An infinite (no end-caps) O'Neill cylinder is held together by its rind: a thick, layered, braced foam — a Voronoi space-frame whose edges form a "monster truss" and whose plates seal compartments without cutting the load path. The spin that gives the interior its gravity also tries to tear the shell apart in hoop tension. rind is the toolkit for sizing that shell, scoring it with a real frame solver, and walking through the structure it generates.
The O'Neill cylinder model is built as four independent surfaces. rind is the structure; its siblings model the air inside, the ecology the air sustains, and the game played within.
Spin gravity g(r)=ω²r is full at the rim and falls to zero at the
axis. The same spin that makes the floor habitable loads the shell.
Every tonne on the inner surface pulls outward. The rind must take that as hoop tension and radial compression — at huge radius, a shell patch is a near-flat slab.
A layered Voronoi cell-cloud: the edges are the space-frame, the plates seal compartments. Doors and stairs are openings in plates, never cuts in edges — so every chamber is reachable without weakening the skeleton.
The geometry is generated in JS; the structural scoring is a real Rust/WASM frame solver (banded RCM + Cholesky). Dial it and watch the cylinder pass or tear.
Size the cylinder, generate the foam, solve it for stress, then read it in 3D — or walk through it on foot.
The structural + radiative scratchpad. Dial the radius, spin, material and safety factor; the closed-form estimate sizes the cable weave, and the frame solver sizes the real foam shell from its cell section. A live play-slice shows stacked floors of the foam coloured by the solver's actual stress — green holds, red overstresses — with the deflection exaggerated so you can see it carry load.
A 3D read of the layered foam: the annular shell slab as a cell cloud, density graded toward the hull where the spin-load lands. Orbit it, zoom, and slide a radial probe through the thickness to watch the structure change layer by layer — the same foam the cylinder tool solves, seen in the round.
Drop in as a denizen of the megastructure and walk a planar cut through the foam — a roguelike level extracted from the 3D cell-cloud by fitting a best-fit plane (PCA) through a region of cells and projecting the rooms and doors it passes. Climb ladders radially and the gravity shifts: lighter toward the core, heavier toward the hull.
Continuum tactics on the hull. Pick a faction hand, and a solver proves a fight winnable
before it's summoned — foes scaled to your stats and gear, terrain that blocks line-of-sight,
every encounter certified-but-not-trivial. Hold the field and climb the streak. (A combat sandbox
living on the structure wing; the tuner is at /combat/dojo.html.)
The upper rind's industrial deck: eight production engines (foundry · chemworks · mill · fab · weave · assembly · fluid · reclaim) as voronoi facilities with material flowing along each engine's line and the closed inter-engine supply chain, and six white-collar surfaces woven over all eight so every one touches every one. The contact is the complete bipartite graph K(6,8) realised as a plain weave (not the old gyroid) across two voronoi decks — enter once, pick a surface, tour all eight from its point of view.