To prevent anything beyond a certain distance from being rendered, distance-culling, You could add these keys to the worldspawn-entity:
"_fog" "textures/mapname/fogshader"
"fogclip" "4096"
"_farplanedist" "4096"
A shader like this will create the fog. Anything further than 4096 units (opacity) away from the player will go up in fog, and will not be seen…you just see the fog-color ( r g b ):
textures/mapname/fogshader
{
qer_editorimage textures/mapname/qer_fogshader.tga
surfaceparm nodraw
surfaceparm nonsolid
surfaceparm trans
surfaceparm fog
fogparms ( 0.5 0.5 0.5 ) 4096 // ( r g b ) opacity
}
Use the console-command /r_showtris 2 to see that anything beyond 4096 units is not drawn at all.
…these forums have lots of topics about fog issues,
like this one from 2003:
http://www.splashdamage.com/forums/viewtopic.php?t=2106