Exact movement rules

walkable face (45° or less)   steep face   other

walk points the rules applied   points cut off

fall and velocity   a facet touched   the ground

The body is a vertical octagonal prism under kinematic rules (engine/DESIGN-EXACT-MOVEMENT.md). The kernel (engine/kernel, in WebAssembly) computes each tick and names its witness; the page's own checker (exact-rules.js, written from engine/SPEC-EXACT-FALL.md and SPEC-EXACT-WALK.md) checks it before it is applied.

It stands on a walkable face, or in a level crease where gravity cannot move it; anywhere else it slides. It walks up to 1 m a tick, steps up by up to 0.35 m, strides across gaps up to 1 m, and can jump from a steep face it rests on, with less force. Air steering works only when touching nothing.

Between ticks you see the client's prediction of the tick in progress. Walking starts the moment you press a key, and the walk sent at the tick is the one you saw. Jumps and air steering take effect at the next tick. Turn off Smooth between ticks to see only the positions the ticks applied.

The magnifier shows the feet from the side at grid scale: one cell is one grid unit, 2⁻⁹ m ≈ 1.95 mm.

Cells draws the index's cells around the body, 2 × 1 × 2 m, green where they list few solids and red near the cap of 128 (a solid is listed in every cell its box, grown by the body's reach, meets). In the full city it also draws the 32 m sectors solids are stored in (grey), the 128 m tiles (orange), and the tiles the kernel holds (blue), at the body's feet.

San Andreas (full city) is the whole map. Its collision is the map's hulls, baked for the prism, held to the index's density cap, in tiles of 128 m. The kernel and the checker hold the 3×3 tiles around the body, and the overlay draws them. The textured city is the San Andreas web viewer's bake (~/build/web3d), drawn by its rendering code, ported here. It needs a desktop GPU, and loads about 750 MB once.