Isometrisk spil matematik

Kode 

var Vector = function(x, y) {
    this.x = x;
    this.y = y;
};

Vector.prototype.set = function(x, y) {
    this.x = x;
    this.y = y;
};

Vector.prototype.dot = function(other) {
    return this.x * other.x + this.y * other.y;
};


var Polygon = function(points) {
    this.points = new Array(points.length);
    for (i in points) {
        this.points[i] = points[i];
    }

    //These two are used to avoid creating new vectors
    //each time containsPoint is called
    this.v1 = new Vector(0, 0);
    this.v2 = new Vector(0, 0);
};

Polygon.prototype.containsPoint = function(point) {
    var p = this.points, p1, p2, i,
        v1 = this.v1, v2 = this.v2;

    for (i = 0; i < p.length; i++) {
        p1 = p[i];
        p2 = p[(i + 1) % p.length];
        v1.set(-(p2.y - p1.y), p2.x - p1.x);
        v2.set(point.x - p2.x, point.y - p2.y);

        if (v1.dot(v2) < 0) {
            return false;
        }
    }
    return true;
};

//Test
var p = new Polygon([
    new Vector(1,1),
    new Vector(2,1),
    new Vector(2,2),
    new Vector(1,2)
]);
var point = new Vector(0, 0);

for (var i = 0; i < 10; i++) {
    point.set(Math.random() * 3, Math.random() * 3);
    console.log(point, p.containsPoint(point));
}