I need some clarification on what the "correct" (as in will be supported by the engine) way of putting skies on walls. And I'd like to know what has been the popular method in most famous mods and map packs in the last few years.
Basically, take this screenshot from UDB's visual mode:
The cyan numbers label map elements with null textures. 1 and 3 are single-sided lines with null mid-textures. 2 has a null upper texture (though it doesn't really matter what texture you put there). 4 is a floor with null texture.
2 will show a sky and this is the proper id way to throw a sky on a wall.
3 is typically also used in doom mapping.
1 will show the sky as long as some flat with F_SKY1 is close to or within the visible camera frustrum (fov view cone). Otherwise it will show a black (or clearcolor) void.
4 will show the sky for the same reason 1 does. Technically 3 is also showing the sky for the same reason.
So the question is, should 1, 3, and 4 be treated as valid skies for:
a) Trace hits.
b) Projectile explosions and puffs.
c) Projectile bounces.
Right now, only 2 and the F_SKY1 flats (ceilings and floors) are treated as skies for the above three. Line horizons will nullify projectile explosions, puffs and bounces, but will not set the TRACE_HasHitSky flag on a linetracer even if ceiling or floor are set to F_SKY1.
There are many map making tutorials that show 3 as a valid way to make a recessed window in the wall show a sky. But the engine can certainly take a stand that method 2 is the only one that is owed support (in terms of behaviors (a), (b), and (c)). I don't know if the method-2-only path will allow for maps like those floating-platform ones from quake 3 without the use of stacked sector portals or 3d floors.
This should probably include reps from other ports, but unified consensus for this is important for some potential PRs to the engine concerning traces and skyviewpoint sectors.
