About Felinotype

Felinotype is a small interactive demonstration of a remarkable idea: that the patterns we observe on living animals — the stripes of a tabby, the spots of a leopard, the spirals on a shell — can be generated by the same kind of mathematics that governs how chemicals react and spread.

The idea is Alan Turing's. In a 1952 paper, The Chemical Basis of Morphogenesis, he proposed that a system of two interacting substances — one activator, one inhibitor — diffusing across a tissue could spontaneously break symmetry and produce stable, complex patterns. These are now called Turing patterns, and the family of equations that produce them are reaction-diffusion systems.

Gray-Scott

The particular system Felinotype uses is the Gray-Scott model, a two-variable reaction-diffusion equation:

∂u/∂t = D_u ∇²u − uv² + f(1 − u)
∂v/∂t = D_v ∇²v + uv² − (f + k)v

Two scalars, u and v, drift across a grid and react with each other. The parameters f (feed rate) and k (kill rate) shape the result: a narrow region in (f, k) space produces spots, stripes, mazes, and a peculiar slowly-shifting marble pattern. Outside that region everything either dies or fills uniformly.

Each input string in Felinotype is hashed and used to pick a deterministic (f, k) pair from inside this region. The pattern is then simulated for 240 timesteps on a 64×64 grid, masked by one of five hand-drawn cat silhouettes, and rendered as pixel art.

The cat

The silhouette is not procedural — it's one of five poses (sit, loaf, sleep, play, stretch), selected from the same hash. The eyes are drawn on top with a colour pulled from a small set of accent hues. The name and lineage come from a Markov chain over real feline names and a modest library of Latin-style epithets.

Every cat is fully deterministic from its seed. Two visitors typing the same string will see the same animal.

Further reading

• Turing, A.M. The Chemical Basis of Morphogenesis. Phil. Trans. R. Soc. B 237 (641): 37–72.
• Pearson, J.E. (1993) Complex Patterns in a Simple System. Science 261: 189–192.
• Notes — short pieces on the mathematics