GEOM
[TILFMT_8BIT] = GEOM(0, 0, 1),
[TILFMT_16BIT] = GEOM(0, 1, 2),
[TILFMT_32BIT] = GEOM(1, 1, 4),
[TILFMT_PAGE] = GEOM(SLOT_WIDTH_BITS, SLOT_HEIGHT_BITS, 1),