vis doesn't render brushes with the 'detail' flag set. Much easier than func_walls.
func_walls and the "detail" flag do very different things.
Brushes with the "detail" flag will be ignored for VIS calculations.
Brushes that are made into func_walls are treated like entities, and are ignored by the BSP world vertex calculations and the VIS calculations.
For example: If you had an 8 sided barrel sitting in a square room, setting the barrel to detail would make the barrel invisible to the VIS process, but not the BSP process. Making it a func_wall would stop the barrel from chopping up the square room into irregular pieces, and be ignored by the VIS process. It would, however, draw the bottom face of the barrel over the floor, introducing the overdraw Jitspoe was talking about.
When Jitspoe suggested making brushes "detail", he did not mean they were substitutes for a func_walls, only that they will improve the compilation time because VIS will ignore them, and that func_walls shouldn't be used for compilation time improvements.
I will be leaving many of the barrels and boxes as func_walls because they are located next to complex triangle brushwork, and I do not want to exponentially increase the number of triangles in those areas. However, for large terrain pieces, I can make all of those brushes detail because I don't want them to contribute to VIS, and because the overdraw on such large irregular faces negates the improvements of making them func_walls.
- Cusoman