VertexLitGeneric Textures On Brush Faces
Materials that use the VertexLitGeneric as their shader will render incorrectly when applied to brush faces, which require lightmapped materials. If the lightmaps flicker, the brightness changes relative to where the player views the texture, or the face is displayed full black, a vertex lit material is likely to have been used. Materials listed in Hammer in the
models/ directory are all vertex lit, and should not be used on brushes, but they may not be the only textures with this shader. The
decals/ directory also contains vertex lit materials, and should not be used on brush geometry.
The easiest fix is to look for equivalent materials with the same name that are not in these directories. These materials will render correctly as they use the correct shader.
Another approach is to write a new VMT that changes the shader to LightmappedGeneric, the .vmt will need to be copied out of the GCF file first and given a new name. Further instructions on writing and editing a .vmt can be found in the Material tutorial, the .vtf is already included with the game so the first part of the tutorial may be skipped.
To do: Get some pictures of classic examples