+// clip.cpp
+int clip_rect(double& x1, double& y1, double& x2, double& y2, const double rect[4]);
+int clip_segment(double& x1, double& y1, double& x2, double& y2, const double u, const double v);
+int clip_sector(double& x1, double& y1, double& x2, double& y2, const double u, const double v);
+int clip_circle(double& x1, double& y1, double& x2, double& y2, const double cx, const double cy, const double radius, double t1, double t2);
+int clip_triangle(double& x1, double& y1, double& x2, double& y2, const double u, const double v, const int clip_xaxis);
+
+// norm_ang.cpp
+double norm_ang (double theta);
+
+// xform.cpp