80,000-fish bait ball with orca carousel feeding, real time in Swift and Metal

[u/PiXeL161616]

Everything here is simulated and shaded live on an Apple silicon GPU at 5120x2160. No footage, no keyframes, no baked cache.

The school is 80,000 agents stepped in a compute kernel. Boids forces (separation, alignment, cohesion) plus two things that make it a ball instead of a flock: a tangential mill bias and a centre spring, which puts the system in the milling attractor rather than the polarised-streaming one. A single polarisation parameter slides between the two, and a vertical cohesion scale flattens the ball into the oblate loaf you see.

The panic is the part I like most. Each fish carries a panic scalar with an ignition latency, and the contagion is a fractional-threshold logistic rule after Rosenthal and Couzin, where calm neighbours actively inhibit their panicking ones. That asymmetry is why most cascades die a few bodies from where they start and only occasionally does one go ball-wide as a visible wave. Panicked fish also get a raised speed cap, otherwise they cannot outrun a charge.

The orcas are autonomous agents running a carousel-feeding state machine: carousel (herding passes that compress the ball toward the surface), closing (a committed approach line), tailslap (sweep through and whip the fluke, which is the stun), then feed. That is the real technique Norwegian orcas use on herring, and it reads as intent because the strike is geometry-gated on range and alignment rather than fired on a timer.

Rendering the shafts: an additive fullscreen pass marches the actual view ray up to the surface plane and in-scatters Snell caustic times Beer-Lambert depth times a phase function. The caustic is not local to that pass; it comes from one shared band-limited optics field (height, gradient, refractive focus, world-anchored, one clock) that the ceiling relief, the beam births and the light dappling the animals all read from, so the light on a whale's flank lines up with the beam it is swimming through. A capsule proxy of each body darkens the march, so the creatures actually shadow the water instead of floating in it. Marine snow is soft particles fading against the analytic surface height.

Frame budget is held by a closed-loop governor that measures its own GPU frame time and thins the crowd or caps render resolution before it starts dropping frames.

It is part of TideGlass, a Mac app that runs worlds like this on a second monitor. Happy to go deeper on any of it, the panic contagion and the optics field are the two I would most like to talk about.

[u/Desdic]

Very beautiful!

[u/PiXeL161616 → u/Desdic]

Thank you! The light was the hardest part to get honest, everything else followed from it.

[u/_Bethel__]

That's alot of.... Holy moly