Vision-Based Fish Schooling (2D Ray-Cast Occlusion + Startle Cascade)

This 2D companion to the 3D vision-based schooling simulator keeps the same underlying idea — alignment driven by a limited field of view with line-of-sight occlusion, not omnidirectional metric sensing — but computes and measures it independently. Occlusion here is resolved by rasterized ray-casting rather than the 3D model's analytic bearing-interval sweep; close-range avoidance is driven by time-to-collision (τ) rather than plain inverse-distance repulsion, a real biologically-documented collision-avoidance variable; and a single-fish startle lets you measure — via a live regression fit — how fast the fright response actually propagates through the school as a wave, the same quantity behavioral ecologists measure in real schooling fish. Tune blind-zone width, vision range, school size, turning agility and ray-casting resolution, then startle one fish and watch the cascade speed converge.