web/math.js

// Pure fact primitives — no model, no state. (her-pattern: code owns the facts.)
// MediaPipe Hands 21-landmark indices we care about.
export const H = {
  WRIST: 0,
  THUMB_TIP: 4,
  INDEX_MCP: 5, INDEX_TIP: 8,
  MIDDLE_MCP: 9, MIDDLE_TIP: 12,
  RING_MCP: 13, RING_TIP: 16,
  PINKY_MCP: 17, PINKY_TIP: 20,
};

export const dist = (a, b) => Math.hypot(a.x - b.x, a.y - b.y);
export const mid = (a, b) => ({ x: (a.x + b.x) / 2, y: (a.y + b.y) / 2 });

// Exponential moving average — kills landmark jitter before it hits the audio.
export const ema = (prev, next, a = 0.5) => (prev == null ? next : prev * (1 - a) + next * a);

export const clamp = (v, lo, hi) => Math.max(lo, Math.min(hi, v));
// Linear normalize v in [lo,hi] -> [0,1], clamped.
export const norm = (v, lo, hi) => clamp((v - lo) / (hi - lo), 0, 1);
export const lerp = (a, b, t) => a + (b - a) * t;
// Exponential map t in [0,1] -> [lo,hi] (for perceptually-correct cutoff/freq).
export const expmap = (t, lo, hi) => lo * Math.pow(hi / lo, clamp(t, 0, 1));