计算机几何算法库（编程常用）

const   double   INF=1e100;   
  const   double   ZERO=1e-6;   
  const   double   PI=2*asin(1.0);   
    
  struct   XYpoint{     //(x,y)   
        double   x;   
        double   y;   
  };   
    
  struct   XYline{       //   Ax+By+C=0;   
        double   A;   
        double   B;   
        double   C;   
  };   
    
  struct   XYsegment{   
        XYpoint   a,b;   
  };   
    
  struct   XYround{     //   圆   
        XYpoint   center;   
        double   r;   
  };   
    
  inline   double   min(double   a,double   b)   
  {   
        return   a<b?a:b;   
  }   
  inline   double   max(double   a,double   b)   
  {   

        return   a>b?a:b;   
  }   
    
    
  /********************************************/   
  /*                         两点确定一条直线                             */   
  /********************************************/   
  XYline   makeLine(double   x1,double   y1,double   x2,double   y2)   
  {   
        XYline   line;   
        line.A=(y2-y1);   
        line.B=(x1-x2);   
        line.C=y1*(x2-x1)+x1*(y1-y2);   
        return   line;   
  }   
    
  /********************************************/   
  /*                               两点间距离                                   */   
  /********************************************/   
  inline   double   dis_PP(double   x1,double   y1,double   x2,double   y2)   
  {   
        return   sqrt(   (x1-x2)*(x1-x2)   +   (y1-y2)*(y1-y2)   );   
  }   
    
  /********************************************/   
  /*                               点直线距离                                   */   
  /********************************************/   
  double   dis_PL(double   x,double   y,XYline   line)   
  {   
        return   fabs(line.A*x   +   line.B*y   +   line.C)   /   sqrt(line.A*line.A   +   line.B*line.B);