Fable and I built beautiful, modern recreation of OE-CAKE, a beloved physics sandbox toy, with a high-performance deterministic particle physics engine under the hood! Introducing: SunaBox (and SunaEngine). Runs in your browser, and check out the "Pachinko Proof"!

SunaBox is a love letter to OE-CAKE, the viral physics simulator released by Prometech in 2008!

It includes a 1:1 recreation of the OE-CAKE interface (select Classic mode at the top!) and even lets you import your old OE-CAKE .oec files directly. I would say OE-CAKE parity is around 93%, and getting better all the time.

SunaEngine is a novel, cross-platform particle physics simulator that relies on integer calculations (rather than floating-point) and order-independent accumulation to always deliver the same result in any WebGPU-compatible browser.

SunaBox takes advantage of this by letting you export recordings of your sessions as lightweight .sunar files, which only needs to store the simulator's initial state plus your inputs. Recorded and shared simulations can be scrubbed back and forth smoothly like video, and they always play back exactly the same, on any device, *bit-identically*.

This enables all sorts of interesting possibilities, like low-latency, cross-platform multiplayer physics! If every machine calculates physics the same way, then the physics data doesn't need to be streamed over the network, only the inputs.

Three live proof demos on the SunaEngine site, all simulating live on your GPU, all hashing their entire state as you watch:

- The Twin Simulations: two independent sims, same scene, same input schedule, never communicating. Stir either one with your cursor; your input is quantized to substep indices and fed to both. The 256-bit hashes stay identical, interaction after interaction.

- The Pachinko Proof: an ordinary float solver runs the same pachinko machine twice. One pane adds contact forces in ascending order, the other descending. That is exactly the difference two GPUs or two drivers introduce on their own. The balls never finish in the same bins twice. The integer engine runs the same machine to the same digest, loop after loop.

- Recording, playback, and smooth rewind: particle fluids cannot be rewound in floating point. Chaos amplifies the last bit of every velocity in reverse too. Here you stir a pool, it records your inputs, verifies the replay byte for byte against the run you just performed, and then hands you a scrubber. Drag your own splash backwards through time.

Replay hashes have been verified matching across Apple M series, an iPhone, a Steam Deck (AMD), Intel Integrated and NVIDIA (RTX 2070S).

Our workflow was fairly simple: I came up with the ideas, Claude did the math, the code, and the adversarial review. I provide the qualia-type feedback, shaping and tuning the feel of everything in the sandbox:

You can also wishlist SunaBox on Steam ! 140k particle caps, community/workshop features, hardware optimization, and more, coming soon!