ty = top Y      tx = top X      by = bottom Y   bx = bottom X
A1 -> ty 0 tx 0 by 49 bx 49
A2 -> ty 0 tx 50 by 49 bx 99
B1 -> ty 50 tx 0 by 99 bx 49
B2 -> ty 50 tx 50 by 99 bx 99