SKY texture Last edited 11 months ago2023-12-21 20:40:44 UTC

SKY is a tool texture used to place skyboxes. Wherever it's applied to a brush face in a level will instead have the skybox rendered instead. A skybox is a set of 6 textures that wraps around an inverted box, and is statically rendered relative to the player i.e. moving around the map doesn't shift the perspective of the skybox textures in any way.

The actual texture shown during play is controlled by the map properties setting "Enviroment Map (cl_skyname)". The default is desert. Custom skies are normally added to the gfx/env/ folder and then selected in the map properties before compiling. You can find all the sky names that come with HL by looking in the gfx/env/ folder (for legacy WON installations, you will find them inside the pak0.pak file which you can open with any software that is capable of reading Quake PAKs files like PAKScape).

SKY textures must be applied to visible faces while the rest can be textured with NULL. SKY textures must be applied to ALL faces of the sky brushes, otherwise it will cause problems with sky lighting in newer versions of VHLT's HLRAD.exe.

VHLT also automatically generates clipnodes on SKY brushes, the same effect as a CLIP brush. This can be turned off by passing argument -noskyclip to HLCSG.exe. The original Half-Life SDK's compilers don't do this, allowing players to swim inside SKY brushes as if they were water brushes. Sky texture applied to brushes is treated differently during rendering. It does not generate extra wpoly's as normal texture does. Some tutorials tell you that it is good idea to use sky texture as a filler for large unseen areas, I have no evidence that this is a good method of reducing r_speeds, when the hint and skip textures are available. However, current best practice to reduce wpolys is to apply NULL on faces that shouldn't be visible e.g. backsides of walls that players can't get around to see.

In GL mode [not tested in software mode] the skybox doesn't hide level geometry behind it. The solution is to either further optimize VIS splitting using HINT brushes to try force occlusion of the offending areas, or to cover up problem areas with geometry or foliage.