Function isPointInPolygon

packages/ui/src/hooks/use-pointer-in-transit.ts:45–60

(point: Point, polygon: Polygon)

// Determine if a point is inside of a polygon.
// Based on https://github.com/substack/point-in-polygon
function isPointInPolygon(point: Point, polygon: Polygon) {
  const { x, y } = point
  let inside = false
  for (let i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
    const xi = polygon[i].x
    const yi = polygon[i].y
    const xj = polygon[j].x
    const yj = polygon[j].y

    // prettier-ignore
    const intersect = ((yi > y) !== (yj > y)) && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
    if (intersect) inside = !inside
  }

  return inside
}

// Returns a new array of points representing the convex hull of the given set of points.
// https://www.nayuki.io/page/convex-hull-algorithm