Let say I wanted to make a level-based game taking place inside a bunker. Would I just make the underlying level geometry as one 3d model including all walls, ceilings and floors, or would I divide it into models for each room, or even for each surface?
The most common practice nowadays is to build it with modular assets, and part of the games build process is to combine static meshes that share a material so it can be rendered more efficiently. This is a oversimplification of a complex topic, and there are far more advanced tools now. Most terrains aren’t even modelled anymore, but generated and sculpted in engine using PCG tooling.
Note, this is mostly for the contemporary AA and AAA games industry.
From what I remember ftom modding and just playing games from a while ago, often there is “level geometry” (which can be subdivided into parts if needed), for example, ground and hills in Fallout, city block in GTA; and then there is “decor”, repeated assets, such as trees, fences, pipes, obstacles, etc. This asset repetition is particularly noticeable in Fallout 3/NV, and somewhat in Stalker (mostly on abandoned cars)
Usually modular.
Depends on the game engine, and the game. But it’s usually not one big thing. Also keep in mind a lot of how a game engine imports the data could be doing quite a bit behind the scene. So, refer to the engine docs or communities.
It depends on what you’re going for and how much time you want to spend on it.
If the bunker is far off in the distance from the player and they’re never meant to see it up close, you’re best off making one big 3D object that contains everything.
If you want to be more detailed, like you’re making a VR game and want realistic effects like what you see from Half Life Alyx, you’ll want to take your time and build the bunker into as many small pieces as you can. The player will likely be picking up objects and holding them and examining them, turning it around and looking at all sides. For best results, you’ll want each object to be its own thing built from the ground up.
But it really depends on what you’re aiming for. And Half Life Alyx is actually the exception for VR games. Most use very low quality assets and don’t put too much thought like Valve did. But if that’s what you’re aiming for, that’s your best bet.
It depends on how much time you want to spend, or money if you’re going to pay others to make the assets for you. Most solo devs aren’t putting that much effort or money into their project. A bigger team may do it.
As for the bunker itself, same deal here. Some people will build out the bunker into separate pieces. I’ve done this in some levels where I’ve taken 4 long rectangles to make a room rather than getting a solid rectangle room and then hollowing it out.