@technobuddha/library
Version:
A large library of useful functions
46 lines • 3.23 kB
JavaScript
import { crossProduct } from "./cross-product.js";
/**
* Computes the convex hull of a set of 2D points using the Monotone Chain algorithm.
* @see {@link https://en.wikibooks.org/wiki/Algorithm_Implementation/Geometry/Convex_hull/Monotone_chain#JavaScript| Monotone Chain}
* @param vertices - An array of points.
* @returns The convex hull as an array of points in counterclockwise order, or `undefined` if there are fewer than 3 vertices.
* @example
* ```typescript
* convexHull([
* { x: 0, y: 0 },
* { x: 1, y: 1 },
* { x: 2, y: 0 },
* { x: 1, y: -1 }
* ]);
* // hull is now the convex hull of the points
* ```
* @remarks
* - The returned array does not repeat the starting point at the end.
* - Points on the edge of the hull may be included or excluded depending on their order.
* @group Geometry
* @category Polygon
*/
export function convexHull(vertices) {
if (vertices.length < 3) {
return undefined;
}
const points = vertices.toSorted((a, b) => a.x - b.x || a.y - b.y);
const lower = [];
for (const point of points) {
while (lower.length >= 2 && crossProduct(lower.at(-2), lower.at(-1), point) <= 0) {
lower.pop();
}
lower.push(point);
}
const upper = [];
for (const point of points.reverse()) {
while (upper.length >= 2 && crossProduct(upper.at(-2), upper.at(-1), point) <= 0) {
upper.pop();
}
upper.push(point);
}
upper.pop();
lower.pop();
return lower.concat(upper);
}
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