point in quad

                int i, j, n, hit;
                outline_pt *poly;
                hit = 0;
                n    = 4;
                poly = part->outline;

                for (i = 0, j = n - 1; i < n; j = i++) {
                    if (((poly[i].y > pos.y) != (poly[j].y > pos.y)) &&
                            (pos.x < (poly[j].x - poly[i].x) * (pos.y - poly[i].y) / (poly[j].y - poly[i].y) + poly[i].x))
                        hit = !hit;
                }

// if hit != 0, then point is in quad.