Angle of a vector

vectorAngle

// angle of a vector (defined as AB)
float R2Point::angle(R2Point A, R2Point B)
{
        // tg(o) = y / x
        float diffy = B.y - A.y;
        float diffx = B.x - A.x;
        float ang = 0;

        // special case;
        if ((diffy == 0) & (diffx == 0))
                return ang;

        // general case - 3 steps
        float PI = 4*atan(1.0f);
        if (diffx == 0) ang = (float) PI / 2;
        else ang = atan(fabs(diffy) / fabs(diffx)); // angle assuming absolute
        if (diffx < 0) ang = (float) PI - ang;
        if (diffy < 0) ang = -ang;
        
        return ang;
}