Render modes (GoldSrc)
0 - Normal
Brushes are lightmapped and opaque, regardless of if they have { textures. renderamt and rendercolor are unused outside of scrolling textures. worldspawn brushes always use this render mode.
1 - Color
Allows sprites to be tinted with rendercolor. Same as texture on brushes and MDLs.
2 - Texture
Enables translucency via renderamt, and alpha-tests { textures on brushes. Causes brushes to be fullbright.
3 - Glow
Only valid on sprites. Like additive, but renders the sprite at the same size regardless of distance from the camera.
4 - Solid
Same as Normal, but alpha-tests { textures on brushes. renderamt 0 is treated as invisible, but all other values are full opacity for non-alphatested texels.
Bug:Sorted as translucent by the renderer, even though it should be part of the opaque pass; this can cause sorting issues with fog. If this is an issue, use an MDL instead. (tested in: hl25)4 - Additive
Renders the sprite, brush, or MDL using additive translucency (glBlendFunc(GL_ONE, GL_ONE)). renderamt can be used to reduce opacity.