Things aren't nonlocal in geometrical optics though. Something happens at C at the instant in time when the particle is at C. You can start a ray at any point i

Things aren't nonlocal in geometrical optics though. Something happens at C at the instant in time when the particle is at C. You can start a ray at any point in any direction, and just follow a straight line until you hit something. Then you determine what happens next based on local information at that point, and you continue. Ordinary tennis balls have the same property that the path from A to B can be altered by putting a wall at C. By the way, wave optics is already QM in some sense. Maxwell's equations are the analogue of the Schrödinger equation for light. Geometrical optics is the analogue of classical mechanics.