Core

import { closestIndex, invertValue, makeScale, scaleValue } from "@delacour/react-native-charts/core";

@delacour/react-native-charts/core is every number the package computes and nothing that draws. Nothing under it imports a runtime value from React, React Native, Skia, Reanimated or Gesture Handler, which is what lets a legend or a tooltip do scale arithmetic without mounting a canvas — and what lets the whole of it run under bun test with no simulator.

import { buildTicks, makeScale, scaleValue } from "@delacour/react-native-charts/core";

const y = makeScale({ kind: "linear", domain: [0, 240], range: [200, 0], nice: true });
const ticks = buildTicks(y, { count: 4 });
const zero = scaleValue(y, 0);

A scale is data

d3's scales are closures, and a closure cannot be read on the UI thread. makeScale lets d3 do the nicing and the time arithmetic, then throws the closure away and returns a ScaleDescriptor of plain numbers. Everything downstream — the marks, the ticks, the scrub — reads that.

type ScaleDescriptor =
  | { kind: "linear"; domain: [number, number]; range: [number, number] }
  | { kind: "time"; domain: [number, number]; range: [number, number] }
  | { kind: "log"; domain: [number, number]; range: [number, number]; base: number };

A degenerate input returns a finite number, never NaN: a zero-width domain maps to the range midpoint, a collapsed plot rect stays a rect, an unreadable log domain yields no ticks rather than -Infinity ones. One NaN written into a shared value freezes a chart permanently with nothing on screen to say why, so the guard is at the bottom rather than at every call site.

The flat worklets

Six functions carry a "worklet" directive and run on the UI thread every frame of a scrub: scaleValue, invertValue, closestIndex, getYForX, readAt and sliceIndexAt. Each calls nothing and closes over nothing but module-scope constants — a module-scope worklet that called another would bind at import time and hand the UI thread undefined is not a function the moment a finger landed. A worklet you build inside a hook is captured by ordinary closure and may call any of them, which is how the scrub gesture composes closestIndex and getYForX without duplicating either.

Scales and ticks

Curves and paths

Every builder returns an SVG path string. This module cannot import Skia's path builder; toSkPath in the React surface parses the string.

Geometry

Interaction

Animation

Polar

Utilities