Function ibilerp

source/lerp.js:32–66

(point, corners)

// based on https://iquilezles.org/articles/ibilinear/
// adapted by Magnogen https://magnogen.net/
export const ibilerp = (point, corners) => {
  const p = point;
  const [a, b, d, c] = corners;

  const e = subtractVector(b, a);
  const f = subtractVector(d, a);
  const g = addVector(subtractVector(a, b), subtractVector(c, d));
  const h = subtractVector(p, a);

  const k2 = crossProductVector(g, f);
  const k1 = crossProductVector(e, f) + crossProductVector(h, g);
  const k0 = crossProductVector(h, e);

  // If edges are parallel, this is a linear equation
  if (Math.abs(k2) < 0.0001) {
    const x = (h[0] * k1 + f[0] * k0) / (e[0] * k1 - g[0] * k0);
    const y = -k0 / k1;
    return [x, y];
  }

  // Otherwise, it's a quadratic
  let w = k1 * k1 - 4 * k0 * k2;
  w = Math.sqrt(w);

  const ik2 = 0.5 / k2;
  let v = (-k1 - w) * ik2;
  let u = (h[0] - f[0] * v) / (e[0] + g[0] * v);

  if (u < 0.0 || u > 1.0 || v < 0.0 || v > 1.0) {
    v = (-k1 + w) * ik2;
    u = (h[0] - f[0] * v) / (e[0] + g[0] * v);
  }

  return [u, v];
};