Interview Questions - Design a circuit to detect which way the wheel is moving. Do not assume any fixed position for start.

We have a circular wheel with half painted black and the other half painted white. There are 2 censors mounted 45 degree apart at the surface of this wheel( not touching the wheel) which give a "1" for black and "0" for white passing under them. Design a circuit to detect which way the wheel is moving. Do not assume any fixed position for start.