This enumeration restricts barcode searching to certain orientations, or prioritizes one orientation over the other.

Values:

IG_TW_BD_HORZ	Horizontal mode.
IG_TW_BD_HORZVERT	Horizontal/Vertical mode.
IG_TW_BD_VERT	Vertical mode.
IG_TW_BD_VERTHORZ	Vertical/Horizontal mode.