From DoomWiki.org
this is research into tall skies across ports and games. the info here may eventually be folded into Sky
doom skies are 128 tall 256 wide
they tile horizontally up to 4 times (default) but the skies can be defined as wider textures up to 1024 for no horizontal tiling
they tile vertically when the sky is visible low enough on the screen, either continuously or separately (e.g. exit teleport in MAP20:_Gotcha!_(Doom_II))
heretic/hexen
...add limited look up/down which made the sky tiling problem more acute. Therefore they made the sky patches taller - 200px - but the texture definitions remained at 128
hexen's texture definitions redefine the skies as 200px tall
XXX can you still cause the texture to wrap?