Overpicnum

overpicnum is similar to picnum, except it is used for walls to determine the picnum of a masked wall. Tile 0 is the ugly brown-brick texture, while 230 is the BIGFORCE texture, and 663 is H_FORCEFIELD. Other tiles can also be used with this. This does not set the overpicnum's visibility, which is done with bits 16 or 32 of Cstat(wall) instead.