@typeonce/ritmo-math

ritmo-math holds the 2D helpers most games would otherwise rewrite, as plain data in and plain data out, built on Ops so they replay the same on every engine; it never ports a third-party algorithm, and determinism alone is never a reason to add one.

• Vec2: vector arithmetic on { x, y }, lengths, perpendicular, fromAngle and angle, moveToward, clampLength, and decayToward, an ease that is the same at any step rate.
• Angle: wrap into [-π, π) and turnToward the short way at a capped rate, for headings stored as one number.
• Scalar: moveToward, lerp, decayToward, and spring, a value with momentum that overshoots and wobbles back (squash, a pop), on plain numbers; both eases are the same at any step rate.
• Box2 edge boxes and Segment2 walls at any angle, with circle overlap tests and Box2.closestPoint.
• Collide2: swept circle collision against boxes and segments that slides along walls and never tunnels through them, circle against circle, and pushOut.
• FlowField: one search toward a goal that leads every body around the walls.

import { Collide2, FlowField, Vec2 } from "@typeonce/ritmo-math"

// Once: a flow field with 30-unit cells (a typed failure for a bad size).
const made = FlowField.make(30)
if (!made.ok) throw new Error(`bad cell size ${made.error.value}`)
const paths = made.value

// Each step: chase the player around the walls, sliding along them.
paths.setWalls(walls, radius)
paths.setGoal(player)
const way = paths.way(enemy) ?? Vec2.normalizeOr(Vec2.subtract(player, enemy), Vec2.zero)
const moved = Collide2.moveCircle(enemy, Vec2.scale(way, speed * dt), radius, { boxes: walls })

pnpm add @typeonce/ritmo-math @typeonce/ritmo

Values come in already validated: a position is a component the game's own schema checked when it entered the world (z.object({ x: z.number(), y: z.number() }) and the like), and every helper reads and returns that plain shape. There are no math value types to construct and no codecs here.

Determinism

Every helper that needs a non-exact function (cos, sin, atan2, exp, hypot) calls Ops from @typeonce/ritmo, so a session recorded in one browser replays on any other engine. Angle, Box2, Segment2, perpendicular, and the rest use only operations every engine rounds exactly. Game code that needs other math calls Ops directly; the ritmo/use-ops-for-math rule of @typeonce/oxlint-plugin-ritmo reports a Math call left in simulation code, and oxlint --fix rewrites it.

A broad phase (a spatial grid) is not here: the skill has one to copy into the game, sized to its own data.

Released together with @typeonce/ritmo, always with the same version.

Source: https://github.com/typeonce-dev/ritmo