Find the center point of a polygon.

getCentroidOfPolygon.pde

//http://en.wikipedia.org/wiki/Centroid#Centroid_of_polygon
Point getCentroidOfPolygon(Point[] points) {
	float a = 0.0;
	int len = points.length;
	
	Point p0;
	Point p1;
	float _x = 0.0;
	float _y = 0.0;
	for(int i = 0; i < len; i++){

		if(i < len - 1) {
			p0 = points[i];
			p1 = points[i + 1];
		} else {
			p0 = points[i];
			p1 = points[0];
		}

		a += ((p0.x * p1.y) - (p1.x * p0.y));
		_x += ((p0.x + p1.x) * ((p0.x * p1.y) - (p1.x * p0.y)));
		_y += ((p0.y + p1.y) * ((p0.x * p1.y) - (p1.x * p0.y)));
	}

	a = a * 0.5;

	_x = _x / (6.0 * a);
	_y = _y / (6.0 * a);

	return new Point(_x, _y);
}