Function cross2

Geometry/Half Plane Intersection Dynamic.cpp:50–50

    return acos(max((double)-1.0, min((double)1.0, costheta)));
}
double cross2(PT a, PT b, PT c) { return cross(b - a, c - a); }
// intersection point between ab and cd assuming unique intersection exists
PT line_line_intersection(PT a, PT b, PT c, PT d) {
    double a1 = a.y - b.y, b1 = b.x - a.x, c1 = cross(a, b);