jsketcher/web/app/math/convex-hull.js

export function ConvexHull2D(points) {
  points.sort(function (a, b) {
    return a.x != b.x ? a.x - b.x : a.y - b.y;
  });

  const n = points.length;
  const hull = [];

  for (let i = 0; i < 2 * n; i++) {
    const j = i < n ? i : 2 * n - 1 - i;
    while (hull.length >= 2 && removeMiddle(hull[hull.length - 2], hull[hull.length - 1], points[j])) {
      hull.pop();
    }
    hull.push(points[j]);
  }
  hull.pop();
  return hull;
}

function removeMiddle(a, b, c) {
  var cross = (a.x - b.x) * (c.y - b.y) - (a.y - b.y) * (c.x - b.x);
  var dot = (a.x - b.x) * (c.x - b.x) + (a.y - b.y) * (c.y - b.y);
  return cross < 0 || cross == 0 && dot <= 0;
}