Source: d:/wamp/www/phaser/src/pixi/geom/Polygon.js

/**
 * @author Adrien Brault <adrien.brault@gmail.com>
 */

/**
 * @class Polygon
 * @constructor
 * @param points* {Array(Point)|Array(Number)|Point...|Number...} This can be an array of Points that form the polygon,
 *      a flat array of numbers that will be interpreted as [x,y, x,y, ...], or the arguments passed can be
 *      all the points of the polygon e.g. `new PIXI.Polygon(new PIXI.Point(), new PIXI.Point(), ...)`, or the
 *      arguments passed can be flat x,y values e.g. `new PIXI.Polygon(x,y, x,y, x,y, ...)` where `x` and `y` are
 *      Numbers.
 */
PIXI.Polygon = function(points)
{
    //if points isn't an array, use arguments as the array
    if(!(points instanceof Array))points = Array.prototype.slice.call(arguments);

    //if this is a flat array of numbers, convert it to points
    if(points[0] instanceof PIXI.Point)
    {
        var p = [];
        for(var i = 0, il = points.length; i < il; i++)
        {
            p.push(points[i].x, points[i].y);
        }

        points = p;
    }

    this.closed = true;
    this.points = points;
};

/**
 * Creates a clone of this polygon
 *
 * @method clone
 * @return {Polygon} a copy of the polygon
 */
PIXI.Polygon.prototype.clone = function()
{
    var points = this.points.slice();
    return new PIXI.Polygon(points);
};

/**
 * Checks whether the x and y coordinates passed to this function are contained within this polygon
 *
 * @method contains
 * @param x {Number} The X coordinate of the point to test
 * @param y {Number} The Y coordinate of the point to test
 * @return {Boolean} Whether the x/y coordinates are within this polygon
 */
PIXI.Polygon.prototype.contains = function(x, y)
{
    var inside = false;

    // use some raycasting to test hits
    // https://github.com/substack/point-in-polygon/blob/master/index.js
    var length = this.points.length / 2;

    for(var i = 0, j = length - 1; i < length; j = i++)
    {
        var xi = this.points[i * 2], yi = this.points[i * 2 + 1],
            xj = this.points[j * 2], yj = this.points[j * 2 + 1],
            intersect = ((yi > y) !== (yj > y)) && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);

        if(intersect) inside = !inside;
    }

    return inside;
};

// constructor
PIXI.Polygon.prototype.constructor = PIXI.Polygon;