bool clip_rect (double& x1, double& y1, double& x2, double& y2, const double rect[4]);
bool clip_segment (double& x1, double& y1, double& x2, double& y2, const double u, const double v);
bool clip_sector (double& x1, double& y1, double& x2, double& y2, const double u, const double v);
bool clip_rect (double& x1, double& y1, double& x2, double& y2, const double rect[4]);
bool clip_segment (double& x1, double& y1, double& x2, double& y2, const double u, const double v);
bool clip_sector (double& x1, double& y1, double& x2, double& y2, const double u, const double v);