Point inside the polygon

gistfile1.txt

//http://alienryderflex.com/polygon/
bool tricks::math::pointInsidePolygon(ofVec2f &p, const vector<ofVec2f> &polygon, int resolution){
	int counter = 0;
	int i;
	double xinters;
	ofVec2f p1,p2;
	
	float x = p.x;
	float y = p.y;
	
	int N = polygon.size();
	
	p1 = polygon[0];
	for (i=1;i<=N;i+=resolution) {
		p2 = polygon[i % N];
		if (y > MIN(p1.y,p2.y)) {
			if (y <= MAX(p1.y,p2.y)) {
				if (x <= MAX(p1.x,p2.x)) {
					if (p1.y != p2.y) {
						xinters = (y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y)+p1.x;
						if (p1.x == p2.x || x <= xinters)
							counter++;
					}
				}
			}
		}
		p1 = p2;
	}
	
	if (counter % 2 == 0) return false;
	else return true;
}