could be more, as the areas are defined in a variable-sized data structure). The only interaction between these areas is when a ship jumps from one to another. Doing this in the FreeSpace engine would require a ton of work, and I think that work would have the end result of making my code unupdatable (that is, future changes to the engine could not be merged into my code, or vice-versa).
In effect, you would need to create a new object type (equivalent to my game's StarSystem class), containing all of the lists/arrays/vectors/whatnot that store ships, explosions, weapons, nebulas, backgrounds, beams, shots, missiles, etc.! Sure, some variables are global, but a lot have to be local to the StarSystem, and some have to be movable between them (ships, in particular).
On a sadder note,
I'm having trouble getting OpenGL to run right on Linux. Apparently, everything is dependent on Mesa, a software implementation of OpenGL. There is something called DRI, which uses hardware rendering, but I can't seem to enable it because I can never tell where stuff gets installed on Linux. So, until I get hardware rendering to work, there will be almost no advances in the code.
Also, future releases may require SDL to run, as that is what I have been using in Linux and I frankly think some of its built-in features trump some of those in Windoze (although it lacks some stuff that would be quite useful). For example, it is very easy to code joystick support in SDL (something Nuke has requested that I do when I get the chance, but that I was refusing on the grounds of my not having a joystick with which to test it).
I was wondering, though, how does FS1/FS2 do the 3d engine glows (retail, where they had 3d engine glows (i miss them oh-so-much))? Did they not scale slightly as the ship's velocity changed? Or was it that the uv-mapping of the flames scaled instead?