function getKeypoints(glyphs) {
  /** @type { [ number, number, number ] } */
  const keypoints = [];
  const strokeWidth = hStrokeWidth();
  glyphs.forEach((glyph, gi) => glyph.forEach((contour, ci) => {
    const ends = detectEnds(contour, { maxStroke: strokeWidth * 1.5 });
    ends.forEach(pi => keypoints.push([gi, ci, pi]))
  }));
  return keypoints;
}
TODO: This is temporary
@param { { x: number, y: number, on: boolean }[][] } glyphs
@returns { [ number, number, number ][] }