recursive_bezier
void recursive_bezier(double x1, double y1,
void recursive_bezier(double x1, double y1,
recursive_bezier(x1, y1, x12, y12, x123, y123, level + 1);
recursive_bezier(x123, y123, x23, y23, x3, y3, level + 1);
recursive_bezier(x1, y1, x2, y2, x3, y3, 0);
recursive_bezier(x1, y1, x12, y12, x123, y123, x1234, y1234, level + 1);
recursive_bezier(x1234, y1234, x234, y234, x34, y34, x4, y4, level + 1);
recursive_bezier(x1, y1, x2, y2, x3, y3, x4, y4, 0);