: Oh yeah for sure. I didn't choose my words properly - the Halo skyboxes
: clealy make use of 2D 'matte' backgrounds. I was more referring to tricks
: for accessible environments. That doesn't really translate well from
: movie-context matte paintings :P (perhaps more like the difference between
: a green-screen matte background, and Indiana Jones' warehouse foreground
: matte; though that's still nothing like video game graphical 'tricks', per
: the link GB provided in the parent reply).

: I do believe I've seen 3D skyboxes though, mostly in the context of
: cityscapes, where if you move a lot, you can slightly see the parallax
: effect on some background rendered 'objects'; I would presume the player
: location is reduced a number of factors and used for rendering within an
: external box that's nowhere near the size of the outside environment (eg,
: move 5m here, move 5 mm there).
: butanywhay...

There are a lot of ways to do it. There's the method you linked, of course. Having a texture or a few textures mapped onto the inside of a cube or sphere is kind of the "traditional" way to do it, and you can choose between having it be real geometry that's really in the direction it looks like it's in with fake distance and depth or having a sort of surrogate that's mapped onto/into that area-- this was how Half-Life (and maybe other games in the series?) did its skybox, it would have a (very) small room in some inaccessible place in the map geometry (or outside of the geometry) that had the appropriate texture(s) applied to its insides, which would be mapped to the skybox, so you could just change the texture(s) in there to change the skybox, and IIRC if you used noclip to get inside it the graphics would get glitchy. Along with any of those, you can have flat objects in front of the skybox with the point generally being to add an illusion of much more depth while actually having only a little more depth (a 2D object has no depth at all, actually, but two of them layered together do). Having these distant extra 2D objects became more feasible along with having simple 3D objects way out there so the graphics engine can use most of the same tricks that make the main area of a map look three-dimensional to add depth to the background.
I think so anyway, someone could come and correct me and that would be fine.