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))
...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?
from ETTiNGRiNDER (talk) 10:06, 5 November 2018 (CST): Nwhen it comes to vanilla Heretic and if I'm not mistaken vanilla Hexen to the same degree, you can't really get the default skies to tile vertically in a nice manner. Restrictions on freelook angle prevent you from seeing above the top of the sky, but if you construct a level that lets you see below the bottom, which is fairly easy to pull off by putting the player in a sector with a high floor and letting them look out across a vista that uses the lowered sky ceiling trick to bring the background sky area below their foot height, you get tutti-frutti effect at the point of tiling due (I presume, as it's how TFE generally works) to 200 not being a "proper" texture height. I've been meaning to try making a WAD with a 128-tall (256-tall might be worth trying as well) vertically tileable sky texture to see what result it gets in those games but I've yet to do so.
allows alternative sky textures but does not alter the rendering approach
skybox portals: completely alternative sky rendering http://eternity.youfailit.net/index.php?title=Portal#Skybox_Portals
in software only: sky stretching
- solves tiling above the horizon but not below it.
- tweaked by a client console variable, so not a map property
- minimum height to avoid any vertical tiling is 544px
- possibly a deprecated feature (r_stretchsky is marked as deprecated)
hardware rendering (gzdoom): spherical projection instead of standard
- sky rendered twice; upper rendering takes priority if sky patch (or texture?) is taller
alternatives: sky boxes (software or hardware rendering)
provides custom sky patches to avoid vertical tiling (no engine changes to the behaviour from vanilla?)
seems 420px tall is required to avoid tiling (interesting lower number to software zdoom)
does that mean russian doom supports tall (>255) patches? https://doomwiki.org/wiki/Picture_format#Tall_patches
alternative skybox in GL only via https://zdoom.org/wiki/GLDEFS