freesewing/packages/tutorial/src/step3.js

export default function(part) {
  let { Point, points, Path, paths, measurements, options } = part.shorthand();

  let tweak = 1;
  let target = (measurements.headCircumference * options.neckRatio) / 4;
  let delta;
  do {
    points.right = new Point((tweak * measurements.headCircumference) / 10, 0);
    points.bottom = new Point(0, (tweak * measurements.headCircumference) / 12);

    points.rightCp1 = points.right.shift(
      90,
      points.bottom.dy(points.right) / 2
    );
    points.bottomCp2 = points.bottom.shift(
      0,
      points.bottom.dx(points.right) / 2
    );

    paths.neck = new Path()
      .move(points.right)
      .curve(points.rightCp1, points.bottomCp2, points.bottom);

    delta = paths.neck.length() - target;
    if (delta > 0) tweak = tweak * 0.99;
    else tweak = tweak * 1.02;
  } while (Math.abs(delta) > 1);

  return part;
}