How can I determine whether a 2D Point is within a Polygon?

Question

I\'m trying to create a fast 2D point inside polygon algorithm, for use in hit-testing (e.g. Polygon.contains(p:Point)). Suggestions for effective tech

Answer 1

Swift version of the answer by nirg:

extension CGPoint {
    func isInsidePolygon(vertices: [CGPoint]) -> Bool {
        guard !vertices.isEmpty else { return false }
        var j = vertices.last!, c = false
        for i in vertices {
            let a = (i.y > y) != (j.y > y)
            let b = (x < (j.x - i.x) * (y - i.y) / (j.y - i.y) + i.x)
            if a && b { c = !c }
            j = i
        }
        return c
    }
}