The Terrain Texture
In Q3:TA, there are two “terrain” textures in the common shader script. One handles all the uses of terrain where the designer does not want “dust” to rise up as the player jumps onto the terrain (common/terrain). The second (common/terrain2) has an enable_dust surface parameter. The terrain texture should be applied to all visible (in game) surfaces of the terrain entity.
Q3map looks for the word “terrain” in the name of the shader when texturing terrain entities. If a shader is used without the word "terrain" in it, and it’s not marked as nodraw, q3map will still do a planar projection, but using that texture. It will not blend between textures, however. This can be used to create hard edge texture transitions, or in cases where you want to apply textures manually, and aren’t concerned about blending.
If the terrain texture is applied to a non-terrain entity brush, the surface will not draw. The projected terrain surface textures only work on surfaces that are a part of entities with the proper terrain entity keys and values.
Their scripts for terrain are as follows: