   Sky system.
  I wonder about the sky system in, for example, Halo. Is it just a skybox with a high-res texture, or do they use something else?/ Christoffer   
  Both actually. A skybox made with hi-res textures.You have the option of your typical skybox, or a skydome like in Morrowind or WoW, or a skyplane a la Cube, HL, Q2, those age games. You can even do atmosphereic scattering which looks really good, but is a little more resource hungry and isn't really suited for shooters.   ;  for stuff like this i usually refer to The good-looking textured light-sourced bouncy fun smart and stretchy page.Check out this clouds article.  You would use this to texture a skybox   ;  There are also some nice links in Forum FAQ.   ;  Cube, HL and Q2 all used regular skyboxes. Unreal had an additional moving plane for clouds, and Q3A does a funny texture mapping trick to create a sky dome with cubical geometry (drawn on the same polygons as the skybox perhaps?).   ;  Half-life 2 does something a bit different - as far as I can see it's a box containing geometry with billboarded clouds rendered behind all level geometry (although usually the only geometry in it is the tower in the middle of city 17).   