// brushside    n_brushsides    texture
00 00 00 00     01 00 00 00     00 00 00 00
01 00 00 00     02 00 00 00     01 00 00 00
00 00 00 00     00 00 00 00     02 00 00 00

// brushsides lump
// plane        texture
00 00 00 00     00 00 00 00
01 00 00 00     01 00 00 00
02 00 00 00     02 00 00 00