Returns whether or not a point lies within a polygon (an array of vertices).

pointInPolygon.ts

// Hit testing algorithm

const ccw = (A: [number, number], B: [number, number], C: [number, number]) =>
	(C[1] - A[1]) * (B[0] - A[0]) > (B[1] - A[1]) * (C[0] - A[0])

export const intersect = (
	A: [number, number],
	B: [number, number],
	C: [number, number],
	D: [number, number]
) => ccw(A, C, D) !== ccw(B, C, D) && ccw(A, B, C) !== ccw(A, B, D)

/**
 * Get whether or not a given point lies within a polygon.
 * @param point A point (x and y).
 * @param vertices: An array of points.
 * @param minX (optional) The minimum x value to check against.
 */

export function pointInPolygon(
	point: { x: number; y: number },
	vertices: { x: number; y: number }[],
	minX?: number
): boolean

export function pointInPolygon(
	point: [number, number],
	vertices: [number, number][],
	minX?: number
): boolean

export function pointInPolygon(point: any, vertices: any[], minX = -999) {
	let ps = !!(point as { x: number; y: number }).x
		? [
				(point as { x: number; y: number }).x,
				(point as { x: number; y: number }).y,
		  ]
		: point
	let ts: [number, number][] = !!(vertices[0] as { x: number; y: number }).x
		? (vertices as { x: number; y: number }[]).map((p) => [p.x, p.y])
		: (vertices as [number, number][])

	let inside = false
	let i = 0
	let j = ts.length - 1

	while (i < ts.length) {
		if (intersect([minX, ps[1]], [ps[0], ps[1]], ts[i], ts[j])) {
			inside = !inside
		}
		j = i++
	}

	return inside
}